LTC2986/LTC2986-1 Multi-Sensor High Accuracy Digital Temperature Measurement System with EEPROM DESCRIPTION FEATURES Directly Digitizes 2-, 3- or 4-Wire RTDs, Thermocouples, Thermistors, and Diodes nn On-Chip EEPROM (LTC2986-1) Stores Channel Configuration Data and Custom Coefficients nn Single 2.85V to 5.25V Supply nn 10 Flexible Inputs Allow Interchanging Sensors nn Automatic Thermocouple Cold Junction Compensation nn Built-In Standard and User-Programmable Coefficients for Thermocouples, RTDs and Thermistors nn Measures Negative Thermocouple Voltages nn Automatic Burn Out, Short-Circuit and Fault Detection nn Buffered Inputs Allow External Protection nn Simultaneous 50Hz/60Hz Rejection nn Includes 15ppm/C (Max) Reference nn Includes Special Protection Modes nn APPLICATIONS Direct Thermocouple Measurements Direct RTD Measurements nn Direct Thermistor Measurements nn Custom Sensor Applications nn nn The LTC 2986 measures a wide variety of temperature sensors and digitally outputs the result, in C or F, with 0.1C accuracy and 0.001C resolution. The LTC2986 can measure the temperature of virtually all standard (Type B, E, J, K, N, S, R, T) or custom thermocouples, automatically compensate for cold junction temperatures and linearize the results. The device can also measure temperature with standard 2-, 3- or 4-wire RTDs, thermistors, and diodes. The LTC2986 includes excitation current sources and fault detection circuitry appropriate for each type of temperature sensor. (R) The LTC2986/LTC2986-1 are 10-channel software and pincompatible versions of the 20-channel LTC2983/LTC2984. Additional features include special modes that enable easy protection in universal multi-sensor applications, custom tables for generic ADC readings, and direct temperature readout from active analog temperature sensors. The LTC2986-1 is the EEPROM version of the LTC2986. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents Pending TYPICAL APPLICATION Thermocouple Measurement with Automatic Cold Junction Compensation Typical Temperature Error Contribution 2.85V TO 5.25V 0.5 1k 0.4 LTC2986-1 0.1F 0.3 24-BIT ADC RSENSE 2k 24-BIT ADC 0.2 LINEARIZATION/ FAULT DETECTION ERROR (C) 1k SPI INTERFACE C/F THERMISTOR THERMOCOUPLE 0.1 0 -0.1 -0.2 -0.3 3904 DIODE RTD -0.4 4 3 2 -0.5 -200 0 PT-100 RTD 24-BIT ADC 200 400 600 800 1000 1200 1400 TEMPERATURE (C) 29861 TA01b 1 VREF (15ppm/C) EEPROM COM 29861 TA01a 29861fa For more information www.linear.com/LTC2986 1 LTC2986/LTC2986-1 TABLE OF CONTENTS Features............................................................................................................................. 1 Applications........................................................................................................................ 1 Typical Application ................................................................................................................ 1 Description......................................................................................................................... 1 Absolute Maximum Ratings...................................................................................................... 3 Order Information.................................................................................................................. 3 Pin Configuration.................................................................................................................. 3 Complete System Electrical Characteristics................................................................................... 4 ADC Electrical Characteristics................................................................................................... 4 Reference Electrical Characteristics............................................................................................ 5 Digital Inputs and Digital Outputs............................................................................................... 5 LTC2986-1 EEPROM Characteristics............................................................................................ 6 Typical Performance Characteristics........................................................................................... 7 Pin Functions......................................................................................................................10 Block Diagram.....................................................................................................................11 Test Circuits.......................................................................................................................12 Timing Diagram...................................................................................................................12 Overview...........................................................................................................................13 Applications Information........................................................................................................17 EEPROM Overview (LTC2986-1)........................................................................................................................... 23 EEPROM Read/Write Validation............................................................................................................................. 23 EEPROM Write Operation...................................................................................................................................... 23 EEPROM Read Operation (LTC2986-1).................................................................................................................. 24 Thermocouple Measurements............................................................................................................................... 25 Diode Measurements............................................................................................................................................. 28 RTD Measurements............................................................................................................................................... 32 Thermistor Measurements..................................................................................................................................... 51 Global Configuration Register................................................................................................................................ 60 Input Overvoltage Protection - Overview.............................................................................................................. 60 Active Analog Temperature Sensors...................................................................................................................... 66 Direct ADC Measurements..................................................................................................................................... 70 2- and 3-Cycle Conversion Modes......................................................................................................................... 75 Running Conversions Consecutively on Multiple Channels.................................................................................... 75 Entering/Exiting Sleep Mode.................................................................................................................................. 76 MUX Configuration Delay....................................................................................................................................... 76 Reference Considerations...................................................................................................................................... 76 Custom Thermocouples..........................................................................................................77 Custom RTDs......................................................................................................................80 Custom Thermistors..............................................................................................................83 Package Description.............................................................................................................88 Revision History..................................................................................................................89 Typical Application...............................................................................................................90 Related Parts......................................................................................................................90 29861fa 2 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) 12 11 10 9 8 7 6 5 4 3 2 1 GND VREF_BYP NC GND VDD GND VDD GND VDD GND VDD GND TOP VIEW 13 14 15 16 17 18 19 20 21 22 23 24 48 47 46 45 44 43 42 41 40 39 38 37 Q1 Q2 Q3 VDD GND LDO RESET CS SDI SDO SCK INTERRUPT 25 26 27 28 29 30 31 32 33 34 35 36 VREFOUT VREFP GND CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 CH10 GND GND GND GND GND GND GND GND GND GND COM Supply Voltage (VDD).................................... -0.3V to 6V Analog Input Pins (CH1 to CH10, COM).................................. -0.3V to (VDD + 0.3V) Input Current (CH1 to CH10, COM)....................... 15mA Digital Inputs (CS, SDI, SCK, RESET)................................. -0.3V to (VDD + 0.3V) Digital Outputs (SDO, INTERRUPT). -0.3V to (VDD + 0.3V) VREFP......................................................... -0.3V to 2.8V Q1, Q2, Q3, LDO, VREFOUT, VREF_BYP (Note 18) Reference Short-Circuit Duration...................... Indefinite Operating Temperature Range LTC2986C................................................. 0C to 70C LTC2986I..............................................-40C to 85C LTC2986H........................................... -40C to 125C LX PACKAGE 48-LEAD (7mm x 7mm) PLASTIC LQFP TJMAX = 150C, JA = 57C/W ORDER INFORMATION LEAD FREE FINISH TRAY http://www.linear.com/product/LTC2986#orderinfo PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2986CLX#PBF LTC2986CLX#PBF LTC2986LX 48-Lead (7mm x 7mm) LQFP 0C to 70C LTC2986ILX#PBF LTC2986ILX#PBF LTC2986LX 48-Lead (7mm x 7mm) LQFP -40C to 85C LTC2986HLX#PBF LTC2986HLX#PBF LTC2986LX 48-Lead (7mm x 7mm) LQFP -40C to 125C LTC2986CLX-1#PBF LTC2986CLX-1#PBF LTC2986LX-1 48-Lead (7mm x 7mm) LQFP 0C to 70C LTC2986ILX-1#PBF LTC2986ILX-1#PBF LTC2986LX-1 48-Lead (7mm x 7mm) LQFP -40C to 85C LTC2986HLX-1#PBF LTC2986HLX-1#PBF LTC2986LX-1 48-Lead (7mm x 7mm) LQFP -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ 29861fa For more information www.linear.com/LTC2986 3 LTC2986/LTC2986-1 COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS which apply over the full operating temperature range, otherwise specifications are at TA = 25C. PARAMETER CONDITIONS MIN Supply Voltage l Supply Current l Sleep Current The l denotes the specifications TYP 2.85 UNITS 5.25 15 25 l MAX V 20 mA 60 A VDD - 0.3 V Input Range All Analog Input Channels l -0.05 Output Rate Two Conversion Cycle Mode (Notes 6, 9) l 150 164 170 ms Output Rate Three Conversion Cycle Mode (Notes 6, 9) l 225 246 255 ms Input Common Mode Rejection 50Hz/60Hz (Note 4) l 120 dB Input Normal Mode Rejection 60Hz (Notes 4, 7) l 120 dB Input Normal Mode Rejection 50Hz (Notes 4, 8) l 120 dB Input Normal Mode Rejection 50Hz/60Hz (Notes 4, 6, 9) l 75 Power-On Reset Threshold dB 2.25 V Analog Power-Up (Note 11) l 100 ms Digital Initialization (Note 12) l 100 ms ADC ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. PARAMETER CONDITIONS Resolution (No Missing Codes) -VREFOUT/2 VIN +VREFOUT/2 l Integral Nonlinearity VIN(CM) = 1.25V (Note 15) l 2 30 ppm of VREF l 0.5 2 V 10 Offset Error MIN Offset Error Drift (Note 4) l Positive Full-Scale Error (Notes 3, 15) l TYP MAX 24 UNITS Bits nV/C ppm of VREF Positive Full-Scale Drift (Notes 3, 15) l 0.5 ppm of VREF/C Input Leakage (Note 19) H-Grade l l 1 10 nA nA Negative Full-Scale Error (Notes 3, 15) l 100 ppm of VREF Negative Full-Scale Drift (Notes 3, 15) l 0.1 0.5 ppm of VREF/C Input Referred Noise (Note 5) H-Grade l l 0.8 1.5 2.0 VRMS VRMS Common Mode Input Range 0.1 20 100 l -0.05 (Note 16) l -25 RTD Excitation Current Matching Continuously Calibrated l Thermistor Excitation Current (Note 16) l RTD Excitation Current Table 33 VDD - 0.3 V 25 % Error within Noise Level of ADC -37.5 Table 57 37.5 % 29861fa 4 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 REFERENCE ELECTRICAL CHARACTERISTICS the full operating temperature range, otherwise specifications are at TA = 25C. PARAMETER The l denotes the specifications which apply over CONDITIONS MIN TYP 2.49 MAX UNITS Output Voltage VREFOUT (Note 10) Output Voltage Temperature Coefficient I-Grade, H-Grade l 3 15 ppm/C Output Voltage Temperature Coefficient C-Grade l 3 Output Voltage Noise Output Short-Circuit Current Turn-On Time 20 ppm/C 10 ppm/V IOUT(SOURCE) = 100A l 5 mV/mA IOUT(SINK) = 100A l 5 mV/mA 0.1Hz f 10Hz 4 VP-P 10Hz f 1kHz 4.5 VP-P Short VREFOUT to GND 40 mA Short VREFOUT to VDD 30 mA 0.1% Setting, CLOAD = 1F 115 s 60 ppm/kHr 30 70 ppm ppm Long Term Drift of Output Voltage (Note 13) Hysteresis (Note 14) T = 0C to 70C T = -40C to 85C DIGITAL INPUTS AND DIGITAL OUTPUTS full operating temperature range, otherwise specifications are at TA = 25C. SYMBOL V l Line Regulation Load Regulation 2.51 PARAMETER The l denotes the specifications which apply over the CONDITIONS MIN TYP MAX External SCK Frequency Range l 0 External SCK LOW Period l 250 ns External SCK HIGH Period l 250 ns t1 CS to SDO Valid l 0 200 ns t2 CS to SDO Hi-Z l 0 200 ns t3 CS to SCK l 100 t4 SCK to SDO Valid l t5 SDO Hold After SCK l 10 ns t6 SDI Setup Before SCK l 100 ns t7 SDI HOLD After SCK l 100 ns VDD - 0.5 V High Level Input Voltage CS, SDI, SCK, RESET l Low Level Input Voltage CS, SDI, SCK, RESET l Digital Input Current CS, SDI, SCK, RESET l Digital Input Capacitance CS, SDI, SCK, RESET -10 IO = -800A l IO = 1.6mA l VDD - 0.5 l -10 ns 0.5 V 10 A 10 LOW Level Output Voltage (SDO, INTERRUPT) MHz ns 225 High Level Output Voltage (SDO, INTERRUPT) Hi-Z Output Leakage (SDO) 2 UNITS pF 0.4 V V 10 A 29861fa For more information www.linear.com/LTC2986 5 LTC2986/LTC2986-1 LTC2986-1 EEPROM CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. These specifications apply only to LTC2986-1, LTC2986 does not include EEPROM. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Retention Notes 4 and 17 l 10 Years Endurance Note 4 l 10000 Cycles Programming Time Complete Transfer from RAM to EEPROM l 2600 ms Read Time Complete Transfer EEPROM to RAM l 20 ms Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All voltage values are with respect to GND. Note 3: Full scale ADC error. Measurements do not include reference error. Note 4: Guaranteed by design, not subject to test. Note 5: The input referred noise includes the contribution of internal calibration operations. Note 6: MUX configuration delay = default 1ms. Note 7: Global configuration set to 60Hz rejection. Note 8: Global configuration set to 50Hz rejection. Note 9: Global configuration default 50Hz/60Hz rejection. Note 10: The exact value of VREF is stored in the LTC2986 and used for all measurement calculations. Temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. Note 11: Analog power-up. Command status register inaccessible during this time. Note 12: Digital initialization. Begins at the conclusion of Analog Power-Up. Command status register is 0x80 at the beginning of digital initialization and 0x40 at the conclusion. Note 13: Long-term stability typically has a logarithmic characteristic and therefore, changes after 1000 hours tend to be much smaller than before that time. Total drift in the second thousand hours is normally less than one third that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stability will also be affected by differential stresses between the IC and the board material created during board assembly. Note 14: Hysteresis in output voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25C, but the IC is cycled to the hot or cold temperature limit before successive measurements. Hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles. For instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature), it is usually not a dominant error source. Typical hysteresis is the worst-case of 25C to cold to 25C or 25C to hot to 25C, preconditioned by one thermal cycle. Note 15: Differential Input Range is VREF/2. Note 16:RTD and thermistor measurements are made ratiometrically. As a result, current source excitation variation does not affect absolute accuracy. Choose an excitation current such that largest sensor or RSENSE resistance value, when driven by the nominal excitation current, will drop 1V or less. The extended ADC input range will accommodate variation in excitation current and the ratiometric calculation will negate the absolute value of the excitation current. Note 17: 10-year data retention guaranteed for up to 1000 program cycles. Note 18: Do not apply voltage or current sources to these pins. They must be connected to capacitive loads only. Otherwise, permanent damage may occur. Note 19: Input leakage measured with VIN = -10mV and VIN = 2.5V. 29861fa 6 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 TYPICAL PERFORMANCE CHARACTERISTICS Type K Thermocouple Error and RMS Noise vs Temperature 1.0 0.8 0.8 0.6 0.6 0.6 0.4 0.2 0 -0.2 -0.4 ERROR/RMS NOISE (C) 1.0 0.8 -0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -400 RMS NOISE ERROR -1.0 -400 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (C) 0.2 0 -0.2 -0.4 -0.8 -1.0 -400 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (C) Type S Thermocouple Error and RMS Noise vs Temperature Type T Thermocouple Error and RMS Noise vs Temperature 0.8 0.8 0.8 0.6 0.6 0.6 0 -0.2 -0.4 -0.6 ERROR/RMS NOISE (C) 1.0 ERROR/RMS NOISE (C) 1.0 0.2 0.4 0.2 T 0 -0.2 -0.4 -1.0 -400 RMS NOISE ERROR -0.8 -1.0 -400 0 400 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (C) 0.4 0.2 0 -0.2 -0.4 -0.6 -0.6 -0.8 29861 G04 RMS NOISE ERROR -0.8 -1.0 -400 0 400 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (C) Type B Thermocouple Error and RMS Noise vs Temperature 0.8 0.6 0.6 0.6 -0.2 -0.4 -1.0 -400 0.2 0 -0.2 -0.4 -0.6 -0.6 -0.8 ERROR/RMS NOISE (C) 0.8 ERROR/RMS NOISE (C) 1.0 0.8 0.4 RMS NOISE ERROR 0 400 800 1200 THERMOCOUPLE TEMPERATURE (C) 29861 G07 -0.8 -1.0 400 600 RTD PT-1000 Error and RMS Noise vs Temperature 1.0 0 -200 0 200 400 THERMOCOUPLE TEMPERATURE (C) 29861 G06 1.0 0.2 RMS NOISE ERROR 29861 G05 Type E Thermocouple Error and RMS Noise vs Temperature 0.4 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (C) 29861 G03 1.0 0.4 RMS NOISE ERROR 29861 G02 Type R Thermocouple Error and RMS Noise vs Temperature ERROR/RMS NOISE (C) 0.4 -0.6 RMS NOISE ERROR -0.8 29861 G01 ERROR/RMS NOISE (C) Type N Thermocouple Error and RMS Noise vs Temperature 1.0 ERROR/RMS NOISE (C) ERROR/RMS NOISE (C) Type J Thermocouple Error and RMS Noise vs Temperature 0.4 0.2 0 -0.2 -0.4 -0.6 RMS NOISE ERROR 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (C) 29861 G08 -0.8 -1.0 -400 RMS NOISE ERROR 0 400 RTD TEMPERATURE (C) 800 29861 G09 29861fa For more information www.linear.com/LTC2986 7 LTC2986/LTC2986-1 TYPICAL PERFORMANCE CHARACTERISTICS 1.0 1.0 0.8 0.8 0.8 0.6 0.6 0.6 0.2 0 -0.2 -0.4 -0.6 ERROR/RMS NOISE (C) 1.0 0.4 0.4 0.2 0 -0.2 -0.4 -1.0 -400 RMS NOISE ERROR 0.2 0 -0.2 -0.4 0 400 RTD TEMPERATURE (C) -0.6 RMS NOISE ERROR -0.8 -1.0 -400 -200 800 0 200 400 600 RTD TEMPERATURE (C) 29861 G10 -0.8 -1.0 -100 800 1000 3k Thermistor Error vs Temperature 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 ERROR (C) 0.8 ERROR (C) 1.0 0 -0.2 300 5k Thermistor Error vs Temperature 1.0 -0.2 0 100 200 RTD TEMPERATURE (C) 29861 G12 1.0 0 RMS NOISE ERROR 29861 G11 2.252k Thermistor Error vs Temperature 0 -0.2 -0.4 -0.4 -0.4 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) 29861 G13 29861 G14 29861 G15 30k Thermistor Error vs Temperature 10k Thermistor Error vs Temperature YSI-400 Thermistor Error vs Temperature 1.0 1.0 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 ERROR (C) 1.0 0 -0.2 ERROR (C) ERROR (C) 0.4 -0.6 -0.8 ERROR (C) RTD NI-120 RTD Error and RMS Noise vs Temperature RTD PT-100 Error and RMS Noise vs Temperature ERROR/RMS NOISE (C) ERROR/RMS NOISE (C) RTD PT-200 Error and RMS Noise vs Temperature 0 -0.2 0 -0.2 -0.4 -0.4 -0.4 -0.6 -0.6 -0.6 -0.8 -0.8 -0.8 -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) -1.0 -40 -20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (C) 29861 G16 29861 G17 29861 G18 29861fa 8 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 TYPICAL PERFORMANCE CHARACTERISTICS Diode Error and Repeatability vs Temperature Offset vs Temperature 1.0 2.0 0.8 1.5 0.6 0.2 0 -0.2 -0.4 NOISE (VRMS) OFFSET (V) ERROR (C) 1.0 1.0 0.4 0.5 0 -0.5 VDD = 5.25V VDD = 4.1V VDD = 2.85V -1.5 -0.8 -1.0 -40 20 80 DIODE TEMPERATURE (C) -2.0 -50 140 -25 0 25 50 75 100 LTC2986 TEMPERATURE (C) 0.4 16.0 60 VDD = 5.25V VDD = 4.1V VDD = 2.85V 50 0 -50 125 -25 0 25 50 75 100 LTC2986 TEMPERATURE (C) 15.6 2.5005 VREFOUT (V) IIDLE (mA) 15.2 15.0 14.8 20 14.6 2.5 2.49975 14.4 10 VVREFOUT vs Temperature Temperature REFOUT vs 2.50025 15.4 40 125 29861 G21 VDD = 5.25V VDD = 4.1V VDD = 2.85V 15.8 30 VDD = 5.25V VDD = 4.1V VDD = 2.85V 0.2 One Shot Conversion Current vs Temperature ISLEEP vs Temperature ISLEEP (A) 0.6 29861 G20 29861 G19 14.2 0 -50 -25 0 25 50 75 100 LTC2986 TEMPERATURE (C) 0 -50 125 -25 Channel Input Leakage Current vs Temperature 1.0 0.8 0.6 0.4 -1 0 1 2 3 4 INPUT VOLTAGE (V) 5 6 29861 G25 29861 G24 Adjacent Channel Offset Error vs Input Fault Voltage 2.5 2.5 2.0 2.0 1.5 1.0 0.5 -0.5 4.95 1.5 1.0 0.5 0 0 0.2 2.4995 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) CH2 OFFSET ERROR (V) 1.2 CH2 OFFSET ERROR (V) 125C 90C 25C -45C 125 Adjacent Channel Offset Error vs Input Fault Voltage (VDD = 5V) Temperature 1.4 0 25 50 75 100 LTC2986 TEMPERATURE (C) 29861 G23 29861 G22 INPUT LEAKAGE (nA) 0.8 -1.0 -0.6 0 Noise vs Temperature 1.2 5 5.05 5.1 5.15 5.2 5.25 5.3 5.35 CH1 FAULT VOLTAGE (V) 29861 G26 -0.5 0 -0.05 -0.1 -0.15 -0.2 -0.25 -0.3 -0.35 CH1 FAULT VOLTAGE (V) 29861 G27 29861fa For more information www.linear.com/LTC2986 9 LTC2986/LTC2986-1 PIN FUNCTIONS GND (Pins 1, 3, 5, 7, 9, 12, 15, 26-35, 44): Ground. Connect each of these pins to a common ground plane through a low impedance connection. All 18 pins must be grounded for proper operation. VDD (Pins 2, 4, 6, 8, 45): Analog Power Supply. Tie all five pins together and bypass as close as possible to the device, to ground with 0.1F and 10F capacitors. VREF_BYP( Pin 11): Internal Reference Power. This is an internal supply pin, do not load this pin with external circuitry. Decouple with a 0.1F capacitor to GND. VREFOUT (Pin 13): Reference Output Voltage. Short to VREFP. A minimum 1F capacitor to ground is required. Do not load this pin with external circuitry. VREFP (Pin 14): Positive Reference Input. Tie to VREFOUT. CH1 to CH10 (Pin 16 to Pin 25): Analog Inputs. May be programmed for single-ended, differential, or ratiometric operation. The voltage on these pins can have any value between GND - 50mV and VDD - 0.3V. Unused pins can be grounded or left floating. COM (Pin 36): Analog Input. The common negative input for all single-ended configurations. The voltage on this pin can have any value between GND - 50mV and VDD - 0.3V. This pin is typically tied to ground for temperature measurements. INTERRUPT (Pin 37): This pin outputs a LOW when the device is busy either during start-up or while a conversion cycle is in progress. This pin goes HIGH at the conclusion of the start-up state or conversion cycle. SCK (Pin 38): Serial Clock Pin. Data is shifted out of the device on the falling edge of SCK and latched by the device on the rising edge. SDO (Pin 39): Serial Data Out. During the data output state, this pin is used as the serial data output. When the chip select pin is HIGH, the SDO pin is in a high impedance state. SDI (Pin 40): Serial Data Input. Used to program the device. Data is latched on the rising edge of SCK. CS (Pin 41): Active Low Chip Select. A low on this pin enables the digital input/output. A HIGH on this pin places SDO in a high impedance state. A falling edge on CS marks the beginning of a SPI transaction and a rising edge marks the end. RESET (Pin 42): Active Low Reset. While this pin is LOW, the device is forced into the reset state. Once this pin is returned HIGH, the device initiates its start-up sequence. LDO (Pin 43): 2.5V LDO Output. Bypass with a 10F capacitor to GND. This is an internal supply pin, do not load this pin with external circuitry. Q3, Q2, Q1 (Pins 46, 47, 48): External Bypass Pins for -200mV Integrated Charge Pump. Tie a 10F X7R capacitor between Q1 and Q2 close to each pin. Tie a 10F X7R capacitor from Q3 to Ground. These are internal supply pins, do not make additional connections. 29861fa 10 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 BLOCK DIAGRAM 1F VREFOUT VREFP VREF_BYP 10F 0.1F 0.1F VDD Q1 15ppm/C REFERENCE CHARGE PUMP Q2 10F Q3 10F LDO LDO 10F ADC1 CH1 TO CH10 ROM EEPROM LTC2986-1 11:6 MUX COM RAM ADC2 INTERRUPT SDO PROCESSOR SCK SDI ADC3 CS RESET EXCITATION CURRENT SOURCES GND 29861 BD 29861fa For more information www.linear.com/LTC2986 11 LTC2986/LTC2986-1 TEST CIRCUITS VDD 1.69k SDO SDO 1.69k CLOAD = 20pF CLOAD = 20pF Hi-Z TO VOH VOL TO VOH VOH TO Hi-Z Hi-Z TO VOL VOH TO VOL VOL TO Hi-Z 29861 TC01 TIMING DIAGRAM SPI Timing Diagram t4 CS SDO t1 t2 t7 SCK t5 SDI 29861 TD01 t3 t6 29861fa 12 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 OVERVIEW The LTC2986 measures the temperature of the most common sensors (thermocouples, RTDs, thermistors, active analog temperature sensors, and diodes). It includes all necessary active circuitry, switches, measurement algorithms, and mathematical conversions to determine the temperature for each sensor type. Thermocouples can measure temperatures from as low as -265C to over 1800C. Thermocouples generate a voltage as a function of the temperature difference between the tip (thermocouple temperature) and the electrical connection on the circuit board (cold junction temperature). In order to determine the thermocouple temperature, an accurate measurement of the cold junction temperature is required; this is known as cold junction compensation. The cold junction temperature is usually determined by placing a separate (non-thermocouple) temperature sensor at the cold junction. The LTC2986 allows diodes, active analog temperature sensors, RTDs, and thermistors to be used as cold junction sensors. In order to convert the voltage output from the thermocouple into a temperature result, a high order polynomial equation (up to 14th order) must be solved. The LTC2986 has these polynomials built in for virtually all standard thermocouples (J, K, N, E, R, S, T, and B). Additionally, inverse polynomials must be solved for the cold junction temperature. The LTC2986 simultaneously measures the thermocouple output and the cold junction temperature and performs all required calculations to report the thermocouple temperature in C or F. It directly digitizes both positive and negative voltages (down to 50mV below ground) from a single ground referenced supply, includes sensor burn-out detection, and allows external protection/anti-aliasing circuits without the need of buffer circuits. Diodes are convenient low cost sensor elements and are often used to measure cold junction temperatures in thermocouple applications. Diodes are typically used to measure temperatures from -60C to 130C, which is suitable for most cold junction applications. Diodes generate an output voltage that is a function of temperature and excitation current. When the difference of two diode output voltages are taken at two different excitation current levels, the result (VBE) is proportional to temperature. The LTC2986 accurately generates excitation currents, measures the diode voltages, and calculates the temperature in C or F. RTDs and thermistors are resistors that change value as a function of temperature. RTDs can measure temperatures over a wide temperature range, from as low as -200C to 850C while thermistors typically operate from -40C to 150C. In order to measure one of these devices a precision sense resistor is tied in series with the sensor. An excitation current is applied to the network and a ratiometric measurement is made. The value, in , of the RTD/thermistor can be determined from this ratio. This resistance is used to determine the temperature of the sensor element using a table lookup (RTDs) or solving Steinhart-Hart equations (thermistors). The LTC2986 automatically generates the excitation current, simultaneously measures the sense resistor and thermistor/RTD voltage, calculates the sensor resistance and reports the result in C. The LTC2986 can digitize most RTD types (PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120), has built in coefficients for many curves (American, European, Japanese, and ITS-90), and accommodates 2-wire, 3-wire, and 4-wire configurations. It also includes coefficients for calculating the temperature of standard 2.252k, 3k, 5k, 10k , and 30k thermistors. It can be configured to share one sense resistor among multiple RTDs/thermistors and to rotate excitation current sources to remove parasitic thermal effects. In addition to built-in linearization coefficients, the LTC2986 provides the means of inserting custom coefficients for both RTDs and thermistors. The LTC2986 includes the capability to measure active analog output temperature sensors. These sensors output voltage as a function of temperature. The relationship between voltage and temperature can be stored in the LTC2986. These sensors can be used as a stand alone temperature sensor or as the cold junction compensation for thermocouple measurements. 29861fa For more information www.linear.com/LTC2986 13 LTC2986/LTC2986-1 OVERVIEW Table 1 shows the estimated system accuracy and noise associated with specific temperature sensing devices. System accuracy and peak-to-peak noise include the effects of the ADC, internal amplifiers, excitation current sources, and integrated reference. Accuracy and noise are the worst-case errors calculated from the guaranteed maximum ADC and reference specifications. Peak-topeak noise values are calculated at 0C (except Type B was calculated at 400C) and diode measurements use AVG = ON mode. Thermocouple errors do not include the errors associated with the cold junction measurement. Errors associated with a specific cold junction sensor within the operating temperature range can be combined with the errors for a given thermocouple for total temperature measurement accuracy. Table 1. LTC2986 Error Contribution and Peak Noise Errors SENSOR TYPE TEMPERATURE RANGE ERROR CONTRIBUTION PEAK-TO-PEAK NOISE Type K Thermocouple -200C to 0C 0C to 1372C (Temperature * 0.23% + 0.05)C (Temperature * 0.12% + 0.05)C 0.08C Type J Thermocouple -210C to 0C 0C to 1200C (Temperature * 0.23% + 0.05)C (Temperature * 0.12% + 0.05)C 0.07C Type E Thermocouple -200C to 0C 0C to 1000C (Temperature * 0.18% + 0.05)C (Temperature * 0.10% + 0.05)C 0.06C Type N Thermocouple -200C to 0C 0C to 1300C (Temperature * 0.27% + 0.08)C (Temperature * 0.10% + 0.08)C 0.13C Type R Thermocouple 0C to 1768C (Temperature * 0.10% + 0.4)C 0.62C Type S Thermocouple 0C to 1768C (Temperature * 0.10% + 0.4)C 0.62C Type B Thermocouple 400C to 1820C (Temperature * 0.10%)C 0.83C Type T Thermocouple -250C to 0C 0C to 400C (Temperature * 0.15% + 0.05)C (Temperature * 0.10% + 0.05)C 0.09C External Diode (2 Reading) -40C to 85C 0.25C 0.05C External Diode (3 Reading) Platinum RTD - PT-10, RSENSE = 1k Platinum RTD - PT-100, RSENSE = 2k Platinum RTD - PT-500, RSENSE = 2k Platinum RTD - PT-1000, RSENSE = 2k Thermistor, RSENSE = 10k -40C to 85C 0.25C 0.2C -200C to 800C -200C to 800C -200C to 800C -200C to 800C 0.1C 0.1C 0.1C 0.1C 0.05C 0.05C 0.02C 0.01C -40C to 85C 0.1C 0.01C 29861fa 14 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 OVERVIEW Memory Map The LTC2986 channel assignment, configuration, conversion start, and results are all accessible via the RAM (see Table 2A). Table 2B details the valid SPI instruction bytes for accessing memory. The channel conversion results are mapped into memory locations 0x010 to 0x037 and can be read using the SPI interface as shown in Figure 1. A read is initiated by sending the read instruction byte = 0x03 followed by the address and then data. Channel assignment data resides in memory locations 0x200 to 0x227 and can be programmed via the SPI interface as shown in Figure 2. A write is initiated by sending the write instruction byte = 0x02 followed by the address and then data. Conversions are initiated by writing the conversion control byte (see Table 6) into memory location 0x000 (command status register). Table 2A. Memory Map LTC2986 MEMORY MAP SEGMENT START ADDRESS END ADDRESS SIZE (BYTES) Command Status Register 0x000 0x0000 1 Reserved 0x001 0x000F 15 Temperature Result Memory 10 Words - 40 Bytes 0x010 0x037 40 Reserved 0x038 0x0AF 120 EEPROM Key 0x0B0 0x0B3 4 Reserved 0x0B4 0x0CF 44 EEPROM Read Result Code 0x0D0 0x0D0 1 Reserved 0x0D1 0x0EF 15 Global Configuration Register 0x0F0 0x0F0 1 Reserved 0x0F1 0x0F3 3 Measure Multiple Channels Bit Mask 0x0F4 0x0F7 4 Reserved 0x0F8 0x0F8 1 EEPROM Status Register 0x0F9 0x0F9 1 Reserved 0x0FA 0x0FE 5 MUX Configuration Delay 0x0FF 0x0FF 1 Reserved 0x100 0x1FF 256 Channel Assignment Data 0x200 0x227 40 Reserved 0x228 0x24F 40 Custom Sensor Table Data 0x250 0x3CF 384 Reserved 0x3D0 0x3FF 48 DESCRIPTION See Table 6 and 12, Initiate Conversion, Sleep Command, EEPROM Command See Tables 8 to 10, Read Result See Table 11 (LTC2986-1 Only, Otherwise Reserved) See Table 11 (LTC2986-1 Only, Otherwise Reserved) See Table 67 for Global Configuration See Tables 84, 85, Run Multiple Conversions See Table 13 (LTC2986-1 Only, Otherwise Reserved) See MUX Configuration Delay Section of Data Sheet See Tables 3, 4, Channel Assignment Table 2B. SPI Instruction Byte INSTRUCTION SPI INSTRUCTION BYTE DESCRIPTION Read 0b00000011 See Figure 1 Write 0b00000010 See Figure 2 Invalid 0bxxxxxx0x 29861fa For more information www.linear.com/LTC2986 15 LTC2986/LTC2986-1 OVERVIEW CS * * * SCK RECEIVER SAMPLES DATA ON RISING EDGE SDI TRANSMITTER TRANSITIONS DATA ON FALLING EDGE I7 I6 I5 I4 I3 I2 I1 I0 0 0 0 0 0 0 1 1 0 0 0 0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 SDO D6 D5 D4 D3 D2 D1 D0 * * * SUBSEQUENT DATA BYTES MAY FOLLOW SPI INSTRUCTION BYTE READ = 0x03 16-BIT ADDRESS FIELD FIRST DATA BYTE USER MEMORY READ TRANSACTION 29861 F01 Figure 1. Memory Read Operation CS * * * SCK RECEIVER SAMPLES DATA ON RISING EDGE SDI TRANSMITTER TRANSITIONS DATA ON FALLING EDGE I7 I6 I5 I4 I3 I2 I1 I0 0 0 0 0 0 0 1 0 SPI INSTRUCTION BYTE WRITE = 0x02 0 0 0 0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 * * * SUBSEQUENT DATA BYTES MAY FOLLOW 16-BIT ADDRESS FIELD USER MEMORY WRITE TRANSACTION FIRST DATA BYTE 29861 F02 Figure 2. Memory Write Operation 29861fa 16 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION The LTC2986 combines high accuracy with ease of use. The basic operation is simple and is composed of five states (see Figure 3). POWER-UP, SLEEP OR RESET START-UP 200ms(MAX) CHANNEL ASSIGNMENT INITIATE CONVERSION 4. Conversion. A new conversion begins automatically following an Initiate Conversion command. In this state, the ADC is running a conversion on the specified channel and associated cold junction or RSENSE channel (if applicable). The user is locked out of RAM access while in the state (except for reading status location 0x000). The end of conversion is indicated by both the INTERRUPT pin going HIGH and a status register START bit going LOW and DONE bit going HIGH. 5. Read Results. In this state, the user has access to RAM and can read the completed conversion results and fault status bits. It is also possible for the user to modify/append the channel assignment data during the read results state. CONVERSION (OPTIONAL) STATUS CHECK COMPLETE? 0x000. This command is a pointer to the channel in which the conversion will be performed. NO YES READ RESULTS Conversion State Details State 1: Start-Up 29861 F03 Figure 3. Basic Operation Conversion States Overview 1. Start-Up. After power is applied to the LTC2986 (VDD > 2.6V), there is a 200ms wake up period. During this time, the LDO, charge pump, ADCs, and reference are powered up and the internal RAM is initialized. Once start-up is complete, the INTERRUPT pin goes HIGH and the command status register will return a value of 0x40 (Start bit = 0, Done bit = 1) when read. 2. Channel Assignment. The device automatically enters the channel assignment state after start-up is complete. While in this state, the user writes sensor specific data for each input channel into RAM. For the LTC2986-1, the user can also load it from the EEPROM (see the EEPROM section for more details). The assignment data contains information about the sensor type, pointers to cold junction sensors or sense resistors, and sensor specific parameters. 3. Initiate Conversion. A conversion is initiated by writing a measurement command into RAM memory location The start-up state automatically occurs when power is applied to the LTC2986. If the power drops below a threshold of 2.6V and then returns to the normal operating voltage (2.85V to 5.25V), the LTC2986 resets and enters the powerup state. Note that the LTC2986 also enters the start-up state at the conclusion of the sleep state. The start-up state can also be entered at any time during normal operation by pulsing the RESET pin low. In the first phase of the start-up state all critical analog circuits are powered up. This includes the LDO, reference, charge pump and ADCs. During this first phase, the command status register will be inaccessible to the user. This phase takes a maximum of 100ms to complete. Once this phase completes, the command status register will be accessible and return a value of 0x80 until the LTC2986 is completely initialized. Once the LTC2986 is initialized and ready to use, the INTERRUPT pin will go high and the command status register will return a read value of 0x40 (Start bit = 0, Done bit = 1). At this point the LTC2986 is fully initialized and is ready to perform a conversion. State 2: Channel Assignment The LTC2986 RAM can be programmed with up to 10 sets of 32-bit (4-byte) channel assignment data. These reside sequentially in RAM with a one-to-one correspondence 29861fa For more information www.linear.com/LTC2986 17 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 3. Channel Assignment Memory Map CHANNEL ASSIGNMENT NUMBER CONFIGURATION DATA START ADDRESS CONFIGURATION DATA ADDRESS + 1 CONFIGURATION DATA ADDRESS + 2 CONFIGURATION DATA END ADDRESS + 3 SIZE (BYTES) CH1 0x200 0x201 0x202 0x203 4 CH2 0x204 0x205 0x206 0x207 4 CH3 0x208 0x209 0x20A 0x20B 4 CH4 0x20C 0x20D 0x20E 0x20F 4 CH5 0x210 0x211 0x212 0x213 4 CH6 0x214 0x215 0x216 0x217 4 CH7 0x218 0x219 0x21A 0x21B 4 CH8 0x21C 0x21D 0x21E 0x21F 4 CH9 0x220 0x221 0x222 0x223 4 CH10 0x224 0x225 0x226 0x227 4 29861fa 18 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION to each of the 10 analog input channels (see Table 3). Channels that are not used should have their channel assignment data set to all zeros (default at START-UP). to memory locations of custom linearization data, sense resistor values and diode ideality factors. Also included in this data are, if applicable, the excitation current level, single-ended/differential input mode, as well as sensor specific controls. Separate detailed operation sections for thermocouples, RTDs, diodes, thermistors, analog temperature sensors, and sense resistors describe the assignment data associated with each sensor type in more detail. The LTC2986 demonstration software includes a utility for checking configuration data and generating annotated C-code for programming the channel assignment data. The channel assignment data contains all the necessary information associated with the specific sensor tied to that channel (see Table 4). The first five bits determine the sensor type (see Table 5). Associated with each sensor are sensor specific configurations. These include pointers to cold junction or sense resistor channels, pointers Table 4. Channel Assignment Data SENSOR TYPE Channel Assignment Memory Location Configuration Data Start Address 31 30 29 28 27 Unassigned (Default) Type = 0 Thermocouple Type = 1 to 9 RTD Thermistor SENSOR SPECIFIC CONFIGURATION 26 25 Configuration Data Start Address + 1 24 23 22 21 20 19 Configuration Data Start Address + 2 18 Configuration Data Start Address + 3 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Channel Disabled Cold Junction Channel Assignment [4:0] Type = 10 to 18 RSENSE Channel Assignment [4:0] SGL=1 OC DIFF=0 Check OC Current [1:0] 2, 3, 4 Wire Excitation Mode Type = 19 to 27 RSENSE Channel Assignment SGL=1 [4:0] DIFF=0 Excitation Mode 0 0 0 0 0 0 Custom Address [5:0] Custom Length - 1 [5:0] Excitation Curve Current [3:0] [1:0] Custom Address [5:0] Custom Length - 1 [5:0] Custom Address [5:0] Custom Length - 1 [5:0] Excitation Current 0 0 [3:0] 0 Diode Type = 28 SGL=1 2 to 3 Avg Current Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution DIFF=0 Reading on [1:0] All Zeros Use Factory Set Default in ROM Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to 131,072 with 1/1024 Resolution Direct ADC Type = 30 SGL=1 Table DIFF=0 Mode Active Analog Temperature Sensor Type = 31 SGL=1 DIFF=0 Not Used Not Used Custom Address [5:0] Custom Length - 1 [5:0] Custom Address [5:0] Custom Length - 1 [5:0] 29861fa For more information www.linear.com/LTC2986 19 LTC2986/LTC2986-1 APPLICATIONS INFORMATION State 3: Initiate Conversion Table 5. Sensor Type Selection 31 30 29 28 27 SENSOR TYPE 0 0 0 0 0 Unassigned 0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple 0 1 0 1 0 RTD PT-10 Once the channel assignment is complete, the device is ready to begin a conversion. A conversion is initiated by writing Start (B7 = 1) and Done (B6 = 0) followed by the desired input channel (B4 - B0) into RAM memory location 0x000 (see Tables 6 and 7). It is possible to initiate a measurement cycle on multiple channels by setting the channel selection bits (B4 to B0) to 00000; see the Running Conversions Consecutively on Multiple Channels section of the data sheet. Table 6. Command Status Register B7 B6 Start = 1 Done = 0 B5 B4 B3 B2 B1 B0 0 EEPROM Command and Channel Selection 1 to 10 0 1 Start Conversion 0 1 0 1 1 RTD PT-50 0 1 1 0 0 RTD PT-100 0 1 1 0 1 RTD PT-200 0 1 1 1 0 RTD PT-500 0 1 1 1 1 RTD PT-1000 1 0 0 0 0 RTD 1000 (0.00375) 1 0 0 0 1 RTD NI-120 1 0 0 1 0 RTD Custom 1 0 0 1 1 Thermistor 44004/44033 2.252k at 25C 1 0 1 0 0 Thermistor 44005/44030 3k at 25C 1 0 1 0 1 Thermistor 44007/44034 5k at 25C 1 0 1 1 0 Thermistor 44006/44031 10k at 25C 1 0 1 1 1 Thermistor 44008/44032 30k at 25C 1 0 0 0 0 1 1 1 CH7 1 1 0 0 0 Thermistor YSI 400 2.252k at 25C 1 0 0 0 1 0 0 0 CH8 1 1 0 0 1 Thermistor Spectrum 1003k 1k 1 0 0 0 1 0 0 1 CH9 1 1 0 1 0 Thermistor Custom Steinhart-Hart 1 0 0 0 1 0 1 0 CH10 1 1 0 1 1 Thermistor Custom Table 1 0 0 1 0 1 1 1 Sleep 1 1 1 0 0 Diode 1 1 1 0 1 Sense Resistor 1 1 1 1 0 Direct ADC 1 1 1 1 1 Analog Temperature Sensor 1 0 0 1 1 1 Initiate Sleep Table 7. Input Channel Mapping B7 B6 B5 B4 B3 B2 B1 B0 CHANNEL SELECTED 1 0 0 0 0 0 0 0 Multiple Channels 1 0 0 0 0 0 0 1 CH1 1 0 0 0 0 0 1 0 CH2 1 0 0 0 0 0 1 1 CH3 1 0 0 0 0 1 0 0 CH4 1 0 0 0 0 1 0 1 CH5 1 0 0 0 0 1 1 0 CH6 All Other Combinations Reserved 29861fa 20 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Bits B4 to B0 determine which input channel the conversion is performed upon and are simply the binary equivalent of the channel number (see Table 7). These bits are also used for EEPROM read and write operations (LTC2986-1, see Table 12). Bit B5 should be set to 0. Bits B7 and B6 serve as start/done bits. In order to start a conversion, these bits must be set to "10" (B7=1 and B6=0). When the conversion begins, the INTERRUPT pin goes LOW. Once the conversion is complete, bits B7 and B6 will toggle to "01" (B7=0 and B6=1) (Address = 0x000) and the INTERRUPT pin will go HIGH, indicating the conversion is complete and the result is available. State 4: Conversion The measurement cycle starts after the Initiate Conversion command is written into RAM location 0x000 (Table 6). The LTC2986 simultaneously measures the selected input sensor, sense resistors (RTDs and thermistors), and cold junction temperatures if applicable (thermocouples). Once the conversion is started, the user is locked out of the RAM, with the exception of reading status data stored in RAM memory location 0x000. Once the conversion is started the INTERRUPT pin goes low. Depending on the sensor configuration, two or three 82ms cycles are required per temperature result. These correspond to conversion rates of 167ms and 251ms, respectively (assuming a filter frequency setting of 55Hz). Details describing these modes are described in the 2- and 3-cycle Conversion Modes section of the data sheet. The end of conversion can be monitored either through the INTERRUPT pin (LOW to HIGH transition), or by reading the command status register in RAM memory location 0x000 (start bit, B7, toggles from 1 to 0 and DONE bit, B6, toggles from 0 to 1). State 5: Read Results Once the conversion is complete, the conversion results can be read from RAM memory locations corresponding to the input channel (see Table 8). The conversion result is 32 bits long and contains both the sensor temperature (D23 to D0) and sensor fault data (D31 to D24) (see Tables 9A and 9B). The result is reported in C for all temperature sensors with a range of -273.15C to 8192C and 1/1024C resolution or in F with a range of -459.67F to 8192F with 1/1024F resolution. Included with the conversion result are seven sensor fault bits and a valid bit. These sensor fault bits are set to a 1 if there was a problem associated with the corresponding conversion result (see Table 10). Two types of errors are reported: hard errors and soft errors. Hard errors indicate the reading is invalid and the resulting temperature reported is -999C or F. Soft errors indicate operation beyond the normal temperature range of the sensor or the input range of the ADC. In this case, the calculated temperature is reported but the accuracy may be compromised. Details relating to each fault type are sensor specific and are described in detail in the sensor specific sections of this data sheet. Bit D24 is the valid bit and will be set to a 1 for valid data. Once the data read is complete, the device is ready for a new Initiate Conversion command. In cases where new channel configuration data is required, the user has access to the RAM in order to modify existing channel assignment data. Table 8. Conversion Result Memory Map CONVERSION CHANNEL START ADDRESS CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 CH10 0x010 0x014 0x018 0x01C 0x020 0x024 0x028 0x02C 0x030 0x034 END ADDRESS SIZE (BYTES) 0x013 0x017 0x01B 0x01F 0x023 0x027 0x02B 0x02F 0x033 0x037 4 4 4 4 4 4 4 4 4 4 29861fa For more information www.linear.com/LTC2986 21 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 9A. Example Data Output Words (C) START ADDRESS D31 D30 D29 D28 D27 D26 START ADDRESS + 1 D25 D24 START ADDRESS + 2 START ADDRESS + 3 (END ADDRESS) D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Fault Data SIGN MSB Temperature Sensor ADC CJ CJ Sensor Sensor ADC Valid Hard Hard Hard Soft Over Under Out If 1 Fault Fault Fault Fault Range Range of Fault Fault Range Fault 8191.999C LSB 1C 4096C 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1/1024C 1 1 1 1 1 1 1 1 1 1 1 1024C 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1/1024C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 -273.15C 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 Table 9B. Example Data Output Words (F) START ADDRESS D31 D30 D29 D28 D27 D26 START ADDRESS + 1 D25 START ADDRESS + 2 START ADDRESS + 3 (END ADDRESS) D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Fault Data SIGN MSB Temperature Sensor ADC CJ CJ Sensor Sensor ADC Valid Hard Hard Hard Soft Over Under Out If 1 Fault Fault Fault Fault Range Range of Fault Fault Range Fault LSB 1F 4096F 1/1024F 8191.999F 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024F 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1/1024F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 -459.67F 1 1 1 1 1 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 Table 10. Sensor Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Bad Sensor Reading -999C or F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) -999C or F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error -999C or F D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Sensor Reading Is Above Normal Range Suspect Reading D26 Sensor Under Range Soft Sensor Reading Is Below Normal Range Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond 1.125 * VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Suspect Reading 29861fa 22 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION EEPROM OVERVIEW (LTC2986-1) EEPROM WRITE OPERATION The LTC2986-1 contains 512 bytes of EEPROM, which shadows the upper sensor configuration segment of USER RAM (locations 0x200-0x3CF, see Figure 4). Prior to initial usage, the user programs the USER RAM with all channel assignment and custom sensor data. Once the USER RAM has been programmed, the user can save this segment of memory into the EEPROM. After subsequent power down or sleep cycles, the user can reload the USER RAM with this stored EEPROM data bypassing the channel assignment and customer sensor programming normally required. The EEPROM write operation requires 5 states (see Figure 5). BYTE ADDRESS 0000 LTC2986-1 READY WRITE CHANNEL ASSIGNMENT AND CUSTOM SENSOR DATA TO LTC2986-1 WRITE EEPROM KEY TO LTC2986-1 SEND EEPROM WRITE COMMAND (COMMAND 21) WAIT FOR EEPROM COMMAND TO COMPLETE LTC2986 SPI ADDRESS SPACE CHECK EEPROM STATUS REGISTER USER COMMAND REGISTERS, RESULTS DATA, GLOBAL CONFIGURATION AND STATUS PROGRAM FAILED STATUS BIT SET USER DEFINED EEPROM ERROR HANDLER ELSE DONE 29861 F05 Figure 5. EEPROM Write Operation 01FF 0200 SENSOR CONFIGURATION MEMORY SEGMENT (CHANNEL ASSIGNMENT AND CUSTOM SENSOR DATA) 03CF 03DO 03FF COMMAND 21 (0x15) COMMAND 22 (0x16) RESERVED* 1. Sensor Configuration. Write all desired channel assignment and custom sensor data to the LTC2986-1 USER RAM. EEPROM SHADOW RESERVED 29861 F04 *NOTE: 03D0-03FF IS RESERVED AND IS NOT SHADOWED BY EEPROM Figure 4. Shadow EEPROM Memory Map EEPROM READ/WRITE VALIDATION Access to the EEPROM is key-protected to prevent inadvertent access. The EEPROM also has two levels of data integrity protection. The first level is implemented using an error correcting code (ECC) on each 32-bit word of data in the EEPROM. The ECC is capable of correcting any single bit error per word and detecting 2-bit errors per word. The second level of protection is implemented using a 32-bit checksum, which covers the entire contents of user EEPROM. Status bits are available to the user for reporting ECC status and checksum error conditions. 2. Set EEPROM Key. Write the EEPROM Key (0xA53C0F5A) to the key register space of the LTC2986-1 USER RAM (Address range 0x0B0-0x0B3, see Table 11). Note the key is written MSB first. 3. Send EEPROM Write Command. Write the EEPROM write command (0x15) and start bit (0x80) to the LTC2986-1 command register (Address 0x000). The command plus start bit is 0x80 + 0x15 = 0x95 (see Table 12). 4. Wait for EEPROM Command to Complete. Completion of the write operation is indicated by both the INTERRUPT pin going HIGH and the status register START bit going LOW and DONE bit going HIGH. 5. Check EEPROM Status Register. Read EEPROM Status register (Address 0x0F9) and checks the Program-Failed status bit (Bit 2) to determine whether the EEPROM write operation was successful (see Table 13). The Program-Failed status bit being set indicates that the write operation failed. Upon successful completion of steps 1-5, the EEPROM will now contain the image that was present in USER RAM locations 0x200-0x3CF. 29861fa For more information www.linear.com/LTC2986 23 LTC2986/LTC2986-1 APPLICATIONS INFORMATION EEPROM READ OPERATION (LTC2986-1) Table 11. LTC2986-1 EEPROM Related Registers The LTC2986-1 EEPROM read operation is comprised of 4 states (see Figure 6) ADDRESS LTC2986-1 READY WRITE EEPROM KEY TO LTC2986-1 REGISTER NAME DESCRIPTION 0x0B0 EEPROM Key [3] (MSB) EEPROM Key byte 3 - Set to 0xA5 0x0B1 EEPROM Key [2] EEPROM Key byte 2 - Set to 0x3C 0x0B2 EEPROM Key [1] EEPROM Key byte 1 - Set to 0x0F 0x0B3 EEPROM Key [0] (LSB) EEPROM Key byte 0 - Set to 0x5A 0x0D0 EEPROM Read Result Code This register indicates the Pass/Fail status of the most recent EEPROM read operation 0x00 = PASS 0xFF = FAIL 0x0F9 EEPROM Status Register See LTC2986-1 EPROM Status Register Tables 12 and 13 SEND EEPROM READ COMMAND (COMMAND 0x16) WAIT FOR EEPROM COMMAND TO COMPLETE CHECK EEPROM READ RESULT CODE ELSE USER DEFINED EEPROM ERROR HANDLER PASS: READ RESULT CODE == 0 DONE Table 12. LTC2986-1 EEPROM Related Commands and Status B7 B6 B5 B4 B3 B2 B1 B0 DESCRIPTION 1 0 0 1 0 1 0 1 EEPROM Write Command - Transfer the contents of user memory locations 0x200-0x3CF to the on-chip shadow EEPROM 1 0 0 1 0 1 1 0 EEPROM Read Command - Transfer the contents of the onchip shadow EEPROM to user memory locations 0x200-0x3CF 29861 F06 Figure 6. Read Operation 1. Set EEPROM Key. Write the EEPROM Key (0xA53C0F5A) to the key register space of the LTC2986-1 USER RAM (Address range 0x0B0-0x0B3, see Table 11). Note the key is written MSB first. 2. Send EEPROM Read Command. Write the EEPROM read command (0x16) and start bit (0x80) to the LTC2986-1 command register (Address 0x000). The command plus start bit would be 0x80 + 0x16 = 0x96 (see Table 12). 3. Wait for EEPROM Command to Complete. Completion of the read operation is indicated by both the INTERRUPT pin going HIGH and the status register START bit going LOW and DONE bit going HIGH. 4. Check EEPROM Read Result Code. Read the EEPROM read result code register address (0x0D0) to determine the pass/fail status of the read operation. A value of zero indicates that the command completed successfully and a non-zero value indicates that an error has occurred. Additional read operation status bits are also available in the EEPROM Status Register (see Tables 13 and 14). Upon successful completion of steps 1-4, USER RAM locations 0x200-0x3CF will now contain the data that was stored in the LTC2986-1's shadow EEPROM. Table 13. EEPROM Status Bits EEPROM STATUS BIT DESCRIPTION ECC Used Error Correcting Code Used - This bit indicates that ECC was used to correct data on one or more locations during the EEPROM read process (Note 20) ECC Failure Error Correcting Code Failure - This bit indicates that ECC failed to correct data on one or more locations during the EEPROM read process. If this bit is set one or more locations has invalid data (Note 20) Program Failure Program Failure - This bit indicates that a write data error occurred on one or more locations during the EEPROM programming process (Note 20) Checksum Error Checksum Error - This bit indicates that a checksum error occurred during the EEPROM read process (Note 20) Note 20: Once bits in the EEPROM status register are set they will remain set until cleared by the user. The EEPROM status register bits are cleared by writing 0x00 to address 0x0F9. These bits are also cleared on reset and after exiting sleep mode. Table 14. LTC2986-1 EEPROM Status Register (Address 0x0F9) 7 6 5 4 3 2 1 0 - - - - Checksum Error Program Failure ECC Failure ECC Used 29861fa 24 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION (3) Sensor Configuration THERMOCOUPLE MEASUREMENTS The sensor configuration field (see Table 18) is used to select single-ended (B21=1) or differential (B21=0) input and allows selection of open circuit current if internal open-circuit detect is enabled (bit B20). Single-ended readings are measured relative to the COM pin and differential are measured between the selected CHTC and adjacent CHTC-1 (see Figure 7). If open-circuit detection is enabled, B20=1, then the user can select the pulsed current value applied during opencircuit detect using bits B18 and B19 . The user determines the value of the open circuit current based on the size of the external protection resistor and filter capacitor (typically 10A). This network needs to settle within 50ms to 1V or less. The duration of the current pulse is approximately 8ms and occurs 50ms before the normal conversion cycle. Channel Assignment - Thermocouples For each thermocouple tied to the LTC2986, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 15). This word includes (1) thermocouple type, (2) cold junction channel pointer, (3) sensor configuration, and (4) custom thermocouple data pointer. (1) Thermocouple Type The thermocouple type is determined by the first five input bits B31 to B27 as shown in Table 16. Standard NIST coefficients for types J, K, E, N, R, S, T and B thermocouples are stored in the device ROM. If custom thermocouples are used, the custom thermocouple sensor type can be selected. In this case, user-specific data can be stored in the on-chip RAM starting at the address defined in the custom thermocouple data pointer. Thermocouple channel assignments follow the general convention shown in Figure 7. The thermocouple positive terminal ties to CHTC (where TC is the selected channel number) for both the single-ended and differential modes of operation. For single-ended measurements the thermocouple negative terminal and the COM pin are grounded. The thermocouple negative terminal is tied to CHTC-1 for differential measurements. This node can either be grounded or tied to a bias voltage. (2) Cold Junction Channel Pointer The cold junction compensation can be a diode, active analog temperature sensor, RTD, or thermistor. The cold junction channel pointer tells the LTC2986 which channel (1 to 10) the cold junction sensor is assigned to (see Table 17). When a conversion is performed on a channel tied to a thermocouple, the cold junction sensor is simultaneously and automatically measured. The final output data uses the embedded coefficients stored in ROM to automatically compensate the cold junction temperature and output the thermocouple sensor temperature. Table 15. Thermocouple Channel Assignment Word (1) THERMOCOUPLE (2) COLD JUNCTION TYPE CHANNEL POINTER TABLES 4, 16 Measurement Type Thermocouple (4) CUSTOM THERMOCOUPLE DATA POINTER TABLE 18 TABLES 86 TO 88 TABLE 17 31 30 29 28 27 26 25 24 23 22 Types 1 to 9 (3) SENSOR CONFIGURATION 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 0 0 0 0 Cold Junction SGL=1 OC OC Channel Assignment DIFF=0 Check Current [1:0] [4:0] 0 Custom Address [5:0] Custom Length -1 [5:0] 29861fa For more information www.linear.com/LTC2986 25 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 16. Thermocouple Type (1) THERMOCOUPLE TYPE B31 B30 B29 B28 B27 THERMOCOUPLE TYPES 0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple Table 17. Cold Junction Channel Pointer 0.1F SINGLE-ENDED - COM CHANNEL = CH (2 TC 10) TC ASSIGNMENT CHTC + 0.1F DIFFERENTIAL CHTC-1 - 29861 F07 Figure 7. Thermocouple Channel Assignment Convention Table 18. Sensor Configuration (2) COLD JUNCTION CHANNEL POINTER (3) SENSOR CONFIGURATION B26 B25 B24 B23 B22 COLD JUNCTION CHANNEL No Cold Junction Compensation, 0C Used for Calculations SGL OC CHECK 0 0 0 0 0 B21 B20 B19 B18 0 0 0 0 1 CH1 0 0 X 1 0 CH2 0 1 0 0 0 0 0 0 0 1 1 CH3 0 1 0 1 0 0 CH4 0 1 0 0 0 1 0 1 CH5 0 0 0 1 1 0 CH6 0 0 1 1 1 CH7 0 1 0 0 0 CH8 0 1 0 0 1 CH9 0 1 0 1 0 CH10 All Other Combinations CHANNEL = CH (1 TC 10) TC ASSIGNMENT CHTC + OC CURRENT SINGLE-ENDED/ DIFFERENTIAL OPEN-CIRCUIT CURRENT X Differential External 0 Differential 10A 0 1 Differential 100A 1 0 Differential 500A 1 1 1 Differential 1mA 1 0 X X Single-Ended External 1 1 0 0 Single-Ended 10A 1 1 0 1 Single-Ended 100A 1 1 1 0 Single-Ended 500A 1 1 1 1 Single-Ended 1mA Invalid 29861fa 26 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION are a hard error and -999C or F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bit D29 indicates a hard fault occurred at the cold junction sensor and -999C or F is reported. Refer to the specific sensor (diode, themistor, or RTD) used for cold junction compensation. Bit D28 indicates a soft fault occurred at the cold junction sensor. A valid temperature is reported, but the accuracy may be compromised since the cold junction sensor is operating outside its normal temperature range. Bits D27 and D26 indicate over or under temperature limits have been exceeded for specific thermocouple types, as defined in Table 20. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. This fault reflects a reading that is well beyond the normal range of a thermocouple. (4) Custom Thermocouple Data Pointer See Custom Thermocouples section near the end of this data sheet for more information. Fault Reporting - Thermocouple Each sensor type has a unique fault reporting mechanism indicated in the upper byte of the data output word. Table 19 shows faults reported in the measurement of thermocouples. Bit D31 indicates the thermocouple sensor is open (broken or not plugged in), the cold junction sensor has a hard fault, or the ADC is out of range. This is indicated by a reading well beyond the normal operating range. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). Either of these Table 19. Thermocouple Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Open Circuit or Hard ADC or Hard CJ -999C or F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) -999C or F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Thermocouple Reading Greater Than High Limit Suspect Reading D26 Sensor Under Range Soft Thermocouple Reading Less Than Low Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond 1.125 * VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 -999C or F Valid Reading Table 20. Thermocouple Temperature Limits THERMOCOUPLE TYPE LOW TEMP LIMIT C HIGH TEMP LIMIT C J-Type -210 1200 K-Type -265 1372 E-Type -265 1000 N-Type -265 1300 R-type -50 1768 S-Type -50 1768 T-Type -265 400 B-Type 40 1820 Custom Lowest Table Entry Highest Table Entry 29861fa For more information www.linear.com/LTC2986 27 LTC2986/LTC2986-1 APPLICATIONS INFORMATION DIODE MEASUREMENTS Channel Assignment - Diode For each diode tied to the LTC2986, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 21). This word includes (1) diode sensor selection, (2) sensor configuration, (3) excitation current, and (4) diode ideality factor. 1) Sensor Type The diode is selected by the first five input bits B31 to B27 (see Table 22). Bit B24 enables a running average of the diode temperature reading. This reduces the noise when the diode is used as a cold junction temperature element on an isothermal block where temperatures change slowly. The algorithm used for diode averaging is a simple recursive running average. The new value is equal to the average of the current reading plus the previous value. NEW VALUE = CURRENT READING PREVIOUS VALUE + 2 2 If the current reading is 2C above or below the previous value, the new value is reset to the current reading. (3) Excitation Current (2) Sensor Configuration The sensor configuration field (bits B26 to B24) is used to define various diode measurement properties. Configuration bit B26 is set high for single-ended (measurement relative to COM) and low for differential. Bit B25 sets the measurement algorithm. If B25 is low, two conversion cycles (one at 1I and one at 8I current excitation) are used to measure the diode. This is used in applications where parasitic resistance between the LTC2986 and the diode is small. Parasitic resistance effects can be removed by setting bit B25 high, enabling three conversion cycles (one at 1I, one at 4I and one at 8I). The next field in the channel assignment word (B23 to B22) controls the magnitude of the excitation current applied to the diode (see Table 23). In the two conversion cycle mode, the device performs the first conversion at a current equal to 8x the excitation current 1I. The second conversion occurs at 1I. Alternatively, in the three conversion cycle mode the first conversion excitation current is 8I, the second is 4I and the 3rd is 1I. Table 21. Diode Channel Assignment Word (1) SENSOR TYPE (2) SENSOR CONFIGURATION TABLE 22 Measurement Class 31 30 29 28 27 Diode Type = 28 26 25 24 SGL=1 2 or 3 Avg DIFF=0 Readings on (3) EXCITATION CURRENT (4) DIODE IDEALITY FACTOR VALUE TABLE 23 TABLE 24 23 22 Current [1:0] 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Non-Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution All Zeros Uses a Factory Set Default of 1.003 Table 23. Diode Excitation Current Selection Table 22. Diode Sensor Selection (3) EXCITATION CURRENT (1) SENSOR TYPE B31 B30 B29 B28 B27 SENSOR TYPE B23 B22 1I 4I 8I 1 1 1 0 0 Diode 0 0 10A 40A 80A 0 1 20A 80A 160A 1 0 40A 160A 320A 1 1 80A 320A 640A 29861fa 28 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION (4) Diode Ideality Factor Fault Reporting - Diode The last field in the channel assignment word (B21 to B0) sets the diode ideality factor within the range 0 to 4 with 1/1048576 (2-20) resolution. The top two bits (B21 to B20) are the integer part and bits B19 to B0 are the fractional part of the ideality factor (see Table 24). Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 25 shows faults reported in the measurement of diodes. Bit D31 indicates the diode is open, shorted, not plugged in, wired backwards, or the ADC reading is bad. Any of these are hard faults and -999C or F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This is a hard error and -999C or F is reported. In the case of Diode channel assignments follow the general convention shown in Figure 8. The anode ties to CHD (where D is the selected channel number) for both the single-ended and differential modes of operation, and the cathode is grounded. For differential diode measurements, the cathode is also tied to CHD-1. CHANNEL = CH (1 D 10) D ASSIGNMENT CHD SINGLE-ENDED COM CHANNEL= CH (2 D 10) D ASSIGNMENT CHD DIFFERENTIAL CHD-1 29861 F08 Figure 8. Diode Channel Assignment Convention Table 24. Programming Diode Ideality Factor (4) DIODE IDEALITY FACTOR VALUE B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 Example h 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 2-15 2-16 2-17 2-18 2-19 2-20 1.25 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.003 (Default) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.006 0 1 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 1 Table 25. Diode Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Open, Short, Reversed, or Hard ADC -999C or F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) -999C or F D29 Not Used for Diodes N/A Always 0 D28 Not Used for Diodes N/A Always 0 D27 Sensor Over Range Soft T > 130C Suspect Reading D26 Sensor Under Range Soft T < -60C Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond 1.125 * VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading 29861fa For more information www.linear.com/LTC2986 29 LTC2986/LTC2986-1 APPLICATIONS INFORMATION an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bits D29 and D28 are not used for diodes. Bits D27 and D26 indicate over or under temperature limits (defined as T > 130C or T < -60C). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a diode is used as the cold junction element, any hard or soft error is flagged in the corresponding thermocouple result (bits D28 and D29 in Table 19). Example: Single-Ended Type K and Differential Type T Thermocouples with Shared Diode Cold Junction Compensation Figure 9 shows a typical temperature measurement system where two thermocouples share a single cold junction diode. In this example, a Type K thermocouple is tied to CH1 and a Type T thermocouple is tied to CH3 and CH4. They both share a single cold junction diode with ideality factor of =1.003 tied to CH2. Channel assignment data for both thermocouples and the diode are CH1 TYPE K THERMOCOUPLE ASSIGNED TO CH1 (CHTC=1) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x200 TO 0x203 RESULT MEMORY LOCATIONS 0x010 TO 0x013 CH2 DIODE COLD JUNCTION ASSIGNED TO CH2 (CHD=2) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x204 TO 0x207 RESULT MEMORY LOCATIONS 0x014 TO 0x017 0.1F TYPE K = 1.003 shown in Tables 26 to 28. Thermocouple #1 (Type K) sensor type and configuration data are assigned to CH1. 32-bits of binary configuration data are mapped directly into memory locations 0x200 to 0x203 (see Table 26). The cold junction diode sensor type and configuration data are assigned to CH2. 32-bits of binary configuration data are mapped directly into memory locations 0x204 to 0x207 (see Table 27). Thermocouple #2 (Type T) sensor type and configuration data are assigned to CH4. 32-bits of binary configuration data are mapped directly into memory locations 0x20C to 0x20F (see Table 28). A conversion is initiated on CH1 by writing 10000001 into memory location 0x000. Both the Type K thermocouple and the diode are measured simultaneously. The LTC2986 calculates the cold junction compensation and determines the temperature of the Type K thermocouple. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000001. Similarly, a conversion can be initiated on CH4 by writing 10000100 into memory location 0x000. The results (in C) can be read from memory locations 0x010 to 0x013 for CH1 and 0x01C to 0x01F for CH4. CH3 TYPE T CH4 0.1F TYPE T THERMOCOUPLE JUNCTION ASSIGNED TO CH4 (CHTC=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F RESULT MEMORY LOCATIONS 0x01C TO 0x01F COM 29861 F09 Figure 9. Dual Thermocouple with Diode Cold Junction Example 29861fa 30 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 26. Thermocouple #1 Channel Assignment (Type K, Cold Junction CH2, Single-Ended, 10A Open-Circuit Detect) CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 0x200 (1) Thermocouple Type Type K 5 00010 0 0 0 1 0 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Single-Ended, 10A Open-Circuit 4 1100 Not Used Set These Bits to 0 6 000000 Not Custom 12 000000000000 (4) Custom Thermocouple Data Pointer MEMORY ADDRESS 0x201 MEMORY ADDRESS 0x202 MEMORY ADDRESS 0x203 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 27. Diode Channel Assignment (Single-Ended 3-Reading, Averaging On, 20A/80A Excitation, Ideality Factor = 1.003)) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type BINARY DATA Diode 5 (2) Sensor Configuration Single-Ended, 3-Reading, Average On 3 111 (3) Excitation Current 20A, 80A, 160A 2 01 1.003 22 0100000000110001001001 (4) Ideality Factor MEMORY ADDRESS 0x204 MEMORY ADDRESS 0x205 MEMORY ADDRESS 0x206 MEMORY ADDRESS 0x207 11100 1 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 Table 28. Thermocouple #2 Channel Assignment (Type T, Cold Junction CH2, Differential, 100A Open-Circuit Detect) CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 0x20C (1) Thermocouple Type Type T 5 00111 0 0 1 1 1 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Differential, 100A OpenCircuit Current 4 0101 Not Used Set These Bits to 0 6 000000 Not Custom 12 000000000000 (4) Custom Thermocouple Data Pointer MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 31 LTC2986/LTC2986-1 APPLICATIONS INFORMATION RTD MEASUREMENTS (3) Sensor Configuration Channel Assignment - RTD The sensor configuration field is used to define various RTD properties. Configuration bits B20 and B21 determine if the RTD is a 2-, 3-, or 4-wire type (see Table 32). For each RTD tied to the LTC2986, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 29). This word includes (1) RTD type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) RTD curve, and (6) custom RTD data pointer. The simplest configuration is the 2-wire configuration. While this setup is simple, parasitic errors due to IR drops in the leads result in systematic temperature errors. The 3-wire configuration cancels RTD lead resistance errors (if the lines are equal resistance) by applying two matched current sources to the RTD, one per lead. Mismatches in the two current sources are removed through transparent background calibration. 4-wire RTDs remove unbalanced RTD lead resistance by measuring directly across the sensor using a high impedance Kelvin sensing. 4-wire measurements with Kelvin RSENSE are useful in applications where sense resistor wiring parasitics can lead to errors; this is especially useful for low resistance PT-10 type RTDs. In this case, both the RTD and sense resistor have Kelvin sensing connections. (1) RTD Type The RTD type is determined by the first five input bits B31 to B27 as shown in Table 30. Linearization coefficients for RTD types PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120 with selectable common curves ( = 0.003850, = 0.003911, = 0.003916, and = 0.003926) are built into the device. If custom RTDs are used, RTD Custom can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined by the custom RTD data pointers. The next sensor configuration bits (B18 and B19) determine the excitation current mode. These bits are used to enable RSENSE sharing, where one sense resistor is used for multiple 2-, 3-, and/or 4-wire RTDs. In this case, the RTD ground connection is internal and each RTD points to the same RSENSE channel. (2) Sense Resistor Channel Pointer RTD measurements are performed ratiometrically relative to a known RSENSE resistor. The sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the RTD (see Table 31). Sense resistors are always measured differentially. Bits B18 and B19 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connected between the RTD and the measurement instrument. This mode is available for all 4-wire configurations using internal current source excitation. Table 29. RTD Channel Assignment Word (1) RTD TYPE (2) SENSE RESISTOR CHANNEL POINTER (3) SENSOR CONFIGURATION TABLE 30 TABLE 31 TABLE 32 Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 RTD Type = 10 to 18 RSENSE Channel Assignment [4:0] 2, 3, 4 Wire 19 (4) EXCITATION (5) RTD CURRENT CURVE TABLE 33 18 Excitation Mode TABLE 34 17 16 15 14 13 Excitation Current [3:0] (6) CUSTOM RTD DATA POINTER TABLES 92 TO 94 12 11 10 9 8 7 6 5 4 3 2 1 0 Curve [1:0] Custom Address Custom Length-1 [5:0] [5:0] 29861fa 32 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 30. RTD Type (1) RTD TYPE B31 B30 B29 B28 B27 RTD TYPE 0 1 0 1 0 RTD PT-10 0 1 0 1 1 RTD PT-50 0 1 1 0 0 RTD PT-100 0 1 1 0 1 RTD PT-200 0 1 1 1 0 RTD PT-500 0 1 1 1 1 RTD PT-1000 1 0 0 0 0 RTD 1000 ( = 0.00375) 1 0 0 0 1 RTD NI-120 1 0 0 1 0 RTD Custom Table 31. Sense Resistor Channel Pointer (2) SENSE RESISTOR CHANNEL POINTER B26 B25 B24 B23 B22 SENSE RESISTOR CHANNEL 0 0 0 0 0 Invalid 0 0 0 0 1 Invalid 0 0 0 1 0 CH2-CH1 0 0 0 1 1 CH3-CH2 0 0 1 0 0 CH4-CH3 0 0 1 0 1 CH5-CH4 0 0 1 1 0 CH6-CH5 0 0 1 1 1 CH7-CH6 0 1 0 0 0 CH8-CH7 0 1 0 0 1 CH9-CH8 0 1 0 1 0 CH10-CH9 All Other Combinations Invalid 29861fa For more information www.linear.com/LTC2986 33 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 32. RTD Sensor Configuration Selection (3) SENSE CONFIGURATION MEASUREMENT MODE BENEFITS RTDs CANCELS RTD CANCELS RTD CANCELS CANCELS CURRENT SENSE POSSIBLE MATCHED MISMATCH PARASITIC RSENSE NUMBER EXCITATION NUMBER LEAD GROUND SOURCE RESISTOR PER LEAD LEAD THERMOCOUPLE OF WIRES RESISTANCE MODE OF WIRES CONNECTION ROTATION SHARING DEVICE RESISTANCE RESISTANCE EFFECTS B21 B20 B19 B18 0 0 0 0 2-Wire 0 0 0 1 0 1 0 0 0 1 0 0 1 1 0 1 1 External No No 2 2-Wire Internal No Yes 4 3-Wire External No No 2 * 1 3-Wire Internal No Yes 4 * 1 X Reserved 0 0 4-Wire External No No 2 * * 0 0 1 4-Wire Internal No Yes 2 * * 0 1 0 4-Wire Internal Yes Yes 2 * * 1 0 1 1 Reserved 1 1 0 0 4-Wire, Kelvin RSENSE External No No 2 * * * 1 1 0 1 4-Wire, Kelvin RSENSE Internal No Yes 2 * * * 1 1 1 0 4-Wire, Kelvin RSENSE Internal Yes Yes 2 * * 1 1 1 1 Reserved * * * 29861fa 34 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION (4) Excitation Current The next field in the channel assignment word (B17 to B14) controls the magnitude of the excitation current applied to the RTD (see Table 33). The current selected is the total current flowing through the RTD independent of the wiring configuration. The RSENSE current is 2x the sensor excitation current for 3-wire RTDs. Table 33. Total Excitation Current for All RTD Wire Types (5) RTD Curve (4) EXCITATION CURRENT B17 B16 B15 B14 CURRENT 0 0 0 0 External 0 0 0 1 5A 0 0 1 0 10A 0 0 1 1 25A 0 1 0 0 50A 0 1 0 1 100A 0 1 1 0 250A 0 1 1 1 500A 1 0 0 0 1mA In order to prevent soft or hard faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0V. For example, if RSENSE is 10k and the RTD is a PT-100, select an excitation current of 100A for 2-wire and 4-wire RTDs and select 50A for a 3-wire RTD. Alternatively, using a 1k sense resistor with a PT-100 RTD allows 500A excitation for any wiring configuration. Bits B13 and B12 set the RTD curve used and the corresponding Callendar-Van Dusen constants (shown in Table 34). (6) Custom RTD Data Pointer In the case where an RTD not listed in Table 34 is used, a custom RTD table may be entered into the LTC2986. See Custom RTD section near the end of this data sheet for more information. Table 34. RTD Curves: RT = R0 * (1 + a * T + b * T2 + (T - 100C) * c * T3) for T < 0C, RT = R0 * (1 + a * T + b * T2) for T > 0C (5) CURVE B13 B12 CURVE ALPHA a b c 0 0 0 1 European Curve 0.00385 3.908300E-03 -5.775000E-07 -4.183000E-12 American 0.003911 3.969200E-03 -5.849500E-07 -4.232500E-12 1 0 Japanese 0.003916 3.973900E-03 -5.870000E-07 -4.400000E-12 1 1 ITS-90 0.003926 3.984800E-03 -5.870000E-07 -4.000000E-12 X X RTD1000-375 0.00375 3.810200E-03 -6.018880E-07 -6.000000E-12 X X *NI-120 N/A N/A N/A N/A *NI-120 uses table based data. 29861fa For more information www.linear.com/LTC2986 35 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Fault Reporting - RTD for RTDs. Bits D27 and D26 indicate over or under temperature limits (see Table 36). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If an RTD is used as the cold junction element, any hard or soft error is also flagged in the thermocouple result. Each sensor type has unique fault reporting mechanism indicated in the most significant byte of the data output word. Table 35 shows faults reported in the measurement of RTDs. Bit D31 indicates the RTD or RSENSE is open, shorted, or not plugged in. This is a hard fault and -999C or F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This is a hard error and -999C or F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise was a random infrequent event. Bits D29 and D28 are not used Sense Resistor Channel Assignment For each sense resistor tied to the LTC2986, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 37). This word includes (1) sense resistor selection and (2) sense resistor value. Table 35. RTD Fault Reporting BIT FAULT D31 Sensor Hard Fault ERROR TYPE Hard DESCRIPTION Open or Short RTD or RSENSE OUTPUT RESULT D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) -999C or F D29 Not Used for RTDs N/A Always 0 Valid Reading D28 Not Used for RTDs N/A Always 0 Valid Reading D27 Sensor Over Range Soft T > High Temp Limit (See Table 36) Suspect Reading D26 Sensor Under Range Soft T < Low Temp Limit (See Table 36) Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond 1.125 * VREF/2 Suspect Reading D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 -999C or F Valid Reading Table 36. Voltage and Resistance Ranges RTD TYPE MIN MAX LOW TEMP LIMIT C HIGH TEMP LIMIT C PT-10 PT-50 1.95 34.5 -200 850 9.75 172.5 -200 850 PT-100 19.5 345 -200 850 PT-200 39 690 -200 850 PT-500 97.5 1725 -200 850 PT-1000 195 3450 -200 850 NI-120 66.6 380.3 -80 260 Custom Table Lowest Table Entry Highest Table Entry Lowest Table Entry Highest Table Entry Table 37. Sense Resistor Channel Assignment Word Measurement Class Sense Resistor (1) SENSOR TYPE (2) SENSE RESISTOR VALUE () Table 38 Table 39 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 Type = 29 8 7 6 5 4 3 2 1 0 Sense Resistor Value (17, 10) Up to 131,072 with 1/1024 Resolution 29861fa 36 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION (1) Sensor Type Sense resistor channel assignments follow the general convention shown in Figure 11. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the RTD. Channel assignment data (see Table 37) is mapped into a memory location corresponding to CHRSENSE. The sense resistor is selected by setting the first 5 input bits, B31 to B27, to 11101 (see Table 38). Table 38. Sense Resistor Selection (1) SENSOR TYPE B31 B30 B29 B28 B27 SENSOR TYPE 1 1 1 0 1 Sense Resistor CHRSENSE-1 EXCITATION CURRENT FLOW (2) Sense Resistor Value CHRSENSE Figure 11. Sense Resistor Channel Assignment Convention for 2-Wire RTDs Example: 2-Wire RTDs with Shared RSENSE Figure 12 shows a typical temperature measurement system using multiple 2-wire RTDs. In this example, a PT1000 RTD ties to CH7 and CH8 and an NI-120 RTD ties to CH9 and CH10. Using this configuration, the LTC2986 can digitize up to four 2-wire RTDs with a single sense resistor. Example: 2-Wire RTD The simplest RTD configuration is the 2-wire configuration, 2-wire RTDs follow the general convention shown in Figure 10. They require only two connections per RTD and can be tied directly to 2-lead RTD elements. This topology, however, causes errors due to parasitic lead resistance. If sharing is not selected (1 RSENSE per RTD), then CHRTD should be grounded. The ground connection should be removed if sharing is enabled (1 RSENSE for multiple RTDs). RTD #1 sensor type and configuration data are assigned to CH8. 32 bits of binary configuration data are mapped directly into memory locations 0x21C to 0x21F (see Table 40). RTD #2 sensor type and configuration data are assigned to CH10. 32-bits of binary configuration data are mapped directly into memory locations 0x224 to 0x227 (see Table 41). The sense resistor is assigned to CH6. The user-programmable value of this resistor is 5001.5. 32 bits of binary configuration data are mapped directly into memory locations 0x214 to 0x217 (see Table 42). 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) EXCITATION CURRENT FLOW CHRTD-1 1 CHRTD CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F11 The last field in the channel assignment word (B26 to B0) sets the value of the sense resistor within the range 0 to 131,072 with 1/1024 precision (see Table 39). The top 17 bits (B26 to B10) create the integer and bits B9 to B0 create the fraction of the sense resistor value. 2 RSENSE CHANNEL = CH RTD (2 RTD 10) ASSIGNMENT A conversion is initiated on CH8 by writing 10001000 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001000. The resulting temperature in C can be read from memory locations 0x02C to 0x02F (corresponding to CH8). A conversion can be initiated and read from CH10 in a similar fashion. OPTIONAL GND, REMOVE FOR RSENSE SHARING 29861 F10 Figure 10. 2-Wire RTD Channel Assignment Convention Table 39. Example Sense Resistor Values (2) SENSE RESISTOR VALUE () B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 Example R 216 215 214 213 212 211 210 29 28 27 26 25 24 23 22 21 B6 B5 B4 B3 B2 B1 B0 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 10,000.2 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 1 99.99521k 1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1 1 0 0 1 1 0 1 0 1 1 1 1.0023k 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 1 0 0 1 0 0 1 1 0 0 1 1 29861fa For more information www.linear.com/LTC2986 37 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CH5 RSENSE 5001.5 0.01F SENSE RESISTOR ASSIGNED TO CH6 (CHRSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 CH6 0.01F 2 CH7 0.01F 2-WIRE PT-1000 1 RTD #1 ASSIGNED TO CH8 (CHRTD=8) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x21C TO 0x21F RESULT MEMORY LOCATIONS 0x02C TO 0x02F CH8 0.01F 2 CH9 0.01F 2-WIRE NI-120 1 RTD #2 ASSIGNED TO CH10 (CHRTD=10) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x224 TO 0x227 RESULT MEMORY LOCATIONS 0x034 TO 0x037 CH10 0.01F 29861 F12 Figure 12. Shared 2-Wire RTD Example Table 40. Channel Assignment Data for 2-Wire RTD #1 (PT-1000, RSENSE on CH6, 2-Wire, Shared RSENSE, 10A Excitation Current, = 0.003916 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x21C PT-1000 5 01111 0 1 1 1 1 CH6 5 00110 (3) Sensor Configuration 2-Wire with Shared RSENSE 4 0001 (4) Excitation Current 10A 4 0010 Japanese, = 0.003916 2 10 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x21D MEMORY ADDRESS 0x21E MEMORY ADDRESS 0x21F 0 0 1 1 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa 38 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 41. Channel Assignment Data for 2-Wire RTD #2 (NI-120, RSENSE on CH6, 2-Wire, Shared RSENSE, 100A Excitation Current) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x224 NI-120 5 10001 1 0 0 0 1 CH6 5 00110 (3) Sensor Configuration 2-Wire with Shared RSENSE 4 0001 (4) Excitation Current 100A 4 0101 (5) Curve European = 0.00385 2 00 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x225 MEMORY ADDRESS 0x226 MEMORY ADDRESS 0x227 0 0 1 1 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 42. Channel Assignment Data for Sense Resistor (Value = 5001.5) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 5001.5 27 MEMORY MEMORY BINARY DATA ADDRESS 0x214 ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000010011100010011000000000 0 0 0 0 1 00 1 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 39 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: 3-Wire RTD 3-wire RTD channel assignments follow the general convention shown in Figure 13. Terminals 1 and 2 tie to the input/excitation current sources and terminal 3 connects to the sense resistor. Channel assignment data is mapped to memory locations corresponding to CHRTD. Sense resistor channel assignments follow the general convention shown in Figure 14. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 3rd terminal of the RTD and CHRSENSE-1 is tied to ground (or left floating for RSENSE sharing). Channel assignment data (see Table 37) is mapped into the memory location corresponding to CHRSENSE. Figure 15 shows a typical temperature measurement system using a 3-wire RTD. In this example, a 3-wire RTD's terminals tie to CH9, CH8, and CH7. The sense resistor ties to CH7 and CH6. The sense resistor and RTD connect together at CH7. The 3-wire RTD reduces the errors associated with parasitic lead resistance by applying excitation current to each RTD input. This first order cancellation removes matched lead resistance errors. This cancellation does not remove errors due to thermocouple effects or mismatched lead resistances. The RTD sensor type and configuration data are assigned to CH9. 32 bits of binary configuration data are mapped directly into memory locations 0x220 to 0x223 (see Table 43). The sense resistor is assigned to CH7. The user-programmable value of this resistor is 12150.39. 32 bits of binary configuration data are mapped directly into memory locations 0x218 to 0x21B (see Table 44). A conversion is initiated on CH9 by writing 10001001 into memory location 0x000 . Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001. The resulting temperature in C can be read from memory locations 0x030 to 0x033 (corresponding to CH9). 29861fa 40 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CHRSENSE 3 EXCITATION CURRENT FLOW 2 CHRTD-1 1 CHRTD 3RD TERMINAL TIES TO SENSE RESISTOR CHANNEL = CH RTD (2 RTD 10) ASSIGNMENT 29861 F13 Figure 13. 3-Wire RTD Channel Assignment Convention (OPTIONAL GND, REMOVE FOR RSENSE SHARING) CHRSENSE-1 2x EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F14 Figure 14. 3-Wire Sense Resistor Channel Assignment Convention for 3-Wire RTDs CH6 RSENSE 12,150.39 CH7 RSENSE ASSIGNED TO CH7 (CHRSENSE=7) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x218 TO 0x21B 0.01F 3 2 CH8 0.01F 3-WIRE PT-200 1 CH9 3-WIRE RTD ASSIGNED TO CH9 (CHRTD=9) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULT MEMORY LOCATIONS 0x030 TO 0x033 0.01F 29861 F15 Figure 15. 3-Wire RTD Example 29861fa For more information www.linear.com/LTC2986 41 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 43. Channel Assignment Data for 3-Wire RTD (PT-200, RSENSE on CH7, 3-Wire, 50A Excitation Current, = 0.003911 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x220 PT-200 5 01101 0 1 1 0 1 CH7 5 00111 (3) Sensor Configuration 3-Wire 4 0100 (4) Excitation Current 50A 4 0100 American, = 0.003911 2 01 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x221 MEMORY ADDRESS 0x222 MEMORY ADDRESS 0x223 0 0 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 44. Channel Assignment Data for Sense Resistor (Value = 12150.39) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor (2) Sense Resistor 12150.39 Value 5 27 MEMORY MEMORY BINARY DATA ADDRESS 0x218 ADDRESS 0x219 MEMORY ADDRESS 0x21A MEMORY ADDRESS 0x21B 11101 1 1 1 0 1 000101111011101100110001111 0 0 0 1 0 1 11 1 0 1 1 1 0 1 1 0 0 1 1 0 0 0 1 1 1 0 29861fa 42 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Standard 4-Wire RTD (No Rotation or RSENSE Sharing) Standard 4-wire RTD channel assignments follow the general convention shown in Figure 16. Terminal 1 is tied to ground, terminals 2 and 3 (Kelvin sensed signal) tie to CHRTD and CHRTD-1, and the 4th terminal ties to the sense resistor. Channel assignment data (see Table 29) is mapped to memory locations corresponding to CHRTD. Sense resistor channel assignments follow the general convention shown in Figure 17. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 4th terminal of the RTD. Channel assignment data (see Table 37) is mapped into a memory location corresponding to CHRSENSE. Figure 18 shows a typical temperature measurement system using a 4-wire RTD. In this example, a 4-wire RTD's CHRSENSE 4 EXCITATION CURRENT FLOW terminals tie to GND, CH4, CH3, and CH2. The sense resistor ties to CH2 and CH1. The sense resistor and RTD share a common connection at CH2. The RTD sensor type and configuration data are assigned to CH4. 32 bits of binary configuration data are mapped directly into memory locations 0x20C to 0x20F (see Table 45). The sense resistor is assigned to CH2. The user-programmable value of this resistor is 5000.2. 32 bits of binary configuration data are mapped directly into memory locations 0x204 to 0x207 (see Table 46). A conversion is initiated on CH4 by writing 10000100 into the data byte at memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000100. The resulting temperature in C can be read from memory locations 0x01C to 0x01F (corresponding to CH4). 4TH TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) 3 CHRTD-1 2 CHRTD CHANNEL = CH RTD (2 RTD 10) ASSIGNMENT 1 29861 F16 Figure 16. 4-Wire RTD Channel Assignment Convention CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F17 Figure 17. Sense Resistor Channel Assignment Convention for 4-Wire RTDs 29861fa For more information www.linear.com/LTC2986 43 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CH1 0.01F RSENSE 5000.2 SENSE RESISTOR ASSIGNED TO CH2 (CHRSENSE=2) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x204 TO 0x207 CH2 0.01F 4 3 CH3 0.01F 4-WIRE PT-1000 2 RTD ASSIGNED TO CH4 (CHRTD=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F RESULT MEMORY LOCATIONS 0x01C TO 0x01F CH4 1 0.01F 29861 F18 Figure 18. Standard 4-Wire RTD Example Table 45. Channel Assignment Data for 4-Wire RTD (PT-1000, RSENSE on CH2, Standard 4-Wire, 25A Excitation Current, = 0.00385 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x20C PT-1000 5 01111 0 1 1 1 1 CH2 5 00010 (3) Sensor Configuration 4-Wire, No Rotate, No Share 4 1000 (4) Excitation Current 25A 4 0011 (5) Curve European, = 0.00385 2 00 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 46. Channel Assignment Data for Sense Resistor (Value = 5000.2) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 5000.2 27 MEMORY BINARY DATA ADDRESS 0x204 MEMORY ADDRESS 0x205 MEMORY ADDRESS 0x206 MEMORY ADDRESS 0x207 11101 1 1 1 0 1 000010011100010000011001100 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 00 0 1 1 0 0 1 1 0 0 29861fa 44 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: 4-Wire RTD with Rotation data is mapped into a memory location corresponding to CHRSENSE. One method to improve the accuracy of an RTD over the standard 4-wire implementation is by rotating the excitation current source. Parasitic thermocouple effects are automatically removed through autorotation. In order to perform autorotation, the 1st terminal of the RTD ties to CHRTD+1 instead of GND, as in the standard case. This allows the LTC2986 to automatically change the direction of the current source without the need for additional external components. Figure 21 shows a typical temperature measurement system using a rotating 4-wire RTD. In this example a 4-wire RTD's terminals tie to CH10, CH9, CH8, and CH6. The sense resistor is tied to CH6 and CH5. The sense resistor and RTD connect together at CH6. The RTD sensor type and configuration data are assigned to CH9. 32 bits of binary configuration data are mapped directly into memory locations 0x220 to 0x223 (see Table 47). The sense resistor is assigned to CH6. The user programmable value of this resistor is 10.0102k. 32 bits of binary configuration data are mapped directly into memory locations 0x214 to 0x217 (see Table 48). 4-wire RTD with rotation channel assignments follow the general convention shown in Figure 19. Terminal 1 is tied to CHRTD+1, terminals 2 and 3 (Kelvin sensed signal) tie to CHRTD and CHRTD-1, and the 4th terminal ties to the sense resistor. Channel assignment data (see Table 29) is mapped to memory locations corresponding to CHRTD. A conversion is initiated on CH9 by writing 10001001 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001. The resulting temperature in C can be read from memory locations 0x030 to 0x033 (corresponding to CH9). Sense resistor channel assignments follow the general convention shown in Figure 20. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 4th terminal of the RTD. Channel assignment CHRSENSE 4TH TERMINAL TIES TO SENSE RESISTOR 4 EXCITATION CURRENT FLOW 3 CHRTD-1 2 CHRTD CHANNEL = CH RTD (2 RTD 9) ASSIGNMENT 1 CHRTD+1 29861 F19 Figure 19. 4-Wire RTD Channel Assignment Convention CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F20 Figure 20. Sense Resistor Channel Assignment Convention for 4-Wire RTDs with Rotation 29861fa For more information www.linear.com/LTC2986 45 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CH5 0.01F RSENSE 10.0102k SENSE RESISTOR ASSIGNED TO CH6 (CHRSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 CH6 0.01F 4 3 CH8 0.01F PT-100 2 RTD ASSIGNED TO CH9 (CHRTD=9) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULT MEMORY LOCATIONS 0x030 TO 0x033 CH9 1 0.01F CH10 0.01F 29861 F21 Figure 21. Rotating 4-Wire RTD Example Table 47. Channel Assignment Data for Rotating 4-Wire RTD (PT-100, RSENSE on CH6, Rotating 4-Wire, 100A Excitation Current, = 0.003911 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x220 PT-100 5 01100 0 1 1 0 0 CH6 5 00110 (3) Sensor Configuration 4-Wire with Rotation 4 1010 (4) Excitation Current 100A 4 0101 American, = 0.003911 2 01 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x221 MEMORY ADDRESS 0x222 MEMORY ADDRESS 0x223 0 0 1 1 0 1 0 1 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 48. Channel Assignment Data for Sense Resistor (Value = 10.0102k) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.0102k 27 MEMORY BINARY DATA ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0 29861fa 46 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Multiple 4-Wire RTDs with Shared RSENSE supports both rotated and non-rotated RTD excitations. Channel assignment data for each sensor is shown in Tables 49 to 51. Figure 22 shows a typical temperature measurement system using two 4-wire RTDs with a shared RSENSE. The LTC2986 can support up to two 4-wire RTDs with a single sense resistor. In this example, the first 4-wire RTD's terminals tie to CH5, CH4, CH3, and CH2 and the 2nd ties to CH8, CH7, CH6, and CH2. The sense resistor ties to CH1 and CH2. The sense resistor and both RTDs connect together at CH2. This channel assignment convention is identical to that of the rotating RTD. This topology A conversion is initiated on CH4 by writing 10000100 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000100. The resulting temperature in C can be read from memory locations 0x01C to 0x01F (corresponding to CH4). A conversion can be initiated and read from CH7 in a similar fashion. CH1 0.01F RSENSE 10k SENSE RESISTOR ASSIGNED TO CH2 (CHRSENSE=2) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x204 TO 0x207 CH2 0.01F 4 3 CH3 0.01F 4-WIRE PT-100 2 RTD #1 ASSIGNED TO CH4 (CHRTD=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F RESULT MEMORY LOCATIONS 0x01C TO 0x01F CH4 1 0.01F CH5 0.01F 4 3 CH6 0.01F 4-WIRE PT-500 2 RTD #2 ASSIGNED TO CH7 (CHRTD=7) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x218 TO 0x21B RESULT MEMORY LOCATIONS 0x028 TO 0x02B CH7 1 0.01F CH8 0.01F 29861 F22 Figure 22. Shared RSENSE 4-Wire RTD Example Table 49. Channel Assignment Data for 4-Wire RTD #1 (PT-100, RSENSE on CH2, 4-Wire, Shared RSENSE, Rotated 100A Excitation Current, = 0.003926 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x20C PT-100 5 01100 0 1 1 0 0 CH2 5 00010 (3) Sensor Configuration 4-Wire Rotated 4 1010 (4) Excitation Current 100A 4 0101 ITS-90, = 0.003926 2 11 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 0 0 0 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 47 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 50. Channel Assignment Data for 4-Wire RTD #2 (PT-500, RSENSE on CH2, 4-Wire, Rotated 50A Excitation Current, = 0.003911 Curve) CONFIGURATION FIELD DESCRIPTION # BITS (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x218 PT-500 5 01110 0 1 1 1 0 CH2 5 00010 (3) Sensor Configuration 4-Wire Shared, No Rotation 4 1001 (4) Excitation Current 50A 4 0100 American, = 0.003911 2 01 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x219 MEMORY ADDRESS 0x21A MEMORY ADDRESS 0x21B 0 0 0 1 0 1 0 0 1 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 51. Channel Assignment Data for Sense Resistor (Value = 10.000k) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.000k 27 MEMORY BINARY DATA ADDRESS 0x204 MEMORY ADDRESS 0x205 MEMORY ADDRESS 0x206 MEMORY ADDRESS 0x207 11101 1 1 1 0 1 000100111000100000000000000 0 0 0 10 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 00 29861fa 48 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: 4-Wire RTD with Kelvin RSENSE It is possible to cancel the parasitic lead resistance in the sense resistors by configuring the 4-wire RTD with a 4-wire (Kelvin connected) sense resistor. This is useful when using a PT-10 or PT-50 with a small valued RSENSE or when the sense resistor is remotely located or in applications requiring extreme precision. The 4-wire RTD channel assignments follow the general conventions previously defined (Figure 19) for a standard 4-wire RTD. The sense resistor follows the convention shown in Figure 23. Figure 24 shows a typical temperature measurement system using a 4-wire RTD with a Kelvin connected RSENSE. In this example, the 4-wire RTD's terminals tie to CH10, CH9, CH8, and CH6. The sense resistor ties to CH6, CH5, and CH4 and excitation current is applied to CH4 and CH10. The sense resistor's nominal value is 1k in order to accommodate a 1mA excitation current. The sense resistor and RTD connect together at CH6. This topology supports rotated, shared and standard 4-wire RTD topologies. If rotated or shared configuration are not used then terminal 1 of the RTD is tied to ground instead of CH10, freeing up one input channel. Channel assignment data is shown in Tables 52 and 53. A conversion is initiated on CH9 by writing 10001001 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001 (see Table 6). The resulting temperature in C can be read from memory locations 0x030 to 0x033 (corresponding to CH9). CHRSENSE-2 4 EXCITATION CURRENT FLOW 3 CHRSENSE-1 2 CHRSENSE RSENSE CHANNEL = CH RSENSE (3 RSENSE 10) ASSIGNMENT 1 TIES TO RTD TERMINAL 4 29861 F23 Figure 23. Sense Resistor with Kelvin Connections Channel Assignment Convention CH4 0.01F 4 3 CH5 0.01F RSENSE 1k 2 1 4 CH6 0.01F 3 CH8 0.01F 4-WIRE PT-10 2 1 SENSE RESISTOR ASSIGNED TO CH6 (CHRSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 CH9 RTD ASSIGNED TO CH9 (CHRTD=9) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULTS MEMORY LOCATIONS 0x030 TO 0x033 0.01F CH10 0.01F 29861 F24 Figure 24. Sense Resistor with Kelvin Connections Example 29861fa For more information www.linear.com/LTC2986 49 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 52. Channel Assignment Data for 4-Wire RTD with Kelvin Connected RSENSE (PT-10, RSENSE on CH6, 4-Wire, Kelvin RSENSE with Rotated 1mA Excitation Current, = 0.003916 Curve) CONFIGURATION FIELD # BITS PT-10 5 01010 0 1 0 1 0 CH6 5 00110 4-Wire Kelvin RSENSE and Rotation 4 1110 1mA 4 1000 Japanese, = 0.003916 2 10 Not Custom 12 000000000000 (1) RTD TYPE (2) Sense Resistor Channel Pointer (3) Sensor Configuration (4) Excitation Current (5) Curve (6) Custom RTD Data Pointer BINARY DATA MEMORY ADDRESS 0x220 DESCRIPTION MEMORY ADDRESS 0x221 MEMORY ADDRESS 0x222 MEMORY ADDRESS 0x223 0 0 1 1 0 1 1 1 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 53. Channel Assignment Data for Sense Resistor (Value = 1000) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 27 1000 BINARY DATA MEMORY ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa 50 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION used Thermistor types 44004/44033, 44005/44030, 44006/44031, 44007/44034, 44008/44032 and YSI-400 are built into the device. If other custom thermistors are used, Thermistor Custom Steinhart-Hart or Thermistor Custom Table (temperature vs resistance) can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined in Thermistor Custom Steinhart-Hart or Thermistor Custom Table address pointers. THERMISTOR MEASUREMENTS Channel Assignment - Thermistor For each thermistor tied to the LTC2986, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 54). This data includes (1) thermistor type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) Steinhart-Hart address pointer or custom table address pointer. (2) Sense Resistor Channel Pointer (1) Thermistor Type Thermistor measurements are performed ratiometrically relative to a known RSENSE resistor. The sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the current thermistor (see Table 31). The thermistor type is determined by the first five input bits (B31 to B27) as shown in Table 55. Linearization coefficients based on Steinhart-Hart equation for commonly Table 54. Thermistor Channel Assignment Word (1) THERMISTOR (2) SENSE RESISTOR TYPE CHANNEL POINTER TABLE 55 Type = 19 to 27 (4) EXCITATION CURRENT (5) CUSTOM THERMISTOR DATA POINTER TABLE 56 TABLE 57 TABLES 96, 97, 98, 100, 101 TABLE 31 Measurement Class 31 30 29 28 27 26 25 24 23 22 Thermistor (3) SENSOR CONFIGURATION RSENSE Channel Pointer [4:0] 21 SGL = 1 DIFF = 0 20 19 Excitation Mode 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Excitation Current Not Used [3:0] 0 0 0 Custom Address [5:0] Custom Length -1 [5:0] Table 55. Thermistor Type: 1/T = A + B * ln(R) + C * ln(R)2 + D * ln(R)3 + E * ln(R)4 + F *ln(R)5 B31 B30 B29 B28 B27 THERMISTOR TYPE A B C D E F 1 0 0 1 1 Thermistor 44004/44033 2.252k at 25C 1.46800E-03 2.38300E-04 0 1.00700E-07 0 0 1 0 1 0 0 Thermistor 44005/44030 3k at 25C 1.40300E-03 2.37300E-04 0 9.82700E-08 0 0 1 0 1 0 1 Thermistor 44007/44034 5k at 25C 1.28500E-03 2.36200E-04 0 9.28500E-08 0 0 1 0 1 1 0 Thermistor 44006/44031 10k at 25C 1.03200E-03 2.38700E-04 0 1.58000E-07 0 0 1 0 1 1 1 Thermistor 44008/44032 30k at 25C 9.37600E-04 2.20800E-04 0 1.27600E-07 0 0 1 1 0 0 0 Thermistor YSI-400 2.252k at 25C 1.47134E-03 2.37624E-04 0 1.05034E-07 0 0 1 1 0 0 1 Spectrum 1003k 1k at 25C 1.445904E-3 2.68399E-04 0 1.64066E-07 0 0 1 1 0 1 0 Thermistor Custom Steinhart-Hart user input user input user input user input user input user input 1 1 0 1 1 Thermistor Custom Table not used not used not used not used not used not used 29861fa For more information www.linear.com/LTC2986 51 LTC2986/LTC2986-1 APPLICATIONS INFORMATION (3) Sensor Configuration (4) Excitation Current The sensor configuration field is used to define various thermistor properties. Configuration bit B21 is set high for single-ended (measurement relative to COM) and low for differential (see Table 56). The next field in the channel assignment word (B18 to B15) controls the magnitude of the excitation current applied to the thermistor (see Table 57). In order to prevent hard or soft faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0V. The LTC2986 has no special requirements related to the ratio between the voltage drop across the sense resistor and the sensor. Consequently, it is possible to have a sense resistor several orders of magnitude smaller than the maximum sensor value. For optimal performance over the full thermistor temperature range, auto ranged current can be selected. In this case, the LTC2986 conversion is performed in three cycles (instead of the standard two cycles) (see Table 83). The first cycle determines the optimal excitation current for the sensor resistance value and RSENSE value. The following two cycles use that current to measure the thermistor temperature. Table 56. Sensor Configuration Data (3) SENSOR CONFIGURATION SGL EXCITATION MODE B21 B20 B19 0 0 0 0 SINGLE-ENDED/ DIFFERENTIAL SHARE RSENSE ROTATE 0 Differential No No 0 1 Differential Yes Yes 1 0 Differential Yes No 0 1 1 1 0 0 1 0 1 Reserved 1 1 0 Reserved 1 1 1 Reserved Reserved Single-Ended No No The next sensor configuration bits (B19 and B20) determine the excitation current mode. These bits are used to enable RSENSE sharing, where one sense resistor is used for multiple thermistors. In this case, the thermistor ground connection is internal and each thermistor points to the same RSENSE channel. Bits B19 and B20 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connection between the thermistor and the measurement instrument. This mode is available for differential thermistor configurations using internal current source excitation. (5) Steinhart-Hart Address/Custom Table Address See Custom Thermistors section near the end of this data sheet for more information. Table 57. Excitation Current for Thermistors (4) EXCITATION CURRENT B18 B17 B16 B15 CURRENT 0 0 0 0 Reserved 0 0 0 1 250nA 0 0 1 0 500nA 0 0 1 1 1A 0 1 0 0 5A 0 1 0 1 10A 0 1 1 0 25A 0 1 1 1 50A 1 0 0 0 100A 1 0 0 1 250A 1 0 1 0 500A 1 0 1 1 1mA 1 1 0 0 Auto Range* 1 1 0 1 Invalid 1 1 1 0 Invalid 1 1 1 1 External *Auto Range not allowed for custom sensors. 29861fa 52 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Fault Reporting - Thermistor This is a hard error and -999C is output. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random infrequent event. Bits D29 and D28 are not used for thermistors. Bits D27 and D26 indicate the reading is over or under temperature limits (see Table 59). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a thermistor is used as the cold junction element, any hard or soft error is flagged in the thermocouple result. Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 58 shows faults reported during the measurement of thermistors. Bit D31 indicates the thermistor or RSENSE is open, shorted, or not plugged in. This is a hard fault and -999C is reported. Bit D30 indicates a bad ADC reading. This could be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). Table 58. Thermistor Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Open or Short Thermistor or RSENSE D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) D29 Not Used for Thermistors N/A Always 0 Valid Reading D28 Not Used for Thermistors N/A Always 0 Valid Reading D27 Sensor Over Range* Soft T > High Temp Limit Suspect Reading D26 Sensor Under Range* Soft T < Low Temp Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond 1.125 * VREF/2 Suspect Reading D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 -999C -999C Valid Reading *Do not apply to custom Steinhart-Hart sensor type. Custom table thermistor over/under range is determined by the resistor table values, see custom thermistor table example for details. Table 59. Thermistor Temperature/Resistance Range THERMISTOR TYPE MIN () MAX () LOW Temp Limit (C) HIGH Temp Limit (C) Thermistor 44004/44033 2.252k at 25C 41.9 75.79k -40 150 Thermistor 44005/44030 3k at 25C 55.6 101.0k -40 150 Thermistor 44007/44034 5k at 25C 92.7 168.3k -40 150 Thermistor 44006/44031 10k at 25C 237.0 239.8k -40 150 Thermistor 44008/44032 30k at 25C 550.2 884.6k -40 150 Thermistor YSI 400 2.252k at 25C 6.4 1.66M -80 250 Spectrum 1003K 1k at 25C 51.1 39.51k -50 125 Thermistor Custom Steinhart-Hart N/A N/A N/A N/A Second Table Entry Last Table Entry Thermistor Custom Table 29861fa For more information www.linear.com/LTC2986 53 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Single-Ended Thermistor The simplest thermistor configuration is the single-ended configuration. Thermistors using this configuration share a common ground (COM) between all sensors and are each tied to a unique sense resistor (RSENSE sharing is not allowed for single-ended thermistors). Single-ended thermistors follow the convention shown in Figure 25. Terminal 1 ties to ground (COM) and terminal 2 ties to CHTHERM and the sense resistor. Channel assignment data (see Table 54) is mapped to memory locations corresponding to CHTHERM. 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) 2 EXCITATION CURRENT FLOW 1 CHTHERM CHANNEL = CH THERM (1 THERM 10) ASSIGNMENT COM 29861 F25 Figure 25. Single-Ended Thermistor Channel Assignment Convention Sense resistor channel assignments follow the general convention shown in Figure 26. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 37) is mapped into the memory location corresponding to CHRSENSE. CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F26 Figure 26. Sense Resistor Channel Assignment Convention Figure 27 shows a typical temperature measurement system using a single-ended thermistor. In this example a 10k (44031 type) thermistor is tied to a 10.1k sense resistor. The thermistor is assigned channel CH5 (memory locations 0x210 to 0x213) and the sense resistor to CH4 (memory locations 0x20C to 0x20F). Channel assignment data are shown in Tables 60 and 61. A conversion is initiated on CH5 by writing 10000101 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000101. The resulting temperature in C can be read from memory locations 0x020 to 0x023 (corresponding to CH5). CH3 RSENSE 10.1k 100pF CH4 100pF 2 CH5 100pF TYPE 44031 SENSE RESISTOR ASSIGNED TO CH4 (CHRSENSE=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F THERMISTOR ASSIGNED TO CH5 (CHTHERM=5) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x210 TO 0x213 RESULT MEMORY LOCATIONS 0x020 TO 0x023 1 COM 29861 F27 Figure 27. Single-Ended Thermistor Example 29861fa 54 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 60. Channel Assignment Data for Single-Ended Thermistor (44006/44031 10k at 25C Type Thermistor, Single-Ended Configuration, RSENSE on CH4, 1A Excitation Current) CONFIGURATION FIELD DESCRIPTION # BITS (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x210 44006/44031 10k at 25C 5 10110 1 0 1 1 0 CH4 5 00100 (3) Sensor Configuration Single-Ended 3 100 (4) Excitation Current 1A 4 0011 Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x211 MEMORY ADDRESS 0x212 MEMORY ADDRESS 0x213 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 61. Channel Assignment Data for Sense Resistor (Value = 10.1k) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.1k 27 MEMORY BINARY DATA ADDRESS 0x20C MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 11101 1 1 1 0 1 000100111011101000000000000 0 0 0 1 0 0 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 00 29861fa For more information www.linear.com/LTC2986 55 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Differential Thermistor The differential thermistor configuration allows separate ground sensing for each sensor. In this standard differential configuration, one sense resistor is used for each thermistor. Differential thermistors follow the convention shown in Figure 28. Terminal 1 ties to CHTHERM and is shorted to ground and terminal 2 ties CHTHERM-1 to and the sense resistor. Channel assignment data (see Table 54) is mapped to memory locations corresponding to CHTHERM. 2ND TERMINAL TIES TO SENSE RESISTOR EXCITATION CURRENT FLOW 2 CHTHERM-1 1 CHTHERM CHANNEL = CH THERM (2 THERM 10) ASSIGNMENT 1ST TERMINAL TIES TO GND 29861 F28 Figure 28. Differential Thermistor Channel Assignment Convention Sense resistor channel assignments follow the general convention shown in Figure 29. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 37) is mapped into a memory location corresponding to CHRSENSE. CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F29 Figure 29. Sense Resistor Channel Assignment Convention Figure 30 shows a typical temperature measurement system using a differential thermistor. In this example a 30k (44032 type) thermistor is tied to a 9.99k sense resistor. The thermistor is assigned channel CH9 (memory locations 0x220 to 0x223) and the sense resistor to CH7 (memory locations 0x218 to 0x21B). Channel assignment data is shown in Table 62 and Table 63). A conversion is initiated on CH9 by writing 10001001 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001. The resulting temperature in C can be read from memory locations 0x030 to 0x033 (Corresponding to CH9). CH6 RSENSE 9.99k 100pF CH7 SENSE RESISTOR ASSIGNED TO CH7 (CHRSENSE=7) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x218 TO 0x21B 100pF 2 CH8 100pF TYPE 44032 1 CH9 THERMISTOR ASSIGNED TO CH9 (CHTHERM=9) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULT MEMORY LOCATIONS 0x030 TO 0x033 29861 F30 Figure 30. Differential Thermistor Example 29861fa 56 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 62. Channel Assignment Data for Differential Thermistor (44008/44032 30k at 25C Type Thermistor, Differential Configuration, RSENSE on CH7, Auto Range Excitation) CONFIGURATION FIELD DESCRIPTION # BITS (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x220 44008/44032 30k at 25C 5 10111 1 0 1 1 1 CH7 5 00111 (3) Sensor Configuration Differential, No Share, No Rotate 3 000 (4) Excitation Current Auto Range 4 1100 Set These Bits to 0 2 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x221 MEMORY ADDRESS 0x222 MEMORY ADDRESS 0x223 0 0 1 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 63. Channel Assignment Data for Sense Resistor (Value = 9.99k) CONFIGURATION FIELD DESCRIPTION # BITS (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 9.99k 27 MEMORY BINARY DATA ADDRESS 0x218 MEMORY MEMORY ADDRESS 0x219 ADDRESS 0x21A MEMORY ADDRESS 0x21B 11101 1 1 1 0 1 000100111000001100000000000 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 57 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Shared/Rotated Differential Thermistor CHRSENSE-1 The differential thermistor configuration allows separate internal ground sensing for each sensor. In this configuration, one sense resistor can be used for multiple thermistors. Differential thermistors follow the convention shown in Figure 31. Terminal 1 ties to CHTHERM and terminal 2 ties to CHTHERM-1 and the sense resistor. Channel assignment data (see Table 54) is mapped to memory locations corresponding to CHTHERM. 2ND TERMINAL TIES TO SENSE RESISTOR EXCITATION CURRENT FLOW 2 CHTHERM-1 1 CHTHERM CHANNEL = CH THERM (2 THERM 10) ASSIGNMENT 29861 F31 Figure 31. Thermistor with Shared RSENSE Channel Assignment Convention Sense resistor channel assignments follow the general convention shown in Figure 32. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 37) is mapped into a memory location corresponding to CHTHERM. EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 RSENSE 10) ASSIGNMENT 29861 F32 Figure 32. Sense Resistor Channel Assignment Convention for Thermistors Figure 33 shows a typical temperature measurement system using a shared sense resistor and one rotated/ non-rotated differential thermistors. In this example a 30k (44032 Type) thermistor is tied to a 10.0k sense resistor and configured as rotated/shared. The second thermistor a 2.25k (44033 type) is configured as a non-rotated/shared. Channel assignment data are shown in Tables 64 to 66. A conversion is initiated on CH8 by writing 10001000 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001000. The resulting temperature in C can be read from memory locations 0x02C to 0x02F (corresponding to CH8). A conversion can be initiated and read from CH10 in a similar fashion. CH5 RSENSE 10k 100pF CH6 SENSE RESISTOR ASSIGNED TO CH6 (CHRSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 100pF 2 CH7 100pF TYPE 44032 1 CH8 THERMISTOR #1 ASSIGNED TO CH8 (CHTHERM=8) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x21C TO 0x21F RESULT MEMORY LOCATIONS 0x02C TO 0x02F 100pF 2 CH9 100pF TYPE 44033 1 CH10 THERMISTOR #2 ASSIGNED TO CH10 (CHTHERM=10) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x224 TO 0x227 RESULT MEMORY LOCATIONS 0x034 TO 0x037 100pF 29861 F33 Figure 33. Rotated and Shared Thermistor Example 29861fa 58 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 64. Channel Assignment Data Differential Thermistor (44008/44032 30k at 25C Type Thermistor, Differential Configuration with Sharing and Rotation, RSENSE on CH6, 250nA Excitation Current) CONFIGURATION FIELD DESCRIPTION # BITS (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x21C 44008/44032 30k at 25C 5 10111 1 0 1 1 1 CH6 5 00110 (3) Sensor Configuration Differential, Rotate and Shared 3 001 (4) Excitation Current 250nA Excitation Current 4 0001 Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x21D MEMORY ADDRESS 0x21E MEMORY ADDRESS 0x21F 0 0 1 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 65. Channel Assignment Data Differential Thermistor (44004/44033 2.252k at 25C Type Thermistor, Differential Configuration with Sharing and No Rotation, RSENSE on CH6, 10A Excitation Current) Configuration Field (1) Thermistor Type Description # Bits Binary Data MEMORY ADDRESS 0x224 44004/44033 2.252k at 25C 5 10011 1 0 0 1 1 CH6 5 00110 (3) Sensor Configuration Differential, No Rotate and Shared 3 010 (4) Excitation Current 10A Excitation Current 4 0101 Not Used Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Custom RTD Data Pointer MEMORY ADDRESS 0x225 MEMORY ADDRESS 0x226 MEMORY ADDRESS 0x227 0 0 1 1 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 66. Channel Assignment Data for Sense Resistor (Value = 10.0k) Configuration Field Description # Bits (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 27 10.0k MEMORY Binary Data ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 59 LTC2986/LTC2986-1 APPLICATIONS INFORMATION GLOBAL CONFIGURATION REGISTER Table 67 shows a summary of the global configuration register. The global configuration register is 1 byte long and is at memory location 0x0F0. Bits G0 - G1 set the notch frequency of the on chip digital filter, Bit G2 sets the temperature results unit (C or F), Bits G3 and G7 are reserved and should be set low, Bits G4 - G6 determine the Kelvin current excitation mode. Table 67. Global Configuration Register Bit # Field Name Description G0 G1 Filter Frequency Select [1:0] 00 = 55Hz 01 = 60Hz 10 = 50Hz G2 Temperature Result Format 0 = Celsius 1 = Fahrenheit G3 Reserved Set to 0 G4 3-Wire RTD Kelvin Current Excitation Mode Excitation Current on Adjacent Channels G5 2-Wire RTD Kelvin Current Excitation Mode Excitation Current on Adjacent Channels G6 Thermistor Kelvin Current Excitation Mode Excitation Current on Adjacent Channels G7 Reserved Set to 0 INPUT OVERVOLTAGE PROTECTION - OVERVIEW Temperature sensors are often used in harsh environments. The sensors or leads can short to high voltages or each other. Resistive circuits can protect the LTC2986 from these fault conditions. These external resistors can potentially introduce measurement errors; however, the LTC2986 includes special modes and features that reduce these effects The tip of a thermocouple is often unshielded, creating a low impedance conductive path to the input of the measurement device. In order to protect the LTC2986 from damage due to overvoltage conditions, current-limiting resistors can be placed between the input channels and the thermocouple sensor. The value of this resistor is chosen such that at the maximum overvoltage, the current entering the LTC2986 is less than 15mA. Errors due to these protection resistors are minimal during normal operation due to the very low input leakage (1nA) specifications of the LTC2986. Most RTD sensor elements are electrically isolated from the sensor leads either through a non-conductive encapsulation or a separate grounding shield. While these types of sensors may not require input overvoltage protection, certain applications may require current limiting resistors between the RTD and the LTC2986. One such application is a universal input device where an input terminal can see either an RTD or a thermocouple. Other applications may require protection against erroneous connections, for example, connecting a voltage source accidentally to the RTD input terminals. The protection circuits implemented for RTDs should accommodate 2-wire, 3-wire, and 4-wire configurations. Thermistors are 2-wire resistance to temperature sensors with a non-conductive encapsulation enclosing the sensor element. Similar to the RTD, overvoltage protection for thermistors may be required for both universal sensor input applications and inadvertent user applied overvoltage. The LTC2986 offer several current excitation modes for eliminating errors due to resistive overvoltage protection circuits. The following sections describe overvoltage protection circuits for thermocouples, 2-, 3-, and 4-wire RTDs and thermistors with an emphasis on universality (sharing the same protection scheme for all sensor types). Input Overvoltage Protection - Resistor Value Selection The maximum continuous current the LTC2986 can sustain without damage is 15mA. In order to determine the value of the overvoltage protection resistor and its power rating, the maximum voltage is required. This voltage is application specific and depends on the maximum anticipated overvoltage. For example, a system with possible overvoltage of 40V would require a resistance R > 2.7k and a power rating (see Figure 34 and Figure 35): P > 600mW, where R > VMAX - VDD 15mA 29861fa 60 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION vs Minimum Protection Resistance MINIMUM PROTECTION RESISTANCE (k) 13.3 12.0 10.7 9.3 8.0 6.7 2k 1nA (MAX) 2k ERROR = 4V + CH1 5.3 4.0 - 2.7 COM 1.3 0 0 40 80 120 160 MAXIMUM FAULT VOLTAGE (V) 200 29861 F34 Figure 34. Maximum Fault Voltage vs Minimum Protection Resistance Power Rating 3.0 29861 F36 Figure 36. Thermocouple with Protection Resistors RTDs are resistive devices that require excitation current in order to determine their temperature. The excitation is applied to the series network consisting of the RTD and a sense resistor in order to make a ratiometric measurement. Overvoltage protection is implemented by placing a resistor between each RTD terminal and the LTC2986 input channels. 2.4 2.1 1.8 1.5 1.2 0.9 0.6 0.3 0 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. Input Overvoltage Protection - RTDs 2.7 MINIMUM PROTECTION RESISTOR WATTAGE (W) In addition to the protection resistors, 100pF capacitors should be added to each input for anti-alias filtering; these are not shown in the following schematics for simplicity. 0 40 80 120 160 MAXIMUM FAULT VOLTAGE (V) 200 29861 F35 Figure 35. Maximum Fault Voltage vs Minimum Protection Resistor Power Rating Input Overvoltage Protection - Thermocouples Thermocouples are low impedance devices that generate voltage as a function of temperature differences. Since the LTC2986 input impedance is very high (input leakage < 1nA) external overvoltage protection resistors have minimal effect on the temperature measurement accuracy. For example, a 2k protection resistor results in a worstcase error of 4V (see Figure 36). This corresponds to a 0.1C error for a Type K thermocouple at 25C. 4-Wire RTDs The simplest RTD configuration to protect is the 4-wire RTD. A protection resistor is tied to each of the 4 RTD terminals (see Figure 37). Excitation current flows through the sense resistor (RSENSE), the RTD, and protection resistors RP1 and RP4. The LTC2986 measures the voltage drop across the RTD using CH3 and CH4 through protection resistors RP2 and RP3. Since the excitation current does not flow through RP2 and RP3, errors due to the protection resistance are negligible. Measurement errors are dominated by input leakage current (I < 1nA). For example, errors due to leakage current for a PT-100 RTD with 1k sense resistor and 1k protection resistors are below 0.025C. 29861fa For more information www.linear.com/LTC2986 61 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CH1 RP1 4 EXCITATION CURRENT FLOW 3 RSENSE CH2 RP2 CH3 ILEAK 2 RP3 CH4 ILEAK 1 RP4 CH5 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. 29861 F37 Figure 37. 4-Wire RTD with Protection Resistors The LTC2986 offers a 3-wire RTD Kelvin current source mode in order to remove errors due to mismatched protection resistors. This feature is enabled by setting the global 3-wire RTD Kelvin current excitation mode bit (G4 = 1, see Table 67) prior to initiating a conversion start. This mode uses the adjacent channels (in this example CH5 and CH6) for the current source excitation and performs the measurement on CH3 and CH4 (see Figure 39). Two additional resistors are placed between the RTD and the channels tied to the excitation current sources, but the protection resistor matching constraint is removed for all resistors. The excitation current no longer flows through RP2 or RP3, removing the voltage drop across them. Figure 40 shows the channel assignment convention for this mode. 3-Wire RTDs 3-wire RTDs are more difficult to protect than 4-wire RTDs. Normally, protection resistors are tied to each of the 3 RTD terminals (see Figure 38). The LTC2986 provides two matched excitation currents, I1 and I2. These currents flow from CH3 and CH4 through RP2 and RP3 into the RTD. The resulting voltage is measured between CH3 and CH4. Assuming RP2 = RP3 and I1 = I2, the errors resulting from the protection resistors are cancelled. While the LTC2986 provides matched current source excitation, external protection resistors may be difficult to match. Every 1 mismatch in RP2 and RP3 translates to a 1 error in the RTD measurement. CH1 RP1 RP1 3 EXCITATION CURRENT FLOW RP2 2 EXCITATION CURRENT FLOW 2 RP2 RP3 1 I1 CH5 I2 RP5 CH6 29861 F39 CH2 CHRSENSE CH3 2 EXCITATION CURRENT FLOW I2 RP3 CH4 ILEAK RP4 3 1 CH3 ILEAK Figure 39. 3-Wire RTD Kelvin Current Mode (G4 = 1) RSENSE I1 CH2 3 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. CH1 RSENSE CH4 1 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. CHRTD-1 CHRTD CHRTD+1 CHANNEL = CH RTD (2 RTD 8) ASSIGNMENT GLOBAL REGISTER G4 = 1 29861 F38 Figure 38. 3-Wire RTD with Protection Resistors CHRTD+2 29861 F40 Figure 40. 3-Wire RTD Kelvin Current Mode Channel Assignment Convention (G4 = 1) 29861fa 62 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION 2-Wire RTDs 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) 2-wire RTDs are difficult to protect because the protection resistor (RP3) is in series with the RTD (see Figure 41). Every 1 of protection resistance adds 1 measurement error to the RTD. The LTC2986 offers a 2-wire Kelvin current source mode in order to remove the errors associated with protection resistors. This feature is enabled by setting the global 2-wire RTD Kelvin current excitation mode bit (G5 = 1, see Table 67) prior to initiating a conversion start. This current excitation mode uses the adjacent channel (CH5 for this example) for the internal ground connection (see Figure 42). One additional protection resistor is added between the RTD and CH5. The excitation current no longer flows through RP3, removing the voltage drop across it. Figure 43 shows the channel assignment convention for this mode. 2 EXCITATION CURRENT FLOW 1 CHRTD-1 CHRTD EXCITATION CURRENT FLOW 29861 F43 Figure 43. 2-Wire Kelvin Current Mode Channel Assignment Convention (G5 = 1) Thermistors Similar to the 2-wire RTD, thermistors are difficult to protect because the protection resistor RP3 is in series with the sensor (see Figure 44). Every 1 of protection resistance adds 1 measurement error to the thermistor. CH1 RP1 RSENSE CH2 RP2 2 I1 EXCITATION CURRENT FLOW CH3 CH4 1 CH5 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. Figure 41. 2-wire RTD with Protection Resistors CH1 2 RSENSE CH2 RP2 I1 ILEAK RP3 1 ILEAK RP4 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. RSENSE CH2 11 CH3 CH4 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. 29861 F41 EXCITATION CURRENT FLOW RP2 RP3 RP3 RP1 GLOBAL REGISTER G5 = 1 CHRTD+1 CH1 RP1 CHANNEL = CH RTD (2 RTD 9) ASSIGNMENT CH3 CH4 CH5 29861 F42 Figure 42. 2-Wire RTD Kelvin Current Mode (G5 = 1) 29861 F44 Figure 44. Thermistor with Protection Resistors The LTC2986 offers a thermistor Kelvin current source mode in order to remove the errors associated with protection resistors. This feature is enabled by setting the global thermistor Kelvin current excitation mode bit (G6 = 1, see Table 67) prior to initiating a conversion start. This current excitation mode uses the adjacent channel (CH5 for this example) for the internal ground connection (see Figure 45). One additional protection resistor is added between the thermistor and CH5. The excitation current no longer flows through RP3, removing the voltage drop across it. Figure 46 shows the channel assignment convention for this mode. 29861fa For more information www.linear.com/LTC2986 63 LTC2986/LTC2986-1 APPLICATIONS INFORMATION CH1 RP1 EXCITATION CURRENT FLOW RSENSE RP2 I1 ILEAK RP3 ILEAK RP4 = EXTERNAL TERMINAL CAN BE EXPOSED TO FAULT VOLTAGE. RP1 CH2 T1 RP2 CH3 T2 RP3 MULTI SENSOR: 2-, 3,- 4-WIRE RTD THERMISTOR THERMOCOUPLE RSENSE CH2 CH3 CH4 RP4 CH4 T3 RP5 T4 RP7 CH5 CH6 CH7 RP8 CH8 RP6 CH5 CH1 CH9 29861 F45 COM Figure 45. Thermistor Kelvin Current Source Mode (G6 = 1) 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) EXCITATION CURRENT FLOW CHTHERM-1 CHTHERM CHTHERM+1 CHANNEL = CH THERM (2 THERM 9) ASSIGNMENT 29861 F47 Figure 47. Universal Multi-Sensor Schematic In Figure 48, a 4-wire RTD is tied directly to the 4 input terminals. In this case, the 4-wire RTD is assigned to CH6 and the sense resistor is tied to CH2. The excitation current flows through protection resisters RP1 and RP6. Since RP6 is grounded, RSENSE sharing and excitation current rotation are off. GLOBAL REGISTER G6 = 1 29861 F46 RP1 Figure 46. Thermistor Kelvin Current Mode Channel Assignment Convention (G6 = 1) 4 3 T1 RP2 T2 RP3 Universal Example RP4 The LTC2986 is capable of sharing one protected interface with multiple sensor types (see Figure 47). This includes all RTD configurations (2-, 3- and 4-wire), thermistors, and thermocouples. Switching between sensors only requires a new channel assignment word via software control. The multi-sensor circuit provides 4 input terminals, each protected against external overvoltage conditions. In order to enable Kelvin current excitation mode for all sensors set all 3 global configuration bits G4, G5, and G6 to 1 (see Table 67). 2 1 T3 RP5 T4 RP7 RP6 RP8 RSENSE CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 COM 29861 F48 Figure 48. Protected Multi-Sensor 4-Wire RTD Connection 29861fa 64 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Figure 49 shows the interface to a 3-wire RTD using the multi-sensor circuit. In this case, the RTD ties directly to terminals T1 - T3 and terminal T4 is left floating. Matched excitation currents flow from CH7 and CH8 through protection resistors RP7 and RP8 while the RTD measurement occurs at CH5 and CH6. The 3-wire RTD is assigned to CH6 and RSENSE sharing is turned on. RP1 3 2 T1 RP2 T2 RP3 RP4 1 T3 RP5 T4 RP7 RP6 RP8 RSENSE RP1 2 T1 RP2 1 T2 RP3 RSENSE CH2 CH3 CH4 RP4 CH1 T3 RP5 T4 RP7 RP6 CH2 CH1 CH5 CH6 CH7 RP8 CH8 CH9 CH3 CH4 COM 29861 F50 CH5 Figure 50. Protected Multi-Sensor 2-Wire RTD Connection CH6 CH7 CH8 CH9 COM 29861 F49 Figure 49. Protected Multi-Sensor 3-Wire RTD Connection Figure 50 shows the interface to a 2-wire RTD using the LTC2986 multi-sensor circuit. In this case, the RTD ties directly to terminals T1 and T2 while terminals T3 and T4 are left floating. The excitation currents flows from CH1 through RSENSE and protection resistors RP1 and RP4 (CH5 is internally grounded) while the RTD measurement occurs at CH3 and CH4. The 2-wire RTD is assigned to CH4 and RSENSE sharing is turned on. Figure 51 shows the interface to a thermistor using the LTC2986 multi-sensor circuit. In this case, the thermistor ties directly to terminals T1 and T2 while terminals T3 and T4 are left floating. The excitation current flows from CH1 through RSENSE and protection resistors RP1 and RP4 (CH5 is internally grounded) while the thermistor differential measurement occurs at CH3 and CH4. The thermistor is assigned to CH4 and RSENSE sharing is enabled in order to provide an internal ground connection. RP1 T1 RP2 T2 RP3 RP4 T3 RP5 T4 RP7 RP6 RP8 RSENSE CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 COM 29861 F51 Figure 51. Protected Multi-Sensor Thermistor Connection 29861fa For more information www.linear.com/LTC2986 65 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Figure 52 shows the interface to a thermocouple using the LTC2986 multi-sensor circuit. In this case, the thermocouple ties directly to terminals T3 and T4 while terminals T1 and T2 can be left floating or tied to an RTD (Global Register G5 = 1) or thermistor (Global Register G6 = 1) for cold junction compensation. Alternatively, a diode (tied to CH9) can be used for cold junction compensation. The thermocouple is assigned to CH6 with single ended measurement mode. OPTIONAL RTD FOR CJ G5 = 1 2 OPTIONAL THERMISTOR FOR CJ G6 = 1 T1 RP2 1 T2 RP3 RP1 RSENSE THERMOCOUPLE T4 CH4 CH5 CH6 RP7 RP6 For the active analog temperature sensor type = 31 (see Table 4 and Figure 53), the channel assignment word is 0xF800 0000 for differential measurements and 0xFC00 0000 for single-ended. When the LTC2986 is configured for the active analog temperature sensor type, it will take the measured voltage value from the ADC and perform a table lookup to produce a temperature result. The result format of the table lookup will be a 24-bit signed fixedpoint temperature result along with the error status byte. The fixed-point format of the temperature is identical to all the other LTC2986 temperature sensor types. This format can be seen in Table 9. CH3 RP5 T3 CH7 RP8 CH8 CH9 OPTIONAL DIODE FOR CJ In addition to passive type temperature sensors, the LTC2986 also supports active analog temperature sensors (i.e. LTC2997). In this mode, the LTC2986 measures the voltage output from the analog temperature sensor and does a table lookup to convert the measured voltage to temperature. This sensor option is fully customizable and can be used for direct temperature measurement or cold junction compensation. Analog Sensor Channel Assignment and Result Formats CH1 CH2 RP4 ACTIVE ANALOG TEMPERATURE SENSORS COM 29861 F52 Figure 52. Protected Multi-Sensor Thermocouple Connection CHANNEL = CHADC (1 CHADC 10) ASSIGNMENT VDD ACTIVE ANALOG TEMPERATURE SENSOR CHADC COM SINGLE-ENDED DIFFERENTIAL - 24-BIT ADC LOOKUP TABLE WITH INTERPOLATION TEMPERATURE OUTPUT CHANNEL = CHADC (2 CHADC 10) ASSIGNMENT VDD ACTIVE ANALOG TEMPERATURE SENSOR + CHADC CHADC-1 + 24-BIT ADC - LOOKUP TABLE WITH INTERPOLATION TEMPERATURE OUTPUT 29861 F53 Figure 53. Active Analog Temperature Sensor Channel Assignment Conventions 29861fa 66 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION The error status byte is located in the upper byte of the data output word. Table 68 shows format of the error status byte for the analog sensor type. Bit D31 and D30 indicate a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). Either of these are a hard error and -999C or F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bits D27 and D26 indicate over or under temperature limits have been exceeded the table limits as described in Table 68. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. Example: Differential Active Analog Temperature Sensor In this example, a simplified temperature curve is implemented (see Figure 54). Points P1 to P9 represent the normal operating range of the custom device. Voltage readings above point P9 result in a soft fault and the reported result is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Voltage readings below point P1 are also reported as soft faults. The reported result is the extrapolation between point P1 and P0, where P0 is typically the lowest possible sensor output voltage. Sensor output voltages below P0 (in mV) will report P0 output. In order to program the LTC2986 with an active analog temperature sensor table, both the mV data and the Kelvin data are converted to 24-bit binary values (represented as two, 3-byte table entries, see Table 69). Since some analog sensors generate negative output voltages, the table mV values are 2's compliment. The sensor output voltage (units = mV) follows the convention shown in Table 71, where the first bit is the sign, the next 11 bits are the integer part and the remaining 12 bits are the fractional part. Table 68. Active Analog Temperature Sensor Fault Data Byte BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Hard Fault Hard VADC < -1.75 * VREF/2 or VADC > 1.75 * VREF/2 -999 D30 Range Hard Fault Hard VADC < -1.75 * VREF/2 or VADC > 1.75 * VREF/2 -999 D29 Not Used N/A NA D28 Not Used N/A NA D27 Soft Above Soft VADC > Last Table Point Voltage Suspect Reading D26 Soft Below Soft VADC < Second Table Point (P1) Voltage Suspect Reading D25 Soft Range Soft VADC < -1.125 * VREF/2 or VADC > 1.125 * VREF/2 Suspect Reading D24 Result Valid (Always 1) NA NA NA NA NA Active Analog Temperature Sensor Table Format Table 69. Active Analog Temperature Sensor Table Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 0x250 + 6 * Start Address Table Entry #1 (mV) Table Entry #1 (Kelvin) 0x250 + 6 * Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Kelvin) 0x250 + 6 * Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Kelvin) * * * * * * * * * Table Entry #64 (mV) Table Entry #64 (Kelvin) Max Address = 0x3CA BYTE 5 29861fa For more information www.linear.com/LTC2986 67 LTC2986/LTC2986-1 APPLICATIONS INFORMATION The temperature values are input in Kelvin as unsigned fixed-point values, but the final temperatures reported by the LTC2986 are reported in C or F. The sensor temperature (Kelvin) follows the convention shown in Table 72, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. In this example, a custom analog sensor is tied to CH2, and is programmed with the channel assignment data shown in Table 73. In this case the custom data begins at memory location 0x250 (starting address is 0). The starting address (offset from 0x250) is entered in the analog sensor data pointer field of the channel assignment data. The table data length -1 (9 in this example) is entered into the data length field of the analog temperature sensor channel assignment word. Refer to Table 70 for the location and format of the 10 six-byte table entries. TEMPERATURE (K) VOLTAGE < p1 SOFT FAULT CONDITION VOLTAGE > p9 SOFT FAULT CONDITION p7 p9 p8 p6 p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0K p4 p3 p1 p2 (0mV, 0K) p0 VOLTAGE (mV) 29861 F54 Figure 54. Active Analog Temperature Sensor Table Example Table 70. Active Analog Temperature Sensor Example Table Data Memory Map POINT SENSOR OUTPUT TEMPERATURE START VOLTAGE (mV) KELVIN ADDRESS STOP ADDRESS P0 -50.22 0 0x250 0x255 P1 -30.2 99.1 0x256 0x25B P2 -5.3 135.4 0x25C 0x261 P3 20.33 220.3 0x262 0x267 P4 40.2 361.2 0x268 0x26D P5 55.3 522.1 0x26E 0x273 P6 88.3 720.3 0x274 0x279 P7 132.2 811.2 0x27A 0x27F P8 188.7 922.5 0x280 0x285 P9 460.4 1000 0x286 0x28B BYTE 0 BYTE 1 mV Data BYTE 2 BYTE 3 BYTE 4 BYTE 5 Temperature Data 29861fa 68 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 71. Example Active Analog Temperature Sensor Voltage Values BYTE 0 BYTE 1 BYTE 2 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 mV Sign 210 29 28 27 26 25 24 23 22 21 20 2-1 B5 B4 B3 2-2 2-3 2-4 2-5 2-6 2-7 B8 B7 B6 2-8 2-9 2-10 2-11 2-12 B2 B1 B0 -50.22 1 1 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 -30.2 1 1 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 -5.3 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 20.33 0 0 0 0 0 0 0 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 0 0 40.2 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 55.3 0 0 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 1 88.3 0 0 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 1 132.2 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 188.7 0 0 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 460.4 0 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 B2 B1 B0 Table 72. Example Active Analog Temperature Sensor Temperature Values BYTE 3 BYTE 4 BYTE 5 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Temperature 213 212 211 210 29 28 27 26 25 24 23 22 21 20 B8 B7 B6 B5 B4 B3 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 0 135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1 220.3 0 0 0 0 0 0 1 1 0 1 1 1 0 0 0 1 0 0 1 1 0 0 1 1 361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0 522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0 720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 811.2 0 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 73. Example Active Analog Temperature Sensor Channel Assignment Data CONFIGURATION FIELD (1) Analog Temp Sensor (2) SE/Diff (3) Not Used DESCRIPTION # BITS BINARY DATA Sensor Type 5 Single-Ended or Differential 1 0 Set to 0 MEMORY ADDRESS 214 MEMORY ADDRESS 215 MEMORY ADDRESS 216 MEMORY ADDRESS 217 11110 1 1 1 1 0 14 00000000000000 (4) Direct ADC Table Start Address = 0 Data Pointer (Start at 0x250) 6 000000 (5) Direct ADC Table Data Length-1 = 9 Data Length-1 6 001001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 29861fa For more information www.linear.com/LTC2986 69 LTC2986/LTC2986-1 APPLICATIONS INFORMATION DIRECT ADC MEASUREMENTS 20 In addition to measuring temperature sensors, the LTC2986 can perform direct ADC (i.e. voltage) measurements. Any channel may be configured to perform direct single-ended or differential measurements. Direct ADC channel assignments follow the general convention shown in Figure 55. The 32-bit channel assignment word is programmed into a memory location corresponding to the input channel. 15 There are two result mode options for direct ADC operation. The first mode is direct voltage output and the second is table-driven output. When configured for direct voltage output, the LTC2986 will return a 24-bit fixed-point voltage result along with the 8-bit fault status byte. When configured for table-lookup, the LTC2986 will perform a table lookup on the raw ADC voltage and return a 24-bit signed-integer table-lookup result along with the 8-bit fault status byte. Figures 56 to Figures 58 show typical integral nonlinearity variation as a function of supply voltage and temperature for a differential input voltage (VREF/2) and VREF/2 common mode input voltage. INL ERROR (ppm) 0 -5 -15 -20 -1.5 90C 25C -45C -1 -0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 1.5 29861 F37 Figure 56. Integral Nonlinearity as a Function of Temperature at VDD = 5.25V 20 15 10 5 0 -5 -10 -15 -20 -1.5 90C 25C -45C -1 -0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 1.5 29861 F38 Figure 57. Integral Nonlinearity as a Function of Temperature at VDD = 3.3V 20 15 10 + SINGLE-ENDED COM - 24-BIT ADC CHANNEL ASSIGNMENT = CHADC (1 CHADC 10) INL ERROR (ppm) CHADC 5 -10 INL ERROR (ppm) The Direct ADC mode is configurable to single-ended as well as differential inputs. The positive input channel ties to CHADC for both single-ended and differential modes. For single-ended measurements the ADC negative input is COM while for differential measurements it is CHADC-1. For single-ended measurements, COM can be driven with any voltage above GND - 50mV and below VDD - 0.3V. The direct ADC results are available in memory at a location corresponding to the conversion channel. 10 5 0 -5 -10 CHADC DIFFERENTIAL CH ADC-1 -15 + 24-BIT ADC - CHANNEL ASSIGNMENT = CHADC (2 CHADC 10) -20 -1.5 90C 25C -45C -1 -0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 1.5 29861 F39 29861 F55 Figure 55. Direct ADC Channel Assignment Conventions Figure 58. Integral Nonlinearity as a Function of Temperature at VDD = 2.85V 29861fa 70 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION ADC readings hard fault errors do not clamp the digital output. Readings beyond 1.125 * VREF/2 exceed the normal accuracy range of the LTC2986 and flag a soft error; these results should be discarded. Readings beyond 1.75 *VREF/2 exceed the usable range of the LTC2986; these result in a hard fault and should be discarded. Voltage Output Mode For standard (non table mode) voltage output mode, the channel assignment word is 0xF000 0000 for differential readings and 0xF400 0000 for single-ended (see Table 75). The data is represented as a 32-bit word (see Table 74) where the eight most significant bits are fault bits and the bottom 24 are the ADC reading in volts. For direct Table 74. Direct ADC Voltage Output Result Format START ADDRESS D31 D30 D29 D28 D27 START ADDRESS + 1 D26 D25 D24 D23 D22 D21 D20 Fault Data START ADDRESS + 3 (END ADDRESS) D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 SIGN MSB Sensor Range NA NA Soft Soft Soft Valid Above Below Range Always Hard Hard 1 Fault Fault Volts START ADDRESS + 2 LSB 2V 1V 0.5V 0.25V ... Integer >VREF 1 1 0 0 1 0 1 1 Fraction CLAMPED to Factory Programmed Value of VREF 1.75 * VREF/2 1 1 0 0 1 0 1 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.125 * VREF/2 0 0 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VREF/2 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2-21V 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -2-21V 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -VREF/2 0 0 0 0 0 0 0 1 1 1 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1.125 * VREF 0 0 0 0 0 1 1 1 1 1 0 1 0 0 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 -1.75 * VREF 1 1 0 0 0 1 1 1 1 0 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 < -VREF 1 1 0 0 0 1 1 1 CLAMPED to Factory Programmed Value of -VREF Example: Direct ADC with Differential Input Table 75. Direct ADC Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA (1) Direct ADC Directly Measure ADC 5 (2) SE/Diff Single-Ended or Differential 1 0 Table Lookup 1 0 Set to 0 13 0000000000000 (4) Direct ADC Table Start Address = 0 Data Pointer 6 000000 (5) Direct ADC Table Data Length-1 = 0 Data Length-1 6 000000 (3) TBL (4) Not Used MEMORY ADDRESS 0x200 MEMORY ADDRESS 0x201 MEMORY ADDRESS 0x202 MEMORY ADDRESS 0x203 11110 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 71 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table Lookup Mode For table-driven output mode, the channel assignment word's 1st two bytes are 0xF200 for differential readings and 0xF600 for single-ended. The 12 least significant bits contain length and pointer information for the custom table data. When the LTC2986 is configured for tabledriven output data, it will take the voltage value from the ADC and perform a table lookup. The result format of the table lookup will be a 24-bit signed integer along with the error status byte. Table 76. Direct ADC Table Lookup Result Format START ADDRESS D31 D30 D29 D28 D27 D26 START ADDRESS + 1 D25 D24 Fault Data START ADDRESS + 3 (END ADDRESS) START ADDRESS + 2 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 SIGN MSB LSB Sensor Range NA NA Soft Soft Soft Valid Above Below Range Always Hard Hard 1 Fault Fault Table Lookup Result - Signed Integer Table 77. Direct ADC Table Lookup Fault Data Byte BIT FAULT DESCRIPTION D31 Sensor Hard Fault VADC < -1.75 * VREF/2 or VADC > 1.75 * VREF/2 D30 Range Hard Fault VADC < -1.75 * VREF/2 or VADC > 1.75 * VREF/2 D29 Not Used NA D28 Not Used NA D27 Soft Above VADC > Last Table Point Voltage D26 Soft Below VADC < Second Table Point (P1) Voltage D25 Soft Range VADC < -1.125 * VREF/2 or VADC > 1.125 * VREF/2 D24 Result Valid (Always 1) NA Table 78. Direct ADC Table Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 0x250 + 6 * Start Address Table Entry #1 (mV) Table Entry #1 (Integer Value) 0x250 + 6 * Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Integer Value) 0x250 + 6 * Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Integer Value) * * * * * * * * * Max Address = 0x3CA Table Entry #64 (mV) Table Entry #64 (Integer Value) BYTE 5 29861fa 72 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Example: Direct ADC with Differential Input and Table Lookup In this example, a simplified custom curve is implemented (see Figure 59). Points P1 to P9 represent the normal operating range of the custom device. Voltage readings above point P9 result in a soft fault and the reported result is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Voltage readings below point P1 are also reported as soft faults. The reported result is the extrapolation between point P1 and P0, where P0 is typically the lowest possible sensor output voltage. Sensor output voltages below P0 (in mV) will report P0 output. TABLE OUTPUT VALUE VOLTAGE < p1 SOFT FAULT CONDITION VOLTAGE > p9 SOFT FAULT CONDITION p7 p8 p9 p6 p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO LOWEST EXPECTED VOLTAGE p4 p3 p1 VOLTAGE (mV) p2 In order to program the LTC2986 with the custom ADC table, both the mV data and the result data are converted to 24-bit binary values (represented as two 3-byte table entries). To accommodate sensors with bipolar output voltages, the mV values input to the LTC2986 are 2's compliment. The sensor output voltage (units = mV) follows the convention shown in Table 80, where the first bit is the sign, the next 11 bits are the integer part and the remaining 12 bits are the fractional part. The result-side of table entries are input as signed 24-bit integers, the final result reported by the LTC2986 is also a 24-bit integer. The result format follows the convention shown in Table 81, where the first bit is the sign bit and the remaining 23 bits are the integer magnitude. In this example, a custom differential sensor is tied to CH2 with the channel assignment data shown in Table 82. In this case the custom data begins at memory location 0x250 (starting address is 0). The starting address (offset from 0x250) is entered in the data pointer field of the channel assignment data. The table data length -1 (9 in this example) is entered into the data length field of the sensor channel assignment word. Refer to Table 79 for the location and format of the 10 six-byte table entries. (0mV, 0 INTEGER) p0 29861 F59 Figure 59. Direct ADC Table Example Table 79. Direct ADC Table Example Data Memory Map POINT SENSOR OUTPUT INTEGER VOLTAGE (mV) OUTPUT DATA START ADDRESS STOP ADDRESS 0x250 0x255 P0 -50.22 -100 P1 -30.2 -50 0x256 0x25B P2 -5.3 0 0x25C 0x261 P3 20.33 2203 0x262 0x267 P4 40.2 3612 0x268 0x26D P5 55.3 5221 0x26E 0x273 P6 88.3 7203 0x274 0x279 P7 132.2 8112 0x27A 0x27F P8 188.7 9225 0x280 0x285 P9 460.4 10000 0x286 0x28B BYTE 0 BYTE 1 mV Data BYTE 2 BYTE 3 BYTE 4 BYTE 5 Integer Output Data 29861fa For more information www.linear.com/LTC2986 73 LTC2986/LTC2986-1 APPLICATIONS INFORMATION Table 80. Example ADC Voltage Values BYTE 0 BYTE 1 BYTE 2 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 mV Sign 210 29 28 27 26 25 24 23 22 21 20 2-1 B5 B4 B3 2-2 2-3 2-4 2-5 2-6 2-7 B8 B7 B6 2-8 2-9 2-10 2-11 2-12 B2 B1 B0 -50.22 1 1 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 -30.2 1 1 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 -5.3 1 1 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 20.33 0 0 0 0 0 0 0 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 0 0 40.2 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 55.3 0 0 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 1 88.3 0 0 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 1 132.2 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 188.7 0 0 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 460.4 0 1 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 Table 81. Example Table Output Values BYTE 3 BYTE 4 BYTE 5 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Temperature Sign 222 221 220 219 218 217 216 215 214 213 212 B8 B7 B6 B5 B4 B3 B2 B1 B0 211 210 29 28 27 26 25 24 23 22 21 20 -100 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 0 0 -50 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2203 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 1 0 1 1 3612 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 1 1 1 0 0 5221 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 1 1 0 0 1 0 1 7203 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 1 0 0 0 1 1 8112 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 1 0 0 0 0 9225 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 0 0 1 10000 0 0 0 0 0 0 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 Table 82. Example Table Lookup Mode Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA (1) Direct ADC Directly Measure ADC 5 (2) SE/Diff Single-Ended or Differential 1 0 Table Lookup 1 1 Set to 0 (3) TBL (4) Not Used MEMORY ADDRESS 214 MEMORY ADDRESS 215 MEMORY ADDRESS 216 MEMORY ADDRESS 217 11110 1 1 1 1 0 13 00000000000000 (5) Direct ADC Table Start Address = 0 Data Pointer (Start at 0x250) 6 000000 (5) Direct ADC Table Data Length-1 = 9 Data Length-1 6 001001 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 29861fa 74 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 SUPPLEMENTAL INFORMATION 2- AND 3-CYCLE CONVERSION MODES The LTC2986 performs multiple internal conversions in order to determine the sensor temperature. Normally, two internal conversion cycles are required for each temperature result providing a maximum output time of 167.2ms. The LTC2986 uses these two cycles to automatically remove offset/offset drift errors, reduce 1/f noise, autocalibrate matched internal current sources, and provide simultaneous 50/60Hz noise rejection. In addition to performing two conversion cycles per result, the LTC2986 also offers several unique features by utilizing a 3rd conversion cycle. In this case, the maximum output time is 251ms and all the benefits of the 2-cycle modes are present (see Table 83). measurement, the thermocouple conversion result is ready after three cycles. A third feature requiring a 3rd conversion cycle is the three current diode measurement. In this mode, three ratioed currents are applied to the external diode in order to cancel parasitic lead resistance effects. This is useful in applications where the diode is remotely located and significant, unknown parasitic lead resistance requires cancellation. If a 3-cycle diode or thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles. Table 83. 2- and 3-Cycles Conversion Modes CONFIGURATION NUMBER OF CONVERSION CYCLES MAXIMUM OUTPUT TIME OC = 0 2 167.2ms All 2 167.2ms Thermistor Non-Autorange Current 2 167.2ms Diode One feature utilizing the three conversion cycle mode is the internal open circuit detect mode. Typically, thermocouple open circuit detection is performed by adding a high resistance pull-up between the thermocouple and VDD. This method can be used with the LTC2986 while operating in the two conversion cycle mode (OC=0). This external pull-up can interact with the input protection circuitry and lead to temperature measurement errors and increased noise. These problems are eliminated by selecting the internal open circuit detection mode (OC=1). In this case, a current is pulsed for 8ms and allowed to settle during one conversion cycle. This is followed by the normal two conversion cycle measurement of the thermocouple. If the thermocouple is broken, the current pulse will result in an open circuit fault. TYPE OF SENSOR A second feature taking advantage of the 3rd conversion cycle is thermistor excitation current auto ranging. Since a thermistor's resistance varies many orders of magnitude, the performance in the low resistance regions are compromised by the small currents required by the high resistance regions of operation. The auto ranging mode applies a test current during the first conversion cycle in order to determine the optimum current for the resistance state of the thermistor. It then uses that current to perform the thermistor measurement using the normal 2-cycle measurement. If a 3-cycle thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple Generally, during the Initiate Conversion state, a conversion measurement is started on a single input channel determined by the channel number (bits B[4:0] = 00001 to 01010) written into memory location 0x000. Multiple consecutive conversions can be initiated by writing bits B[4:0]=00000 into memory location 0. Conversions will be initiated on each channel selected in the mask register (see Table 84). Thermocouple RTD Two Readings 2 167.2ms Thermocouple OC = 1 3 251ms Thermocouple OC = 0, 3-Cycle Cold Junction 3 251ms Autorange Current 3 251ms Three Readings 3 251ms Thermistor Diode RUNNING CONVERSIONS CONSECUTIVELY ON MULTIPLE CHANNELS For example, using the mask data shown in Table 85, after 1000000 is written into memory location 0, conversions are initiated consecutively on CH10, CH8, CH6, and CH1. 29861fa For more information www.linear.com/LTC2986 75 LTC2986/LTC2986-1 SUPPLEMENTAL INFORMATION Once the conversions begin, the INTERRUPT pin goes LOW and remains LOW until all conversions are complete. If the mask register is set for a channel that has no assignment data, that conversion step is skipped. All the results are stored in the conversion result memory locations and can be read at the conclusion of the measurement cycle. ENTERING/EXITING SLEEP MODE The LTC2986 can be placed into sleep mode by writing 0x97 to memory location 0x000. On the rising edge of CS following the memory write (see Figure 2) the device enters the low power sleep state. It remains in this state until CS is brought low or RESET is asserted. Once one of these two signals is asserted, the LTC2986 begins its start-up cycle as described in State 1: Start-Up section of this data sheet. MUX CONFIGURATION DELAY The LTC2986 performs 2 or 3 internal conversion cycles per temperature result. Each conversion cycle is performed with different excitation and input multiplexer configurations. Prior to each conversion, these excitation circuits and input switch configurations are changed and an internal 1ms (typical) delay ensures settling prior to the conversion cycle in most cases. If excessive RC time constants are present in external sensor circuits (large bypass capacitors used for thermistors or RTDs) it is possible to increase the settling time between current source excitation and MUX switching. The extra delay is determined by the value written into the MUX configuration delay register (memory location 0x0FF). The value written into this memory location is multiplied by 100s; therefore, the maximum extra MUX delay is 25.5ms (i.e. 0x0FF = 255 * 100s). REFERENCE CONSIDERATIONS The mechanical stress of soldering the LTC2986 to a PC board can cause the output voltage reference to shift and temperature coefficient to change. These two changes are not correlated. For example, the voltage may shift but the temperature coefficient may not. To reduce the effects of stress-related shifts, mount the reference near the short edge of the PC board or in a corner. Table 84. Multiple Conversion Mask Register MEMORY LOCATION B7 0x0F4 B6 B5 B4 B3 B2 B1 B0 CH10 CH9 Reserved 0x0F5 0x0F6 0x0F7 CH8 CH7 CH6 CH5 CH4 CH3 CH2 CH1 B4 B3 B2 B1 B0 1 0 0 1 Table 85. Example Mask Register Select CH10, CH8, CH6, and CH1 MEMORY LOCATION B7 0x0F4 B6 B5 Reserved 0x0F5 0x0F6 0x0F7 1 0 1 0 0 0 29861fa 76 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM THERMOCOUPLES In addition to digitizing standard thermocouples, the LTC2986 can also digitize user-programmable, custom thermocouples (thermocouple type=0b01001, see Table 16). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data as mV vs temperature (see Table 86). Table 86. Custom Thermocouple Tabular Data Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 0x250 + 6 * Start Address Custom Thermocouple Example In this example, a simplified thermocouple curve is implemented (see Figure 60). Points P1 to P9 represent the normal operating range of the custom thermocouple. Voltage readings above point P9 result in a soft fault and TEMPERATURE (K) VOLTAGE < p1 SOFT FAULT CONDITION VOLTAGE > p9 SOFT FAULT CONDITION (0mV, 273.15K) Table Entry #1 (mV) Table Entry #1 (Kelvin) p7 0x250 + 6 * Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Kelvin) * * * * * * * * p9 p6 0x250 + 6 * Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Kelvin) * p8 p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0K p4 p1 p0 p2 p3 (0mV, 0K) VOLTAGE (mV) 29861 F60 Max Address = 0x3CA Table Entry #64 (mV) Table Entry #64 (Kelvin) Figure 60. Custom Thermocouple Example (mV vs Kelvin) 29861fa For more information www.linear.com/LTC2986 77 LTC2986/LTC2986-1 CUSTOM THERMOCOUPLES the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries in Table 87). Voltage readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is typically the sensor output voltage at 0 Kelvin. If P0 is above 0 Kelvin, then all sensor output voltages below P0 (in mV) will report 0 Kelvin. Sensor readings below P1 are reported as soft faults In order to program the LTC2986 with the custom thermocouple table, both the mV data and the Kelvin data are converted to 24-bit binary values (represented as two 3-byte table entries). Since most thermocouples generate negative output voltages, the mV values input to the LTC2986 are 2's compliment. The sensor output voltage (units=mV), follows the convention shown in Table 88, where the first bit is the sign, the next nine are the integer part and the remaining 14 bits are the fractional part. Table 87. Thermocouple Example mV vs Kelvin (K) Data Memory Map SENSOR OUTPUT TEMPERATURE START VOLTAGE (mV) KELVIN ADDRESS POINT STOP ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 P0 -50.22 0 0x250 0x255 P1 -30.2 99.1 0x256 0x25B P2 -5.3 135.4 0x25C 0x261 P3 0 273.15 0x262 0x267 P4 40.2 361.2 0x268 0x26D mV Data Temperature Data (see Table 88) (see Table 89) P5 55.3 522.1 0x26E 0x273 P6 88.3 720.3 0x274 0x279 P7 132.2 811.2 0x27A 0x27F P8 188.7 922.5 0x280 0x285 P9 460.4 1000 0x286 0x28B Table 88. Example Thermocouple Output Voltage Values (mV) BYTE 0 BYTE 1 BYTE 2 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 mV Sign B8 B7 B6 B5 B4 B3 B2 B1 B0 28 27 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 2-11 2-12 2-13 2-14 -50.22 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0 -30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 0 0 -5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1 132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 29861fa 78 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM THERMOCOUPLES In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2986 are reported in C or F (see Table 9). The sensor temperature (Kelvin), follows the convention shown in Table 89, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. nel assignment data shown in Table 90 (refer to Figure 9 for similar format). In this case the custom data begins at memory location 0x250 (starting address is 0). The starting address (offset from 0x250) is entered in the custom thermocouple data pointer field of the channel assignment data. The table data length -1 (9 in this example) is entered into the custom thermocouple data length field of the thermocouple channel assignment word. Refer to Table 87 where the number of six byte entries is 10. In this example, a custom thermocouple tied to CH1, with a cold junction sensor on CH2, is programmed with the chanTable 89. Example Thermocouple Temperature Values BYTE 3 BYTE 4 BYTE 5 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 0 Temperature 135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1 273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1 361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0 522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0 720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 811.2 0 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 90. Custom Thermocouple Channel Assignment Data CONFIGURATION FIELD BINARY DATA MEMORY ADDRESS 0x200 DESCRIPTION # BITS (1) Thermocouple Type Type Custom 5 01001 0 1 0 0 1 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Single-Ended, 10A Open Circuit 4 1100 Not Used Set These Bits to 0 6 000000 (4) Custom Thermocouple Data Pointer Start Address = 0 (Start at 0x250) 6 000000 Custom Data Length -1 Thermocouple Data =9 Length-1 (10 Paired Entries) 6 001001 MEMORY ADDRESS 0x201 MEMORY ADDRESS 0x202 MEMORY ADDRESS 0x203 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 29861fa For more information www.linear.com/LTC2986 79 LTC2986/LTC2986-1 CUSTOM RTDS Table 91. Custom RTD/Thermistor Tabular Data Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 0x250 + 6 * Start Address Table Entry #1 () Table Entry #1 (Kelvin) 0x250 + 6 * Start Address + 6 Table Entry #2 () Table Entry #2 (Kelvin) 0x250 + 6 * Start Address + 12 Table Entry #3 () Table Entry #3 (Kelvin) * * * * * * * * * Table Entry #64 () Table Entry #64 (Kelvin) Max Address = 0x3CA Custom RTD Example In this example, a simplified RTD curve is implemented (see Figure 61). Points P1 to P9 represent the normal operating range of the custom RTD. Resistance readings above point P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0 (This point should be 0 for proper interpolation below point P1). RESISTANCE < p1 SOFT FAULT CONDITION TEMPERATURE (K) In addition to digitizing standard RTDs, the LTC2986 can also digitize custom RTDs (RTD type=0b10010, see Table 30). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data vs temperature (see Table 91). RESISTANCE > p9 SOFT FAULT CONDITION p7 p9 p6 p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0 0 p8 p4 p3 p1 p0 0 p2 RESISTANCE () 29861 F61 Figure 61. Custom RTD Example ( vs Kelvin ) 29861fa 80 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM RTDS Custom RTD table data is formatted in (sensor output resistance) vs Kelvin (see Table 92). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end at or below 0x3CF. In order to program the LTC2986 with the custom RTD table, both the resistance data and the Kelvin data are converted to 24-bit binary values. The sensor output resistance (units=) follows the convention shown in Table 93, where the first 13 bits are the integer part and the remaining 11 bits are the fractional part. In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2986 are reported in C or F. The sensor temperature (Kelvin) follows the Table 92. RTD Example Resistance vs Kelvin Data Memory Map SENSOR OUTPUT TEMPERATURE START RESISTANCE () (K) ADDRESS POINT STOP ADDRESS P0 0 112.3 0x28C 0x291 P1 80 200.56 0x292 0x297 P2 150 273.16 0x298 0x29D P3 257.36 377.25 0x29E 0x2A3 P4 339.22 489.66 0x2A4 0x2A9 P5 388.26 595.22 0x2AA 0x2AF P6 512.99 697.87 0x2B0 0x2B5 P7 662.3 765.14 0x2B6 0x2BB P8 743.5 801.22 0x2BC 0x2C1 P9 2001.89 900.5 0x2C2 0x2C7 BYTE 2 BYTE 1 BYTE 3 BYTE 1 Resistance Data BYTE 2 BYTE 3 Temperature Data Table 93. Example RTD Resistance Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Resistance 212 211 210 29 28 27 26 25 24 23 22 21 20 B5 B4 B3 B2 2-1 2-2 2-3 2-4 2-5 2-6 B8 B7 B6 2-7 2-8 2-9 2-10 2-11 B1 B0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 150 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 257.36 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 1 1 0 0 0 0 1 339.22 0 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 0 388.26 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0 512.99 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 0 1 1 662.3 0 0 0 1 0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0 743.5 0 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 2001.89 0 0 1 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0 29861fa For more information www.linear.com/LTC2986 81 LTC2986/LTC2986-1 CUSTOM RTDS at memory location 0x28C (starting address is 10). The starting address (offset from 0x250) is entered in the custom RTD data pointer field of the channel assignment data. The table data length -1 (9 in this case) is entered into the custom RTD data length field of the channel assignment word. Refer to Table 91 where the total number of paired entries is 10. convention shown in Table 94, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. In this example, a custom RTD tied to CH3/CH4, with a sense resistor on CH1/CH2, is programmed with the channel assignment data shown in Table 95 (refer to Figure 18 for a similar format). In this case, the custom data begins Table 94. Example RTD Temperature Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 112.3 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 200.56 0 0 0 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 1 273.16 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 1 1 377.25 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0 489.66 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1 595.22 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 697.87 0 0 0 0 1 0 1 0 1 1 1 0 0 1 1 1 0 1 1 1 1 0 1 0 765.14 0 0 0 0 1 1 0 1 1 1 1 1 0 1 0 0 1 0 0 0 1 1 1 1 801.22 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 1 900.5 0 0 0 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 Temperature Table 95. Custom RTD Channel Assignment Data CONFIGURATION FIELD (1) RTD Type DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 0x20C Custom 5 10010 1 0 0 1 0 CH2 5 00010 4-Wire, No Rotate, No Share 4 1000 25A 4 0011 (5) Curve Not Used for Custom 2 00 (6) Custom RTD Data Pointer Start Address = 10 6 001010 6 001001 (2) Sense Resistor Channel Pointer (3) Sensor Configuration (4) Excitation Current (6) Custom RTD Data Data Length -1 Length-1 =9 10 Paired Entries MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 0 0 1 0 1 0 0 0 1 0 0 1 29861fa 82 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM THERMISTORS In addition to digitizing standard thermistors, the LTC2986 can also digitize custom thermistors (thermistor type=0b11011, see Table 55). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data vs temperature (see Table 91). Custom Thermistor Table Example In this example, a simplified thermistor NTC (negative temperature coefficient) curve is implemented (see Figure 62). Points P1 to P9 represent the normal operating range of the custom thermistor. Resistance readings above point In addition to NTC type thermistors, it is also possible to implement PTC (positive temperature coefficient) type thermistors (see Figure 63). In both cases, table entries start at the minimum resistance and end at the maximum resistance value. RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION TEMPERATURE (K) RESISTANCE < p1 SENSOR UNDER-RANGE SOFT FAULT CONDITION TEMPERATURE (K) P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0 (This point must be 0 for proper interpolation below point P1). p0 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0 p9 RESISTANCE < p1 SENSOR UNDER-RANGE SOFT FAULT CONDITION p8 p1 p3 p4 0 0 p7 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0 p2 p5 p1 p6 p7 p8 p9 0 p0 0 p2 p3 p6 p4 p5 RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION RESISTANCE () 29861 F63 RESISTANCE () 29861 F62 Figure 62. Custom NTC Thermistor Example ( vs Kelvin) Figure 63. Custom PTC Thermistor Example ( vs Kelvin) 29861fa For more information www.linear.com/LTC2986 83 LTC2986/LTC2986-1 CUSTOM THERMISTORS Custom thermistor table data is formatted in (sensor output resistance) vs Kelvin (see Table 96). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end below 0x3CF. In order to program the LTC2986 with the custom thermistor table, both the resistance data and the Kelvin data are converted to 24-bit binary values. The sensor output resistance (units = ) follows the convention shown in Table 97, where the first 20 bits are the integer part and the remaining four bits are the fractional part. In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2986 are reported in C or F. The sensor temperature (Kelvin) follows the convention shown in Table 98, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. Table 96. NTC Thermistor Example Resistance vs Kelvin Data Memory Map POINT SENSOR OUTPUT TEMPERATURE START RESISTANCE() (K) ADDRESS STOP ADDRESS P0 0 457.5 0x2C8 0x2CD P1 80 400.2 0x2CE 0x2D3 P2 184 372.3 0x2D4 0x2D9 P3 423.2 320.1 0x2DA 0x2DF P4 973.36 290.55 0x2E0 0x2E5 P5 2238.728 249.32 0x2E6 0x2EB P6 5149.0744 240.3 0x2EC 0x2F1 P7 26775.18688 230 0x2F2 0x2F7 P8 139230.9718 215.3 0x2F8 0x2FD P9 724001.0532 200 0x2FE 0x303 BYTE 1 BYTE 2 BYTE 3 BYTE 1 Resistance Data BYTE 2 BYTE 3 Temperature Data Table 97. Example Thermistor Resistance Values BYTE 1 Resistance BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 219 218 217 216 215 214 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2-1 2-2 2-3 2-4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 184 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 423.2 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 1 973.36 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1 2238.728 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 1 1 1 0 1 0 1 1 5149.074 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 1 26775.19 0 0 0 0 0 1 1 0 1 0 0 0 1 0 0 1 0 1 1 1 0 0 1 1 139231 0 0 1 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 0 0 724001.1 1 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 29861fa 84 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM THERMISTORS In this example, a custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 99 (refer to Figure 27 for similar format). In this case the custom data begins at memory location 0x2C8 (starting address is 20). The starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The table data length -1 (9 in this case) is entered into the custom thermistor data length field of the thermistor channel assignment word. Table 98. Example Thermistor Temperature Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Temperature 213 212 211 210 29 28 27 26 25 24 23 22 21 20 B8 B7 B6 B5 B4 B3 B2 B1 B0 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 457.5 0 0 0 0 0 1 1 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 400.2 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 1 1 0 0 372.3 0 0 0 0 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 1 1 1 0 0 0 0 1 1 320.1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0 290.55 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 0 1 1 249.32 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1 240.3 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 230 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 215.3 0 0 0 0 0 0 1 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 200 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 99. Custom Thermistor Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS (1) Thermistor Type Custom Table 5 11011 1 1 0 1 1 (2) Sense Resistor Channel Pointer CH4 5 00100 Single-Ended 3 100 1A 4 0011 Set These Bits to 0 3 00 (5) Custom Thermistor Start Address Data Pointer = 20 6 010100 (5) Custom Thermistor Length -1 = 9 Length-1 6 001001 (3) Sensor Configuration (4) Excitation Current Not Used BINARY DATA MEMORY ADDRESS 0x210 MEMORY ADDRESS 0x211 MEMORY ADDRESS 0x212 MEMORY ADDRESS 0x213 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 1 0 1 0 0 0 0 1 0 0 1 29861fa For more information www.linear.com/LTC2986 85 LTC2986/LTC2986-1 CUSTOM THERMISTORS In addition to custom table driven thermistors, it is also possible to directly input Steinhart-Hart coefficients into the LTC2986 (thermistor Type 11010, see Table 55). Steinhart-Hart coefficients are commonly specified parameters provided by thermistor manufacturers. The Steinhart-Hart equation is: Steinhart-Hart data is stored sequentially in any memory location greater than or equal to 0x250 and below 0x3CF. Each coefficient is represented by a standard, singleprecision, IEEE754 32-bit value (see Table 100). 1 = A +B *ln(R)+C *ln(R)2 +D*ln(R)3 +E *ln(R)4 T +F *ln(R)5 In this example a Steinhart-Hart equation is entered into memory starting at location 0x2C8 (see Table 101). Example Custom Steinhart-Hart Thermistor Table 100. Steinhart-Hart Custom Thermistor Data Format ADDRESS COEFFICIENT VALUE 0x250 + 4 * Start Address A 32-Bit Single-Precision Floating Point Format 0x250 + 4 * Start Address + 4 B 32-Bit Single-Precision Floating Point Format 0x250 + 4 * Start Address + 8 C 32-Bit Single-Precision Floating Point Format 0x250 + 4 * Start Address + 12 D 32-Bit Single-Precision Floating Point Format 0x250 + 4 * Start Address + 16 E 32-Bit Single-Precision Floating Point Format 0x250 + 4 * Start Address + 20 F 32-Bit Single-Precision Floating Point Format Table 101. Custom Steinhart-Hart Data Example COEFFICIENT START VALUE ADDRESS SIGN MSB EXPONENT MANTISSA LSB MSB LSB A 1.45E-03 0x2C8 0 0 1 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 B 2.68E-04 0x2CC 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 1 1 0 1 0 C 0 0x2D0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D 1.64E-07 0x2D4 0 0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 0 1 0 E 0 0x2D8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 F 0 0x2DC 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 29861fa 86 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 CUSTOM THERMISTORS A custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 102 (refer to Figure 27 for a similar format). In this case the custom data begins at memory location 0x2C8 (starting address is 30). The starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The data length (set to 0) is always six 32-bit floating point words. Table 102. Custom Steinhart-Hart Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 0x210 (1) Thermistor Type Custom Steinhart-Hart 5 11010 1 1 0 1 0 (2) Sense Resistor Channel Pointer CH4 5 00100 Single-Ended 3 100 1A 4 0011 Set These Bits to 0 3 00 (5) Custom Thermistor Start Address Data Pointer = 30 6 011110 (5) Custom SteinhartHart Length Always Set to 0 6 000000 (3) Sensor Configuration (4) Excitation Current Not Used Fixed at Six 32-Bit Words MEMORY ADDRESS 0x211 MEMORY ADDRESS 0x212 MEMORY ADDRESS 0x213 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 29861fa For more information www.linear.com/LTC2986 87 LTC2986/LTC2986-1 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LTC2986#packaging for the most recent package drawings. LX Package 48-Lead Plastic LQFP (7mm x 7mm) (Reference LTC DWG # 05-08-1760 Rev A) 7.15 - 7.25 9.00 BSC 5.50 REF 7.00 BSC 48 0.50 BSC 1 2 48 SEE NOTE: 4 1 2 9.00 BSC 5.50 REF 7.00 BSC 7.15 - 7.25 0.20 - 0.30 A A PACKAGE OUTLINE C0.30 - 0.50 1.30 MIN RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 1.60 1.35 - 1.45 MAX 11 - 13 R0.08 - 0.20 GAUGE PLANE 0.25 0 - 7 11 - 13 0.09 - 0.20 1.00 REF 0.50 BSC 0.17 - 0.27 0.05 - 0.15 0.45 - 0.75 SECTION A - A COMPONENT PIN "A1" TRAY PIN 1 BEVEL XXYY LTCXXXX LX-ES Q_ _ _ _ _ _ e3 NOTE: 1. PACKAGE DIMENSIONS CONFORM TO JEDEC #MS-026 PACKAGE OUTLINE 2. DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.25mm ON ANY SIDE, IF PRESENT 4. PIN-1 INDENTIFIER IS A MOLDED INDENTATION, 0.50mm DIAMETER 5. DRAWING IS NOT TO SCALE LX48 LQFP 0113 REV A PACKAGE IN TRAY LOADING ORIENTATION 29861fa 88 For more information www.linear.com/LTC2986 LTC2986/LTC2986-1 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 09/16 Added H-grade. 3-5 29861fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. For more information www.linear.com/LTC2986 89 LTC2986/LTC2986-1 TYPICAL APPLICATION Universal Inputs Allow Common Hardware Sharing for Thermocouples, Diodes, Thermistors, 3-Wire RTDs, and 4-Wire RTDs 2.85V TO 5.25V UNIVERSAL PROTECTED MULTI-SENSOR INPUT THERMOCOUPLE 16 RP1 RSENSE 17 T1 RP2 18 T2 RP3 19 RP4 20 T3 RP5 21 T4 RP7 22 RP8 23 THERMISTOR 2-WIRE RTD 3-WIRE RTD 4-WIRE RTD 2 1 3 4 2 3 2 1 1 RP6 COLD JUNCTION RTD OR THERMISTOR OR DIODE OR ANALOG TEMP 24 25 CH1 VDD CH2 Q1 CH3 CH4 LTC2986 Q2 Q3 CH5 VREFOUT CH6 VREFP CH7 VREF_BYP CH8 LDO 2, 4, 6, 8, 45 0.1F 47 RESET 10F 13 14 1F 11 1F 43 10F 42 41 CS 40 SDI 39 SDO 38 SCK 37 INTERRUPT 36 COM GND 10F 46 CH9 CH10 10F 48 (OPTIONAL, DRIVE LOW TO RESET) SPI INTERFACE 1, 3, 5, 7, 9, 12, 15, 26-35, 44 29861 TA02 29861 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC2983 Multi-Sensor High Accuracy Digital Temperature Measurement System Pin/Software Compatible 20-Channel Version of LTC2986 LTC2984 Multi-Sensor High Accuracy Digital Pin/Software Compatible 20-Channel Version of LTC2986-1 Temperature Measurement System with EEPROM LTC2990 Quad I2C Temperature, Voltage and Current Monitor Remote and Internal Temperatures, 14-Bit Voltages and Current, Internal 10ppm/C Reference LTC2991 Octal I2C Voltage, Current, Temperature Monitor Remote and Internal Temperatures, 14-Bit Voltages and Current, Internal 10ppm/C Reference LTC2995 Temperature Sensor and Voltage Monitor with Alert Outputs Monitors Temperature and Two Voltages, Adjustable Thresholds, Open-Drain Alert Outputs, Temperature to Voltage Output with Integrated 1.8V Reference, 1C (Max) Accuracy LTC2996 Temperature Sensor with Alert Outputs Monitors Temperature, Adjustable Thresholds, Open-Drain Alert Outputs, Temperature to Voltage Output with Integrated 1.8V Reference, 1C (Max) Accuracy LTC2997 Remote/Internal Temperature Sensor Temperature to Voltage Output with Integrated 1.8V Reference, 1C (Max) Accuracy LTC2943 20V I2C Coulomb Counter Monitors Charge, Current, Voltage and Temperature with 1% Accuracy. Works with Any Battery Chemistry and Capacity 29861fa 90 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC2986 (408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC2986 LT 0916 REV A * PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2016