FEATURES APPLICATIONS Power monitoring/power budgeting Central office equipment Telecommunications and data communications equipment PCs/servers GENERAL DESCRIPTION The ADM1178 is an integrated hot swap controller and current sense amplifier that offers digital current and voltage monitoring via an on-chip 12-bit analog-to-digital converter (ADC), communicated through an I2C(R) interface. An internal current sense amplifier measures voltage across the sense resistor in the power path via the VCC pin and the SENSE pin. FUNCTIONAL BLOCK DIAGRAM ADM1178 MUX V VCC 0 SDA 12-BIT ADC I I2C 1 A SCL ADR SENSE CURRENT SENSE AMPLIFIER ALERT FET DRIVE CONTROLLER ON ALERTB GATE 1.3V UNDERVOLTAGE COMPARATOR GND 06048-001 Allows safe board insertion and removal from a live backplane Controls supply voltages from 3.15 V to 16.5 V Precision current sense amplifier Precision voltage input 12-bit ADC for current and voltage readback Charge-pumped gate drive for external N-channel FET Adjustable analog current limit with circuit breaker 3% accurate hot swap current limit level Fast response limits peak fault current Automatic retry or latch-off on current fault Programmable hot swap timing via TIMER pin Active high ON pin ALERTB output for overcurrent interrupt I2C fast mode-compliant interface (400 kHz maximum) 10-lead MSOP TIMER Figure 1. 3.15V TO 16.5V RSENSE VCC N-CHANNEL FET SENSE CONTROLLER GATE ADM1178 SDA SCL ON ALERTB P = VI SDA SCL INTERRUPT TIMER GND ADR 06048-002 Data Sheet Hot Swap Controller and Digital Power Monitor with ALERTB Output ADM1178 Figure 2. Applications Diagram The ADM1178 limits the current through this resistor by controlling the gate voltage (via the GATE pin) of an external N-channel FET in the power path. The voltage across the sense resistor (and therefore the inrush current) is kept below a preset maximum. A 12-bit ADC can measure the current seen in the sense resistor, as well as the supply voltage on the VCC pin. An alert output can be set to trigger when the ADC current reading exceeds a programmed overcurrent limit threshold. The ADM1178 protects the external FET by limiting the time that the maximum current runs through it. This current limit period is set by the value of the capacitor attached to the TIMER pin. Additionally, the device provides protection from overcurrent events that may occur after the hot swap event is complete. In case of a short-circuit event, the current in the sense resistor exceeds an overcurrent trip threshold, and the FET is switched off immediately by pulling down the GATE pin. An industry-standard I2C interface allows a controller to read current and voltage data from the ADC. Measurements can be initiated by an I2C command. Alternatively, the ADC can run continuously, and the user can read the latest conversion data whenever it is required. Up to four unique I2C addresses can be created, depending on how the ADR pin is connected. The ADM1178 is packaged in a 10-lead MSOP. Rev. D Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 (c)2006-2012 Analog Devices, Inc. All rights reserved. ADM1178 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Initial Timing Cycle ................................................................... 13 Applications ....................................................................................... 1 Hot Swap Retry Cycle on the ADM1178-1 ............................. 14 General Description ......................................................................... 1 Voltage and Current Readback ..................................................... 15 Functional Block Diagram .............................................................. 1 Serial Bus Interface..................................................................... 15 Revision History ............................................................................... 2 Identifying the ADM1178 on the I2C Bus............................... 15 Specifications..................................................................................... 3 General I2C Timing .................................................................... 15 Absolute Maximum Ratings ............................................................ 5 Write and Read Operations ........................................................... 17 Thermal Characteristics .............................................................. 5 Quick Command ........................................................................ 17 ESD Caution .................................................................................. 5 Write Command Byte ................................................................ 17 Pin Configuration and Function Descriptions ............................. 6 Write Extended Command Byte .............................................. 18 Typical Performance Characteristics ............................................. 7 Read Voltage and/or Current Data Bytes ................................ 19 Overview of the Hot Swap Function ............................................ 12 Applications Information .............................................................. 21 Undervoltage Lockout ............................................................... 12 Applications Waveforms............................................................ 21 ON Function ............................................................................... 12 ALERTB Output ......................................................................... 22 TIMER Function ........................................................................ 12 Kelvin Sense Resistor Connection ........................................... 22 GATE and TIMER Functions During a Hot Swap Operation ....................................................................................................... 13 Outline Dimensions ....................................................................... 23 Ordering Guide .......................................................................... 23 Calculating Current Limits and Fault Current Limit Time .. 13 REVISION HISTORY 6/12--Rev. C to Rev. D Changes to Low Level Input Voltage, VIL Parameter, Test Conditions/Comments Column, Table 1 and High Level Input Voltage, VIH Parameter, Test Conditions/Comments Column, Table 1 ................................................................................................ 3 Changes to ALERTB Output Section and Kelvin Sense Resistor Connection Section ........................................................................ 22 Deleted Figure 50; Renumbered Sequentially............................. 23 Updated Outline Dimensions ....................................................... 23 Changes to Table 5.......................................................................... 16 Changes to Quick Command Section ......................................... 18 Changes to Figure 38...................................................................... 18 Changes to Table 7.......................................................................... 18 Changes to Write Extended Command Byte Section ................ 19 Changes to Figure 40...................................................................... 19 Changes to Table 9 and Table 11 .................................................. 19 Changes to Converting ADC Codes to Voltage and Current Readings Section.............................................................. 20 5/09--Rev. B to Rev. C Changes to Figure 1 .......................................................................... 1 4/07--Rev. 0 to Rev. A Changes to Table 1.............................................................................3 Changes to GATE and TIMER Functions During a Hot Swap Section ......................................................................... 14 Changes to Calculating Current Limits and Fault Current Limit Time Section ................................................ 14 Changes to Initial Timing Cycle Section ..................................... 15 Changes to Table 5.......................................................................... 16 Changes to Figure 35 and Figure 36 ............................................ 17 Changes to Figure 40...................................................................... 19 Changes to Figure 42 and Figure 43 ............................................ 20 Added Applications Information Heading ................................. 22 2/08--Rev. A to Rev. B Changed VVCC to VCC Throughout ................................................. 3 Changes to Input Current for 11 Decode, IADRHIGH, Parameter... 3 Changes to Input Current for 00 Decode, IADRLOW, Parameter ... 3 Added ADC Conversion Time Parameter .................................... 5 Added Fast Overcurrent Response Time Parameter ................... 5 Added Endnote 2 and Endnote 3 ................................................... 5 Changes to Figure 14 ........................................................................ 9 Changes to Figure 15 Caption......................................................... 9 Changes to Figure 24 ...................................................................... 11 Changes to TIMER Function Section .......................................... 13 Changes to General I2C Timing Section, Step 3 ......................... 16 9/06--Revision 0: Initial Version Rev. D | Page 2 of 24 Data Sheet ADM1178 SPECIFICATIONS VCC = 3.15 V to 16.5 V, TA = -40C to +85C, typical values at TA = 25C, unless otherwise noted. Table 1. Parameter VCC PIN Operating Voltage Range, VCC Supply Current, ICC Undervoltage Lockout, VUVLO Undervoltage Lockout Hysteresis, VUVLOHYST ON PIN Input Current, IINON Rising Threshold, VONTH Trip Threshold Hysteresis, VONHYST Glitch Filter Time ALERTB PIN Output Low Voltage, VALERTOL Input Current, IALERT SENSE PIN Input Leakage, ISENSE Overcurrent Fault Timing Threshold, VOCTRIM Overcurrent Limit Threshold, VLIM Min Typ 3.15 1.7 2.8 80 -100 -2 1.26 35 1.3 50 3 0.05 1 -1 -1 92 97 100 Fast Overcurrent Trip Threshold, VOCFAST GATE PIN Drive Voltage, VGATE Pull-Up Current Pull-Down Current TIMER PIN Pull-Up Current (Power-On Reset), ITIMERUPPOR Pull-Up Current (Fault Mode), ITIMERUPFAULT Pull-Down Current (Retry Mode), ITIMERDNRETRY Pull-Down Current, ITIMERDN Trip Threshold High, VTIMERH Trip Threshold Low, VTIMERL ADR PIN Set Address to 00, VADRLOWV Set Address to 01, RADRLOWZ Max Unit 16.5 2.5 V mA V mV Test Conditions/Comments VCC rising +100 +2 1.34 65 nA A V mV s ON < 1.5 V 0.1 1.5 +1 V V A IALERT = -100 A IALERT = -2 mA VALERT = VCC; ALERTB not asserted +1 A mV 103 mV 115 mV VSENSE = VCC VOCTRIM = (VCC - VSENSE), fault timing starts on the TIMER pin VLIM = (VCC - VSENSE), closed-loop regulation to a current limit VOCFAST = (VCC - VSENSE), gate pull-down current turned on ON rising 3 9 7 8 6 11 10 12.5 1.5 5 7 9 13 13 17 V V V A mA mA mA VGATE - VCC, VCC = 3.15 V VGATE - VCC, VCC = 5 V VGATE - VCC, VCC = 16.5 V VGATE = 0 V VGATE = 3 V, VCC = 3.15 V VGATE = 3 V, VCC = 5 V VGATE = 3 V, VCC = 16.5 V -3.5 -40 -5 -60 2 -6.5 -80 3 A A A 100 1.3 0.2 1.34 0.225 A V V Initial cycle, VTIMER = 1 V During current fault, VTIMER = 1 V After current fault and during a cooldown period on a retry device, VTIMER = 1 V Normal operation, VTIMER = 1 V TIMER rising TIMER falling 150 0.8 165 V k +1 A 5.5 10 V A A 1.26 0.175 0 135 Set Address to 10, IADRHIGHZ -1 Set Address to 11, VADRHIGHV Input Current for 11 Decode, IADRHIGH Input Current for 00 Decode, IADRLOW 2 -40 3 -22 Rev. D | Page 3 of 24 Low state Resistor to ground state, load pin with specified resistance for 01 decode Open state, maximum load allowed on ADR pin for 10 decode High state VADR = 2.0 V to 5.5 V VADR = 0 V to 0.8 V ADM1178 Parameter MONITORING ACCURACY 1 Current Sense Absolute Accuracy 0C to +70C 0C to +85C -40C to +85C VSENSE for ADC Full Scale 2 Voltage Sense Accuracy 0C to +70C 0C to +85C -40C to +85C VCC for ADC Full Scale 3 Low Range (VRANGE = 1) High Range (VRANGE = 0) 2 I C TIMING Low Level Input Voltage, VIL High Level Input Voltage, VIH Low Level Output Voltage on SDA, VOL Output Fall Time on SDA from VIHMIN to VILMAX Maximum Width of Spikes Suppressed by Input Filtering on SDA and SCL Pins Input Current, II, on SDA/SCL When Not Driving a Logic Low Output Input Capacitance on SDA/SCL SCL Clock Frequency, fSCL Low Period of the SCL Clock High Period of the SCL Clock ADC Conversion Time 4 Fast Overcurrent Response Time 5 Setup Time for a Repeated Start Condition, tSU;STA SDA Output Data Hold Time, tHD;DAT Setup Time for a Stop Condition, tSU;STO Bus Free Time Between a Stop and a Start Condition, tBUF Capacitive Load for Each Bus Line Data Sheet Min Typ -1.45 -1.8 -2.8 -5.7 -1.5 -1.8 -2.95 -6.1 -1.95 -2.45 -3.85 -6.7 Max Unit Test Conditions/Comments +1.45 +1.8 +2.8 +5.7 +1.5 +1.8 +2.95 +6.1 +1.95 +2.45 +3.85 +6.7 % % % % % % % % % % % % mV VSENSE = 75 mV VSENSE = 50 mV VSENSE = 25 mV VSENSE = 12.5 mV VSENSE = 75 mV VSENSE = 50 mV VSENSE = 25 mV VSENSE = 12.5 mV VSENSE = 75 mV VSENSE = 50 mV VSENSE = 25 mV VSENSE = 12.5 mV +0.85 +0.9 +0.85 +0.9 +0.9 +1.15 % % % % % % VCC = 3 V minimum (low range) VCC = 6 V minimum (high range) VCC = 3 V minimum (low range) VCC = 6 V minimum (high range) VCC = 3 V minimum (low range) VCC = 6 V minimum (high range) 105.84 -0.85 -0.9 -0.85 -0.9 -0.9 -1.15 6.65 26.35 V V 0.3 VBUS 20 + 0.1 CBUS 50 0.4 250 250 V V V ns ns -10 +10 A 0.7 VBUS 5 400 600 1300 150 4 600 100 600 1300 10 900 400 VBUS = 3.0 V to 5.5 V VBUS = 3.0 V to 5.5 V IOL = 3 mA CBUS = bus capacitance from SDA to GND pF kHz ns ns s s ns ns ns ns pF Monitoring accuracy is a measure of the error in a code that is read back for a particular voltage/current. This is a combination of amplifier error, reference error, ADC error, and error in ADC full-scale code conversion factor. This is an absolute value to be used when converting ADC codes to current readings; any inaccuracy in this value is factored into absolute current accuracy values (see the Specifications for the Current Sense Absolute Accuracy parameter). 3 These are absolute values to be used when converting ADC codes to voltage readings; any inaccuracy in these values is factored into voltage accuracy values (see the Specifications for the Voltage Sense Accuracy parameter). 4 Time between the receipt of the command byte and the actual ADC result being placed in the register. 5 Guaranteed by design; not production tested. 1 2 Rev. D | Page 4 of 24 Data Sheet ADM1178 ABSOLUTE MAXIMUM RATINGS THERMAL CHARACTERISTICS Table 2. Parameter VCC Pin SENSE Pin TIMER Pin ON Pin ALERTB Pin GATE Pin SDA Pin, SCL Pin ADR Pin Storage Temperature Range Operating Temperature Range Lead Temperature (Soldering, 10 sec) Junction Temperature Rating 20 V 20 V -0.3 V to +6 V -0.3 V to +20 V 30 V 30 V -0.3 V to +6 V -0.3 V to +7 V -65C to +125C -40C to +85C 300C 150C JA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Table 3. Thermal Resistance Package Type 10-Lead MSOP ESD CAUTION Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. D | Page 5 of 24 JA 137.5 Unit C/W ADM1178 Data Sheet PIN CONFIGURATION AND FUNCTION DESCRIPTIONS VCC 1 ADM1178 9 GATE ON 3 TOP VIEW (Not to Scale) 8 ADR 7 SDA 6 SCL GND 4 TIMER 5 06048-003 10 ALERTB SENSE 2 Figure 3. Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 Mnemonic VCC 2 SENSE 3 ON 4 5 GND TIMER 6 7 8 SCL SDA ADR 9 GATE 10 ALERTB Description Positive Supply Input Pin. The operating supply voltage range is from 3.15 V to 16.5 V. An undervoltage lockout (UVLO) circuit resets the ADM1178 when a low supply voltage is detected. Current Sense Input Pin. A sense resistor between the VCC pin and the SENSE pin sets the analog current limit. The hot swap operation of the ADM1178 controls the external FET gate to maintain the (VCC - VSENSE) voltage at or below 100 mV. Undervoltage Input Pin. Active high pin. An internal undervoltage comparator has a trip threshold of 1.3 V, and the output of this comparator is used as an enable for the hot swap operation. With an external resistor divider from VCC to GND, the ON pin can be used to enable the hot swap operation for a specific voltage on VCC, providing an undervoltage function. Chip Ground Pin. Timer Pin. An external capacitor, CTIMER, sets a 270 ms/F initial timing cycle delay and a 21.7 ms/F fault delay. The GATE pin turns off when the TIMER pin is pulled beyond the upper threshold. An overvoltage detection with an external Zener can be used to force this pin high. I2C Clock Pin. Open-drain input requires an external resistive pull-up. I2C Data I/O Pin. Open-drain input/output. Requires an external resistive pull-up. I2C Address Pin. This pin can be tied low, tied high, left floating, or tied low through a resistor to set four I2C addresses. GATE Output Pin. This pin is the high-side gate drive of an external N-channel FET. This pin is driven by the FET drive controller, which utilizes a charge pump to provide a 12.5 A pull-up current to charge the FET GATE pin. The FET drive controller regulates to a maximum load current (100 mV through the sense resistor) by modulating the GATE pin. Alert Output Pin. Active low, open-drain configuration. This pin asserts when an overcurrent condition is present. The overcurrent level that causes an alert to be asserted is digitally programmable via the I2C interface. This function can also be enabled/disabled via I2C. Rev. D | Page 6 of 24 Data Sheet ADM1178 2.0 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 1.0 0.8 1.0 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0 2 4 6 8 10 12 14 16 18 VCC (V) 0 -40 10 10 DRIVE VOLTAGE (V) 40 60 80 8 6 4 5V VCC 8 3.15V VCC 6 4 2 2 4 6 8 10 12 14 16 18 VCC (V) 0 -40 06048-029 0 -2 -2 -4 -4 IGATE (A) 0 -6 -8 -12 -12 10 12 14 16 VCC (V) 18 -14 -40 06048-027 8 60 80 -8 -10 6 40 -6 -10 4 20 Figure 8. Drive Voltage (VGATE - VCC) vs. Temperature 0 2 0 TEMPERATURE (C) Figure 5. Drive Voltage (VGATE - VCC) vs. Supply Voltage 0 -20 06048-030 DRIVE VOLTAGE (V) 12 2 IGATE (A) 20 Figure 7. Supply Current vs. Temperature (Gate On) 12 -14 0 TEMPERATURE (C) Figure 4. Supply Current vs. Supply Voltage 0 -20 -20 0 20 40 60 TEMPERATURE (C) Figure 9. Gate Pull-Up Current vs. Temperature Figure 6. Gate Pull-Up Current vs. Supply Voltage Rev. D | Page 7 of 24 80 06048-028 0 06048-022 ICC (mA) 2.0 06048-021 ICC (mA) TYPICAL PERFORMANCE CHARACTERISTICS ADM1178 Data Sheet 2.0 12 1.8 10 TIMER THRESHOLD (V) 1.6 6 4 1.4 HIGH 1.2 1.0 0.8 0.6 0.4 2 LOW 0.2 0 2 4 6 8 10 12 14 16 18 VCC (V) 0 06048-031 0 0 2 4 6 8 10 12 14 16 18 VCC (V) Figure 10. Gate Pull-Down Current vs. Supply Voltage at VGATE = 5 V 06048-038 IGATE (mA) 8 Figure 13. Timer Threshold vs. Supply Voltage 2.0 2 1.8 0 1.6 TIMER THRESHOLD (V) -2 IGATE (A) -4 -6 -8 -10 HIGH 1.4 1.2 1.0 0.8 0.6 0.4 LOW -12 2 4 6 8 10 12 14 16 VGATE (V) 0 -40 -20 0 20 40 60 06048-039 0 06048-040 -14 0.2 80 TEMPERATURE (C) Figure 14. Timer Threshold vs. Temperature Figure 11. Gate Pull-Up Current vs. Gate Voltage at VCC = 5 V 100 20 90 VCC = 12V 80 GATE ON TIME (ms) 10 VCC = 5V 70 60 50 40 30 5 0 0 5 06048-050 20 VCC = 3V 10 10 15 20 VGATE (V) 25 06048-043 IGATE (mA) 15 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 CTIMER (F) Figure 15. Gate On Time vs. Timer Capacitance, During Current Limiting Condition Figure 12. Gate Pull-Down Current vs. Gate Voltage Rev. D | Page 8 of 24 4.5 5.0 ADM1178 0 -1 -1 -2 -2 -3 -4 -4 -5 -5 2 4 6 8 10 12 14 16 18 VCC (V) -6 -40 -10 -20 -20 -30 -30 ITIMER (A) -10 -40 -50 -60 -60 -70 -70 4 6 8 10 12 14 16 18 VCC (V) -80 -40 2.5 2.5 2.0 2.0 ITIMER (A) 3.0 1.5 1.0 0.5 0.5 6 8 10 VCC (V) 12 14 16 18 0 -40 06048-036 4 -20 0 20 40 60 80 1.5 1.0 2 80 Figure 20. Timer Pull-Up Current (Circuit Breaker Delay) vs. Temperature 3.0 0 60 TEMPERATURE (C) Figure 17. Timer Pull-Up Current (Circuit Breaker Delay) vs. Supply Voltage 0 40 -40 -50 06048-034 ITIMER (A) 0 2 20 Figure 19. Timer Pull-Up Current (Initial Cycle) vs. Temperature 0 0 0 TEMPERATURE (C) Figure 16. Timer Pull-Up Current (Initial Cycle) vs. Supply Voltage -80 -20 -20 0 20 40 TEMPERATURE (C) Figure 18. Timer Pull-Down Current (Cooldown/FET Off Cycle) vs. Supply Voltage 06048-035 0 60 80 06048-037 -6 ITIMER (A) -3 06048-033 ITIMER (A) 0 06048-032 ITIMER (A) Data Sheet Figure 21. Timer Pull-Down Current (Cooldown/FET Off Cycle) vs. Temperature Rev. D | Page 9 of 24 ADM1178 Data Sheet 1000 120 900 HITS PER CODE (1000 READS) 115 110 100 95 90 85 4 6 8 10 12 14 16 18 Figure 22. Circuit Breaker Limit Voltage vs. Supply Voltage 400 300 200 0 2046 2047 2048 2049 2050 CODE Figure 25. ADC Noise with Current Channel, Midcode Input, and 1000 Reads 1000 110 108 900 VOCFAST HITS PER CODE (1000 READS) 106 104 102 VLIM 100 98 VOCTRIM 96 94 92 800 700 600 500 400 300 200 100 -20 0 20 40 60 80 TEMPERATURE (C) 00 DECODE 01 DECODE 779 780 781 782 783 CODE Figure 26. ADC Noise with 14:1 Voltage Channel, 5 V Input, and 1000 Reads Figure 23. VOCTRIM, VLIM, VOCFAST vs. Temperature 1000 10 DECODE 11 DECODE HITS PER CODE (1000 READS) 900 800 700 600 500 400 300 200 100 0 -30 -25 -20 -15 -10 -5 0 5 IADR (A) Figure 24. Address Pin Voltage vs. Address Pin Current for Four Addressing Options on Each Address Pin 10 3078 06048-026 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -35 0 06048-042 90 -40 06048-061 VOLTAGE (mV) 500 06048-060 2 VCC (V) VADR 600 100 06048-041 80 700 3079 3080 CODE 3081 3082 06048-062 VLIM (mV) 105 800 Figure 27. ADC Noise with 7:1 Voltage Channel, 5 V Input, and 1000 Reads Rev. D | Page 10 of 24 Data Sheet ADM1178 1.0 4 3 ALERTB OUTPUT LOW (V) 0.8 2 INL (LSB) 1 0 -1 -2 0.6 0.4 0.2 0 500 1000 1500 2000 2500 3000 3500 4000 CODE 0 06048-023 -4 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 VCC (V) 06048-048 -3 Figure 31. ALERTB Output Low Voltage vs. Supply @ 1 mA Figure 28. INL for ADC 2.0 4 1.8 3 ALERTB OUTPUT LOW (V) 1.6 1 0 -1 1.4 1.2 1.0 0.8 0.6 0.4 -2 0.2 -3 0 500 1000 1500 2000 2500 3000 3500 4000 CODE 06048-024 0 -4 0.60 0.55 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 20 40 60 80 TEMPERATURE (C) 06048-047 ALERTB OUTPUT LOW (V) 0.50 -20 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 ILOAD (mA) Figure 32. ALERTB Output Low Voltage vs. Load Current Figure 29. DNL for ADC 0 -40 0 Figure 30. ALERTB Output Low Voltage vs. Temperature @ 1 mA Rev. D | Page 11 of 24 06048-049 DNL (LSB) 2 ADM1178 Data Sheet OVERVIEW OF THE HOT SWAP FUNCTION When circuit boards are inserted into a live backplane, discharged supply bypass capacitors draw large transient currents from the backplane power bus as they charge. Such transient currents can cause permanent damage to connector pins, as well as dips on the backplane supply that can reset other boards in the system. The ADM1178 is designed to turn a circuit board supply voltage on and off in a controlled manner, allowing the circuit board to be safely inserted into or removed from a live backplane. The ADM1178 can reside either on the backplane or on the circuit board itself. The ADM1178 controls the inrush current to a fixed maximum level by modulating the gate of an external N-channel FET placed between the live supply rail and the load. This hot swap function protects the card connectors and the FET itself from damage and limits any problems that can be caused by the high current loads on the live supply rail. The ADM1178 holds the GATE pin down (and therefore holds off the FET) until certain conditions are met. An undervoltage lockout circuit ensures that the device is provided with an adequate input supply voltage. After the input supply voltage is successfully detected, the device goes through an initial timing cycle to provide a delay before it attempts a hot swap. This delay ensures that the board is fully seated in the backplane before the board is powered up. After the initial timing cycle is complete, the hot swap function is switched on under control of the ON pin. When the ON pin is asserted high, the hot swap operation starts. The ADM1178 charges up the gate of the FET to turn on the load. It continues to charge up the GATE pin until the linear current limit (set to 100 mV/RSENSE) is reached. For some combinations of low load capacitance and high current limit, this limit may not be reached before the load is fully charged up. If the current limit is reached, the ADM1178 regulates the GATE pin to keep the current at this limit. For currents above the overcurrent fault timing threshold, nominally 100 mV/RSENSE, the current fault is timed by sourcing a current to the TIMER pin. If the load becomes fully charged before the fault current limit time elapses (when the TIMER pin reaches 1.3 V), the current drops below the overcurrent fault timing threshold. The ADM1178 then continues to further charge up the GATE pin to fully enhance the FET for lowest RON, and the TIMER pin is pulled down again. If the fault current limit time is reached before the load drops below the current limit, a fault has been detected, and the hot swap operation is aborted by pulling down the GATE pin to turn off the FET. The ADM1178-2 is immediately latched off and attempts a hot swap only when the ON pin is deasserted and then asserted again. The ADM1178-1, however, retries the hot swap operation indefinitely, keeping the FET in its safe operating area (SOA) by using the TIMER pin to time a cooldown period between hot swap attempts. The current and voltage threshold combinations on the TIMER pin set the retry duty cycle to 3.8%. The ADM1178 is designed to operate over a range of supplies from 3.15 V to 16.5 V. UNDERVOLTAGE LOCKOUT An internal undervoltage lockout (UVLO) circuit resets the ADM1178 if the voltage on the VCC pin is too low for normal operation. The UVLO has a low-to-high threshold of 2.8 V, with 80 mV hysteresis. When there is a supply voltage greater than 2.8 V, the ADM1178 starts the initial timing cycle. ON FUNCTION The ADM1178 has an active high ON pin. The ON pin is the input to a comparator that has a low-to-high threshold of 1.3 V, an 50 mV hysteresis, and a glitch filter of 3 s. A low input on the ON pin turns off the hot swap operation by pulling the GATE pin to ground, turning off the external FET. The TIMER pin is also reset by turning on a pull-down current on this pin. A low-tohigh transition on the ON pin starts the hot swap operation. A 10 k pull-up resistor connecting the ON pin to the supply is recommended. Alternatively, an external resistor divider at the ON pin can be used to program an undervoltage lockout value that is higher than the internal UVLO circuit, thereby setting the hot swap operation to start at a specific voltage level on the VCC pin. An RC filter can be added at the ON pin to increase the delay time at card insertion if the initial timing cycle delay is insufficient. TIMER FUNCTION The TIMER pin handles several timing functions with an external capacitor, CTIMER. There are two comparator thresholds: VTIMERH (1.3 V) and VTIMERL (0.2 V). The four timing current sources are a 5 A pull-up, a 60 A pull-up, a 2 A pull-down, and a 100 A pull-down. The 100 A pull-down is a nonideal current source, approximating a 7 k resistor below 0.4 V. These current and voltage levels, together with the value of CTIMER chosen by the user, determine the initial timing cycle time, the fault current limit time, and the hot swap retry duty cycle. Rev. D | Page 12 of 24 Data Sheet ADM1178 GATE AND TIMER FUNCTIONS DURING A HOT SWAP OPERATION CALCULATING CURRENT LIMITS AND FAULT CURRENT LIMIT TIME During hot insertion of a board onto a live supply rail at VCC, the abrupt application of supply voltage charges the external FET drain/gate capacitance, which can cause an unwanted gate voltage spike. An internal circuit holds GATE low before the internal circuitry wakes up. This substantially reduces the FET current surges at insertion. The GATE pin is also held low during the initial timing cycle until the ON pin is taken high to start the hot swap operation. The nominal linear current limit is determined by a sense resistor connected between the VCC pin and the SENSE pin, as given by Equation 1. During a hot swap operation, the GATE pin is first pulled up by a 12.5 A current source. If the current through the sense resistor reaches the overcurrent fault timing threshold (VOCTRIM), a pull-up current of 60 A on the TIMER pin, is turned on and the GATE pin starts charging up. At a slightly higher voltage in the sense resistor, the error amplifier servos the GATE pin to maintain a constant current to the load by controlling the voltage across the sense resistor to the linear current limit, VLIM. A normal hot swap operation is complete when the board supply capacitors near full charge and the current through the sense resistor drops to eventually reach the level of the board load current. As soon as the current drops below the overcurrent fault timing threshold, the current into the TIMER pin switches from being a 60 A pull-up to being a 100 A pull-down. The ADM1178 then drives the GATE voltage as high as it can to fully enhance the FET and reduce RON losses to a minimum. A hot swap operation fails if the load current does not drop below the overcurrent fault timing threshold, VOCTRIM, before the TIMER pin has charged up to 1.3 V. In this case, the GATE pin is then pulled down with a 1.5 mA to 7 mA current sink (this varies with supply voltage). The GATE pull-down stays on until a hot swap retry starts, which can be forced by deasserting and then reasserting the ON pin. On the ADM1178-1, the device retries a hot swap operation automatically after a cooldown period. The ADM1178 also features a method of protection from sudden load current surges, such as a low impedance fault, when the current seen across the sense resistor may go well beyond the linear current limit. If the fast overcurrent trip threshold, VOCFAST, is exceeded, the 1.5 mA to 7 mA GATE pull-down is turned on immediately. This pulls the GATE voltage down quickly to enable the ADM1178 to limit the length of the current spike that passes through the external FET and to bring the current through the sense resistor back into linear regulation as quickly as possible. This process protects the backplane supply from sustained overcurrent conditions that may otherwise cause the backplane supply to droop during the overcurrent event. ILIMIT(NOM) = VLIM(NOM)/RSENSE = 100 mV/RSENSE (1) The minimum linear fault current is given by Equation 2. ILIMIT(MIN) = VLIM(MIN)/RSENSE(MAX) = 97 mV/RSENSE(MAX) (2) The maximum linear fault current is given by Equation 3. ILIMIT(MAX) = VLIM(MAX)/RSENSE(MIN) = 103 mV/RSENSE(MIN) (3) The power rating of the sense resistor should be rated at the maximum linear fault current level. The minimum overcurrent fault timing threshold current is given by Equation 4. IOCTRIM(MIN) = VOCTRIM(MIN)/RSENSE(MAX) = 90 mV/RSENSE(MAX) (4) The maximum fast overcurrent trip threshold current is given by Equation 5. IOCFAST(MAX) = VOCFAST(MAX)/RSENSE(MIN) = 115 mV/RSENSE(MIN) (5) The fault current limit time is the time that a device spends timing an overcurrent fault. The fault current limit time is given by Equation 6. tFAULT 21.7 x CTIMER ms/F (6) INITIAL TIMING CYCLE When VCC is first connected to the backplane supply, the internal supply (Time Point 1 in Figure 33) of the ADM1178 must be charged up. A very short time later (significantly less than 1 ms), the internal supply is fully up and, because the undervoltage lockout voltage is exceeded at VCC, the device comes out of reset. During this first short reset period, the GATE pin is held down with a 25 mA pull-down current, and the TIMER pin is pulled down with a 100 A current sink. The ADM1178 then goes through an initial timing cycle. At Time Point 2, the TIMER pin is pulled high with 5 A. At Time Point 3, the TIMER reaches the VTIMERL threshold, and the first portion of the initial cycle ends. The 100 A current source then pulls down the TIMER pin until it reaches 0.2 V at Time Point 4. The initial cycle delay (Time Point 2 to Time Point 4) is related to CTIMER as shown in Equation 7. Rev. D | Page 13 of 24 tINITIAL 270 x CTIMER ms/F (7) ADM1178 Data Sheet When the initial timing cycle terminates, the device is ready to start a hot swap operation (assuming that the ON pin is asserted). In the example shown in Figure 33, the ON pin is asserted at the same time as VCC is applied; therefore, the hot swap operation starts immediately after Time Point 4. At this point, the FET gate is charged up with a 12.5 A current source. (1) (3)(4) (5) (5)(6) (7) VON VTIMER At Time Point 6, VGATE and VOUT have reached their full potential, and the load current has settled to its nominal level. Figure 34 illustrates the situation where the ON pin is asserted after VCC is applied. (2) (3)(4) VCC At Time Point 5, the threshold voltage of the FET is reached and the load current begins to flow. The FET is controlled to keep the sense voltage at 100 mV (this corresponds to a maximum load current level defined by the value of RSENSE). (1) (2) VGATE VSENSE (6) VCC INITIAL TIMING CYCLE 06048-005 VOUT Figure 34. Startup (ON Asserts After Power Is Applied) VON HOT SWAP RETRY CYCLE ON THE ADM1178-1 With the ADM1178-1, the device turns off the FET after an overcurrent fault and then uses the TIMER pin to time a delay before automatically retrying to hot swap. VTIMER As with all ADM1178 devices, an overcurrent fault is timed by charging the TIMER capacitor with a 60 A pull-up current. When the TIMER pin reaches 1.3 V, the fault current limit time is reached, and the GATE pin is pulled down. On the ADM1178-1, the TIMER pin is then pulled down with a 2 A current sink. When the TIMER pin reaches 0.2 V, it automatically restarts the hot swap operation. VGATE VSENSE INITIAL TIMING CYCLE 06048-004 VOUT The cooldown period is related to CTIMER by Equation 8. tCOOL 550 x CTIMER ms/F Figure 33. Startup (ON Asserts as Power Is Applied) (8) Therefore, the retry duty cycle is as given by Equation 9. tFAULT/(tCOOL + tFAULT) x 100% = 3.8% Rev. D | Page 14 of 24 (9) Data Sheet ADM1178 VOLTAGE AND CURRENT READBACK In addition to providing hot swap functionality, the ADM1178 contains the components to allow voltage and current readback over an I2C bus. The voltage output of the current sense amplifier and the voltage on the VCC pin are fed into a 12-bit ADC via a multiplexer. The device can be instructed to convert voltage and/or current at any time during operation via an I2C command. When all conversions are complete, the voltage and/or current values can be read back with 12-bit accuracy in two or three bytes. SERIAL BUS INTERFACE The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the acknowledge bit, and holding it low during the high period of this clock pulse. All other devices on the bus remain idle while the selected device waits for data to be read from it or written to it. If the R/W bit is 0, the master writes to the slave device. If the R/W bit is 1, the master reads from the slave device. 2. Control of the ADM1178 is carried out via the I2C bus. This interface is compatible with the I2C fast mode (400 kHz maximum). The ADM1178 is connected to this bus as a slave device, under the control of a master device. IDENTIFYING THE ADM1178 ON THE I2C BUS If the operation is a write operation, the first data byte after the slave address is a command byte. This tells the slave device what to expect next. It can be an instruction, such as telling the slave device to expect a block write, or it can be a register address that tells the slave where subsequent data is to be written. The ADM1178 has a 7-bit serial bus slave address. When the device powers up, it does so with a default serial bus address. The three MSBs of the address are set to 111, and the two MSBs are set to 10, resulting in an address of 111x10. Bit A2 and Bit A3 are determined by the state of the ADR pin. There are four configurations available on the ADR pin that correspond to four I2C addresses for these bits (see Table 5). This scheme allows four ADM1178 devices to operate on a single I2C bus. Because data can flow in only one direction, as defined by the R/W bit, it is not possible to send a command to a slave device during a read operation. Before performing a read operation, it may be necessary to first execute a write operation to tell the slave what sort of read operation to expect and/or the address from which data is to be read. GENERAL I2C TIMING Figure 35 and Figure 36 show timing diagrams for general write and read operations using the I2C. The I2C specification defines conditions for different types of read and write operations, which are discussed in the Write and Read Operations section. The general I2C protocol operates as follows: 1. Data is sent over the serial bus in sequences of nine clock pulses: eight bits of data followed by an acknowledge bit from the slave device. Data transitions on the data line must occur during the low period of the clock signal and remain stable during the high period because a low-to-high transition when the clock is high can be interpreted as a stop signal. 3. The master initiates a data transfer by establishing a start condition, defined as a high-to-low transition on the serial data line, SDA, while the serial clock line, SCL, remains high. This indicates that a data stream is to follow. All slave peripherals connected to the serial bus respond to the start condition and shift in the next eight bits, consisting of a 7-bit slave address (MSB first) plus an R/W bit that determines the direction of the data transfer, that is, whether data is written to or read from the slave device (0 = write, 1 = read). When all data bytes are read or written, stop conditions are established. In write mode, the master pulls the data line high during the 10th clock pulse to assert a stop condition. In read mode, the master device releases the SDA line during the SCL low period before the ninth clock pulse, but the slave device does not pull it low. This is known as a no acknowledge. The master then takes the data line low during the SCL low period before the 10th clock pulse and then high during the 10th clock pulse to assert a stop condition. Table 5. Setting I2C Addresses via the ADR Pin Base Address 111AA10 1 ADR Pin State Ground Resistor to ground Floating High ADR Pin Logic State 00 01 10 11 X = don't care. Rev. D | Page 15 of 24 Address in Binary 1 1110010X 1110110X 1111010X 1111110X Address in Hex 0xE4 0xEC 0xF4 0xFC ADM1178 Data Sheet 9 1 9 1 SCL 1 SDA 1 1 1 ADRA ADRB 0 D7 R/W D6 D5 ACKNOWLEDGE BY SLAVE START BY MASTER FRAME 1 SLAVE ADDRESS 1 D4 D2 D3 D0 D1 ACKNOWLEDGE BY SLAVE FRAME 2 COMMAND CODE 1 9 9 SCL (CONTINUED) D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 ACKNOWLEDGE BY SLAVE FRAME 3 DATA BYTE D3 D2 D1 D0 ACKNOWLEDGE BY STOP BY SLAVE MASTER FRAME N DATA BYTE 06048-006 SDA (CONTINUED) Figure 35. General I2C Write Timing Diagram 9 1 9 1 SCL 1 SDA 1 1 1 ADRA ADRB 0 D7 R/W D6 D5 D4 ACKNOWLEDGE BY SLAVE START BY MASTER FRAME 1 SLAVE ADDRESS 1 D2 D3 D0 D1 ACKNOWLEDGE BY MASTER FRAME 2 DATA BYTE 1 9 9 SCL (CONTINUED) D7 D6 D5 D4 D3 FRAME 3 DATA BYTE D2 D1 D0 D7 D6 D5 ACKNOWLEDGE BY MASTER D4 D3 FRAME N DATA BYTE D2 D1 D0 NO ACKNOWLEDGE STOP BY MASTER Figure 36. General I2C Read Timing Diagram tLOW tR tHD;STA tF SCL tHD;STA tSU;STA tHIGH tHD;DAT tSU;DAT tSU;STO tBUF P S S Figure 37. Serial Bus Timing Diagram Rev. D | Page 16 of 24 P 06048-008 SDA 06048-007 SDA (CONTINUED) Data Sheet ADM1178 WRITE AND READ OPERATIONS Table 6. I2C Abbreviations Abbreviation S P R W A N Condition Start Stop Read Write Acknowledge No acknowledge WRITE COMMAND BYTE In the write command byte operation, the master device sends a command byte to the slave device, as follows: 1. 2. 3. 4. 5. 6. QUICK COMMAND 1 The quick command operation allows the master to check if the slave is present on the bus, as follows: 3. 4. The master device asserts a start condition on SDA. The master sends the 7-bit slave address, followed by the write bit (low). The addressed slave device asserts an acknowledge on SDA. The master asserts a stop condition on SDA to end the transaction. 1 2 2 3 4 5 6 SLAVE COMMAND S ADDRESS W A A P BYTE Figure 39. Write Command Byte The seven LSBs of the command byte are used to configure and control the ADM1178. Table 7 provides details of the function of each bit. 3 4 SLAVE S ADDRESS W A P 06048-009 1. 2. The master device asserts a start condition on SDA. The master sends the 7-bit slave address, followed by the write bit (low). The addressed slave device asserts an acknowledge on SDA. The master sends the command byte. The command byte is identified by an MSB = 0. An MSB = 1 indicates an extended register write (see the Write Extended Command Byte section). The slave asserts an acknowledge on SDA. The master asserts a stop condition on SDA to end the transaction. 06048-010 The I2C specification defines several protocols for different types of read and write operations. The operations used in the ADM1178 are discussed in this section. Table 6 shows the abbreviations used in the command diagrams (see Figure 38 to Figure 43). Figure 38. Quick Command Table 7. Command Byte Operations Bit Default Name C0 0 V_CONT C1 0 V_ONCE C2 0 I_CONT C3 0 I_ONCE C4 0 VRANGE C5 C6 0 0 Not applicable STATUS_RD Function LSB, set to convert voltage continuously. If readback is attempted before the first conversion is complete, the ADM1178 asserts an acknowledge and returns all 0s in the returned data. Set to convert voltage once. Self-clears. I2C asserts a no acknowledge on attempted reads until the ADC conversion is complete. Set to convert current continuously. If readback is attempted before the first conversion is complete, the ADM1178 asserts an acknowledge and returns all 0s in the returned data. Set to convert current once. Self-clears. I2C asserts a no acknowledge on attempted reads until the ADC conversion is complete. Selects different internal attenuation resistor networks for voltage readback. A 0 in C4 selects a 14:1 voltage divider. A 1 in C4 selects a 7:2 voltage divider. With an ADC full scale of 1.902 V, the voltage at the VCC pin for an ADC full-scale result is 26.35 V for VRANGE = 0 and 6.65 V for VRANGE = 1. Unused. Status read. When this bit is set, the data byte read back from the ADM1178 is the status byte. This contains the status of the device alerts. See Table 15 for full details of the status byte. Rev. D | Page 17 of 24 ADM1178 Data Sheet WRITE EXTENDED COMMAND BYTE 1. 2. 3. 4. 5. 6. The master device asserts a start condition on SDA. The master sends the 7-bit slave address, followed by the write bit (low). The addressed slave device asserts an acknowledge on SDA. The master sends the register address byte. The MSB of this byte is set to 1 to indicate an extended register write. The two LSBs indicate which of the three extended registers is written to (see Table 8). All other bits should be set to 0. The slave asserts an acknowledge on SDA. The master sends the extended command byte (refer to Table 9, Table 10, and Table 11). The slave asserts an acknowledge on SDA. The master asserts a stop condition on SDA to end the transaction. 1 2 3 4 5 6 7 8 EXTENDED SLAVE REGISTER S ADDRESS W A ADDRESS A COMMAND A P BYTE 06048-011 7. 8. In the write extended command byte operation, the master device writes to one of the three extended registers of the slave device, as follows: Figure 40. Write Extended Byte Table 9, Table 10, and Table 11 provide the details of each extended register. Table 8. Extended Register Addresses A6 0 0 0 A5 0 0 0 A4 0 0 0 A3 0 0 0 A2 0 0 0 A1 0 1 1 A0 1 0 1 Extended Register ALERT_EN ALERT_TH CONTROL Table 9. ALERT_EN Register Operations Bit 0 1 Default 0 0 Name EN_ADC_OC1 EN_ADC_OC4 2 1 EN_HS_ALERT 3 0 EN_OFF_ALERT 4 0 CLEAR Function LSB, enabled if a single ADC conversion on the I channel exceeds the threshold set in the ALERT_TH register. Enabled if four consecutive ADC conversions on the I channel exceed the threshold set in the ALERT_TH register. Enabled if the hot swap operation either has latches off or enters a cooldown cycle because of an overcurrent event. Enables an alert if the hot swap operation is turned off by a transition that deasserts the ON pin or by an operation that writes the SWOFF bit high. Clears the OFF_ALERT, HS_ALERT, and ADC_ALERT status bits in the STATUS register. The value of these bits may immediately change if the source of the alert is not cleared and the alert function is not disabled. The CLEAR bit self-clears to 0 after the STATUS register bits are cleared. Table 10. ALERT_TH Register Operations Bit [7:0] Default FF Function The ALERT_TH register sets the current level at which an alert occurs. Defaults to ADC full scale. The ALERT_TH 8-bit value corresponds to the top eight bits of the current channel data. Table 11. CONTROL Register Operations Bit 0 Default 0 Name SWOFF Function LSB, forces the hot swap operation off. Equivalent to deasserting the ON pin. Rev. D | Page 18 of 24 Data Sheet ADM1178 2 3 4 1 The ADM1178 digitizes both voltage and current. Three bytes are read back in the format shown in Table 12. SLAVE S R A ADDRESS Byte 1 2 3 Contents Voltage MSBs Voltage MSBs Voltage LSBs B7 V11 I11 V3 B6 V10 I10 V2 B5 V9 I9 V1 B4 V8 I8 V0 B3 V7 I7 I3 B2 V6 I6 I2 B1 V5 I5 I1 B0 V4 I4 I0 Voltage Readback The ADM1178 digitizes voltage only. Two bytes are read back in the format shown in Table 13. Table 13. Voltage Only Readback Format Byte 1 2 Contents Voltage MSBs Voltage LSBs B7 B6 B5 B4 B3 B2 B1 B0 V11 V10 V9 V8 V7 V6 V5 V4 V3 V2 V1 V0 0 0 0 0 Current Readback The ADM1178 digitizes current only. Two bytes are read back in the format shown in Table 14. Table 14. Current Only Readback Format Byte 1 2 Contents Current MSBs Current LSBs B7 I11 I3 B6 I10 I2 B5 B4 B3 B2 B1 B0 I9 I8 I7 I6 I5 I4 I1 I0 0 0 0 0 The following series of events occurs when the master receives three bytes (voltage and current data) from the slave device: The master device asserts a start condition on SDA. The master sends the 7-bit slave address, followed by the read bit (high). 3. The addressed slave device asserts an acknowledge on SDA. 4. The master receives the first data byte. 5. The master asserts an acknowledge on SDA. 6. The master receives the second data byte. 7. The master asserts an acknowledge on SDA. 8. The master receives the third data byte. 9. The master asserts a no acknowledge on SDA. 10. The master asserts a stop condition on SDA, and the transaction ends. 6 7 8 9 10 Figure 41. Three-Byte Read from ADM1178 Voltage and Current Readback Table 12. Voltage and Current Readback Format 5 SLAVE S ADDRESS R A DATA 1 A DATA 2 A DATA 3 N P 06048-012 1 2 3 4 5 6 7 8 DATA 1 A DATA 2 N P 06048-013 Depending on how the device is configured, ADM1178 can be set up to provide information in three ways after a conversion (or conversions): voltage and current readback, voltage only readback, and current only read back. See the Write Command Byte section for more details. For cases where the master is reading voltage only or current only, two data bytes are read and Step 7 and Step 8 are not required. Figure 42. Two-Byte Read from ADM1178 Converting ADC Codes to Voltage and Current Readings Equation 10 and Equation 11 can be used to convert ADC codes representing voltage and current from the ADM1178 12-bit ADC into actual voltage and current values. Voltage = (VFULLSCALE/4096) x Code (10) where: VFULLSCALE = 6.65 V (7:2 range) or 26.35 V (14:1 range). Code is the ADC voltage code read from the device (Bit V11 to Bit V0). Current = ((IFULLSCALE/4096) x Code)/Sense Resistor (11) where: IFULLSCALE = 105.84 mV. Code is the ADC current code read from the device (Bit I11 to Bit I0). Read Status Register A single register of status data can also be read from the ADM1178 as follows: 1. 2. 3. 4. 5. The master device asserts a start condition on SDA. The master sends the 7-bit slave address, followed by the read bit (high). The addressed slave device asserts an acknowledge on SDA. The master receives the status byte. The master asserts an acknowledge on SDA. 1 1. 2. 2 3 SLAVE S ADDRESS R A 4 5 STATUS BYTE A 06048-014 READ VOLTAGE AND/OR CURRENT DATA BYTES Figure 43. Status Read from ADM1178 Table 15 shows the ADM1178 STATUS registers in detail. Note that Bit 1, Bit 3, and Bit 5 are cleared by writing to Bit 4 (the CLEAR bit) of the ALERT_EN register. Rev. D | Page 19 of 24 ADM1178 Data Sheet Table 15. Status Byte Operations Bit 0 1 2 Name ADC_OC ADC_ALERT HS_OC 3 4 HS_ALERT OFF_STATUS 5 OFF_ALERT Function An ADC-based overcurrent comparison is detected on the last three conversions. An ADC-based overcurrent trip has occurred, causing the alert. Cleared by writing to Bit 4 of the ALERT_EN register. The hot swap operation is off due to an analog overcurrent event. On parts that latch off, this is the same as the HS_ALERT status bit (if EN_HS_ALERT = 1). On the retry parts, this indicates the current state: a 0 can indicate that the data was read during a period when the device was retrying or that it has successfully hot swapped by retrying after at least one overcurrent timeout. The hot swap operation has failed since the last time this was reset. Cleared by writing to Bit 4 of the ALERT_EN register. The state of the ON pin. Set to 1 if the input pin is deasserted. Can also be set to 1 by writing to the SWOFF bit of the CONTROL register. An alert has been caused by either the ON pin or the SWOFF bit. Cleared by writing to Bit 4 of the ALERT_EN register. Rev. D | Page 20 of 24 Data Sheet ADM1178 APPLICATIONS INFORMATION APPLICATIONS WAVEFORMS 1 1 2 2 3 3 4 CH2 1.00V CH4 10.0V M40.0ms CH1 1.5A CH3 20.0V Figure 44. Inrush Current Control into 220 F Load (Channel 1 = ILOAD, Channel 2 = VTIMER, Channel 3 = VGATE, Channel 4 = VOUT) CH2 1.00V CH4 10.0V M10.0ms 06048-073 CH1 1.5A CH3 20.0V 06048-070 4 Figure 47. Overcurrent Condition During Operation (ADM1178-1 Model) (Channel 1 = ILOAD, Channel 2 = VTIMER, Channel 3 = VGATE, Channel 4 = VOUT) 1 1 2 2 3 3 CH2 1.00V CH4 10.0V M10.0ms 06048-071 CH1 1.5A CH3 20.0V CH1 1.5A CH3 20.0V Figure 45. Overcurrent Condition at Startup (ADM1178-1 Model) (Channel 1 = ILOAD, Channel 2 = VTIMER, Channel 3 = VGATE, Channel 4 = VOUT) 2 3 M20.0ms 06048-072 4 CH2 1.00V CH4 10.0V M20.0ms Figure 48. Overcurrent Condition During Operation (ADM1178-2 Model) (Channel 1 = ILOAD, Channel 2 = VTIMER, Channel 3 = VGATE, Channel 4 = VOUT) 1 CH1 1.5A CH3 20.0V CH2 1.00V CH4 10.0V 06048-074 4 4 Figure 46. Overcurrent Condition at Startup (ADM1178-2 Model) (Channel 1 = ILOAD, Channel 2 = VTIMER, Channel 3 = VGATE, Channel 4 = VOUT) Rev. D | Page 21 of 24 ADM1178 Data Sheet ALERTB OUTPUT KELVIN SENSE RESISTOR CONNECTION The ALERTB output is an open-drain pin with 30 V tolerance. This output can be used as an overcurrent flag by connecting it to the general-purpose logic input of a controller. During normal operation, this output is pulled high. (An external pull-up resistor should be used because this is an open-drain pin.) When an overcurrent condition occurs, the ADM1178 pulls this output low. If any of the enabled latched alerts in the status byte (ADC_ALERT, HS_ALERT, and OFF_ALERT) are triggered, the ALERTB output asserts. For a programmable ADC-based overcurrent limit level point, the ADC_ALERT latch must be enabled. The overcurrent threshold that triggers an alert is then programmed via the ALERT_TH register. This pin is disabled by default at power up. See the ALERT_EN register to enable. When using a low value sense resistor for high current measurement, the problem of parasitic series resistance can arise. The pad and solder resistance can be a substantial fraction of the rated resistance, making the total resistance larger than expected. This error problem can be largely avoided by using a Kelvin sense connection. This type of connection separates the high current path through the resistor and the voltage drop across the resistor. A four pad resistor can be used or a split pad layout can be used with a two pad sense resistor to achieve Kelvin sensing. 3.15V TO 16.5V N-CHANNEL FET RSENSE VCC SENSE CONTROLLER GATE ADM1178 SDA SCL ON ALERTB P = VI SDA SCL INTERRUPT GND ADR 06048-100 TIMER Figure 49. Using the ALERTB Output as an Interrupt Rev. D | Page 22 of 24 Data Sheet ADM1178 OUTLINE DIMENSIONS 3.10 3.00 2.90 10 3.10 3.00 2.90 5.15 4.90 4.65 6 1 5 PIN 1 IDENTIFIER 0.50 BSC 0.95 0.85 0.75 15 MAX 1.10 MAX 0.30 0.15 6 0 0.23 0.13 COMPLIANT TO JEDEC STANDARDS MO-187-BA 0.70 0.55 0.40 091709-A 0.15 0.05 COPLANARITY 0.10 Figure 50. 10-Lead Mini Small Outline Package [MSOP] (RM-10) Dimensions shown in millimeters ORDERING GUIDE Model 1 ADM1178-1ARMZ-R7 ADM1178-2ARMZ-R7 EVAL-ADM1178EBZ 1 Hot Swap Retry Option Automatic Retry Version Latched Off Version Temperature Range -40C to +85C -40C to +85C Z = RoHS Compliant Part. Rev. D | Page 23 of 24 Package Description 10-Lead MSOP 10-Lead MSOP Evaluation Board Package Option RM-10 RM-10 Branding M62 M64 ADM1178 Data Sheet NOTES I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors). (c)2006-2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06048-0-6/12(D) Rev. D | Page 24 of 24 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Analog Devices Inc.: EVAL-ADM1178MEBZ