128-Position I2C-Compatible Digital Potentiometer AD5247 128 positions End-to-end resistance: 5 k, 10 k, 50 k, 100 k Ultracompact, SC70-6 (2 mm x 2.1 mm) package I2C-compatible interface Full read/write of wiper register Power-on preset to midscale Single-supply 2.7 V to 5.5 V Low temperature coefficient: 45 ppm/C Low power, IDD = 3 A typical Wide operating temperature range: -40C to +125C Available in Pb-free package Evaluation board available FUNCTIONAL BLOCK DIAGRAM VDD A SDA I2C INTERFACE SCL W WIPER REGISTER B 03876-001 FEATURES GND Figure 1. APPLICATIONS Mechanical potentiometer replacement in new designs Transducer adjustment of pressure, temperature, position, chemical, and optical sensors RF amplifier-biasing LCD brightness and contrast adjustment Automotive electronics adjustment Gain control and offset adjustment GENERAL DESCRIPTION The AD5247 provides a compact, 2 mm x 2.1 mm, packaged solution for 128-position adjustment applications. This device performs the same electronic adjustment function as a mechanical potentiometer or a variable resistor. Available in four different end-to-end resistance values (5 k, 10 k, 50 k, and 100 k), these low temperature coefficient devices are ideal for high accuracy and stability variable resistance adjustments. The wiper settings are controllable through the I2C-compatible digital interface, which can also be used to read back the present wiper register control word. The 10 k and 100 k options each have three hard-coded slave address options available to allow users access to three of these devices on one I2C bus (see Table 8 for a full list of slave address locations). The resistance between the wiper and either end point of the fixed resistor varies linearly with respect to the digital code transferred into the RDAC latch. Note the terms digital potentiometer, VR (variable resistor), and RDAC are used interchangeably in this document. Operating from a 2.7 V to 5.5 V power supply and consuming 3 A allows the AD5247 to be used in portable battery-operated applications. Rev. E 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)2003-2011 Analog Devices, Inc. All rights reserved. AD5247 TABLE OF CONTENTS Features .............................................................................................. 1 I2C Interface .................................................................................... 13 Applications ....................................................................................... 1 Theory of Operation ...................................................................... 14 Functional Block Diagram .............................................................. 1 Programming the Variable Resistor ......................................... 14 General Description ......................................................................... 1 Programming the Potentiometer Divider ............................... 15 Revision History ............................................................................... 2 I2C-Compatible 2-Wire Serial Bus ........................................... 15 Specifications..................................................................................... 3 Level Shifting for Bidirectional Interface ................................ 16 Electrical Characteristics--5 k Version .................................. 3 ESD Protection ........................................................................... 16 Electrical Characteristics--10 k, 50 k, and 100 k Versions.......................................................................................... 4 Terminal Voltage Operating Range ......................................... 16 Timing Characteristics--5 k, 10 k, 50 k, and 100 k Versions.......................................................................................... 5 Power-Up Sequence ................................................................... 16 Absolute Maximum Ratings............................................................ 6 ESD Caution .................................................................................. 6 Pin Configuration and Function Descriptions ............................. 7 Typical Performance Characteristics ............................................. 8 Test Circuits ..................................................................................... 12 Maximum Operating Current .................................................. 16 Layout and Power Supply Bypassing ....................................... 17 Constant Bias to Retain Resistance Setting............................. 17 Evaluation Board ........................................................................ 17 Outline Dimensions ....................................................................... 18 Ordering Guide .......................................................................... 18 REVISION HISTORY 1/11--Rev. D to Rev. E Change to Table 1, Added Output Logic Low .............................. 3 Change to Table 2, Added Output Logic Low .............................. 4 3/10--Rev. C to Rev. D Changes to Table 9 and Table 10................................................... 14 10/09--Rev. B to Rev. C Changes to Zero-Scale Error (10 k) Parameter, Table 2 ........... 4 Changes to Ordering Guide .......................................................... 18 3/07--Rev. A to Rev. B Changes to General Description Section ...................................... 1 Added Table 8.................................................................................. 13 Changes to I2C-Compatible 2-Wire Serial Bus Section............. 15 Changes to Ordering Guide .......................................................... 18 7/06--Rev. 0 to Rev. A Updated Format .................................................................. Universal Changes to Absolute Maximum Ratings section ......................... 6 Changes to Ordering Guide .......................................................... 18 9/03--Revision 0: Initial Version Rev. E | Page 2 of 20 AD5247 SPECIFICATIONS ELECTRICAL CHARACTERISTICS--5 k VERSION VDD = 5 V 10% or 3 V 10%, VA = VDD, -40C < TA < +125C, unless otherwise noted. Table 1. Parameter DC CHARACTERISTICS--RHEOSTAT MODE Resistor Differential Nonlinearity2 Resistor Integral Nonlinearity2 Nominal Resistor Tolerance3 Resistance Temperature Coefficient3 Output Resistance DC CHARACTERISTICS--POTENTIOMETER DIVIDER MODE Differential Nonlinearity4 Integral Nonlinearity4 Voltage Divider Temperature Coefficient Full-Scale Error Zero-Scale Error RESISTOR TERMINALS Voltage Range5 Capacitance A6 Capacitance W6 Common-Mode Leakage DIGITAL INPUTS AND OUTPUTS Input Logic High Input Logic Low Input Logic High Input Logic Low Input Current Input Capacitance6 Output Logic Low (SDA) POWER SUPPLIES Power Supply Range Supply Current Power Dissipation7 Power Supply Sensitivity DYNAMIC CHARACTERISTICS6, 8 Bandwidth -3 dB Total Harmonic Distortion VW Settling Time Resistor Noise Voltage Density Symbol Conditions Min Typ 1 Max Unit R-DNL R-INL RAB RAB/T RWB RWB, VA = no connect RWB, VA = no connect -1.5 -4 -30 0.1 0.75 +1.5 +4 +30 LSB LSB % ppm/C DNL INL VW/T VWFSE VWZSE VA, VW CA CW ICM VIH VIL VIH VIL IIL CIL VOL VDD RANGE IDD PDISS PSSR BW_5 K THDW tS eN_WB 45 75 Code = 0x00 -1 -1 Code = 0x40 Code = 0x7F Code = 0x00 -3 0 0.1 0.2 15 -2 1 GND f = 1 MHz, measured to GND, code = 0x40 f = 1 MHz, measured to GND, code = 0x40 VA = VDD/2 VDD = 5 V VDD = 5 V VDD = 3 V VDD = 3 V VIN = 0 V or 5 V 300 +1 +1 0 2 LSB LSB ppm/C LSB LSB VDD V 45 pF 60 1 pF nA 2.4 0.4 0.6 V V V V A pF V V 0.8 2.1 0.6 1 5 IOL = 3 mA IOL = 6 mA VIH = 5 V or VIL = 0 V VIH = 5 V or VIL = 0 V, VDD = 5 V VDD = 5 V 10%, code = midscale 2.7 3 5.5 8 40 V A W 0.003 0.05 %/% RAB = 5 k, code = 0x40 VA = 1 V rms, VB = 0 V, f = 1 kHz VA = 5 V, 1 LSB error band RWB = 2.5 k, RS = 0 1.2 0.05 1 6 Typical specifications represent average readings at 25C and VDD = 5 V. Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. 3 VA = VDD, wiper (VW) = no connect. 4 INL and DNL are measured at VW, with the RDAC configured as a potentiometer divider similar to a voltage output DAC. VA = VDD and VB = 0 V. DNL specification limits of 1 LSB maximum are guaranteed monotonic under operating conditions. 5 Resistor Terminal A and Resistor Terminal W have no limitations on polarity with respect to each other. 6 Guaranteed by design and not subject to production test. 7 PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation. 8 All dynamic characteristics use VDD = 5 V. 1 2 Rev. E | Page 3 of 20 MHz % s nV/Hz AD5247 ELECTRICAL CHARACTERISTICS--10 k, 50 k, AND 100 k VERSIONS VDD = 5 V 10% or 3 V 10%, VA = VDD, -40C < TA < +125C, unless otherwise noted. Table 2. Parameter DC CHARACTERISTICS--RHEOSTAT MODE Resistor Differential Nonlinearity2 Resistor Integral Nonlinearity2 Nominal Resistor Tolerance3 Resistance Temperature Coefficient3 Output Resistance DC CHARACTERISTICS--POTENTIOMETER DIVIDER MODE Differential Nonlinearity4 Integral Nonlinearity4 Voltage Divider Temperature Coefficient Full-Scale Error (50 k, 100 k) Zero-Scale Error (50 k, 100 k) Full-Scale Error (10 k) Zero-Scale Error (10 k) DNL INL VW/T VWFSE VWZSE VWFSE VWZSE RESISTOR TERMINALS Voltage Range5 Capacitance A6 VA, VW CA Capacitance W6 Common-Mode Leakage DIGITAL INPUTS AND OUTPUTS Input Logic High Input Logic Low Input Logic High Input Logic Low Input Current Input Capacitance6 Output Logic Low (SDA) POWER SUPPLIES Power Supply Range Supply Current Power Dissipation7 Power Supply Sensitivity DYNAMIC CHARACTERISTICS6, 8 Bandwidth -3 dB Total Harmonic Distortion VW Settling Time (10 k/50 k/100 k) Resistor Noise Voltage Density Symbol Conditions Min Typ1 Max Unit R-DNL R-INL RAB RAB/T RWB RWB, VA = no connect RWB, VA = no connect -1 -2 -20 0.1 0.25 +1 +2 +20 LSB LSB % ppm/C CW ICM VIH VIL VIH VIL IIL CIL VOL VDD RANGE IDD PDISS PSSR BW THDW tS eN_WB 45 75 Code = 0x00 -1 -1 Code = 0x40 Code = 0x7F Code = 0x00 Code = 0x7F VDD = 4.5 V to 5.5 V, code = 0x00 VDD = 2.7 V to 4.4 V, code = 0x00 -1 0 -2 0 0 0.1 0.2 15 -1 0.4 -0.5 0.5 0.5 GND f = 1 MHz, measured to GND, code = 0x40 f = 1 MHz, measured to GND, code = 0x40 VA = VDD/2 VDD = 5 V VDD = 5 V VDD = 3 V VDD = 3 V VIN = 0 V or 5 V 300 +1 +1 0 1 0 1 1.2 LSB LSB ppm/C LSB LSB LSB LSB LSB VDD V 45 pF 60 1 pF nA 2.4 0.4 0.6 V V V V A pF V V 5.5 8 40 0.02 V A W %/% 0.8 2.1 0.6 1 5 IOL = 3 mA IOL = 6 mA 2.7 VIH = 5 V or VIL = 0 V VIH = 5 V or VIL = 0 V, VDD = 5 V VDD = 5 V 10%, code = midscale 3 RAB = 10 k/50 k/100 k, code = 0x40 VA =1 V rms, f = 1 kHz, RAB = 10 k VA = 5 V 1 LSB error band RWB = 5 k, RS = 0 600/100/40 0.01 0.05 2 9 Typical specifications represent average readings at 25C and VDD = 5 V. Resistor position nonlinearity error R-INL is the deviation from an ideal value measured between the maximum resistance and the minimum resistance wiper positions. R-DNL measures the relative step change from ideal between successive tap positions. Parts are guaranteed monotonic. 3 VA = VDD, wiper (VW) = no connect. 4 INL and DNL are measured at VW, with the RDAC configured as a potentiometer divider similar to a voltage output DAC. VA = VDD and VB = 0 V. DNL specification limits of 1 LSB maximum are guaranteed monotonic operating conditions. 5 Resistor Terminal A and Resistor Terminal W have no limitations on polarity with respect to each other. 1 2 Rev. E | Page 4 of 20 kHz % s nV/Hz AD5247 Guaranteed by design, not subject to production test. PDISS is calculated from (IDD x VDD). CMOS logic level inputs result in minimum power dissipation. 8 All dynamic characteristics use VDD = 5 V. 6 7 TIMING CHARACTERISTICS--5 k, 10 k, 50 k, AND 100 k VERSIONS VDD = 5 V 10% or 3 V 10%, VA = VDD, -40C < TA < +125C, unless otherwise noted. Table 3. Parameter1, 2, 3 SCL Clock Frequency Bus Free Time Between Stop and Start, tBUF Hold Time (Repeated Start), tHD;STA5 Low Period of SCL Clock, tLOW High Period of SCL Clock, tHIGH Setup Time for Repeated Start Condition, tSU;STA Data Hold Time, tHD;DAT Data Setup Time, tSU;DAT Fall Time of Both SDA and SCL Signals, tF Rise Time of Both SDA and SCL Signals, tR Setup Time for Stop Condition, tSU;STO Symbol fSCL t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 Min 1.3 0.6 1.3 0.6 0.6 Typ4 Max 400 Unit kHz s s s s s s ns ns ns s 50 0.9 100 300 300 0.6 Specifications apply to all parts. Guaranteed by design, not subject to production test. See timing diagrams (Figure 2, Figure 33, and Figure 34) for locations of measured values. 4 Typical specifications represent average readings at 25C and VDD = 5 V. 5 After this period, the first clock pulse is generated. 1 2 3 t8 t2 t9 t6 SCL t2 t3 t4 t8 t5 t7 t10 t9 t1 P S S 2 Figure 2. I C Interface, Detailed Timing Diagram Rev. E | Page 5 of 20 P 03876-031 SDA AD5247 ABSOLUTE MAXIMUM RATINGS TA = 25C, unless otherwise noted. Table 4. Parameter VDD to GND VA, VW to GND Terminal Current, Ax to Bx, Ax to Wx, Bx to Wx Pulsed1 Continuous Digital Inputs and Output Voltage to GND Operating Temperature Range Maximum Junction Temperature (TJMAX) Storage Temperature Range Thermal Resistance JA2: (SC70-6) Reflow Soldering Peak Temperature SnPb Pb-Free Rating -0.3 V to +7 V VDD 20 mA 5 mA 0 V to VDD + 0.3 V -40C to +125C 150C -65C to +150C 340C/W 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. ESD CAUTION 240C 260C Maximum terminal current is bounded by the maximum current handling of the switches, maximum power dissipation of the package, and maximum applied voltage across any two of the A, B, and W terminals at a given resistance. 2 Package power dissipation = (TJMAX - TA)/JA. 1 Rev. E | Page 6 of 20 AD5247 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS VDD 1 6 A GND 2 SCL 3 5 W TOP VIEW (Not to Scale) 4 SDA 03876-043 AD5247 Figure 3. Pin Configuration Table 5. Pin Function Descriptions Pin No. 1 2 3 4 5 6 Mnemonic VDD GND SCL SDA W A Description Positive Power Supply. Digital Ground and B Termination Voltage. Serial Clock Input; Positive Edge Triggered. Serial Data Input/Output. Terminal W. Terminal A. Rev. E | Page 7 of 20 AD5247 TYPICAL PERFORMANCE CHARACTERISTICS 0.25 1.0 TA = 25C RAB = 10k 0.4 0.2 0 VDD = 5.5V -0.2 -0.4 -0.6 -0.8 -1.0 0 16 32 48 64 80 CODE (Decimal) 96 112 0.15 0.10 TA = -40C, +25C, +85C, +125C 0.05 0 -0.05 -0.10 -0.15 03876-005 VDD = 2.7V 03876-002 RHEOSTAT MODE INL (LSB) 0.6 -0.20 -0.25 0 128 Figure 4. R-INL vs. Code vs. Supply Voltages 32 48 64 80 CODE (Decimal) 96 112 128 0.25 TA = 25C RAB = 10k 0.2 VDD = 2.7V 0.1 0 VDD = 5.5V -0.2 03876-003 -0.3 -0.4 -0.5 0 16 32 64 80 48 CODE (Decimal) 96 112 0.15 0.10 VDD = 2.7V 0.05 0 VDD = 5.5V -0.05 -0.10 -0.15 03876-006 0.3 -0.1 TA = 25C RAB = 10k 0.20 POTENTIOMETER MODE INL (LSB) 0.4 RHEOSTAT MODE DNL (LSB) 16 Figure 7. DNL vs. Code vs. Temperature 0.5 -0.20 -0.25 0 128 16 32 64 80 48 CODE (Decimal) 96 112 128 Figure 8. INL vs. Code vs. Supply Voltages Figure 5. R-DNL vs. Code vs. Supply Voltages 0.25 0.20 TA = +25C 0.15 POTENTIOMETER MODE DNL (LSB) VDD = 2.7V RAB = 10k TA = -40C TA = +85C TA = +125C 0.10 TA = +25C, +85C, +125C 0.05 0 -0.05 TA = -40C -0.10 03876-004 -0.15 -0.20 -0.25 0 16 32 64 80 48 CODE (Decimal) 96 112 0.20 VDD = 2.7V 0.15 VDD = 5.5V TA = 25C RAB = 10k 0.10 VDD = 2.7V 0.05 0 -0.05 VDD = 5.5V -0.10 -0.15 03876-007 0.25 POTENTIOMETER MODE INL (LSB) VDD = 2.7V RAB = 10k -40C +25C +85C +125C 0.20 POTENTIOMETER MODE DNL (LSB) 0.8 -0.20 -0.25 0 128 16 32 64 80 48 CODE (Decimal) 96 Figure 9. DNL vs. Code vs. Supply Voltages Figure 6. INL vs. Code vs. Temperature Rev. E | Page 8 of 20 112 128 AD5247 1.50 1.0 0.8 ZERO-SCALE ERROR (LSB) 1.25 0.4 0.2 TA = +125C -0.2 -0.4 TA = -40C TA = +25C -0.6 TA = +125C -1.0 0 16 32 48 64 80 CODE (Decimal) 96 112 VDD = 5.5V, VA = 5.5V 0.75 0.50 0.25 TA = +85C -0.8 1.00 VDD = 2.7V, VA = 2.7V 0 -40 -25 128 Figure 10. R-INL vs. Code vs. Temperature -10 5 20 35 50 65 TEMPERATURE (C) 80 110 125 100 VDD = 2.7V RAB = 10k 0.2 TA = -40C, +25C, +85C, +125C 0.1 0 -0.1 -0.2 03876-009 -0.3 -0.4 -0.5 0 16 32 48 64 80 CODE (Decimal) 96 112 10 VDD = 5.5V 1 VDD = 2.7V 0.1 0.01 -40 -25 -10 128 03876-012 0.3 DIGITAL INPUTS = 0V CODE = 0x40 IDD, SUPPLY CURRENT (A) -40C +25C +85C +125C 0.4 5 20 35 50 65 TEMPERATURE (C) 80 110 125 500 0 VDD = 2.7V RAB = 10k 400 VDD = 5.5V, VA = 5.5V -1.0 -1.5 -2.0 VDD = 2.7V, VA = 2.7V 03876-010 -2.5 -25 -10 5 20 35 50 65 TEMPERATURE (C) 80 95 110 300 TA = -40C to +85C 200 100 0 -100 -200 TA = -40C to +125C -300 03876-013 RHEOSTAT MODE TEMPCO (ppm/C) -0.5 -3.0 -40 95 Figure 14. Supply Current vs. Temperature Figure 11. R-DNL vs. Code vs. Temperature RHEOSTAT MODE INL (LSB) FULL-SCALE ERROR (LSB) 95 Figure 13. Zero-Scale Error vs. Temperature 0.5 RHEOSTAT MODE DNL (LSB) 03876-011 TA = +25C 0 03876-008 RHEOSTAT MODE INL (LSB) TA = -40C TA = +85C 0.6 -400 -500 125 0 Figure 12. Full-Scale Error vs. Temperature 16 32 64 80 48 CODE (Decimal) Figure 15. RWB/T vs. Code Rev. E | Page 9 of 20 96 112 128 AD5247 0 30 0x20 -12 20 0x10 -18 15 TA = -40C TO +85C GAIN (dB) POTENTIOMETER (ppm/C) 0x40 -6 VDD = 2.7V RAB = 10k 25 10 5 0x08 -24 0x04 -30 0x02 -36 0x01 -42 0 03876-014 TA = -40C TO +125C -10 0 16 32 48 64 80 CODE (Decimal) 96 112 -54 -60 1k 128 10k 100k FREQUENCY (Hz) 10M 0 0x40 0x20 -12 0x20 -12 0x10 -18 0x40 -6 0x10 -18 0x08 GAIN (dB) -24 0x04 -30 0x02 0x01 -36 -24 -48 03876-015 -48 10k 100k 1M 0x02 -36 -42 -60 1k 0x04 -30 -42 -54 0x08 0x01 03876-018 0 -6 -54 -60 1k 10M 10k 100k 1M 10M FREQUENCY (Hz) FREQUENCY (Hz) Figure 20. Gain vs. Frequency vs. Code, RAB = 100 k Figure 17. Gain vs. Frequency vs. Code, RAB = 5 k 0 0 0x40 -6 5k 0x20 -12 -12 10k 0x10 -18 -18 100k -24 GAIN (dB) 0x08 0x04 -30 0x02 -36 0x01 -24 -30 -36 -42 -48 -48 03876-016 -42 -54 -60 1k 10k 100k 1M 50k 03876-019 -6 GAIN (dB) 1M Figure 19. Gain vs. Frequency vs. Code, RAB = 50 k Figure 16. VWB/T vs. Code GAIN (dB) 03876-017 -48 -5 -54 -60 1k 10M 10k 100k 1M FREQUENCY (Hz) FREQUENCY (Hz) Figure 18. Gain vs. Frequency vs. Code, RAB = 10 k Figure 21. -3 dB Bandwidth @ Code = 0x80 Rev. E | Page 10 of 20 10M AD5247 0.30 IDD (A) 0.25 VDD = 5.5V VA = 5.0V VB = 0V CODE 0x40 TO CODE 0x3F TA = 25C A-VDD = 5.5V CODE = 0x55 B-VDD = 5.5V CODE = 0x7F 0.20 C-VDD = 2.7V CODE = 0x55 0.15 D-VDD = 2.7V CODE = 0x7F TA = 25C RAB = 10k VW 0.10 A D 10k 100k FREQUENCY (Hz) 03876-020 C 0 1k 03876-023 B 0.05 200ns/DIV 1M Figure 22. IDD vs. Frequency Figure 25. Midscale Glitch, Code 0x40 to Code 0x3F 150 TA = 25C RAB = 50k VDD = 5.5V VA = 5.0V VB = 0V CODE 0x00 TO CODE 0x7F 100 VDD = 2.7V VW 75 50 25 VDD = 5.5V 03876-021 03876-024 WIPER RESISTANCE () 125 TA = 25C RAB = 10k 0 0 16 32 48 64 80 CODE (Decimal) 96 112 4s/DIV 128 Figure 23. Wiper Resistance vs. Code vs. VDD Figure 26. Large Signal Settling Time TA = 25C RAB = 10k FCLK = 100kHz VDD = 5.5V VA = 5.0V VB = 0V VW 5V CLK 03876-022 0V 1s/DIV Figure 24. Digital Feedthrough Rev. E | Page 11 of 20 AD5247 TEST CIRCUITS Figure 27 to Figure 32 define the test conditions used in the Specifications section. VA A VDD W V+ A V+ B V+ = VDD 10% DUT V+ = VDD 1LSB = V+/2N PSSR (%/%) = W B Figure 27. Potentiometer Divider Nonlinearity Error (INL, DNL) VDD% VMS 03876-025 VMS VMS% 03876-028 DUT Figure 30. Power Supply Sensitivity (PSS, PSSR) NO CONNECT DUT DUT IW W W B OP27 B 03876-026 VMS +15V A VIN VOUT 03876-029 A -15V Figure 28. Resistor Position Nonlinearity Error (R-INL, R-DNL) Figure 31. Gain vs. Frequency NC DUT W VW IW = VDD/RNOMINAL VDD B RW = [VMS1 - VMS2]/IW GND B 03876-027 VMS1 A NC Figure 29. Wiper Resistance W ICM VCM 03876-030 A VMS2 DUT Figure 32. Common-Mode Leakage Current Rev. E | Page 12 of 20 AD5247 I2C INTERFACE The following abbreviations are used in this section: * S = start condition * W = write * P = stop condition * R = read * A = acknowledge * A6, A5, A4, A3, A2, A1, A0 = address bits * X = don't care * D6, D5, D4, D3, D2, D1, D0 = data bits Table 6. Write Mode S A6 A5 A4 A3 A2 A1 A0 W A X D6 D5 Slave Address Byte D4 D3 D2 D1 D0 A P D2 D1 D0 A P Data Byte Table 7. Read Mode S A6 A5 A4 A3 A2 A1 Slave Address Byte A0 R A 1 0 9 D6 D5 D4 D3 Data Byte 9 1 1 SCL A6 A5 A4 A3 A2 A1 A0 FRAME 1 SLAVE ADDRESS BYTE START BY MASTER X R/W D6 D5 ACK ACK BY AD5247 D4 D3 D2 D1 D0 ACK BY AD5247 FRAME 2 DATA BYTE STOP BY MASTER 03876-032 SDA Figure 33. Writing to the RDAC Register 1 9 9 1 SCL A5 A4 A3 A2 A1 A0 D6 ACK BY AD5247 FRAME 1 SLAVE ADDRESS BYTE START BY MASTER 0 R/W D5 D4 D3 D2 FRAME 2 RDAC REGISTER D1 D0 NO ACK BY MASTER STOP BY MASTER 03876-033 A6 S Figure 34. Reading from the RDAC Register Table 8. I2C Slave Addresses Model AD5247BKS5-R2 AD5247BKS5-RL7 AD5247BKSZ5-RL7 AD5247BKS10-R2 AD5247BKS10-RL7 AD5247BKSZ10-RL7 AD5247BKSZ10-1RL7 AD5247BKSZ10-2RL7 AD5247BKS50-R2 Slave Addresses A6 A5 A4 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 A3 1 1 1 1 1 1 0 0 1 A2 1 1 1 1 1 1 1 1 1 A1 1 1 1 1 1 1 1 1 1 A0 0 0 0 0 0 0 1 0 0 Model AD5247BKS50-RL7 AD5247BKSZ50-RL7 AD5247BKS100-R2 AD5247BKSZ100-R2 AD5247BKS100-RL7 AD5247BKSZ100-RL7 AD5247BKSZ100-1RL7 AD5247BKSZ100-2RL7 Rev. E | Page 13 of 20 Slave Address A6 A5 A4 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 1 0 0 1 A3 1 1 1 1 1 1 0 0 A2 1 1 1 1 1 1 1 1 A1 1 1 1 1 1 1 1 1 A0 0 0 0 0 0 0 1 0 AD5247 THEORY OF OPERATION The AD5247 is a 128-position, digitally-controlled variable resistor (VR) device. An internal power-on preset places the wiper at midscale during power-on, which simplifies the default condition recovery at power-up. The general equation determining the digitally programmed output resistance between W and B is PROGRAMMING THE VARIABLE RESISTOR where: D is the decimal equivalent of the binary code loaded in the 7-bit RDAC register. RAB is the end-to-end resistance. RW is the wiper resistance contributed by the on resistance of the internal switch. RWB (D) = Rheostat Operation The nominal resistance (RAB) of the RDAC between Terminal A and Terminal B is available in 5 k , 10 k, 50 k, and 100 k. The final two or three digits of the part number determine the nominal resistance value; for example, 10 k = 10 and 50 k = 50. The RAB of the VR has 128 contact points accessed by the wiper terminal, plus the B terminal contact. The 7-bit data in the RDAC latch is decoded to select one of the 128 possible settings. Assuming a 10 k part is used, the wiper's first connection starts at the B terminal for Data 0x00. Because there is a 50 wiper contact resistance, such a connection yields a minimum of 100 (2 x 50 ) resistance between Terminal W and Terminal B. The second connection is the first tap point, corresponding to 178 (RWB = RAB/128 + RW = 78 + 2 x 50 ) for Data 0x01. The third connection is the next tap point, representing 256 (2 x 78 + 2 x 50 ) for Data 0x02, and so on. Each LSB data value increase moves the wiper up the resistor ladder until the last tap point is reached at 10,100 (RAB + 2 x RW). Figure 35 shows a simplified diagram of the equivalent RDAC circuit where the last resistor string is not accessed. Ax D6 D5 D4 D3 D2 D1 D0 (1) In summary, if RAB = 10 k and the Terminal A is open-circuited, the output resistance RWB, shown in Table 9, is set for the indicated RDAC latch codes. Table 9. Codes and Corresponding RWB Resistance D (Decimal) 127 64 1 0 RWB () 10,072 5150 228 150 Output State Full scale (RAB + 2 x RW) Midscale 1 LSB Zero scale (wiper contact resistance) Note that in the zero-scale condition, a finite resistance of 100 between Terminal W and Terminal B is present. Care should be taken to limit the current flow between W and B in this state to a maximum pulse current of no more than 20 mA. Otherwise, degradation or possible destruction of the internal switch contact can occur. Similar to the mechanical potentiometer, the resistance of the RDAC between Wiper W and Terminal A also produces a digitally controlled complementary resistance, RWA. When these terminals are used, the Terminal B can be opened. Set the resistance value for RWA to start at a maximum value of resistance and to decrease the data loaded in the latch increases in value. The general equation for this operation is RS RS Wx RDAC RWA (D) = Bx 03876-034 LATCH AND RS DECODER D x R AB + 2 x RW 128 Figure 35. AD5247 Equivalent RDAC Circuit 128 - D x R AB + 2 x RW 128 (2) If RAB = 10 k and the B terminal is open-circuited, the output resistance, RWA, shown in Table 10, is set for the indicated RDAC latch codes. Table 10. Codes and Corresponding RWA Resistance D (Decimal) 127 64 1 0 RWA () 228 5150 10,071 10,150 Output State Full scale Midscale 1 LSB Zero scale Typical device-to-device matching is process lot dependent and can vary by up to 30%. Because the resistance element is processed in thin film technology, the change in RAB with temperature has a very low 45 ppm/C temperature coefficient. Rev. E | Page 14 of 20 AD5247 PROGRAMMING THE POTENTIOMETER DIVIDER The 2-wire I2C serial bus protocol operates as follows: Voltage Output Operation 1. The master initiates a data transfer by establishing a start condition, which is when a high-to-low transition on the SDA line occurs while SCL is high (see Figure 33). The following byte is the slave address byte, consisting of the 7-bit slave address followed by an R/W bit (this bit determines whether data is read from or written to the slave device). The slave, whose address corresponds to the transmitted address, responds by pulling the SDA line low during the ninth clock pulse (this is termed the acknowledge bit). At this stage, all other devices on the bus remain idle while the selected device waits for data to be written to or read from its serial register. If the R/W bit is high, the master reads from the slave device. If the R/W bit is low, the master writes to the slave device. 2. In write mode, after acknowledgement of the slave address byte, the next byte is the data byte. Data is transmitted over the serial bus in sequences of nine clock pulses (eight data bits followed by an acknowledge bit). The transitions on the SDA line must occur during the low period of SCL and remain stable during the high period of SCL (see Figure 33). 3. In read mode, after acknowledgment of the slave address byte, data is received over the serial bus in sequences of nine clock pulses (a slight difference from write mode, where eight data bits are followed by an acknowledge bit). Similarly, the transitions on the SDA line must occur during the low period of SCL and remain stable during the high period of SCL (see Figure 34). 4. When all data bits have been read or written, a stop condition is established by the master. A stop condition is defined as a low-to-high transition on the SDA line while SCL is high. In write mode, the master pulls the SDA line high during the 10th clock pulse to establish a stop condition (see Figure 33). In read mode, the master issues a no acknowledge for the ninth clock pulse (that is, the SDA line remains high). The master then brings the SDA line low before the 10th clock pulse, which goes high to establish a stop condition (see Figure 34). The digital potentiometer easily generates a voltage divider at wiper-to-B and wiper-to-A, proportional to the input voltage at A-to-B. Unlike the polarity of VDD to GND, which must be positive, voltage across A-to-B, W-to-A, and W-to-B can be at either polarity. If ignoring the effect of the wiper resistance for approximation, connecting the Terminal A to 5 V and the Terminal B to ground produces an output voltage at the wiper-to-B starting at 0 V up to 1 LSB less than 5 V. Each LSB of voltage is equal to the voltage applied across Terminal A and Terminal B divided by the 128 positions of the potentiometer divider. The general equation defining the output voltage at VW with respect to ground for any valid input voltage applied to Terminal A and Terminal B is VW (D) = D xVA 128 (3) A more accurate calculation that includes the effect of wiper resistance, VW, is VW (D) = RWB(D) x VA RAB (4) Operation of the digital potentiometer in the divider mode results in a more accurate operation over temperature. Unlike rheostat mode, divider mode makes the output voltage mainly on the ratio of Internal Resistor RWA to Internal Resistor RWB, and not the absolute values. Therefore, the temperature drift reduces to 15 ppm/C. I2C-COMPATIBLE 2-WIRE SERIAL BUS The first byte of the AD5247 is a slave address byte (see the I2C Interface section). It has a 7-bit slave address and an R/W bit. The 5 k and 50 k options support one 7-bit slave address while the 10 k and 100 k options each have three hard-coded slave address options available (see Table 8 for a full list of slave address locations). The extra hard coded slave addresses on the 10 k and 100 k options allow users to employ up to three of these devices on one I2C bus. The seven MSBs of the slave address are followed by 0 for a write command or 1 to place the device in read mode. A repeated write function gives the user flexibility to update the RDAC output a number of times after addressing the part only once. For example, after the RDAC has acknowledged its slave address in the write mode, the RDAC output updates on each successive byte. If different instructions are needed, the write/read mode has to start again with a new slave address and data byte. Similarly, a repeated read function of the RDAC is also allowed. Rev. E | Page 15 of 20 AD5247 LEVEL SHIFTING FOR BIDIRECTIONAL INTERFACE MAXIMUM OPERATING CURRENT While most legacy systems can be operated at one voltage, a new component can be optimized at another voltage. When two systems operate the same signal at two different voltages, proper level shifting is needed. For instance, users can employ a 3.3 V E2PROM to interface with a 5 V digital potentiometer. A level shifting scheme is needed to enable a bidirectional communication so that the setting of the digital potentiometer can be stored in and retrieved from the E2PROM. Figure 36 shows one of the level-shifting implementations. M1 and M2 can be any N-channel signal FETs, or if VDD falls below 2.5 V, M1 and M2 can be low threshold FETs such as the FDV301N. At low code values, the user should be aware that, due to low resistance values, the current through the RDAC might exceed the 5 mA limit. In Figure 39, a 5 V supply is placed on the wiper, and the current through Terminal W and Terminal B is plotted with respect to code. A line is also drawn denoting the 5 mA current limit. Note that at low code values (particularly for the 5 k and 10 k options), the current level increases significantly. Care should be taken to limit the current flow between W and B in this state to a maximum continuous current of 5 mA and a maximum pulse current of no more than 20 mA. Otherwise, degradation or possible destruction of the internal switch contacts can occur. VDD1 = 3.3V VDD2 = 5V 100 RP RP RP RP G D S SDA2 10 SCL2 M2 3.3V 5V 03876-035 SCL1 D S AD5247 E2PROM IWB CURRENT (mA) G M1 Figure 36. Level-Shifting for Operation at Different Potentials 5mA CURRENT LIMIT RAB = 5k 1 RAB = 10k RAB = 50k 0.1 ESD PROTECTION RAB = 100k All digital inputs are protected with a series input resistor and parallel Zener ESD structures as shown in Figure 37. This applies to digital input pins (SDA and SCL). 340 GND 0.01 0 16 32 64 80 48 CODE (Decimal) 96 112 128 Figure 39. Maximum Operating Current POWER-UP SEQUENCE LOGIC 03876-036 SDA/ SCL 03876-039 SDA1 Figure 37. ESD Protection of Digital Pins TERMINAL VOLTAGE OPERATING RANGE The AD5247 VDD and GND power supply defines the boundary conditions for proper 3-terminal digital potentiometer operation. Supply signals present on Terminal A and Terminal W that exceed VDD or GND are clamped by the internal forward biased diodes (see Figure 38). Because the ESD protection diodes limit the voltage compliance at Terminal A and Terminal W (see Figure 38), it is important to power VDD/GND before applying any voltage to Terminal A and Terminal W; otherwise, the diode is forward-biased such that VDD is powered unintentionally and can affect the rest of the user's circuit. The ideal power-up sequence is in the following order: GND, VDD, digital inputs, VA, and VW. The relative order of powering VA and VW and the digital inputs is not important as long as they are powered after VDD/GND. VDD A GND 03876-038 W Figure 38. Maximum Terminal Voltages Set by VDD and GND Rev. E | Page 16 of 20 AD5247 110% LAYOUT AND POWER SUPPLY BYPASSING 108% It is good practice to employ a compact, minimum lead-length layout design. The leads to the inputs should be as direct as possible with minimum conductor length. Ground paths should have low resistance and low inductance. TA = 25C Similarly, it is good practice to bypass the power supplies with quality capacitors for optimum stability. Supply leads to the device should be bypassed with 0.01 F to 0.1 F disc or chip ceramic capacitors. Low ESR 1 F to 10 F tantalum or electrolytic capacitors should also be applied at the supplies to minimize any transient disturbance and low frequency ripple (see Figure 40). Note that the digital ground should also be joined remotely to the analog ground at one point to minimize the ground bounce. C3 10F + 102% 100% 98% 96% 94% 92% 90% 0 5 10 15 DAYS 20 25 30 Figure 41. Battery Operating Life Depletion This demonstrates that constantly biasing the potentiometer is a practical approach. Most portable devices do not require the removal of batteries for charging. Although the resistance setting of the AD5247 is lost when the battery needs replacement, such events occur rather infrequently. As a result, this inconvenience is justified by the lower cost and smaller size offered by the AD5247. If total power is lost, the user should be provided with a means to adjust the setting accordingly. VDD VDD 104% 03876-041 BATTERY LIFE DEPLETED 106% C1 0.1F AD5247 03876-040 GND Figure 40. Power Supply Bypassing CONSTANT BIAS TO RETAIN RESISTANCE SETTING EVALUATION BOARD For users who desire nonvolatility but cannot justify the additional cost for the EEMEM, the AD5247 can be considered a low cost alternative because it maintains a constant bias to retain the wiper setting. The AD5247 is specifically designed with low power in mind, which allows low power consumption even in battery-operated systems. An evaluation board, along with all necessary software, is available to program the AD5247 from any PC running Windows(R) 98, Windows 2000, or Windows XP. The graphical user interface, shown in Figure 42, is straightforward and easy to use. More information is available in the data sheet that comes with the evaluation board. 03876-042 Figure 41 demonstrates the power consumption from a 3.4 V 450 mA/hr Li-Ion cell phone battery, which is connected to the AD5247. The measurement over time shows that the device draws approximately 1.3 A and consumes negligible power. Over a course of 30 days, the battery was depleted by less than 2%, the majority of which was due to the intrinsic leakage current of the battery itself. Figure 42. AD5247 Evaluation Board Software Rev. E | Page 17 of 20 AD5247 OUTLINE DIMENSIONS 2.20 2.00 1.80 6 5 4 1 2 3 0.65 BSC 1.30 BSC 1.00 0.90 0.70 0.10 MAX COPLANARITY 0.10 2.40 2.10 1.80 1.10 0.80 0.30 0.15 SEATING PLANE 0.40 0.10 0.22 0.08 0.46 0.36 0.26 COMPLIANT TO JEDEC STANDARDS MO-203-AB 072809-A 1.35 1.25 1.15 Figure 43. 6-Lead Thin Shrink Small Outline Transistor Package [SC70] (KS-6) Dimensions shown in millimeters ORDERING GUIDE Model1 AD5247BKSZ5-RL7 AD5247BKSZ10-RL7 AD5247BKSZ10-1RL7 AD5247BKSZ10-2RL7 AD5247BKSZ50-RL7 AD5247BKSZ100-R2 AD5247BKSZ100-RL7 AD5247BKSZ100-1RL7 AD5247BKSZ100-2RL7 AD5247EVAL 1 2 RAB (k) 5 10 10 10 50 100 100 100 100 Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C Package Description2 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] 6-lead Thin Shrink Small Outline Transistor Package [SC70] Evaluation Board Package Option KS-6 KS-6 KS-6 KS-6 KS-6 KS-6 KS-6 KS-6 KS-6 Z = RoHS compliant part. The evaluation board is shipped with the 10 k RAB resistor option; however, the board is compatible with all available resistor value options. Rev. E | Page 18 of 20 Branding D96 D95 D5E DAK D97 D98 D98 DAJ DAL AD5247 NOTES Rev. E | Page 19 of 20 AD5247 NOTES I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors). (c)2003-2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D03876-0-1/11(E) Rev. E | Page 20 of 20