AD5222

a FEATURES 128-Position, 2-Channel Potentiometer Replacement 10 k , 50 k , 100 k , 1 M Very Low Power: 40 A Max 2.7 V Dual Supply Operation or 2.7 V to 5.5 V Single Supply Operation Increment/Decrement Count Control APPLICATIONS Stereo Channel Audio Level Control Mechanical Potentiometer Replacement Remote Incremental Adjustment Applications Instrumentation: Gain, Offset Adjustment Programmable Voltage-to-Current Conversion Line Impedance Matching Increment/Decrement Dual Digital Potentiometer AD5222 FUNCTIONAL BLOCK DIAGRAM VDD U/D AD5222 UP/DOWN COUNTER DECODE A1 W1 B1 POR CS MODE DACSEL CLK GND A2 UP/DOWN COUNTER DECODE W2 B2 VSS DAC SELECT AND ENABLE GENERAL DESCRIPTION The AD5222 provides a dual channel, 128-position, digitally controlled variable-resistor (VR) device. This device performs the same electronic adjustment function as a potentiometer or variable resistor. These products were optimized for instrument and test equipment push-button applications. Choices between bandwidth or power dissipation are available as a result of the wide selection of end-to-end terminal resistance values. The AD5222 contains two fixed resistors with wiper contacts that tap the fixed resistor value at a point determined by a digitally controlled up/down counter. The resistance between the wiper and either end point of the fixed resistor provides a constant resistance step size that is equal to the end-to-end resistance divided by the number of positions (e.g., R STEP = 10 kΩ/128 = 78 Ω). The variable resistor offers a true adjustable value of resistance, between Terminal A and the wiper, or Terminal B and the wiper. The fixed A-to-B terminal resistance of 10 k Ω, 50 kΩ, 100 k Ω, or 1 MΩ has a nominal temperature coefficient of –35 ppm/°C. The chip select CS, count CLK and U/D direction control inputs set the variable resistor position. The MODE determines whether both VRs are incremented together or independently. With MODE at logic zero, both wipers are incremented UP or DOWN without changing the relative settings between the wipers. Also, the relative ratio between the wipers is preserved if either wiper reaches the end of the resistor array. In the independent MODE (Logic 1) only the VR determined by the DACSEL pin is changed. DACSEL (Logic 0) changes RDAC 1. These inputs, which control the internal up/down counter, can be easily generated with mechanical or push-button switches (or other contact closure devices). This simple digital interface eliminates the need for microcontrollers in front panel interface designs. The AD5222 is available in the surface-mount (SO-14) package. For ultracompact solutions, selected models are available in the thin TSSOP-14 package. All parts are guaranteed to operate over the extended industrial temperature range of –40° C to +85°C. For 3-wire, SPI-compatible interface applications, see the AD5203/AD5204/AD5206, AD7376, and AD8400/AD8402/ AD8403 products. 5V VDD CS U/D U/D CLK INCREMENT A1 W1 B1 A2 DACSEL MODE GND W2 B2 VSS Figure 1. Typical Push-Button Control Application R EV. 0 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999 V 10% or 5 V AD5222–SPECIFICATIONS (V = 3otherwise noted.) unless DD 10%, VSS = 0 V, VA = +VDD, VB = 0 V, –40 C < TA < +85 C, Min –1 –1 –30 Typ1 Max ± 1/4 +1 ± 0.4 +1 +30 –35 45 100 0.2 1 Unit LSB LSB % ppm/ °C Ω % Bits LSB LSB LSB ppm/ °C LSB LSB V pF pF nA Parameter Symbol Condition DC CHARACTERISTICS RHEOSTAT MODE (Specifications Apply to All VRs) R-DNL RWB, VA = NC Resistor Differential NL2 Resistor Nonlinearity2 R-INL RWB, VA = NC Nominal Resistor Tolerance ∆R VAB = VDD, Wiper = No Connect, T A = 25°C Resistance Temperature Coefficient RAB/∆T VAB = VDD, Wiper = No Connect Wiper Resistance3 RW IW = VDD /R, VDD = 3 V or 5 V Nominal Resistance Match ∆R/RO CH 1 to 2, V AB = VDD, TA = 25°C DC CHARACTERISTICS POTENTIOMETER DIVIDER MODE (Specifications Apply to All VRs) Resolution N INL RAB = 10 k Ω, 50 kΩ, or 100 kΩ Integral Nonlinearity4 INL RAB = 1 M Ω Differential Nonlinearity4 DNL Voltage Divider Temperature Coefficient ∆VW /∆ T Code = 40H Full-Scale Error VWFSE Code = 7F H Zero-Scale Error VWZSE Code = 00H RESISTOR TERMINALS Voltage Range 5 Capacitance6 A, B Capacitance6 W Common-Mode Leakage DIGITAL INPUTS AND OUTPUTS Input Logic High Input Logic Low Input Current Input Capacitance6 POWER SUPPLIES Power Single-Supply Range Power Dual-Supply Range Positive Supply Current Negative Supply Current Power Dissipation 7 Power Supply Sensitivity DYNAMIC CHARACTERISTICS6, 8, 9 Bandwidth –3 dB VA, B, W CA, B CW ICM VIH VIL IIL CIL VDD RANGE VDD/SS RANGE IDD ISS PDISS PSS BW_10K BW_50K BW_100K BW_1M THDW tS eN_WB 7 –1 –2 –1 –1 0 VSS ± 1/4 ± 1/2 ± 1/4 20 –0.5 0.5 +1 +2 +1 +0 1 VDD f = 1 MHz, Measured to GND, Code = 40 H f = 1 MHz, Measured to GND, Code = 40 H VA = V B = V W VDD = 5 V/3 V VDD = 5 V/3 V VIN = 0 V or 5 V 2.4/2.1 45 60 1 5 VSS = 0 V VIH = 5 V or VIL = 0 V VSS = –2.5 V, VDD = +2.7 V VIH = 5 V or VIL = 0 V, VDD = 5 V 2.7 ± 2.3 V 0.8/0.6 V ±1 µA pF V V µA µA µW %/% kHz kHz kHz kHz % µs nV√Hz ns ns ns ns ns ns ns ns ns 5.5 ± 2.7 15 40 15 40 150 400 0.002 0.05 1000 180 78 7 0.005 2 14 Total Harmonic Distortion VW Settling Time Resistor Noise Voltage RAB = 10 kΩ, Code = 40 H RAB = 50 kΩ, Code = 40 H RAB = 100 k Ω, Code = 40H RAB = 500 k Ω, Code = 40H VA = 1 V rms + 2 V dc, VB = 2 V dc, f = 1 kHz RAB = 10 kΩ, ± 1 LSB Error Band RWB = 5 kΩ, f = 1 kHz 30 20 20 10 30 20 30 20 40 INTERFACE TIMING CHARACTERISTICS (Applies to All Parts) 6, 10 Input Clock Pulsewidth tCH, t CL Clock Level High or Low CS to CLK Setup Time tCSS CS Rise to CLK Hold Time tCSH U/D to Clock Fall Setup Time tUDS U/D to Clock Fall Hold Time tUDH DACSEL to Clock Fall Setup Time tDSS DACSEL to Clock Fall Hold Time tDSH MODE to Clock Fall Setup Time tMDS MODE to Clock Fall Hold Time tMDH NOTES 1Typicals represent average readings at 25 °C, V DD = 5 V. 2Resistor 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. See Figure 22 test circuit. 3Wiper resistance is not measured on the R AB = 1 MΩ models. 4INL and DNL are measured at V with the RDAC configured as a potentiometer divider similar to a voltage output D/A converter. V = V W A DD and VB = 0 V. DNL specification limits of ± 1 LSB maximum are guaranteed monotonic operating conditions. See Figure 21 test circuit. 5Resistor Terminals A, B, W have no limitations on polarity with respect to each other. 6Guaranteed by design and not subject to production test. 7P DISS is calculated from (I DD × V DD). CMOS logic level inputs result in minimum power dissipation. 8Bandwidth, noise and settling time are dependent on the terminal resistance value chosen. The lowest R value results in the fastest settling time and highest bandwidth. The highest R value results in the minimum overall power consumption. 9All dynamic characteristics use V DD = 5 V. 10See timing diagram for location of measured values. All input control voltages are specified with t = t = 2.5 ns (10% to 90% of +3 V) and timed from a voltage level R F of 1.5 V. Switching characteristics are measured using both V DD = 5 V or V DD = 3 V. Specifications subject to change without notice. – 2– REV. 0 AD5222 ABSOLUTE MAXIMUM RATINGS (TA = 25 °C, unless otherwise noted) ORDERING GUIDE Kilo Package Package Ohms Temperature Description Option 10 10 50 50 100 100 1,000 1,000 –40°C/+85°C –40°C/+85°C –40°C/+85°C –40°C/+85°C –40°C/+85°C –40°C/+85°C –40°C/+85°C –40°C/+85°C SO-14 TSSOP-14 SO-14 TSSOP-14 SO-14 TSSOP-14 SO-14 TSSOP-14 R-14 RU-14 R-14 RU-14 R-14 RU-14 R-14 RU-14 VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V, +7 V VSS to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, –5 V VDD to VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V VA, VB, V W to GND . . . . . . . . . . . . . . . . . . . . . . . . . . 0 V, VDD AX – BX , AX – WX , BX – WX . . . . . . . . . . . . . . . . . . . ± 20 mA Digital Input Voltage to GND . . . . . . . . . . . . 0 V, VDD + 0.3 V Operating Temperature Range . . . . . . . . . . . –40°C to +85°C Maximum Junction Temperature (TJ max) . . . . . . . . . . 150°C Storage Temperature . . . . . . . . . . . . . . . . . . –65° C to +150°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . 300°C Package Power Dissipation . . . . . . . . . . . . . (TJ max – TA)/θJA Thermal Resistance θJA, SOIC (SO-14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158°C/W TSSOP-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206°C/W CS Model AD5222BR10 AD5222BRU10 AD5222BR50 AD5222BRU50 AD5222BR100 AD5222BRU100 AD5222BR1M AD5222BRU1M The AD5222 die size is 56 mil × 60 mil, 3360 sq. mil; 1.4224 mm × 1.524 mm, 2.1677 sq. mm. Contains 1503 transistors. Patent Number 5495245 applies. PIN FUNCTION DESCRIPTIONS Pin Name tCSS tCH tCL tCSH Description CLK tUDS U/D tUDH tDSS 1 2 3 4 DACSEL tDSH tMDS MODE tMDH Figure 2. Detail Timing Diagram Truth Table 5 6 7 8 9 10 CS L L H CLK t t X U/D H L X Operation Wiper Increment Toward Terminal A Wiper Decrement Toward Terminal B Wiper Position Fixed 11 12 13 14 Common Mode (MODE = 0) moves both wipers together either UP or DOWN the resistor array without changing the relative distance between the wipers. Also, the distance between both wipers is preserved if either reaches the end of the array. Independent Mode (MODE = 1) allows user to control each RDAC individually: DACSEL = 0 sets RDAC1; DACSEL = 1: sets RDAC2. B Terminal RDAC #1. A Terminal RDAC #1. Wiper RDAC #1, DACSEL = 0. Negative Power Supply. Specified for operation at both 0 V or –2.7 V (Sum of |VDD | + |VSS | < 5.5 V). W2 Wiper RDAC #2, DACSEL = 1. A2 A Terminal RDAC #2. B2 B Terminal RDAC #2. GND Ground. MODE Common MODE = 0, Independent MODE = 1. DACSEL DAC Select determines which wiper is incremented in the Independent MODE = 1. DACSEL = 0 sets RDAC1, DACSEL = 1 sets RDAC2. U/D UP/DOWN Direction Control. CLK Serial Clock Input, Negative Edge Triggered. CS Chip Select Input, Active Low. When CS is high, the UP/DOWN counter is disabled. VDD Positive Power Supply. Specified for operation at both +3 V or +5 V. (Sum of |VDD | + |VSS | < 5.5 V). PIN CONFIGURATION B1 1 A1 2 W1 3 14 VDD 13 CS B1 A1 W1 VSS VSS 4 12 CLK TOP VIEW 11 U/D (Not to Scale) W2 5 10 DACSEL AD5222 A2 6 B2 7 9 MODE 8 GND CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD5222 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. WARNING! ESD SENSITIVE DEVICE REV. 0 –3– AD5222–Typical Performance Characteristics 100 0.25 0.20 PERCENT OF NOMINAL END-TO-END RESISTANCE – % RAB 0.15 75 R-DNL ERROR – LSB 0.10 0.05 0 –0.05 –0.10 –0.15 RWB 0 0 32 64 CODE – Decimal 96 128 RWA –0.20 –0.25 0 16 32 48 64 80 CODE – Decimal 96 112 128 TA = +85 C VDD = +15V VSS = –15V RAB = 50k TA = +25 C TA = –55 C 50 25 Figure 3. Wiper-To-End Terminal Resistance vs. Code Figure 6. R-DNL Relative Resistance Step Position Change vs. Code 5 4.5 4 VWB VOLTAGE – V 3.5 3 2.5 2 1.5 1 0.5 0 3FH 20H 10H R-INL ERROR – LSB 08H 05H 1.0 0.8 0.6 50k 0.4 0.2 0 –0.2 100k –0.4 –0.6 –0.8 7 –1.0 0 16 32 48 64 80 CODE – Decimal 96 112 128 VERSION 1M VERSION VERSION 10k VERSION VDD/VSS = 2.7V/0V TA = 25 C 02H RAB = 10k VDD = 5V TA = 25 C 0 1 2 3 4 IWA CURRENT – mA 5 6 Figure 4. Resistance Linearity vs. Conduction Current Figure 7. R-INL Resistance Nonlinearity Error vs. Code 180 SS = 600 UNITS VDD = 2.7V TA = 25 C 0.6 0.4 0.2 VDD/VSS = 2.7V/0V TA = 25 C 10k VERSION 50k VERSION 150 120 FREQUENCY INL – LSB 0 –0.2 –0.4 –0.6 30 –0.8 0 40 41 42 44 45 47 48 50 51 53 54 56 57 59 60 WIPER RESISTANCE – –1.0 0 16 32 48 64 80 CODE – Decimal 96 112 128 1M VERSION 90 60 100k VERSION Figure 5. Wiper Contact Resistance Figure 8. Potentiometer Divider INL Error vs. Code –4– REV. 0 AD5222 70 POTENTIOMETER MODE TEMPCO – ppm/ C 60 50 40 30 20 10 0 –10 –20 –30 0 16 32 48 64 80 CODE – Decimal 96 112 128 1M VERSION 10k VERSION VDD/VSS = 2.7V/0V TA = 25 C 9 6 3 0 GAIN – dB –3 –6 –9 –12 –15 –18 –21 100 B 100k BW 10k 50k 100k 1M 1k 764kHz 132kHz 64kHz 6.6kHz 100k 1M A W OP42 1M 50k VDD = +2.7V VSS = –2.7V DATA = 40H VA = 50mV rms VB = 0V 10k 100k 50k VERSION VERSION 10k FREQUENCY – Hz Figure 9. VWB / T Potentiometer Mode Tempco Figure 12. Gain vs. Frequency vs. RAB 120 100 RHEOSTAT MODE TEMPCO – ppm/ C 80 60 50k 40 20 0 –20 –40 –60 –80 0 16 32 48 64 80 CODE – Decimal 96 112 128 1M VERSION 10k VERSION VERSION 100k VERSION VDD/VSS = 2.7V/0V TA = 25 C 10 FILTER = 22kHz VDD = 2.7V VIN = 1V rms TA = 25 C 1.0 THD + NOISE – % 0.1 SEE TEST CIRCUIT FIGURE 25 SEE TEST CIRCUIT FIGURE 26 0.01 0.001 10 100 1k FREQUENCY – Hz 10k 100k Figure 10. RWB / T Rheostat Mode Tempco Figure 13. Total Harmonic Distortion Plus Noise vs. Frequency 0 NORMALIZED GAIN FLATNESS – 0.1dB/DIV CODE = 3FH –10 20H 10H GAIN - dB –20 08H 04H –30 02H 01H –40 TA = 25 C SEE TEST CIRCUIT FIGURE 32 –50 10 100 1k 10k 100k FREQUENCY – Hz 1M 10M 100k 10k 1M SEE TEST CIRUIT 27 VDD = 2.7V VSS = –2.7V VA = 50mV rms VB = 0V DATA = 40H A W OP42 50k B 10 100 1k 10k FREQUENCY – Hz 100k 1M Figure 11. 10 kΩ Gain vs. Frequency vs. Code Figure 14. Normalized Gain Flatness vs. Frequency REV. 0 –5– AD5222 1200 A – VDD = 5.5V CODE = 15H B – VDD = 3.3V CODE = 15H C – VDD = 5.5V CODE = 3FH D – VDD = 3.3V CODE = 3FH TA = 25 C VDD = 5.5V VA = 5.5V 10 1000 IDD – SUPPLY CURRENT – A 800 600 A 400 B SUPPLY CURRENT – mA 1 0.1 VDD/VSS = VA = 2.5V 2.5V 0.01 200 C 0 1 10k 100k FREQUENCY – Hz 1M D 10M 0.001 0 1 VDD = 2.7V VA = 2.7V 2 3 4 INPUT LOGIC VOLTAGE – V 5 6 Figure 15. IDD , ISS Supply Current vs. Clock Frequency Figure 18. Supply Current vs. Input Logic Voltage 100 90 80 SWITCH RESISTANCE – 70 60 50 VDD/VSS = 40 2.7V TA = 25 C VDD/VSS = 2.7V/0V VDD = 2.7V VA = 2.7V VB = 0V VW 20mV/DIV 2V/DIV 30 VDD/VSS = 5.5V/0V 20 10 –3 –2 –1 0 1 2 3 COMMON MODE – Volts 4 5 6 CLK Figure 16. Incremental Wiper Contact Resistance vs. VDD / V SS Figure 19. Midscale Transition 3FH to 40H 1 LOGIC = 0V OR VDD VDD = 2.7V VA = 2.7V VB = 0V VWA SUPPLY CURRENT – mA 0.1 VWB 20mV/DIV VDD = 5.5V OR VDD/VSS = 0.01 VDD = 2.7V CLK 2.7V 2V/DIV 0.001 –40 –15 10 35 TEMPERATURE – C 60 85 Figure 17. Supply Current vs. Temperature Figure 20. Stereo Step Transition, Mode = 0 –6– REV. 0 Parametric Test Circuits–AD5222 A DUT A W B V+ = VDD 1LSB = V+/128 DUT B W +5V VIN V+ OP279 VMS VOUT + –5V Figure 21. Potentiometer Divider Nonlinearity Error Test Circuit (INL, DNL) Figure 25. Inverting Programmable Gain Test Circuit +5V NO CONNECT DUT A W B VMS IW VIN W OP279 –5V VOUT A DUT B Figure 22. Resistor Position Nonlinearity Error (Rheostat Operation; R-INL, R-DNL) Figure 26. Noninverting Programmable Gain Test Circuit VMS2 DUT A W B IW = VDD /R NOMINAL VW VIN DUT A W B +15V OP42 VOUT VMS1 RW = [ VMS1 – V MS2]/IW –15V Figure 23. Wiper Resistance Test Circuit Figure 27. Gain vs. Frequency Test Circuit VA V+ = VDD ± 10% V+ MS ( ––––– ) DUT V PSRR (dB) = 20 LOG VMS VMS% PSS (%/%) = ––––––– VDD% W B ISW RSW = 0.1V ISW CODE = 00H 0.1V ~ VDD A B W VDD 0 TO VDD Figure 24. Power Supply Sensitivity Test Circuit (PSS, PSRR) Figure 28. Incremental ON Resistance Test Circuit REV. 0 –7– AD5222 OPERATION The AD5222 provides a 128-position, digitally-controlled, variable resistor (VR) device. Changing the VR settings is accomplished by pulsing the CLK pin while CS is active low. The U/D (UP/ DOWN) control input pin controls the direction of the increment. When the wiper hits the end of the resistor (Terminal A or B) additional CLK pulses no longer change the wiper setting. The wiper position is immediately decoded by the wiper decode logic changing the wiper resistance. Appropriate debounce circuitry is required when push-button switches are used to control the count sequence and direction of count. The exact timing requirements are shown in Figure 2. The AD5222 powers ON in a centered wiper position, exhibiting nearly equal resistances of RWA and R WB. VDD U/D U/D DACSEL RDAC 1 U/D COUNTER MODE CS RDAC 2 U/D COUNTER CLK AD5222 UP/DOWN COUNTER DECODE A1 W1 B1 Figure 30. Detailed Digital Logic Interface Circuit POR CS MODE DACSEL CLK GND A2 UP/DOWN COUNTER DECODE W2 B2 VSS All digital inputs ( CS, U/ D, CLK, MODE, DACSEL) are protected with a series input resistor and parallel Zener ESD structure shown in Figure 31. All potentiometer terminal pins (A, B, W) are protected from ESD as shown in Figure 32. 1k LOGIC VSS DAC SELECT AND ENABLE Figure 31. Equivalent ESD Protection Digital Pins Figure 29. Block Diagram 20 A, B, W DIGITAL INTERFACING OPERATION The AD5222 contains a push-button controllable interface. The active inputs are clock (CLK), CS and up/down (U/D). While the MODE, and DACSEL pins control common updates or individual updates. The negative-edge sensitive CLK input requires clean transitions to avoid clocking multiple pulses into the internal UP/DOWN counter register, Figure 30. Standard logic families work well. If mechanical switches are used for product evaluation a flip-flop or other suitable means should debounce them. When CS is taken active low, the clock begins to increment or decrement the internal up/down counter, dependent upon the state of the U/D control pin. The UP/DOWN counter value (D) starts at 40H at system power ON. Each new CLK pulse will increment the value of the internal counter by 1 LSB until the full-scale value of 7FH is reached, as long as the U/D pin is logic high. If the U/D pin is taken to logic low, the counter will count down, stopping at code 00H (zero-scale). Additional clock pulses on the CLK pin are ignored when the wiper is at either the 00H position or the 7F H position. The detailed digital logic interface circuitry is shown in Figure 30. VSS Figure 32. Equivalent ESD Protection Analog Pins RS A D0 D1 D2 D3 D4 D5 D6 RDAC UP/DOWN CNTR & DECODE RS RS W RS RS = RNOMINAL/128 B Figure 33. AD5222 Equivalent RDAC Circuit –8– REV. 0 AD5222 PROGRAMMING THE VARIABLE RESISTOR Rheostat Operation The nominal resistance of the RDAC between Terminals A and B are available with values of 10 kΩ, 50 kΩ, 100 kΩ, and 1 MΩ The final three characters of the part number determine the nominal resistance value, e.g., 10 kΩ = 10; 50 k Ω = 50; 100 kΩ = 100; 1 M Ω = 1M. The nominal resistance (RAB ) of the VR has 128 contact points accessed by the wiper terminal, plus the B terminal contact. At power ON, the resistance from the wiper to either end Terminal A or B is approximately equal. Pulsing the CLK pin will increase the resistance from the wiper W to Terminal B by one unit of RS resistance, see Figure 33. The resistance RWB is determined by the number of pulses applied to the clock pin. Each segment of the internal resistor string has a nominal resistance value of RS = RAB/128, which becomes 78 Ω in the case of the 10 kΩ AD5222BR10 product. Care should be taken to limit the current flow between W and B in the direct contact state (RWB code = 0) to a maximum value of 20 mA to avoid degradation or possible destruction of the internal switch contact. Like the mechanical potentiometer the RDAC replaces, it is totally symmetrical (see Figure 3). The resistance between the wiper W and Terminal A also produces a digitally controlled resistance RWA. When these terminals are used the B-terminal should be tied to the wiper. The typical part-to-part distribution of R BA i s process-lotdependent having a ± 30% variation. The change in RBA with temperature has a –35 ppm/° C temperature coefficient. The RBA temperature coefficient increases as the wiper is programmed near the B-terminal due to the larger percentage contribution of the wiper contact switch resistance, which has a 0.5%/°C temperature coefficient. Figures 9 and 10 show the effect of the wiper contact resistance as a function of code setting. PROGRAMMING THE POTENTIOMETER DIVIDER Voltage Output Operation The digital potentiometer easily generates an output voltage proportional to the input voltage applied to a given terminal. For example connecting A-terminal to 5 V and B-terminal to ground produces an output voltage at the wiper which can be any value starting at zero volts up to 1 LSB less than 5 V. Each LSB of voltage is equal to the voltage applied across Terminals AB divided by the 128-position resolution of the potentiometer divider. The general equation defining the output voltage with respect to ground for any given input voltage applied to Terminals AB is: VW(D) = D/128 × VAB + VB (1) D represents the current contents of the internal up/down counter. Operation of the digital potentiometer in the divider mode results in more accurate operation over temperature. Here the output voltage is dependent on the ratio of the internal resistors not the absolute value, therefore, the drift improves to 20 ppm/°C. REV. 0 –9– AD5222 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 14-Lead Narrow Body SOIC (R-14) 0.3444 (8.75) 0.3367 (8.55) 0.1574 (4.00) 0.1497 (3.80) 14 1 8 7 14-Lead TSSOP (RU-14) 0.201 (5.10) 0.193 (4.90) 0.2440 (6.20) 0.2284 (5.80) 14 8 0.177 (4.50) 0.169 (4.30) 0.0196 (0.50) 0.0099 (0.25) 0.256 (6.50) 0.246 (6.25) 1 7 PIN 1 0.050 (1.27) BSC 0.0688 (1.75) 0.0532 (1.35) 45 PIN 1 0.0098 (0.25) 0.0040 (0.10) 8 0.0192 (0.49) SEATING 0 0.0099 (0.25) 0.0138 (0.35) PLANE 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) 0.006 (0.15) 0.002 (0.05) 0.0433 (1.10) MAX SEATING PLANE 0.0256 (0.65) BSC 0.0118 (0.30) 0.0075 (0.19) 0.0079 (0.20) 0.0035 (0.090) 8 0 0.028 (0.70) 0.020 (0.50) –10– REV. 0 PRINTED IN U.S.A. C3715–8–10/99