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256-position spi-compatible digital potentiometer ad5160 rev. a 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 ?2003C2009 analog devices, inc. all rights reserved. features 256-position end-to-end resistance: 5 k, 10 k, 50 k, 100 k compact sot-23-8 (2.9 mm 3 mm) package spi-compatible interface power-on preset to midscale single supply: 2.7 v to 5.5 v low temperature coefficient: 45 ppm/c low power, i dd = 8 a wide operating temperature: C40c to +125c evaluation board available applications mechanical potentiometer replacement in new designs transducer adjustment of pressure, temperature, position, chemical, and optical sensors rf amplifier biasing automotive electronics adjustment gain control and offset adjustment functional block diagram spi interface wiper register cs sdi clk gnd v dd a w b figure 1. pin configuration a b cs sdi 1 2 3 4 5 8 7 6 w v dd gnd clk top view (not to scale) ad5160 figure 2. general description the ad5160 provides a compact 2.9 mm 3 mm packaged solution for 256-position adjustment applications. these devices perform the same electronic adjustment function as mechanical potentiometers 1 or variable resistors but with enhanced resolution, solid-state reliability, and superior low temperature coefficient performance. the wiper settings are controllable through an spi-compatible digital interface. 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. operating from a 2.7 v to 5.5 v power supply and consuming less than 5 a allows for usage in portable battery-operated applications. 1 the terms digital potentiometer, vr, and rdac are used interchangeably.
ad5160 rev. a | page 2 of 16 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 functional block diagram .............................................................. 1 pin configuration ............................................................................. 1 general description ......................................................................... 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 electrical characteristics5 k version .................................. 3 10 k, 50 k, 100 k versions .................................................. 4 timing characteristicsall versions ....................................... 5 absolute maximum ratings ............................................................ 6 esd caution .................................................................................. 6 pin configuration and function descriptions ............................. 7 typical performance characteristics ..............................................8 test circuits ..................................................................................... 12 spi interface .................................................................................... 13 theory of operation ...................................................................... 14 programming the variable resistor ......................................... 14 programming the potentiometer divider ............................... 14 spi - compatible 3-wire serial bus ......................... ................. 15 esd protection ........................................................................... 15 power-up sequence ................................................................... 15 layout and power supply bypassing ....................................... 15 outline dimensions ....................................................................... 16 ordering guide .......................................................................... 16 revision histor 1/09rev. 0 to rev. a deleted shutdown supply current parameter and endnote 7, table 1 ............................................................................ 3 changes to resistor noise voltage density parameter, table 1 ................................................................................................ 3 deleted shutdown supply current parameter and endnote 7, table 2 ............................................................................ 4 changes to resistor noise voltage density parameter, table 2 ................................................................................................ 4 added endnote to table 3 ............................................................... 5 changes to table 4 ............................................................................ 6 changes to the rheostat operation section ............................... 14 deleted terminal voltage operating range section and figure 41, renumbered figures sequentially ............................. 13 changes to figure 40 and figure 41 ............................................. 15 changes to ordering guide .......................................................... 17 5/03revision 0: initial version
ad5160 rev. a | page 3 of 16 specifications electrical characteristics5 k version v dd = 5 v 10%, or 3 v 10%; v a = +v dd ; v b = 0 v; C40c < t a < +125c; unless otherwise noted. table 1. parameter symbol conditions min typ 1 max unit dc characteristics rheostat mode resistor differential nonlinearity 2 r-dnl r wb , v a = no connect ?1.5 0.1 +1.5 lsb resistor integral nonlinearity 2 r-inl r wb , v a = no connect ?4 0.75 +4 lsb nominal resistor tolerance 3 ?r ab t a = 25c ?30 +30 % resistance temperature coefficient ?r ab /?t v ab = v dd , wiper = no connect 45 ppm/c wiper resistance r w 50 120 potentiometer divider mode specifications apply to all vrs resolution n 8 bits differential nonlinearity 4 dnl ?1.5 0.1 +1.5 lsb integral nonlinearity 4 inl ?1.5 0.6 +1.5 lsb voltage divider temperature coefficient ?v w /?t code = 0x80 15 ppm/c full-scale error v wfse code = 0xff ?6 ?2.5 0 lsb zero-scale error v wzse code = 0x00 0 +2 +6 lsb resistor terminals voltage range 5 v a, v b, v w gnd v dd v capacitance a, capacitance b 6 c a,b f = 1 mhz, measured to gnd, code = 0x80 45 pf capacitance w 6 c w f = 1 mhz, measured to gnd, code = 0x80 60 pf common-mode leakage i cm v a = v b = v dd /2 1 na digital inputs input logic high v ih 2.4 v input logic low v il 0.8 v input logic high v ih v dd = 3 v 2.1 v input logic low v il v dd = 3 v 0.6 v input current i il v in = 0 v or 5 v 1 a input capacitance 6 c il 5 pf power supplies power supply range v dd range 2.7 5.5 v supply current i dd v ih = 5 v or v il = 0 v 3 8 a power dissipation 7 p diss v ih = 5 v or v il = 0 v, v dd = 5 v 0.2 mw power supply sensitivity pss ?v dd = +5 v 10%, code = midscale 0.02 0.05 %/% dynamic characteristics 6 , 8 bandwidth C3 db bw_5k r ab = 5 k, code = 0x80 1.2 mhz total harmonic distortion thd w v a = 1 v rms, v b = 0 v, f = 1 khz 0.05 % v w settling time t s v a = 5 v, v b = 0 v, 1 lsb error band 1 s resistor noise voltage density e n_wb r wb = 2.5 k 6 nv/hz 1 typical specifications represent average readings at +25c and v dd = 5 v. 2 resistor position nonlinearity error (r-inl) is the deviatio n from an ideal value measured be tween 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 v ab = v dd , wiper (v w ) = no connect. 4 inl and dnl are measured at v w with the rdac configured as a potentiometer divider similar to a voltage output digital-to-analog converter (dac). v a = v dd and v b = 0 v. dnl specification limits of 1 lsb maximum are guaranteed monotonic operating conditions. 5 resistor terminal a, resistor terminal b, 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 p diss is calculated from (i dd v dd ). cmos logic level inputs result in minimum power dissipation. 8 all dynamic characteristics use v dd = 5 v.
ad5160 rev. a | page 4 of 16 10 k, 50 k, 100 k versions v dd = 5 v 10%, or 3 v 10%; v a = v dd ; v b = 0 v; ?40c < t a < +125c; unless otherwise noted. table 2. parameter symbol conditions min typ 1 max unit dc characteristics rheostat mode resistor differential nonlinearity 2 r-dnl r wb , v a = no connect ?1 0.1 +1 lsb resistor integral nonlinearity 2 r-inl r wb , v a = no connect ?2 0.25 +2 lsb nominal resistor tolerance 3 ?r ab t a = 25c ?30 +30 % resistance temperature coefficient ?r ab /?t v ab = v dd , wiper = no connect 45 ppm/c wiper resistance r w v dd = 5 v 50 120 potentiometer divider mode specifications apply to all vrs resolution n 8 bits differential nonlinearity 4 dnl ?1 0.1 +1 lsb integral nonlinearity 4 inl ?1 0.3 +1 lsb voltage divider temperature coefficient ?v w /?t code = 0x80 15 ppm/c full-scale error v wfse code = 0xff ?3 ?1 0 lsb zero-scale error v wzse code = 0x00 0 1 3 lsb resistor terminals voltage range 5 v a,b,w gnd v dd v capacitance a, capacitance b 6 c a,b f = 1 mhz, measured to gnd, code = 0x80 45 pf capacitance w 6 c w f = 1 mhz, measured to gnd, code = 0x80 60 pf common-mode leakage i cm v a = v b = v dd /2 1 na digital inputs input logic high v ih 2.4 v input logic low v il 0.8 v input logic high v ih v dd = 3 v 2.1 v input logic low v il v dd = 3 v 0.6 v input current i il v in = 0 v or 5 v 1 a input capacitance 6 c il 5 pf power supplies power supply range v dd range 2.7 5.5 v supply current i dd v ih = 5 v or v il = 0 v 3 8 a power dissipation 7 p diss v ih = 5 v or v il = 0 v, v dd = 5 v 0.2 mw power supply sensitivity pss ?v dd = +5 v 10%, code = midscale 0.02 0.05 %/% dynamic characteristics 6 , 8 bandwidth C3 db bw r ab = 10 k/50 k/100 k, code = 0x80 600/100/40 khz total harmonic distortion thd w v a =1 v rms, v b = 0 v, f = 1 khz, r ab = 10 k 0.05 % v w settling time (10 k/50 k/100 k) t s v a = 5 v, v b = 0 v, 1 lsb error band 2 s resistor noise voltage density e n_wb r wb = 5 k 9 nv/hz 1 typical specifications represent average readings at +25c and v dd = 5 v. 2 resistor position nonlinearity error r-inl is the deviation from an ideal value measured betw een the maximum re sistance and th e minimum resistance wiper positions. r-dnl measures the relative step change from ideal between successive tap positions. parts are guaranteed monotonic. 3 v ab = v dd , wiper (v w ) = no connect. 4 inl and dnl are measured at v w with the rdac configured as a potentiometer divider similar to a voltage output d/a converter. va = v dd and v b = 0 v. dnl specification limits of 1 lsb maximum are guaranteed monotonic op erating conditions. 5 resistor terminal a, resistor terminal b, 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 p diss is calculated from (i dd v dd ). cmos logic level inputs result in minimum power dissipation. 8 all dynamic characteristics use v dd = 5 v.
ad5160 rev. a | page 5 of 16 timing characteristicsall versions v dd = +5v 10%, or +3v 10%; v a = v dd ; v b = 0 v; C40c < t a < +125c; unless otherwise noted. table 3. parameter symbol conditions min typ 1 max unit spi interface timing characteristics 1, 2 specifications apply to all parts clock frequency f clk 25 mhz input clock pulse width t ch , t cl clock level high or low 20 ns data setup time t ds 5 ns data hold time t dh 5 ns cs setup time t css 15 ns cs high pulse width t csw 40 ns clk fall to cs fall hold time t csh0 0 ns clk fall to cs rise hold time t csh1 0 ns 1 see the timing diagram, figure 38, for location of measured values. all input control voltages are specified with t r = t f = 2 ns (10% to 90% of 3 v) and timed from a voltage level of 1.5 v. 2 guaranteed by design and not subject to production test.
ad5160 rev. a | page 6 of 16 absolute maximum ratings t a = +25c, unless otherwise noted. table 4. parameter rating v dd to gnd ?0.3 v to +7 v v a , v b , v w to gnd v dd maximum current i max 1 i wb , i wa pulsed 20 ma i wb , i wa continuous 5 k, 10 k 4.7 ma 50 k 0.95 ma 100 k 0.48 ma digital inputs and output voltage to gnd 0 v to +7 v temperature operating temperature range ?40c to +125c maximum junction temperature (t jmax ) 150c storage temperature ?65c to +150c thermal resistance (sot-23 package) 2 ja thermal impedance 206oc/w jc thermal impedance 91c/w reflow soldering (pb-free) peak temperature 260c time at peak temperature 10 sec to 40 sec 1 maximum terminal current is bounde d by the maximum current handling of the switches, maximum power dissipat ion of the package, and applied voltage across any two of the a, b, and w terminals at a given resistance. 2 package power dissipation = (t jmax ? t a )/ ja . 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
ad5160 rev. a | page 7 of 16 pin configuration and fu nction descriptions a b cs sdi 1 2 3 4 5 8 7 6 w v dd gnd clk top view (not to scale) ad5160 figure 3. pin configuration table 5. pin function descriptions pin mnemonic description 1 w w terminal. 2 v dd positive power supply. 3 gnd digital ground. 4 clk serial clock input. positive edge triggered. 5 sdi serial data input. 6 cs chip select input, active low. when cs returns high, data loads into the dac register. 7 b b terminal. 8 a a terminal.
ad5160 rev. a | page 8 of 16 typical performance characteristics code (decimal) ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 32 09 6 64 128 160 192 224 256 rheostat mode inl (lsb) 0.8 5v 3v figure 4. r-inl vs. code vs. supply voltages 5v 3v ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 rheostat mode dnl (lsb) 0.8 code (decimal) 32 09 6 64 128 160 192 224 256 figure 5. r-dnl vs. code vs. supply voltages _ 40c +25c +85c +125c ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 potentiometer mode inl (lsb) 0.8 code (decimal) 32 09 6 64 128 160 192 224 256 figure 6. inl vs. code, v dd = 5 v code (decimal) ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 32 09 6 64 128 160 192 224 256 potentiometer mode dnl (lsb) 0.8 ?40c +25c +85c +125c figure 7. dnl vs. code, v dd = 5 v ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 potentiometer mode inl (lsb) 0.8 code (decimal) 32 09 6 64 128 160 192 224 256 5v 3v figure 8. inl vs. code vs. supply voltages 5v 3v code (decimal) ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 0.8 32 09 6 64 128 160 192 224 256 potentiometer mode dnl(lsb) 1.0 figure 9. dnl vs. code vs. supply voltages
ad5160 rev. a | page 9 of 16 ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 rheostat mode inl (lsb) 0.8 code (decimal) 32 09 6 64 128 160 192 224 25 6 c +25c +85c +125c ?40 figure 10. r-inl vs. code, v dd = 5 v ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 1.0 rheostat mode dnl (lsb) 0.8 code (decimal) 32 09 6 64 128 160 192 224 256 _ 40c +25c +85c +125c figure 11. r-dnl vs. code, v dd = 5 v temperature (c) 0 40 80 120 ?40 0 1.5 fse, full-scale error (lsb) 0 40 80 120 ?40 1.0 2.5 v dd = 5.5v v dd = 2.7v 2.0 0.5 figure 12. full-scale error vs. temperature 0 40 80 120 ?40 0 1.5 zse, zero-scale error ( a) temperature (c) 0 40 80 120 ?40 1.0 2.5 v dd = 5.5v v dd = 2.7v 2.0 0.5 figure 13. zero-scale error vs. temperature temperature (c) 0 40 80 120 ?40 0.1 1 10 i dd supply current ( a) v dd = 5.5v v dd = 2.7v figure 14. supply current vs. temperature i a shutdown current (na) temperature (c) 0 0 70 20 10 30 40 50 60 40 80 120 ?40 v dd = 5v figure 15. shutdown current vs. temperature
ad5160 rev. a | page 10 of 16 code (decimal) ?50 0 50 100 150 200 32 09 6 64 128 160 192 224 256 rheostat mode tempco (ppm/c) figure 16. rheostat mode tempco ?r wb /?t vs. code code (decimal) ?20 0 20 40 60 80 100 120 140 160 32 09 6 64 128 160 192 224 256 potentiometer mode tempco (ppm/c) figure 17. potentiometer mode tempco ?v wb /?t vs. code 1k 10k 100k 1m 0 ?6 ?12 ?18 ?24 ?30 ?36 ?42 ?48 ?54 ?60 0x80 0x40 0x20 0x10 0x08 0x04 0x02 0x01 ref level 0.000db /div 6.000db marker 1 000 000.000hz mag (a/r) ?8.918db start 1 000.000hz stop 1 000 000.000hz figure 18. gain vs. frequency vs. code, r ab = 5 k 1k 10k 100k 1m 0 ?6 ?12 ?18 ?24 ?30 ?36 ?42 ?48 ?54 ?60 0x80 0x40 0x20 0x10 0x08 0x04 0x02 0x01 ref level 0.000db /div 6.000db marker 510 634.725hz mag (a/r) ?9.049db start 1 000.000hz stop 1 000 000.000hz figure 19. gain vs. frequency vs. code, r ab = 10 k 1k 10k 100k 1m 0 ?6 ?12 ?18 ?24 ?30 ?36 ?42 ?48 ?54 ?60 0x80 0x40 0x20 0x10 0x08 0x04 0x02 0x01 ref level 0.000db /div 6.000db marker 100 885.289hz mag (a/r) ?9.014db start 1 000.000hz stop 1 000 000.000hz figure 20. gain vs. frequency vs. code, r ab = 50 k 1k 10k 100k 1m 0 ?6 ?12 ?18 ?24 ?30 ?36 ?42 ?48 ?54 ?60 0x80 0x40 0x20 0x10 0x08 0x04 0x02 0x01 ref level 0.000db /div 6.000db marker 54 089.173hz mag (a/r) ?9.052db start 1 000.000hz stop 1 000 000.000hz figure 21. gain vs. frequency vs. code, r ab = 100 k
ad5160 rev. a | page 11 of 16 10k 100k 1m 10m ?5.5 ?6.0 ?6.5 ?7.0 ?7.5 ?8.0 ?8.5 ?9.0 ?9.5 ?10.0 ?10.5 ref level ?5.000db /div 0.500db start 1 000.000hz stop 1 000 000.000hz r = 5k r = 10k r = 50k r = 100k 5k ? 1.026 mhz 10k ? 511 mhz 50k ? 101 mhz 100k ? 54 mhz vw clk ch 1 200mv b w ch 2 5.00 v b w m 100ns a ch2 3.00 v 1 2 figure 22. C3 db bandwidth @ code = 0x80 figure 25. digital feedthrough vw cs ch 1 100mv b w ch 2 5.00 v b w m 200ns a ch1 152mv 1 2 v a = 5v v b = 0v frequency (hz) 10k 100 100k 1m 1k 0 20 40 60 psrr (db) code = 0x80, v a = v dd , v b = 0v psrr @ v dd = 3v dc 10% p-p ac psrr @ v dd = 5v dc 10% p-p ac figure 23. psrr vs. frequency figure 26. midscale glitch, code 0x80 to 0x7f i dd ( a) frequency (hz) 10k 800 700 600 500 400 300 900 200 100 100k 1m 10m 0 code = 0x55 code = 0xff v dd = 5v vw cs ch 1 5.00v b w ch 2 5.00 v b w m 200ns a ch1 3.00 v 1 2 v a = 5v v b = 0v figure 24. i dd vs. frequency figure 27. large signal settling time, code 0xff to 0x00
ad5160 rev. a | page 12 of 16 test circuits figure 28 to figure 36 illustrate the test circuits that define the test conditions used in the product specification tables. v ms a w b dut v+ = v dd 1lsb = v+/2 n v+ figure 28. test circuit for potentiometer divider nonlinearity error (inl, dnl) no connect i w v ms a w b dut figure 29. test circuit for resistor position nonlinearity error (rheostat operation; r-inl, r-dnl) v ms1 i w = v dd /r nominal v ms2 v w r w = [v ms1 ? v ms2 ]/i w a w b dut figure 30. test circuit for wiper resistance v v v v ms % dd % pss (%/%) = v+ = v dd 10% psrr (db) = 20 log ms dd ( ) v dd v a v ms a w b v+ figure 31. test circuit for powe r supply sensitivity (pss, pssr) op279 w 5v b v out offset gnd offset bias a dut v in figure 32. test circuit for inverting gain b a v in op279 w 5v v out offset gnd offset bias dut figure 33. test circuit for noninverting gain +15v ?15v w a 2.5v b v out offset gnd dut ad8610 v in figure 34. test circuit for gain vs. frequency w b v ss to v dd dut i sw code = 0x00 r sw = 0.1v i sw 0.1v figure 35. test circuit for incremental on resistance w b v cm i cm a nc gnd nc v ss v dd dut nc = no connect figure 36. test circuit for common-mode leakage current
ad5160 rev. a | page 13 of 16 spi interface table 6. serial data-word format b7 b6 b5 b4 b3 b2 b1 b0 d7 d6 d5 d4 d3 d2 d1 d0 msb lsb 2 7 2 0 sdi clk cs v out 1 0 1 0 1 0 1 0 d7 d6 d5 d4 d3 d2 d1 d0 rdac register load figure 37. spi interface timing diagram (v a = 5 v, v b = 0 v, v w = v out ) t csho t css t cl t ch t ds t csw t s t cs1 t csh1 t ch sdi clk cs vout 1 0 1 0 1 0 v dd 0 1lsb (data in) dx dx figure 38. spi interface detailed timing diagram (v a = 5 v, v b = 0 v, v w = v out )
ad5160 rev. a | page 14 of 16 theory of operation the ad5160 is a 256-position digitally controlled variable resistor (vr) device. an internal power-on preset places the wiper at midscale during power-on, which simplifies the fault condition recovery at power-up. programming the variable resistor rheostat operation the nominal resistance 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 model number as listed in the ordering guide section determine the nominal resistance value, for example, in model ad5160brjz10, the 10 represents 10 k; and in ad5160brjz50, the 50 represents 50 k. the nominal resistance (r ab ) of the vr has 256 contact points accessed by the wiper terminal, plus the b terminal contact. the 8-bit data in the rdac latch is decoded to select one of the 256 possible settings. assuming a 10 k part is used, the first connection of the wiper starts at the b terminal for data 0x00. because there is a 60 wiper contact resistance, such connection yields a minimum of 60 resistance between terminal w and terminal b. the second connection is the first tap point, which corresponds to 99 (r wb = r ab /256 + r w = 39 + 60 ) for data 0x01. the third connection is the next tap point, representing 138 (2 39 + 60 ) 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 9961 (r ab ? 1 lsb + r w ). figure 39 shows a simplified diagram of the equivalent rdac circuit where the last resistor string is not accessed; therefore, there is 1 lsb less of the nominal resistance at full scale in addition to the wiper resistance. b rdac latch and decoder w a r s r s r s r s d7 d6 d4 d5 d2 d3 d1 d0 figure 39. equivalent rdac circuit the general equation determining the digitally programmed output resistance between w and b is w ab wb rr d dr += 256 )( (1) where: d is the decimal equivalent of the binary code loaded in the 8-bit rdac register. r ab is the end-to-end resistance. r w is the wiper resistance contributed by the on resistance of the internal switch. in summary, if r ab = 10 k and the a terminal is open circuited, the following output resistance r wb is set for the indicated rdac latch codes. table 7. codes and corresponding r wb resistance d (dec.) r wb () output state 255 9961 full scale (r ab ? 1 lsb + r w ) 128 5060 midscale 1 99 1 lsb 0 60 zero scale (wiper contact resistance) note that in the zero-scale condition, a finite wiper resistance of 60 is present. take care 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 the wiper w and terminal a also produces a digitally controlled complementary resistance (r wa ). when these terminals are used, the b terminal can be opened. setting the resistance value for r wa starts at a maximum value of resistance and decreases as the data loaded in the latch increases in value. the general equation for this operation is w ab wa rr d dr + ? = 256 256 )( (2) for r ab = 10 k and the b terminal is open circuited, the following output resistance r wa is set for the indicated rdac latch codes. table 8. codes and corresponding r wa resistance d (dec.) r wa () output state 255 99 full scale 128 5060 midscale 1 9961 1 lsb 0 10,060 zero scale typical device-to-device matching is process lot dependent and may vary by up to 30%. because the resistance element is processed in thin film technology, the change in r ab with temperature has a very low 45 ppm/c temperature coefficient. programming the potentiometer divider voltage output operation 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 v dd to gnd, which must be
ad5160 rev. a | page 15 of 16 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 a terminal to 5 v and the b terminal 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 256 positions of the potentiometer divider. the general equation defining the output voltage at v w with respect to ground for any valid input voltage applied to terminal a and terminal b is b a w v d v d dv 256 256 256 )( ? += (3) for a more accurate calculation, which includes the effect of wiper resistance, v w can be found as b wa a wb w v dr v dr dv 256 )( 256 )( )( + = (4) operation of the digital potentiometer in the divider mode results in a more accurate operation over temperature. unlike the rheostat mode, the output voltage is dependent mainly on the ratio of the internal resistors (r wa and r wb ) and not the absolute values. therefore, the temperature drift reduces to 15 ppm/c. spi- compatible 3-wire serial bus the ad5160 contains a 3-wire spi-compatible digital interface (sdi, cs , and clk). the 8-bit serial word must be loaded msb first. the format of the word is shown in . table 6 the positive-edge sensitive clk input requires clean transitions to avoid clocking incorrect data into the serial input register. standard logic families work well. if mechanical switches are used for product evaluation, they should be debounced by a flip-flop or other suitable means. when cs is low, the clock loads data into the serial register on each positive clock edge (see ). figure 37 the data setup and data hold times in the specification table determine the valid timing requirements. the ad5160 uses an 8-bit serial input data register word that is transferred to the internal rdac register when the cs line returns to logic high. extra msb bits are ignored. esd protection all digital inputs are protected with a series input resistor and parallel zener esd structures are shown in figure 40 and figure 41 . this applies to sdi, clk, and cs , which are the digital input pins. logic 340? gnd figure 40. esd protection of digital pins a ,b,w gnd figure 41. esd protection of resistor terminals power-up sequence because the esd protection diodes limit the voltage compliance at the a, b, and w terminals, it is important to power v dd /gnd before applying any voltage to the a, b, and w terminals; otherwise, the diode forward biases such that v dd is powered unintentionally and may affect the rest of the users circuit. the ideal power-up sequence is in the following order: gnd, v dd , digital inputs, and then v a/b/w . the relative order of powering v a , v b , v w , and the digital inputs is not important as long as they are powered after v dd /gnd. layout and power supply bypassing it is a good practice to employ compact, minimum lead length layout design. keep the leads to the inputs as direct as possible with a minimum conductor length. ground paths should have low resistance and low inductance. similarly, it is also a good practice to bypass the power supplies with quality capacitors for optimum stability. bypass supply leads to the device with disc or chip ceramic capacitors of 0.01 f to 0.1 f. to minimize any transient disturbance and low frequency ripple, apply low esr 1 f to 10 f tantalum or electrolytic capacitors at the supplies (see figure 42 ). to minimize the ground bounce, join the digital ground remotely to the analog ground at a single point. ad5160 v dd c1 c3 gnd 10 f 0.1 f + v dd figure 42. power supply bypassing
ad5160 rev. a | page 16 of 16 outline dimensions compliant to jedec standards mo-178-ba 121608-a 8 4 0 seating plane 1.95 bsc 0.65 bsc 0.60 bsc 76 1234 5 3.00 2.90 2.80 3.00 2.80 2.60 1.70 1.60 1.50 1.30 1.15 0.90 0 .15 max 0 .05 min 1.45 max 0.95 min 0.22 max 0.08 min 0.38 max 0.22 min 0.60 0.45 0.30 pin 1 indicator 8 figure 43. ? 8-lead small outline transistor package [sot-23] (rj-8) dimensions shown in millimeters ordering guide model 1 r ab () temperature package description package option branding ad5160brjz5-r2 2 5 k ?40c to +125c sot-23 rj-8 d6q ad5160brjz5-rl7 2 5 k ?40c to +125c sot-23 rj-8 d6q ad5160brjz10-r2 2 10 k ?40c to +125c sot-23 rj-8 d09 ad5160brjz10-rl7 2 10 k ?40c to +125c sot-23 rj-8 d09 ad5160brjz50-r2 2 50 k ?40c to +125c sot-23 rj-8 d0a ad5160brjz50-rl7 2 50 k ?40c to +125c sot-23 rj-8 d0a AD5160BRJZ100-R2 2 100 k ?40c to +125c sot-23 rj-8 d0b ad5160brjz100-rl7 2 100 k ?40c to +125c sot-23 rj-8 d0b ad5160eval 3 evaluation board 1 the ad5160 contains 2532 transistors. die size: 30.7 mil 76.8 mil = 2358 sq. mil. 2 z = rohs compliant part. 3 the evaluation board is shipped with the 10 k r ab resistor option; however, the board is compatible with all available resistor value options. ?2003C2009 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d03434-0-1/09(a)

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