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multiple output, high precision, dual-tracking reference ad588 rev. l 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 ?1986C2010 analog devices, inc. all rights reserved. features low drift: 1.5 ppm/c low initial error: 1 mv pin programmable output +10 v, +5 v, 5 v tracking, ?5 v, ?10 v flexible output force and sense terminals high impedance ground sense soic_w-16 and cerdip-16 packages mil-std-883-compliant versions available general description the ad588 represents a major advance in state-of-the-art monolithic voltage references. low initial error and low temperature drift give the ad588 absolute accuracy performance previously not available in monolithic form. the ad588 uses a proprietary ion-implanted, buried zener diode and laser-wafer drift trimming of high stability thin film resistors to provide outstanding performance. the ad588 includes the basic reference cell and three additional amplifiers that provide pin programmable output ranges. the amplifiers are laser trimmed for low offset and low drift to maintain the accuracy of the reference. the amplifiers are configured to allow kelvin connections to the load and/or boosters for driving long lines or high current loads, delivering the full accuracy of the ad588 where it is required in the application circuit. the low initial error allows the ad588 to be used as a system reference in precision measurement applications requiring 12-bit absolute accuracy. in such systems, the ad588 can provide a known voltage for system calibration in software. the low drift also allows compensation for the drift of other components in a system. manual system calibration and the cost of periodic recalibration can, therefore, be eliminated. furthermore, the mechanical instability of a trimming potentiometer and the potential for improper calibration can be eliminated by using the ad588 in conjunction with auto calibration software. the ad588 is available in seven versions. the ad588jq and ad588kq are packaged in a 16-lead cerdip and are specified for 0c to +70c operation. the ad588aq and ad588bq are packaged in a 16-lead cerdip, and the ad588arwz is packaged in a 16-lead soic, and they are specified for the ?25c to +85c industrial temperature range. the ceramic ad588te and ad588tq grades are specified for the full military/aerospace temperature range. functional block diagram r3 r b r1 r2 r4 r5 r6 gain adj gnd sense +in gnd sense ?in v low bal adj v ct a4 in ?v s +v s a4 out force a4 out sense a3 out force a3 out sense a3 in v high noise reduction a1 a4 ad588 00531-001 a3 13 11 12 8 10 9 5 1 14 15 2 16 3 4 6 7 a2 figure 1. product highlights 1. the ad588 offers 12-bit absolute accuracy without any user adjustments. optional fine-trim connections are provided for applications requiring higher precision. the fine trimming does not alter the operating conditions of the zener or the buffer amplifiers, and so does not increase the temperature drift. 2. output noise of the ad588 is very low, typically 6 v p-p. a pin is provided for additional noise filtering using an external capacitor. 3. a precision 5 v tracking mode with kelvin output connections is available with no external components. tracking error is less than 1 mv, and a fine trim is available for applications requiring exact symmetry between the +5 v and ?5 v outputs. 4. pin strapping capability allows configuration of a wide variety of outputs: 5 v, +5 v, +10 v, ?5 v, and ?10 v dual o u t p u t s o r + 5 v, ? 5 v, + 1 0 v, a n d ? 1 0 v s i n g l e o u t p u t s .
ad588 rev. l | page 2 of 2 0 table of contents features .............................................................................................. 1 ? general description ......................................................................... 1 ? functional block diagram .............................................................. 1 ? product highlights ........................................................................... 1 ? revision history ............................................................................... 2 ? specifications ..................................................................................... 3 ? absolute maximum ratings ............................................................ 4 ? esd caution .................................................................................. 4 ? pin configuration and function descriptions ............................. 5 ? theory of operation ........................................................................ 6 ? applications information ................................................................ 7 ? calibration ..................................................................................... 7 ? noise performance and reduction ............................................ 9 ? turn-on time ............................................................................ 10 ? temperature performance......................................................... 10 ? kelvin connections .................................................................... 11 ? dynamic performance ............................................................... 13 ? using the ad588 with converters ............................................... 15 ? ad7535 14-bit digital-to-analog converter ......................... 15 ? ad569 16-bit digital-to-analog converter ........................... 15 ? substituting for internal references ........................................ 16 ? ad574a 12-bit analog-to-digital converter ........................ 16 ? resistance temperature detector (rtd) excitation ............. 16 ? boosted precision current source ........................................... 17 ? bridge driver circuits ............................................................... 17 ? outline dimensions ....................................................................... 19 ? ordering guide .......................................................................... 19 ? revision history 10/10rev. k to rev. l changes to amplifier a2 plus and minus input labels in figures ........................................................................ throughout 9/10rev. j to rev. k changes to product title ................................................................. 1 4/10rev. i to rev. j changes to calibration section ...................................................... 8 11/09rev. h to rev. i changes to figure 40 and figure 41 ............................................. 18 10/09rev. g to rev. h changes to general description section ...................................... 1 6/06rev. f to rev. g changes to table 5 ............................................................................ 7 updated outline dimensions ....................................................... 19 3/06rev. e to rev. f replaced figure 5 ............................................................................. 8 updated outline dimensions ....................................................... 19 11/05rev. d to rev. e updated format .................................................................. universal added soic vers ion .......................................................... universal changes to pin 14 in figures ............................................. universal changes to pin 9 and pin 10 in figures ........................... universal changes to specifications section ................................................... 3 added table 3 .................................................................................... 4 added pin configuration and function descriptions section ... 5 added table 4 .................................................................................... 5 changes to grade in reference and in figure 12 ....................... 11 updated outline dimensions ....................................................... 19 changes to ordering guide .......................................................... 19 2/03rev. c to rev. d added kq model and deleted sq and tq models ...... universal changes to general description ..................................................... 1 change to product highlights ......................................................... 1 changes to specifications ................................................................. 2 change to ordering guide ............................................................... 3 updated outline dimensions ....................................................... 15 10/02rev. b to rev. c changes to general description ..................................................... 1 changes to specifications ................................................................. 2 changes to ordering guide ............................................................. 3 changes to table 1 ............................................................................. 5 deleted figure 10c ............................................................................. 7 outline dimensions updated ....................................................... 15
ad588 rev. l | page 3 of 20 specifications typical @ 25c, 10 v output, v s = 15 v, unless otherwise noted. specifications shown in boldface are tested on all production units at final electrical test. results from those tests are used to calculate outgoing quality levels. all minimum and maximum specifications are guaranteed, although only those shown in boldface are teste d on all production units. table 1. ad588jq/aq ad588bq/kq ad588arwz parameter 1 min typ max min typ max min typ max unit output voltage error +10 v, ?10 v outputs 3 ?1 +1 ?5 +5 mv +5 v, ?5 v outputs 3 ?1 +1 ?5 +5 mv 5 v tracking mode symmetry error 1.5 0.75 1.5 mv output voltage drift 0c to 70c (j, k, b) 2 3 1.5 2 3 ppm/c ?25c to +85c (a, b) 3 3 3 ppm/c gain adj and bal adj 2 trim range 4 4 4 mv input resistance 150 150 150 k line regulation t min to t max 3 200 200 200 v/v load regulation t min to t max +10 v output, 0 ma < i out < 10 ma 50 50 50 v/ma ?10 v output, ?10 ma < i out < 0 ma 50 50 50 v/ma supply current t min to t max 6 10 6 10 6 10 ma power dissipation 180 300 180 300 180 300 mw output noise (any output) 0.1 hz to 10 hz 6 6 6 v p-p spectral density, 100 hz 100 100 100 nv/hz long-term stability (@ 25c) 15 15 15 ppm/1000 hr buffer amplifiers offset voltage 100 10 100 v offset voltage drift 1 1 1 v/c bias current 20 20 20 na open-loop gain 110 110 110 db output current (a3, a4) ?10 +10 ?10 +10 ?10 +10 ma common-mode rejection (a3, a4) v cm = 1 v p-p 100 100 100 db short circuit current 50 50 50 ma temperature range specified performance j, k grades 0 70 0 70 c a, b grades ?25 +85 ?25 +85 ?25 +85 c 1 specifications tested using 5 v configura tion, unless otherwise indicated. see through for output configurat ions at +10 v, ?10 v, +5 v, ?5 v and 5 v. figu re 4 figure 6 2 gain and balance adjustments guaranteed capable of tri mming output voltage error an d symmetry error to zero. 3 for 10 v output, v s can be as low as 12 v. see for test conditions at various voltages. table 3
ad588 rev. l | page 4 of 20 absolute maximum ratings table 2. parameter rating +v s to ?v s 36 v power dissipation (25c) 600 mw storage temperature range ?65c to +150c lead temperature (soldering 10 sec) 300c package thermal resistance ( ja / jc ) 90c/25c/w output protection all outputs safe if shorted to ground table 3. test conditions voltage conditions +10 v output ?v s = C15 v, +13.5 v +v s +18 v ?10 v output ?18 v Cv s C13.5 v, +v s = +15 v 5 v output +v s = +18 v, Cv s = C18 v +v s = +10.8 v, ?v s = ?10.8 v 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
ad588 rev. l | page 5 of 20 pin configuration and fu nction descriptions top view (not to scale) 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 a 3 out force +v s a3 out sense a3 in gain adj v high noise reduction v low ?v s a4 out force a4 out sense a4 in bal adj v ct gnd sense ?in gnd sense +in ad588 00531-002 figure 2. pin configuration table 4. pin function descriptions pin o. neonic description 1 a3 out force output from buffering amplifier 3 with kelvin force. connect to pin 3. 2 +v s positive power supply. 3 a3 out sense output from buffering amplifie r 3 with kelvin sense. connect to pin 1. 4 a3 in + input to amplifier 3. connect to v high , pin 6. 5 gain adj reference gain adjustment for calibration. see the calibration section. 6 v high unbuffered reference high output. 7 noise reduction noise filtering pin. connect external 1 f capacitor to ground to reduce the output noise (see the noise performance and reduction section). can be left open. 8 v low unbuffered reference low output. 9 gnd sense positive in + input to the ground sense amplifier. 10 gnd sense negative in ? input to the ground sense amplifier. 11 v ct center tap voltage used for calibration. see the calibration section. 12 bal adj reference centering adjustment for calibration. see the calibration section. 13 a4 in + input to amplifier 4. connect to v low , pin 8. 14 a4 out sense output of buffering amplifier 4 with kelvin sense. connect to pin 15. 15 a4 out force output of buffering amplifier 4 with kelvin force. connect to pin 14. 16 ?v s negative power supply.
ad588 rev. l | page 6 of 20 theory of operation the ad588 consists of a buried zener diode reference, amplifiers used to provide pin programmable output ranges, and associated thin-film resistors, as shown in figure 3 . the temperature compensation circuitry provides the device with a temperature coefficient of 1.5 ppm/c or less. amplifier a1 performs several functions. a1 primarily acts to amplify the zener voltage from 6.5 v to the required 10 v output. in addition, a1 provides for external adjustment of the 10 v output through pin 5, gain adj. using the bias compensation resistor between the zener output and the noninverting input to a1, a capacitor can be added at the noise reduction pin (pin 7) to form a low-pass filter and reduce the noise contribution of the zener to the circuit. two matched 10 k nominal thin-film resistors (r4 and r5) divide the 10 v output in half. pin v ct (pin 11) provides access to the center of the voltage span and bal adj (pin 12) can be used for fine adjustment of this division. ground sensing for the circuit is provided by amplifier a2. the noninverting input (pin 9) senses the system ground, which is transferred to the point on the circuit where the inverting input (pin 10) is connected. this can be pin 6, pin 8, or pin 11. the output of a2 drives pin 8 to the appropriate voltage. thus, if pin 10 is connected to pin 8, the v low pin is the same voltage as the system ground. alternatively, if pin 10 is connected to the v ct pin, it is a ground; and pin 6 and pin 8 are +5 v and ?5 v, respectively. amplifier a3 and amplifier a4 are internally compensated and are used to buffer the voltages at pin 6, pin 8, and pin 11, as well as to provide a full kelvin output. thus, the ad588 has a full kelvin capability by providing the means to sense a system ground and provide forced and sensed outputs referenced to that ground. note that both positive and negative supplies are required for operation of the ad588. r3 r b r1 r2 r4 r5 r6 gain adj gnd sense +in gnd sense ?in v low bal adj v ct a4 in ?v s +v s a4 out force a4 out sense a3 out force a 3 out se n se a3 in v high noise reduction a1 a4 ad588 a2 00531-003 a3 13 11 12 8 10 9 5 1 14 15 2 16 3 4 6 7 figure 3. ad588 functional block diagram
ad588 rev. l | page 7 of 20 applications information the ad588 can be configured to provide +10 v and C10 v reference outputs, as shown in figure 4 and figure 6 , respectively. it can also be used to provide +5 v, ?5 v, or a 5 v tracking reference, as shown in figure 5 . table 5 details the appropriate pin connections for each output range. in each case, pin 9 is connected to system ground, and power is applied to pin 2 and pin 16. the architecture of the ad588 provides ground sense and uncommitted output buffer amplifiers that offer the user a great deal of functional flexibility. the ad588 is specified and tested in the configurations shown in figure 6 . the user can choose to take advantage of the many other configuration options available with the ad588. however, performance in these configurations is not guaranteed to meet the extremely stringent data sheet specifications. as indicated in table 5 , a +5 v buffered output can be provided using amplifier a4 in the +10 v configuration ( figure 4 ). a ?5 v buffered output can be provided using amplifier a3 in the ?10 v configuration ( figure 6 ). specifications are not guaranteed for the +5 v or ?5 v outputs in these configurations. performance is similar to that specified for the +10 v or ?10 v outputs. as indicated in table 5 , unbuffered outputs are available at pin 6, pin 8, and pin 11. loading of these unbuffered outputs impairs circuit performance. amplifier a3 and amplifier a4 can be used interchangeably. however, the ad588 is tested (and the specifications are guaranteed) with the amplifiers connected, as indicated in figure 4 and table 5 . when either a3 or a4 is unused, its output force and sense pins should be connected or the input tied to ground. two outputs of the same voltage can be obtained by connecting both a3 and a4 to the appropriate unbuffered output on pin 6, pin 8, or pin 11. performance in these dual-output configurations typically meets data sheet specifications. calibration generally, the ad588 meets the requirements of a precision system without additional adjustment. initial output voltage error of 1 mv and output noise specs of 10 v p-p allow for accuracies of 12 bits to 16 bits. however, in applications where an even greater level of accuracy is required, additional calibra- tion may be called for. provision for trimming has been made through the use of the gain adj and bal adj pins (pin 5 and pin 12, respectively). the ad588 provides a precision 10 v span with a center tap (v ct ) that is used with the buffer and ground sense amplifiers to achieve the voltage output configurations in table 5 . gain adj and bal adj can be used in any of these configurations to trim the magnitude of the span voltage and the position of the center tap within the span. the gain adjust should be performed first. although the trims are not interactive within the device, the gain trim moves the balance trim point as it changes the magnitude of the span. table 5. pin connections connect unbuffered 1 output on pins buffered output buffered output on pins range pin 10 to pin ?10 v ?5 v 0 v +5 v +10 v connections ?10 v ?5 v 0 v +5 v +10 v +10 v 8 8 11 6 11 to 13, 14 to 15, 15 6 to 4, and 3 to 1 1 ?5 v or +5 v 11 8 11 6 8 to 13, 14 to 15, 15 6 to 4, and 3 to 1 1 ?10 v 6 8 11 6 8 to 13, 14 to 15, 15 11 to 4, and 3 to 1 1 +5 v 11 6 6 to 4 and 3 to 1 1 ?5 v 11 8 8 to 13 and 14 to 15 15 1 unbuffered outputs should not be loaded.
ad588 rev. l | page 8 of 20 figure 5 shows gain and balance trims in a +5 v and ?5 v tracking configuration. a 100 k, 20-turn potentiometer is used for each trim. the potentiometer for gain trim is connected between pin 6 (v high ) and pin 8 (v low ) with the wiper connected to pin 5 (gain adj). the potentiometer is adjusted to produce exactly 10 v between pin 1 and pin 15, the amplifier outputs. the balance potentiometer, also connected between pin 6 and pin 8 with the wiper to pin 12 (bal adj), is then adjusted to center the span from +5 v to ?5 v. trimming in other configurations works in exactly the same manner. when producing +10 v and +5 v, gain adj is used to trim +10 v and bal adj is used to trim +5 v. in the ?10 v and ?5 v configuration, gain adj is again used to trim the magnitude of the span, ?10 v, while bal adj is used to trim the center tap, ?5 v. trimming the ad588 introduces no additional errors over temperature, so precision potentiometers are not required. for single-output voltage ranges, or in cases when balance adjust is not required, pin 12 should be connected to pin 11. if gain adjust is not required, pin 5 should be left floating. in single output configurations, gain adj is used to trim outputs utilizing the full span (+10 v or ?10 v), while bal adj is used to trim outputs using half the span (+5 v or ?5 v). input impedance on both the gain adj and bal adj pins is approximately 150 k. the gain adj trim network effectively attenuates the 10 v across the trim potentiometer by a factor of about 1500 to provide a trim range of ?3.5 mv to +7.5 mv with a resolution of approximately 550 v/turn (20-turn potentiome- ter). the bal adj trim network attenuates the trim voltage by a factor of about 1400, providing a trim range of 4.5 mv with resolution of 450 v/turn. r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 system ground +10v +15v +5v ?15v system ground 0.1f 0.1f 00531-004 1 14 15 2 16 1311 12 8 10 9 5 346 7 a2 figure 4. +10 v output r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 a2 system ground +5v +15v ?5v ?15v system ground 0.1f 0.1f 100k? 20t balance adjust 100k ? 20t gain adjust +15v noise reduction 1f 00531-005 39k? figure 5. +5 v and ?5 v outputs r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 system ground +15v ?10v ?15v system ground 0.1f 0.1f noise reduction ?5v 0.1f 0.1f 00531-006 1 14 15 2 16 346 7 131112 8 10 9 5 a2 figure 6. ?10 v output
ad588 rev. l | page 9 of 20 noise performance and reduction the noise generated by the ad588 is typically less than 6 v p-p over the 0.1 hz to 10 hz band. noise in a 1 mhz bandwidth is approximately 600 v p-p. the dominant source of this noise is the buried zener, which contributes approximately 100 nv/hz. in comparison, the op amps contribution is negligible. figure 7 shows the 0.1 hz to 10 hz noise of a typical ad588. if further noise reduction is desired, an optional capacitor, c n , can be added between the noise reduction pin and ground, as shown in figure 5 . this forms a low-pass filter with the 4 k r b on the output of the zener cell. a 1 f capacitor has a 3 db point at 40 hz and reduces the high frequency noise (to 1 mhz) to about 200 v p-p. figure 8 shows the 1 mhz noise of a typical ad588 both with and without a 1 f capacitor. note that a second capacitor is needed in order to implement the noise reduction feature when using the ad588 in the ?10 v mode ( figure 6 ). the noise reduction capacitor is limited to 0.1 f maximum in this mode. 00531-007 1v figure 7. 0.1 hz to 10 hz noise (0.1 hz to 10 hz bpf with gain of 1000 applied) 00531-008 c n = 1mf no c n figure 8. effect of 1 f noise re duction capacitor on broadband noise
ad588 rev. l | page 10 of 20 turn-on time upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error band is the turn-on settling time. two components normally associated with this are the time for active circuits to settle and the time for thermal gradients on the chip to stabilize. output turn-on time is modified when an external noise reduction capacitor is used. when present, this capacitor presents an additional load to the internal zener diode current source, resulting in a somewhat longer turn-on time. in the case of a 1 f capacitor, the initial turn-on time is approximately 60 ms (see figure 11 ). figure 9 and figure 10 show the turn-on characteristics of the ad588. the settling is about 600 s. note the absence of any thermal tails when the horizontal scale is expanded to 2 ms/cm in figure 10 . note that if the noise reduction feature is used in the 5 v configuration, a 39 k resistor between pin 6 and pin 2 is required for proper startup. 00531-009 +v s v out 0 0531-011 +v s ?v s v out figure 11. turn-on with cn = 1 f figure 9. electrical turn-on temperature performance 00531-010 +v s v out the ad588 is designed for precision reference applications where temperature performance is critical. extensive temperature testing ensures that the devices high level of performance is maintained over the operating temperature range. figure 12 shows typical output temperature drift for the ad588bq and illustrates the test methodology. the box in figure 12 is bounded on the sides by the operating temperature extremes and on top and bottom by the maximum and minimum output voltages measured over the operating temperature range. the slope of the diagonal drawn from the lower left corner of the box determines the performance grade of the device. figure 10. extended time scale turn-on 10.002 v max 10.001 10.000 v min output (volts) ?35 ?15 5 25 45 65 85 v max v min temperature (c) slope = t.c. = = 0.95ppm/c v max ? v min (t max ? t min ) 10 1 ?4 10.0013v ? 10.00025v (85c ? ?25c) 10 10 ?4 00531-012 figure 12. typical ad588bq temperature drift
ad588 rev. l | page 11 of 20 each ad588 a and b grade unit is tested at ?25c, 0c, +25c, +50c, +70c, and +85c. this approach ensures that the variations of output voltage that occur as the temperature changes within the specified range is contained within a box whose diagonal has a slope equal to the maximum specified drift. the position of the box on the vertical scale changes from device to device as initial error and the shape of the curve vary. maximum height of the box for the appropriate temperature range is shown in figure 13 . duplication of these results requires a combination of high accuracy and stable temperature control in a test system. evaluation of the ad588 produces a curve similar to that in figure 12 , but output readings may vary, depending on the test methods and equipment utilized. ad588jq ad588jq ad588jq ad588jq ad588jq ad588jq device grade maximum output change (mv) 0c to +70c 2.10 1.05 1.40 (typ) 1.05 3.30 3.30 10.80 7.20 ?25c to +85c ?55c to +125c 00531-013 figure 13. maximum output changemv kelvin connections force and sense connections, also referred to as kelvin connections, offer a convenient method of eliminating the effects of voltage drops in circuit wires. as seen in figure 14 , the load current and wire resistance produce an error (v error = r i l ) at the load. the kelvin connection of figure 14 overcomes the problem by including the wire resistance within the forcing loop of the amplifier and sensing the load voltage. the amplifier corrects for any errors in the load voltage. in the circuit shown, the output of the amplifier would actually be at 10 v + v error , and the voltage at the load would be the desired 10 v. the ad588 has three amplifiers that can be used to implement kelvin connections. amplifier a2 is dedicated to the ground force-sense function, while uncommitted amplifier a3 and amplifier a4 are free for other force-sense chores. ? + 10v r r load r r v = 10v i = 0 i = 0 i l v = 10v ? ri l v = 10v ? ri l i l r load 00531-014 figure 14. advantage of kelvin connection in some single-output applications, one amplifier can be unused. in such cases, the unused amplifier should be connected as a unity-gain follower (force and sense pin tied together), and the input should be connected to ground. an unused amplifier section can be used for other circuit functions, as well. figure 15 through figure 19 show the typical performance of a3 and a4. frequency (hz) 100 ?20 10 10m 100 open-loop gain (db) 1k 10k 100k 1m 80 60 40 20 0 0 ?180 ?30 ?60 ?90 ?120 ?150 phase (degrees) gain phase 00531-015 figure 15. open-loop freq uency response (a3, a4)
ad588 rev. l | page 12 of 20 frequency (hz) 110 10 10 10m 100 power supply rejection (db) 1k 10k 100k 1m 100 80 60 40 20 00531-016 +supply ?supply v s = 15v with 1v p-p sine wave figure 16. power supply reject ion vs. frequency (a3, a4) 00531-017 figure 17. unity-gain follower pulse response (large signal) 00531-018 figure 18. unity-gain follower pulse response (small signal) frequency (hz) 110 0 10 10m 100 cmrr (db) 1k 10k 100k 1m 100 80 60 40 20 v s = 15v v cm = 1v p-p +25c 00531-019 figure 19. common-mode reject ion vs. frequency (a3, a4) frequency (hz) 1 10k 10 noise spectral density (nv/ hz) 100 1k 100 90 0 80 70 60 50 40 30 20 10 00531-020 figure 20. input noise voltage spectral density
ad588 rev. l | page 13 of 20 dynamic performance the output buffer amplifiers (a3 and a4) are designed to provide the ad588 with static and dynamic load regulation superior to less complete references. many analog-to-digital and digital-to-analog converters present transient current loads to the reference, and poor reference response can degrade the converters performance. figure 21 and figure 22 display the characteristics of the ad588 output amplifier driving a 0 ma to 10 ma load. a3 or a4 v out i l 1k? 10v 0v v l 00531-021 10v figure 21. transient load test circuit 00531-022 v out v l figure 22. large-scale transient response figure 23 and figure 24 display the output amplifier characteristics driving a 5 ma to 10 ma load, a common situation found when the reference is shared among multiple converters or is used to provide a bipolar offset current. 0 0531-023 a3 or a4 v out + ? 2k? i l 10v 0v v l 2k? 10v figure 23. transient and constant load test circuit 00531-024 v out 1mv/cm v out 200mv/cm v l figure 24. transient response 5 ma to10 ma load in some applications, a varying load can be both resistive and capacitive in nature or can be connected to the ad588 by a long capacitive cable. figure 25 and figure 26 display the output amplifier characteristics driving a 1000 pf, 0 ma to 10 ma load. 00531-025 a3 or a4 v out c l 1000pf 10v 0v v l 1k? 10v figure 25. capacitive load transient response test circuit 00531-026 c l = 0 c l = 1000pf v l figure 26. output response with capacitive load figure 27 and figure 28 display the crosstalk between output amplifiers. the top trace shows the output of a4, dc-coupled and offset by 10 v, while the output of a3 is subjected to a 0 ma to 10 ma load current step. the transient at a4 settles in about 1 s, and the load-induced offset is about 100 v. v out a4 a3 + + 00531-027 10v 0v v l 1k? 10v ? 10v ? figure 27. load crosstalk test circuit 00531-028 v out v l figure 28. load crosstalk
ad588 rev. l | page 14 of 20 attempts to drive a large capacitive load (in excess of 1000 pf) can result in ringing or oscillation, as shown in the step response photo ( figure 29 ). this is due to the additional pole formed by the load capacitance and the output impedance of the amplifier, which consumes phase margin. the recommended method of driving capacitive loads of this magnitude is shown in figure 30 . the 150 resistor isolates the capacitive load from the output stage, while the 10 k resistor provides a dc feedback path and preserves the output accuracy. the 1 f capacitor provides a high frequency feedback loop. the performance of this circuit is shown in figure 31 . 00531-029 v in v out figure 29. output ampl ifier step response, c l = 1 f 00531-03 0 v out 10k ? 1f c l 1f 150? + ? in v figure 30. compensation for capacitive loads 00531-031 v in v out figure 31. output amplifier step response using figure 30 compensation
ad588 rev. l | page 15 of 20 using the ad588 with converters the ad588 is an ideal reference for a wide variety of analog-to- digital and digital-to-analog converters. several representative examples follow. ad7535 14-bit digital-to-analog converter high resolution cmos digital-to-analog converters require a reference voltage of high precision to maintain rated accuracy. the combination of the ad588 and ad7535 takes advantage of the initial accuracy, drift, and full kelvin output capability of the ad588, as well as the resolution, monotonicity, and accuracy of the ad7535 to produce a subsystem with outstanding characteristics (see figure 32 ). ad569 16-bit digital-to-analog converter another application that fully utilizes the capabilities of the ad588 is supplying a reference for the ad569, as shown in figure 33 . amplifier a2 senses system common and forces v ct to assume this value, producing +5 v and ?5 v at pin 6 and pin 8, respectively. amplifier a3 and amplifier a4 buffer these voltages out to the appropriate reference force-sense pins of the ad569. the full kelvin scheme eliminates the effect of the circuit traces or wires and the wire bonds of the ad588 and ad569 themselves, which would otherwise degrade system performance. 00531-032 r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 14-bit dac ls input register ms input register dac register v refs v ref agnds agndf +10v n.c. v dd r fs i out ldac cslsb csmsb wr v ss dgnd db0 db13 14 ad7535 1 14 15 2 16 1 2 5 6 13 11 12 8 10 9 5 3 4 6 7 28 26 3 4 23 24 22 25 82 1 7 2 7 a2 figure 32. ad588/ad7535 connections 00531-033 a1 a3 a2 a4 ad588 a 3 + in 10k ? v l ?5v v ct +5v v h 10k ? +v ref force t a p s e l e c t o r 8 msbs 8 lsbs gnd db15 db0 hbe lbe v out ?5v to +5v +12 v ?12v +v s ?v s s e g m e n t s e l e c t o r latches ad569 +v ref sense ?v ref force ?v ref sense ldac cs a 3 ? in a 3 out a 2 + in a 2 ? in a 4 + in a 4 ? in a 4 out 813 216 64 1 3 12 11 10 9 14 15 3 2 16 15 1 28 17 13 14 12 9 7 4 19 22 24 27 8 23 18 figure 33. high accuracy 5 v tracking reference for ad569
ad588 rev. l | page 16 of 20 substituting for internal references many converters include built-in references. unfortunately, such references are the major source of drift in these converters. by using a more stable external reference like the ad588, drift performance can be improved dramatically. ad574a 12-bit analog-t o-digital converter the ad574a is specified for gain drift from 10 ppm/c to 50 ppm/c (depending on grade), using its on-chip reference. the reference contributes typically 75% of this drift. using an ad588 as a reference source can improve the total drift by a factor of 3 to 4. using this combination can result in apparent increases in full-scale error due to the difference between the on-board reference, by which the device is laser-trimmed, and the external reference, with which the device is actually applied. the on-board reference is specified to be 10 v 100 mv, while the external reference is specified to be 10 v 1 mv. this may result in up to 101 mv of apparent full-scale error beyond the 25 mv specified ad574 gain error. external resistor r2 and resistor r3 allow this error to be nulled. their contribution to full-scale drift is negligible. the high output drive capability allows the ad588 to drive up to six converters in a multiconverter system. all converters have gain errors that track to better than 5 ppm/c. resistance temperature detector (rtd) excitation the rtd is a circuit element whose resistance is characterized by a positive temperature coefficient. a measurement of resistance indicates the measured temperature. unfortunately, the resistance of the wires leading to the rtd often adds error to this measurement. the 4-wire ohms measurement overcomes this problem. this method uses two wires to bring an excitation current to the rtd and two additional wires to tap off the resulting rtd voltage. if these additional two wires go to a high input impedance measurement circuit, the effect of their resistance is negligible. they therefore transmit the true rtd voltage. i exc r r i = 0 rtd v out r rtd + ? i = 0 r r 00531-034 figure 34. 4-wire ohms measurement 12 8s t s 00531-035 r3 r b r1 r2 r4 r5 r6 a1 a4 ad588 a3 ao ce ref in ref out bipp off 10v in 20v in ana com high bits middle bits low bits +5v +15v ?15v dig com ad574a ?v s +v s r2 61.9 ? r1 50? r3 500? 20 turn v in 10v cs r/c 15 11 7 1 16 19 20 23 24 27 9 14 13 12 8 10 6 5 4 3 16 2 15 14 1 13 11 12 8 10 9 5 7643 28 2 a2 figure 35. ad588/ad574a connections
ad588 rev. l | page 17 of 20 a practical consideration when using the 4-wire ohms technique with an rtd is the self-heating effect that the excitation current has on the temperature of the rtd. the designer must choose the smallest practical excitation current that still gives the desired resolution. rtd manufacturers usually specify the self-heating effect of each of their models or types of rtds. figure 36 shows an ad588 providing the precision excitation current for a 100 rtd. the small excitation current of 1 ma dissipates a mere 0.1 mw of power in the rtd. boosted precision current source in the rtd current-source application, the load current is limited to 10 ma by the output drive capability of amplifier a3. in the event that more drive current is needed, a series-pass transistor can be inserted inside the feedback loop to provide higher current. accuracy and drift performance are unaffected by the pass transistor. bridge driver circuits the wheatstone bridge is a common transducer. in its simplest form, a bridge consists of four two-terminal elements connected to form a quadrilateral, a source of excitation connected along one of the diagonals and a detector comprising the other diagonal. figure 38 shows a simple bridge driven from a unipolar excitation supply. eo, a differential voltage, is proportional to the deviation of the element from the initial bridge values. unfortunately, this bridge output voltage is riding on a common-mode voltage equal to approximately v in /2. further processing of this signal may necessarily be limited to high common-mode rejection techniques, such as instrumentation or isolation amplifiers. figure 39 shows the same bridge transducer, this time driven from a pair of bipolar supplies. this configuration ideally eliminates the common-mode voltage and relaxes the restrictions on any processing elements that follow. 00531-036 r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 ad588 a3 100? 1.0ma 0.01% + ? v out r c = 10k ? r c vishay s102c or similar rtd = ? k4515 0.24c/mw self-heating ?15v or ground a4 59108 12 11 13 7643 16 2 15 14 1 a2 00531-037 r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 load v cc q 1 i l = 220? limited by q 1 and r c power dissipation 10v r c 13 11 12 8 10 9 5 346 7 1 14 15 2 16 a2 figure 36. precision current source for rtd figure 37. boosted precision current source 00531-038 v in ? + r4 r3 r2 r1 e o +? v 1 r4 r3 r2 r1 e o +? v 2 ? + ? + 00531-039 figure 38. bridge transducer excitationunipolar drive figure 39. bridge transducer excitationbipolar drive
ad588 rev. l | page 18 of 20 as shown in figure 40 , the ad588 is an excellent choice for the control element in a bipolar bridge driver scheme. transistor q1 and transistor q2 serve as series-pass elements to boost the current drive capability to the 28 ma required by a typical 350 bridge. a differential gain stage can still be required if the bridge balance is not perfect. such gain stages can be expensive. additional common-mode voltage reduction is realized by using the circuit illustrated in figure 41 . a1, the ground sense amplifier, serves the supplies on the bridge to maintain a virtual ground at one center tap. the voltage that appears on the opposite center tap is now single-ended (referenced to ground) and can be amplified by a less expensive circuit. 00531-040 r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 q 1 = 2n3904 220 ? +15v ?15v 220? q 2 = 2n3906 e o +? 13 11 12 8 10 9 5 1 14 15 2 16 3 46 7 a2 figure 40. bipolar bridge drive 00531-041 r3 r b r1 r2 r4 r5 r6 ?v s +v s a1 a4 ad588 a3 r1 r2 ad op-07 v out + ? 220? +15 v ?15v 220 ? q 1 = 2n3904 q 2 = 2n3906 13 11 12 8 10 9 5 1 14 15 2 16 3 4 6 7 a2 figure 41. floating bipolar bridge drive with minimum cmv
ad588 rev. l | page 19 of 20 outline dimensions controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design. compliant to jedec standards ms-013- aa 032707-b 10.50 (0.4134) 10.10 (0.3976) 0.30 (0.0118) 0.10 (0.0039) 2.65 (0.1043) 2.35 (0.0925) 10.65 (0.4193) 10.00 (0.3937) 7.60 (0.2992) 7.40 (0.2913) 0 . 7 5 ( 0 . 0 2 9 5 ) 0 . 2 5 ( 0 . 0 0 9 8 ) 45 1.27 (0.0500) 0.40 (0.0157) c oplanarity 0.10 0.33 (0.0130) 0.20 (0.0079) 0.51 (0.0201) 0.31 (0.0122) seating plane 8 0 16 9 8 1 1.27 (0.0500) bsc figure 42. 16-lead standard small outline package [soic_w] wide body (rw-16) dimensions shown in millimeters and (inches) controlling dimensions are in inches; millimeter dimensions (in parentheses) are rounded-off inch equivalents for reference only and are not appropriate for use in design. 0.840 (21.34) max 15 0 0.320 (8.13) 0.290 (7.37) 0.015 (0.38) 0.008 (0.20) 0 .200 (5.08) max 0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.014 (0.36) 0.310 (7.87) 0.220 (5.59) 0.005 (0.13) min 0.098 (2.49) max 0.100 (2.54) bsc pin 1 1 8 9 16 seating plane 0.150 (3.81) min 0.070 (1.78) 0.030 (0.76) 0.060 (1.52) 0.015 (0.38) figure 43. 16-lead ceramic dual in-line package [cerdip] (q-16) dimensions shown in inches and (millimeters) ordering guide model 1, 2 initial error (mv) temperature coefficient 3 temperature range (c) package description package option ad588arwz 5 3 ppm/c ?25 to +85 16-lead st andard small outline package [soic-w] rw-16 ad588aq 3 3 ppm/c ?25 to +85 16-lead ceramic dual in-line package [cerdip] q-16 ad588bq 1 1.5 ppm/c ?25 to +85 16-lead ceramic dual in-line package [cerdip] q-16 ad588jq 3 3 ppm/c 0 to 70 16-lead ceramic dual in-line package [cerdip] q-16 ad588kq 1 1.5 ppm/c 0 to 70 16-lead ceramic dual in-line package [cerdip] q-16 1 for details on grade and packag e offerings screened in accordan ce with mil-std-883, refer to th e analog device s military produ cts databook or current ad588/883b data sheet. 2 z = rohs compliant part. 3 temperature coefficient specified from 0c to 70c.
ad588 rev. l | page 20 of 20 notes ?1986C2010 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d00531-0-10/10(l)

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