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rev. c a adr420/adr421/ADR423/adr425 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. 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 companies. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 ?2003, analog devices, inc. all rights reserved. ultraprecision low noise, 2.048 v/2.500 v/ 3.00 v/5.00 v xfet voltage references pin configuration surface-mount packages 8-lead soic 8-lead msop top view (not to scale) 8 7 6 5 1 2 3 4 nic = no internal connection tp = test pin (do not connect) tp v in nic gnd tp nic v out trim adr42x features low noise (0.1 hz to 10 hz) adr420: 1.75 v p-p adr421: 1.75 v p-p ADR423: 2.0 v p-p adr425: 3.4 v p-p low temperature coefficient: 3 ppm/ c long-term stability: 50 ppm/1000 hours load regulation: 70 ppm/ma line regulation: 35 ppm/v low hysteresis: 40 ppm typical wide operating range adr420: 4 v to 18 v adr421: 4.5 v to 18 v ADR423: 5 v to 18 v adr425: 7 v to 18 v quiescent current: 0.5 ma maximum high output current: 10 ma wide temperature range: ?0 c to +125 c applications precision data acquisition systems high resolution converters battery powered instrumentation portable medical instruments industrial process control systems precision instruments optical network control circuits general description the adr42x series are ultraprecision second-generation xfet voltage references featuring low noise, high accuracy, and excel lent long-term stability in soic and msop footprints. pat ented tem perature drift curvature correction technique and xfet (extra implanted junction fet) technology minimize nonlinearity of the voltage change with temperature. the xfet architecture offers superior accuracy and thermal hysteresis to the band gap references. it also operates at lower power and lower supply headroom than the buried zener references. the superb noise, stable and accurate characteristics of adr42x make them ideal for precision conversion applications such as optical network and medical equipment. the adr42x trim terminal can also be used to adjust the output voltage over a 0.5% range without compromising any other performance. the adr42x series voltage references offer two electrical grades and are specified over the extended industrial temperature range of 40 c to +125 c. devices are available in 8-lead soic-8 or 30% smaller 8-lead msop-8 packages. table i. adr42x products output initial temperature voltage accuracy coefficient model v o mv % (ppm/ c) adr420 2.048 1, 3 0.05, 0.15 3, 10 adr421 2.50 1, 3 0.04, 0.12 3, 10 ADR423 3.00 1.5, 4 0.04, 0.12 3, 10 adr425 5.00 2, 6 0.04, 0.12 3, 10
rev. c ? adr42x?pecifications adr420 electrical specifications parameter symbol conditions min typ max unit output voltage a grade v o 2.045 2.048 2.051 v initial accuracy v oerr ? +3 mv ?.15 +0.15 % output voltage b grade v o 2.047 2.048 2.049 v initial accuracy v oerr ? +1 mv ?.05 +0.05 % temperature coefficient a grade tcv o ?0 c < t a < +125 c210 ppm/ c b grade 1 3 ppm/ c supply voltage headroom v in ?v o 2v line regulation ? v o / ? v in v in = 5 v to 18 v 10 35 ppm/v ?0 c < t a < +125 c load regulation ? v o / ? i load i load = 0 ma to 10 ma 70 ppm/ma ?0 c < t a < +125 c quiescent current i in no load 390 500 a ?0 c < t a < +125 c 600 a voltage noise e n p-p 0.1 hz to 10 hz 1.75 v p-p voltage noise density e n 1 khz 60 nv/ hz turn-on settling time t r 10 s long-term stability ? v o 1,000 hours 50 ppm output voltage hysteresis v o_hys 40 ppm ripple rejection ratio rrr f in = 10 khz 75 db short circuit to gnd i sc 27 ma specifications subject to change without notice. (@ v in = 5.0 v to 15.0 v, t a = 25 c, unless otherwise noted.) adr421 electrical specifications parameter symbol conditions min typ max unit output voltage a grade v o 2.497 2.500 2.503 v initial accuracy v oerr ? +3 mv ?.12 +0.12 % output voltage b grade v o 2.499 2.500 2.501 v initial accuracy v oerr ? +1 mv ?.04 +0.04 % temperature coefficient a grade tcv o ?0 c < t a < +125 c210 ppm/ c b grade 1 3 ppm/ c supply voltage headroom v in ?v o 2v line regulation ? v o / ? v in v in = 5 v to 18 v 10 35 ppm/v ?0 c < t a < +125 c load regulation ? v o / ? i load i load = 0 ma to 10 ma 70 ppm/ma ?0 c < t a < +125 c quiescent current i in no load 390 500 a ?0 c < t a < +125 c 600 a voltage noise e n p-p 0.1 hz to 10 hz 1.75 v p-p voltage noise density e n 1 khz 80 nv/ hz turn-on settling time t r 10 s long-term stability ? v o 1,000 hours 50 ppm output voltage hysteresis v o_hys 40 ppm ripple rejection ratio rrr f in = 10 khz 75 db short circuit to gnd i sc 27 ma specifications subject to change without notice. (@ v in = 5.0 v to 15.0 v, t a = 25 c, unless otherwise noted.)
rev. c ? adr420/adr421/ADR423/adr425 ADR423 electrical specifications parameter symbol conditions min typ max unit output voltage a grade v o 2.996 3.000 3.004 v initial accuracy v oerr ? +4 mv ?.13 +0.13 % output voltage b grade v o 2.9985 3.000 3.0015 v initial accuracy v oerr ?.5 +1.5 mv ?.04 +0.04 % temperature coefficient a grade tcv o ?0 c < t a < +125 c210 ppm/ c b grade 1 3 ppm/ c supply voltage headroom v in ? v o 2v line regulation ? v o / ? v in v in = 5 v to 18 v 10 35 ppm/v ?0 c < t a < +125 c load regulation ? v o / ? i load i load = 0 ma to 10 ma 70 ppm/ma ?0 c < t a < +125 c quiescent current i in no load 390 500 a ?0 c < t a < +125 c 600 a voltage noise e n p-p 0.1 hz to 10 hz 2 v p-p voltage noise density e n 1 khz 90 nv/ hz turn-on settling time t r 10 s long-term stability ? v o 1,000 hours 50 ppm output voltage hysteresis v o_hys 40 ppm ripple rejection ratio rrr f in = 10 khz 75 db short circuit to gnd i sc 27 ma specifications subject to change without notice. adr425 electrical specifications parameter symbol conditions min typ max unit output voltage a grade v o 4.994 5.000 5.006 v initial accuracy v oerr ? +6 mv ?.12 +0.12 % output voltage b grade v o 4.998 5.000 5.002 v initial accuracy v oerr ? +2 mv ?.04 +0.04 % temperature coefficient a grade tcv o ?0 c < t a < +125 c210 ppm/ c b grade 1 3 ppm/ c supply voltage headroom v in ?v o 2v line regulation ? v o / ? v in v in = 7 v to 18 v 10 35 ppm/v ?0 c < t a < +125 c load regulation ? v o / ? i load i load = 0 ma to 10 ma 70 ppm/ma ?0 c < t a < +125 c quiescent current i in no load 390 500 a ?0 c < t a < +125 c 600 a voltage noise e n p-p 0.1 hz to 10 hz 3.4 v p-p voltage noise density e n 1 khz 110 nv/ hz turn-on settling time t r 10 s long-term stability ? v o 1,000 hours 50 ppm output voltage hysteresis v o_hys 40 ppm ripple rejection ratio rrr f in = 10 khz 75 db short circuit to gnd i sc 27 ma specifications subject to change without notice. (@ v in = 5.0 v to 15.0 v, t a = 25 c, unless otherwise noted.) (@ v in = 7.0 v to 15.0 v, t a = 25 c, unless otherwise noted.)
rev. c ? a dr420/adr421/ADR423/adr425 package type ja * unit 8-lead msop (rm) 190 c/w 8-lead soic (r) 130 c/w * ja is specified for the worst-case conditions, i.e., ja is specified for device soldered in circuit board for surface-mount packages. absolute maximum ratings * supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 v output short-circuit duration to gnd . . . . . . . . . indefinite storage temperature range r, rm packages . . . . . . . . . . . . . . . . . . . . ?5 c to +150 c operating temperature range adr42x . . . . . . . . . . . . . . . . . . . . . . . . . . ?0 c to +125 c junction temperature range r, rm packages . . . . . . . . . . . . . . . . . . . . ?5 c to +150 c lead temperature range (soldering, 60 sec) . . . . . . . 300 c * absolute maximum ratings apply at 25 c, unless otherwise noted. pin function descriptions pin mnemonic description 1, 8t p test pin. there are actual connections in tp pins but they are reserved for factory testing purposes. users should not con nect any- thing to tp pins, otherwise the device may not function properly. 2v in input voltage 3, 7 nic no internal connect. nics have no internal connections. 4gnd g round pin = 0 v 5 trim trim terminal. it can be used to adjust the output voltage over a 0.5% range without affecting the temperature coefficient. 6v out output voltage pin configurations msop-8 top view (not to scale) 8 7 6 5 1 2 3 4 nic = no internal connection tp = test pin (do not connect) tp v in nic gnd tp nic v out trim adr42x soic-8 8 7 6 5 tp nic v out trim adr42x 1 2 3 4 tp v in nic gnd nic = no internal connection tp = test pin (do not connect) output initial temperature number of temperature voltage accuracy coefficient package package top parts per range model v o mv % (ppm/ c) description option mark reel ( c) adr420ar 2.048 3 0.15 10 soic r-8 adr420 98 ?0 to +125 adr420ar-reel7 2.048 3 0.15 10 soic r-8 adr420 3,000 ?0 to +125 adr420br 2.048 1 0.05 3 soic r-8 adr420 98 ?0 to +125 adr420br-reel7 2.048 1 0.05 3 soic r-8 adr420 3,000 ?0 to +125 adr420arm-reel7 2.048 3 0.15 10 msop rm-8 r4a 1,000 ?0 to +125 adr421ar 2.50 3 0.12 10 soic r-8 adr421 98 ?0 to +125 adr421ar-reel7 2.50 3 0.12 10 soic r-8 adr421 3,000 ?0 to +125 adr421br 2.50 1 0.04 3 soic r-8 adr421 98 ?0 to +125 adr421br-reel7 2.50 1 0.04 3 soic r-8 adr421 3,000 ?0 to +125 adr421arm-reel7 2.50 3 0.12 10 msop rm-8 r5a 1,000 ?0 to +125 ADR423ar 3.00 4 0.13 10 soic r-8 ADR423 98 ?0 to +125 ADR423ar-reel7 3.00 4 0.13 10 soic r-8 ADR423 3,000 ?0 to +125 ADR423br 3.00 1.5 0.04 3 soic r-8 ADR423 98 ?0 to +125 ADR423br-reel7 3.00 1.5 0.04 3 soic r-8 ADR423 3,000 ?0 to +125 ADR423arm-reel7 3.00 4 0.13 10 msop rm-8 r6a 1,000 ?0 to +125 adr425ar 5.00 6 0.12 10 soic r-8 adr425 98 ?0 to +125 adr425ar-reel7 5.00 6 0.12 10 soic r-8 adr425 3,000 ?0 to +125 adr425br 5.00 2 0.04 3 soic r-8 adr425 98 ?0 to +125 adr425br-reel7 5.00 2 0.04 3 soic r-8 adr425 3,000 ?0 to +125 adr425arm-reel7 5.00 6 0.12 10 msop rm-8 r7a 1,000 ?0 to +125 ordering guide 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 ad42x 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. c adr420/adr421/ADR423/adr425 ? parameter definitions temperature coefficient the change of output voltage over the operating temperature range and normalized by the output voltage at 25 c, expressed in ppm/ c. the equation follows: tcv ppm c vt vt vctt o oo o / () () ()() () = 21 21 6 25 10 where v o (25 c) = v o at 25 c v o ( t 1 ) = v o at temperature 1 v o ( t 2 ) = v o at temperature 2 line regulation the change in output voltage due to a specified change in input voltage. it includes the effects of self-heating. line regulation is expressed in either percent per volt, parts-per-million per volt, or microvolts per volt change in input voltage. load regulation the change in output voltage due to a specified change in load current. it includes the effects of self-heating. load regulation is expressed in either microvolts per milliampere, parts-per-m illion per milliampere, or ohms of dc output resistance. long-term stability typical shift of output voltage at 25 c on a sample of parts subjected to operation life test of 1000 hours at 125 c: ? ? vvt vt v ppm vt vt vt oo o o oo o = = ()? () () ()? () () 01 01 0 6 10 where v o ( t 0 ) = v o at 25 c at time 0 v o ( t 1 ) = v o at 25 c after 1,000 hours operation at 125 c thermal hysteresis thermal hysteresis is defined as the change of output voltage after the device is cycled through temperature from +25 c to ?0 c to +125 c and back to +25 c. this is a typical value from a sample of parts put through such a cycle. vvcv v ppm vcv vc o hys o o tc o hys ootc o __ _ _ = = () () () () 25 25 25 10 6 where v o ( 25 c ) = v o at 25 c v o_tc = v o at 25 c after temperature cycle at +25 c to ?0 c to +125 c and back to +25 c input capacitor input capacitors are not required on the adr42x. there is no limit for the value of the capacitor used on the input, but a 1 f to 10 f capacitor on the input will improve transient response in applications where the supply suddenly changes. an additional 0.1 f in parallel will also help to reduce noise from the supply. output capacitor the adr42x does not need output capacitors for stability under any load condition. an output capacitor, typically 0.1 f, will filter out any low level noise voltage and will not affect the operation of the part. on the other hand, the load transient response can be improved w ith an additional 1 f to 10 f output capacitor in parallel. a capacitor here will act as a source of stored energy for sudden increase in load current. the only parameter that will degrade by adding an output capacitor, is turn-on time, and it depends on the size of the capacitor chosen.
rev. c ? a dr420/adr421/ADR423/adr425 a dr42x series ? ypical performance characteristics 2.0495 2.0493 2.0491 2.0489 2.0487 2.0485 2.0483 2.0481 2.0479 2.0477 2.0475 ?0 ?0 20 50 80 110 125 temperature ? c v out ?v tpc 1. adr420 typical output voltage vs. temperature 2.4995 2.4997 2.4999 2.5001 2.5003 2.5005 2.5007 2.5009 2.5011 2.5013 2.5015 ?0 ?0 20 50 80 110 125 temperature ? c v out ?v tpc 2. adr421 typical output voltage vs. temperature temperature ? c ?0 v out ?v 3.0010 3.0008 3.0006 3.0004 3.0002 3.0000 2.9998 2.9996 2.9994 2.9992 2.9990 ?0 20 40 80 110 125 tpc 3. ADR423 typical output voltage vs. temperature temperature ? c ?0 v out ?v 5.0025 5.0023 5.0021 5.0019 5.0017 5.0015 5.0013 5.0011 5.0009 5.0007 5.0005 ?0 20 40 80 110 125 tpc 4. adr425 typical output voltage vs. temperature input voltage ?v 0.25 4 supply current ?ma 6810 12 14 15 0.30 0.35 0.40 0.45 0.50 0.55 +125 c +25 c ?0 c tpc 5. adr420 supply current vs. input voltage input voltage ?v 0.25 4 supply current ?ma 6810 12 14 15 0.30 0.35 0.40 0.45 0.50 0.55 +125 c +25 c ?0 c tpc 6. adr421 supply current vs. input voltage
rev. c adr420/adr421/ADR423/adr425 ? input voltage ?v 4 supply current ?ma 6810 12 15 0.55 ?0 c +25 c +125 c 0.50 0.45 0.40 0.35 0.30 0.25 14 tpc 7. ADR423 supply current vs. input voltage input voltage ?v 6 supply current ?ma 81012 15 0.55 ?0 c +25 c +125 c 0.50 0.45 0.40 0.35 0.30 0.25 14 tpc 8. adr425 supply current vs. input voltage temperature ? c 0 ?0 load regulation ?ppm/ma ?0 20 50 80 110 125 10 20 30 40 50 60 70 i l = 0ma to 5ma v in = 4.5v v in = 6v tpc 9. adr420 load regulation vs. temperature temperature ? c 0 ?0 load regulation ?ppm/ma ?0 20 50 80 110 125 10 20 30 40 50 60 70 i l = 0ma to 5ma v in = 5v v in = 6.5v tpc 10. adr421 load regulation vs. temperature temperature ? c ?0 load regulation ?ppm/ma 70 60 50 40 30 20 10 0 ?0 20 40 80 110 125 i l = 0ma to 10ma v in = 7v v in = 15v tpc 11. ADR423 load regulation vs. temperature temperature ? c ?0 load regulation ?ppm/ma 35 30 25 20 15 10 5 0 ?0 20 40 80 110 125 v in = 15v i l = 0ma to 10ma tpc 12. adr425 load regulation vs. temperature
rev. c ? a dr420/adr421/ADR423/adr425 0 1 2 3 4 5 6 ?0 ?0 20 50 80 110 t emperature ? c 125 line regulation ppm/v v in = 4.5v to 15v tpc 13. adr420 line regulation vs. temperature 0 1 2 3 4 5 6 ?0 ?0 20 50 80 110 t emperature ? c l ine regulation ?ppm/v 125 v in = 5v to 15v tpc 14. adr421 line regulation vs. temperature temperature ? c ?0 line regulation ?ppm/v 9 7 5 4 3 2 1 0 ?0 20 50 80 110 v in = 5v to 15v 8 6 tpc 15. ADR423 line regulation vs. temperature temperature ? c ?0 line regulation ?ppm/v 14 10 8 6 4 2 0 ?0 20 50 80 110 v in = 7.5v to 15v 12 125 tpc 16. adr425 line regulation vs. temperature load current ?ma 0 0 differential voltage ?v 12345 0.5 1.0 1.5 2.0 2.5 ?0 c +25 c +85 c tpc 17. adr420 minimum input-output voltage differential vs. load current load current ?ma 0 0 differential voltage ? v 12345 0.5 1.0 1.5 2.0 2.5 ?0 c +25 c +125 c tpc 18. adr421 minimum input-output voltage differential vs. load current
rev. c adr420/adr421/ADR423/adr425 ? load current ?ma 0 0 differential voltage ?v 12345 0.5 1.0 1.5 2.0 2.5 ?0 c +25 c +125 c tpc 19. ADR423 minimum input-output voltage differential vs. load current load current ?ma 0 differential voltage ? v 12345 2.5 ?0 c +25 c +125 c 2.0 1.5 1.0 0.5 0 tpc 20. adr425 minimum input-output voltage differential vs. load current deviation ?ppm 0 ?00 more ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 number of parts 5 10 15 20 25 30 sample size ?160 temperature +25 c ?0 c +125 c +25 c tpc 21. adr421 typical hysteresis 1 v /div time ?1s/div tpc 22. adr421 typical noise voltage 0.1 hz to 10 hz 50 v/div time ?1s/div tpc 23. typical noise voltage 10 hz to 10 khz frequency ?hz 10 vo ltag e noise density ?nv/ hz 100 1k 10k 1k 100 10 ADR423 adr421 adr420 adr425 tpc 24. voltage noise density vs. frequency
rev. c ?0 a dr420/adr421/ADR423/adr425 time ?100 s/div c bypass = 0 f line interruption 500mv/div 500mv/div v out v in tpc 25. adr421 line transient response time ?100 s/div c bypass = 0.1 f line interruption 500mv/div 500mv/div v out v in tpc 26. adr421 line transient response time ?100 s/div c l = 0 f 1ma load 2v/div 1v/div v out load on load off tpc 27. adr421 load transient response time ?100 s/div c l = 100nf 1ma load 2v/div 1v/div v out load on load off tpc 28. adr421 load transient response time ?4 s/div c in = 0.01 f no load v out 2v/div v in 2v/div tpc 29. adr421 turn-off response time ?4 s/div c in = 0.01 f no load v out 2v/div v in 2v/div tpc 30. adr421 turn-on response
rev. c adr420/adr421/ADR423/adr425 ?1 time ?4 s/div c load = 0.01 f no input cap v out 2v/div v in 2v/div tpc 31. adr421 turn-off response time ?4 s/div c load = 0.01 f no input cap v out 2v/div v in 2v/div tpc 32. adr421 turn-on response c l = 0 time ?100 s/div c bypass = 0.1 f r l = 500 2v/div 5v/div v in v out tpc 33. adr421 turn-on/turn-off response frequency ?hz 10 100k 100 output impedance ? 1k 10k 10 5 15 20 25 30 35 40 45 50 adr425 adr420 adr421 ADR423 tpc 34. output impedance vs. frequency frequency ?hz ?0 10 1m 100 ripple rejection ?db 1k 10k 100k ?0 ?0 ?0 ?0 ?0 ?0 ?0 ?0 tpc 35. ripple rejection vs. frequency
rev. c ?2 a dr420/adr421/ADR423/adr425 theory of operation the adr42x series of references uses a new reference genera tion technique known as xfet (extra implanted junction fet). this technique yields a reference with low supply current, good thermal hysteresis, and exceptionally low noise. the core of the xfet reference consists of two junction field-effect transistors (jfet), one of which has an extra channel implant to raise its pinch-off voltage. by running the two jfets at the same drain current, the difference in pinch-off voltage can be amplified and used to form a highly stable voltage reference. the intrinsic reference voltage is around 0.5 v with a negative temperature coefficient of about ?20 ppm/ c. this slope is essentially constant to the dielectric constant of silicon and can be closely compensated by adding a correction term generated in the same fashion as the proportional-to-temperature (ptat) term used to compensate band gap references. the big advan tage over a band gap reference is that the intrinsic temperature coefficient is some 30 times lower (therefore requiring less correction), resulting in much lower noise since most of the noise of a band gap reference comes from the temperature com pensation circuitry. figure 1 shows the basic topology of the adr42x series. the temperature correction term is provided by a current source w ith a value designed to be proportional to absolute temperature. the general equation is: vgvri out p ptat = ? () ? 1 (1) where g is the gain of the reciprocal of the divider ratio, ? v p is the difference in pinch-off voltage between the two jfets, and i ptat is the positive temperature coefficient correction current. adr42x are created by on-chip adjustment of r2 and r3 to achieve 2.048 v or 2.500 v at the reference output, respectively. v in * gnd v out adr42x i ptat v out = g( v p ?r1 i ptat ) * extra channel implant v p r1 r3 r2 i 1 i 1 figure 1. simplified schematic device power dissipation considerations the adr42x family of references is guaranteed to deliver load currents to 10 ma with an input voltage that ranges from 4.5 v to 18 v. when these devices are used in applications at higher currents, users should account for the temperature effects due to the power dissipation increases with the following equation: tp t daa jj = + (2) where t j and t a are the junction and ambient temperatures, respectively, p d is the device power dissipation, and j a is the device package thermal resistance. basic voltage reference connections voltage references, in general, require a bypass capacitor connected from v out to gnd. the circuit in figure 2 illus trates the basic configuration for the adr42x family of references. other than a 0.1 f capacitor at the output to help improve noise suppression, a large output capacitor at the output is not required for circuit stability. 10 f top view (not to scale) 8 7 6 5 1 2 3 4 nic = no internal connection tp = test pin (do not connect) tp nic tp nic output adr42x 0.1 f trim 0.1 f + v in figure 2. basic voltage reference configuration noise performance the noise generated by the adr42x family of references is typi cally less than 2 v p-p over the 0.1 hz to 10 hz band for adr420, adr421, and ADR423. tpc 22 shows the 0.1 hz to 10 hz noise of the adr421, which is only 1.75 v p-p. the noise measurement is made with a band -pass filter made of a 2-pole high-pass filter with a corner frequency at 0.1 hz and a 2-pole low-pass filter with a corner frequency at 10 hz. 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 defined as the turn-on settling time. two components normally associated with this are the time for the active circuits to settle, and the time for the thermal gradients on the chip to stabilize. tpc 29 through tpc 33, inclusive, show the turn-on settling time for the adr421. applications output adjustment the adr42x trim terminal can be used to adjust the output voltage over a 0.5% range. this feature allows the system designer to trim system errors out by setting the reference to a voltage other than the nominal. this is also helpful if the part is used in a system at temperature to trim out any error. adjustment of the output has negligible effect on the temperature performance of the device. to avoid degrading temperature coefficients, both the trimming potentiometer and the two resistors need to be low temperature coefficient types, preferably <100 ppm/ c. output 10k (adr420) 15k (adr421) v o = 0.5% r1 470k r2 v in gnd v o trim adr42x input rp 10k figure 3. output trim adjustment
rev. c adr420/adr421/ADR423/adr425 ?3 reference for converters in optical network control circuits in the upcoming high capacity, all-optical router network, figure 4 employs arrays of micromirrors to direct and route optical signals from fiber to fiber, without first converting them to electrical form, which reduces the communication speed. the tiny micromechanical mirrors are positioned so that each is illuminated by a single wavelength that carries unique information and can be passed to any desired input and output fiber. the mirrors are tilted by the dual-axis actuators controlled by precision adcs and dacs within the system. due to the micro scopic movement of the mirrors, not only is the precision of the converters important, but the noise associated with these controlling converters is also extremely critical, because total noise within the system can be multiplied by the numbers of converters employed. as a result, the adr42x is necessary for this application for its excep tional low noise to maintain the stability of the control loop. control electronics preamp ampl ampl adr421 adr421 adr421 dac dac adc dsp mems mirror activator right activator left gimbal + sensor source fiber laser beam destination fiber figure 4. all-optical router network a negative precision reference without precision resistors in many current-output cmos dac applications, where the output signal voltage must be of the same polarity as the refer ence voltage, it is often required to reconfigure a current-switching dac into a voltage-switching dac through the use of a 1.25 v reference, an op amp, and a pair of resistors. using a current- switching dac directly requires the need for an additional operational amplifier at the output to reinvert the signal. a negative voltage reference is then desirable from the point that an additional operational amplifier is not required for either reinversion (current-switching mode) or amplification (voltage- switching mode) of the dac output voltage. in general, any positive voltage reference can be converted into a negative voltage reference through the use of an operational amplifier and a pair of matched resistors in an inverting configuration. the disadvan tage to that approach is that the largest single source of error in the circuit is the relative matching of the resistors used. a negative reference can easily be generated by adding a preci sion op amp and configuring as in figure 5. v out is at virtual g round and, therefore, the negative reference can be taken directly from the output of the op amp. the op amp must be dual supply, low offset, and have rail-to-rail capability if negative supply voltage is close to the reference output. +v dd ? dd ? ref v out v in gnd adr42x a1 = op777, op193 a1 4 6 2 figure 5. negative reference high voltage floating current source the circuit of figure 6 can be used to generate a floating current source with minimal self-heating. this particular configuration can operate on high supply voltages determined by the breakdown voltage of the n-channel jfet. v in gnd +v s adr42x r l 2.10k ? s 2n3904 v out sst111 vishay op90 figure 6. high voltage floating current source kelvin connections in many portable instrumentation applications, where pc board cost and area go hand-in-hand, circuit interconnects are very often of dimensionally minimum width. these narrow lines can cause large voltage drops if the voltage reference is required to provide load currents to various functions. in fact, a circuit? interconnects can exhibit a typical line resistance of 0.45 m ? / square (1 oz. cu, for example). force and sense connections, also referred to as kelvin connections, offer a convenient method of eliminating the effects of voltage drops in circuit wires. load currents flowing through wiring resistance produce an error (v error = r i l ) at the load. however, the kelvin connection of figure 7 overcomes the problem by including the wiring resistance within the forcing loop of the op amp. since the op amp senses the load voltage, op amp loop control forces the output to compensate for the wiring error and to produce the correct voltage at the load. v in gnd r lw adr42x v out force a1 v in v out r lw r l v out sense a1 = op191 2 6 4 figure 7. advantage of kelvin connection
rev. c ?4 a dr420/adr421/ADR423/adr425 dual polarity references v in v out gnd 6 2 4 adr425 u1 5 trim v in 1 f 0.1 f r1 10k +10v ?0v op1177 u2 v+ v ?v r2 10k +5v r3 5k figure 8. +5 v and ? v reference using adr425 v in v out gnd 6 2 4 adr425 u1 5 trim +10v r1 5.6k +2.5v r2 5.6k ?.5v ?0v op1177 u2 v+ v figure 9. +2.5 v and 2.5 v reference using adr425 dual polarity references can easily be made with an op amp and a pair of resistors. in order not to defeat the accuracy obtained by adr42x, it is imperative to match the resistance tolerance as well as the temperature coefficient of all the components. programmable current source ad5232 u2 digital pot a bw u2 r1 50k c2 10pf r2 a 1k r2 b 10 r2 1k c1 10pf r1 50k v in gnd 2 4 v dd v out 6 adr425 u1 5 trim load il vl v ss v dd op2177 a1 v+ v v ss v dd op2177 a2 v+ v figure 10. programmable current source together with a digital potentiometer and a howland current pump, adr425 forms the reference source for a programmable current as i rr r r v l ab b w = + ? ? ? ? ? ? 22 1 2 (3) and v d v w n ref = 2 (4) where d = decimal equivalent of the input code n = number of bits in addition, r1' and r2' must be equal to r 1 and r 2 a + r 2 b , respectively. r 2 b in theory can be made as small as needed to achieve the current needed within a2 output current driving capability. in this example, op2177 is able to deliver a maxi- mum of 10 ma. since the current pump employs both positive and negative feedback, capacitors c1 and c2 are needed to ensure the negative feedback prevails and, therefore, avoids oscillation. this circuit also allows bidirectional current flow if the inputs v a and v b of the digital potentiometer are supplied with the dual polarity references as shown previously. programmable dac reference voltage with a multichannel dac such as a quad 12-bit voltage output dac ad7398, one of its internal dacs and an adr42x voltage reference can be used as a common programmable v refx for the rest of the dacs. the circuit configuration is shown in figure 11. the relationship of v refx to v ref depends upon the digital code and the ratio of r 1 and r 2 and is given by: v v r r dr r refx ref n = + ? ? ? ? ? ? + ? ? ? ? ? ? 1 2 1 1 2 2 1 where d = decimal equivalent of input code and n = number of bits v ref = applied external reference v refx = reference voltage for dac a to d (5)
rev. c adr420/adr421/ADR423/adr425 ?5 table ii. v refx vs. r1 and r2 v in daca v refa v outa dacb v refb v outb dacc v refc v outc dacd v refd v outd ad7398 adr425 r1 0.1% r2 0.1% v ref v ob = v refx (d b ) v oc = v refx (d c ) v od = v refx (d d ) figure 11. programmable dac reference precision voltage reference for data converters the adr42x family has a number of features that make it ideal for use with adcs and dacs converters. the exceptional low noise, tight temperature coefficient, and high accuracy charac- teristics make the adr42x ideal for low noise applica tions such as cellular base station applications. another example of adc for which the adr421 is also well-suited is the ad7701. figure 12 shows the adr421 used as the precision reference for this converter. the ad7701 is a 16-bit adc with on-chip digital filtering in tended for the measurement of w ide dynamic range and low frequency signals such as those representing chemical, physical, or biological processes. it contains a charge- balancing (sigma-delta) adc, calibration microcontroller with on-chip static ram, clock oscillator, and serial communications port. v in gnd adr42x 0.1 f sc1 v out mode clkout 0.1 f 10 f 0.1 f 0.1 f 0.1 f 0.1 f10 f ad7701 ?v analog supply a gnd a in av ss cal bp/ up v ref av dd dv ss dgnd sc2 clkin sclk sdata drdv cs sleep dv dd data ready read (transmit) serial clock serial clock +5v analog supply analog ground analog input calibrate ranges select figure 12. voltage reference for 16-bit adc ad7701 precision boosted output regulator a precision voltage output with boosted current capability can be realized with the circuit shown in figure 13. in this circuit, u2 forces v o to be equal to v ref by regulating the turn on of n1, therefore, the load current will be furnished by v in . in this configuration, a 50 ma load is achievable at v in of 5 v. moderate heat will be generated on the mosfet and higher current can be achieved with a replacement of the larger device. in addition, for heavy capacitive load with step input, a buffer may be added at the output to enhance the transient response. ad8601 v in v o r l 25 n1 2u1 v in gnd 4 5 6 u2 2n7002 5v v+ v adr421 v out trim + figure 13. precision boosted output regulator r1, r2 digital code v ref r1 =r 2 0000 0000 0000 2 v ref r1 =r 2 1000 0000 0000 1.3 v ref r1 =r 2 1111 1111 1111 v ref r1 = 3r2 0000 0000 0000 4 v ref r1 = 3r2 1000 0000 0000 1.6 v ref r1 = 3r2 1111 1111 1111 v ref
rev. c ?6 c02432??/03(c) printed in u.s.a. adr420/adr421/ADR423/adr425 8-lead standard small outline package [soic] narrow body (r-8) dimensions shown in millimeters and (inches) 0.25 (0.0098) 0.19 (0.0075) 1.27 (0.0500) 0.41 (0.0160) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 85 4 1 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.33 (0.0130) coplanarity 0.10 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-012aa 8-lead microsoic package [msop] (rm-8) dimensions shown in millimeters 0.23 0.08 0.80 0.40 8 0 85 4 1 4.90 bsc pin 1 0.65 bsc 3.00 bsc seating plane 0.15 0.00 0.38 0.22 1.10 max 3.00 bsc compliant to jedec standards mo-187aa coplanarity 0.10 revision history location page 1/03?ata sheet changed from rev. b to rev. c. changed mini_soic to msop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . universal changes to ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 corrections to y-axis labels in tpcs 21 and 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 enhancement to figure 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 updated outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3/02?ata sheet changed from rev. a to rev. b. edits to ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 deletion of precision voltage regulator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 addition of precision boosted output regulator section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 addition of figure 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 data sheet changed from rev. 0 to rev. a. addition of ADR423 and adr425 to adr420/adr421 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . universal outline dimensions

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