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ultraprecision, low noise, 2.048 v/2.500 v/ 3.00 v/5.00 v xfet ? voltage references adr420/adr421/adr423/adr425 rev. i 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 ?2001C2011 analog devices, inc. all rights reserved. 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: ?40c to +125c applications precision data acquisition systems high resolution converters battery-powered instrumentation portable medical instruments industrial process control systems precision instruments optical network control circuits pin configuration 02432-001 nic = no internal connection tp = test pin (do not connect) adr420/ adr421/ adr423/ adr425 top view (not to scale) tp 1 v in 2 nic 3 gnd 4 tp 8 nic 7 v out 6 trim 5 figure 1. 8-lead soic, 8-lead msop general description the adr42x are a series of ultraprecision, second generation extra implanted junction fet (xfet) voltage references featuring low noise, high accuracy, and excellent long-term stability in soic and msop footprints. patented temperature drift curvature correction technique and xfet 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 and the stable and accurate characteristics of the adr42x make them ideal for precision conversion applications such as optical networks and medical equipment. the adr42x trim terminal can also be used to adjust the out- put 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 ?40c to +125c. devices have 8-lead soic or 30% smaller, 8-lead msop packages. adr42x products table 1. initial accuracy model output voltage, v out (v) mv % temperature coefficient (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, 0.13 3, 10 adr425 5.00 2, 6 0.04, 0.12 3, 10
adr420/adr421/adr423/adr425 rev. i | page 2 of 24 table of contents features .............................................................................................. 1 ? applications....................................................................................... 1 ? pin configuration............................................................................. 1 ? general description ......................................................................... 1 ? adr42x products............................................................................. 1 ? revision history ............................................................................... 2 ? specifications..................................................................................... 3 ? adr420 electrical specifications............................................... 3 ? adr421 electrical specifications............................................... 4 ? adr423 electrical specifications............................................... 5 ? adr425 electrical specifications............................................... 6 ? absolute maximum ratings............................................................ 7 ? thermal resistance ...................................................................... 7 ? esd caution.................................................................................. 7 ? pin configurations and function descriptions ........................... 8 ? typical performance characteristics ............................................. 9 ? terminology .................................................................................... 15 ? theory of operation ...................................................................... 16 ? device power dissipation considerations.............................. 16 ? basic voltage reference connections ..................................... 16 ? noise performance ..................................................................... 16 ? turn-on time ............................................................................ 16 ? applications..................................................................................... 17 ? output adjustment .................................................................... 17 ? reference for converters in optical network control circuits......................................................................................... 17 ? high voltage floating current source .................................... 17 ? kelvin connections.................................................................... 18 ? dual-polarity references........................................................... 18 ? programmable current source ................................................ 19 ? programmable dac reference voltage .................................. 19 ? precision voltage reference for data converters.................. 20 ? precision boosted output regulator ....................................... 20 ? outline dimensions ....................................................................... 21 ? ordering guide .......................................................................... 22 ? revision history 5/11rev. h to rev. i added endnote 1 in table 2............................................................ 4 added endnote 1 in table 3............................................................ 5 added endnote 1 in table 4............................................................ 6 added endnote 1 in table 5............................................................ 7 deleted a negative precision reference without precision resistors section ............................................................................. 17 deleted figure 42; renumbered sequentially ............................ 17 updated outline dimensions ....................................................... 21 changes to ordering guide .......................................................... 22 6/07rev. g to rev. h changes to table 2............................................................................ 3 changes to table 3............................................................................ 4 changes to table 4............................................................................ 5 changes to table 5............................................................................ 6 updated outline dimensions ....................................................... 21 changes to ordering guide .......................................................... 22 6/05rev. f to rev. g changes to table 1............................................................................ 1 changes to ordering guide .......................................................... 22 2/05rev. e to rev. f updated format..................................................................universal updated outline dimensions ....................................................... 21 changes to ordering guide .......................................................... 22 7/04rev. d to rev. e changes to ordering guide .............................................................5 3/04rev. c to rev. d changes to table i .............................................................................1 changes to ordering guide .............................................................4 updated outline dimensions....................................................... 16 1/03rev. 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 3/02rev. 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 10/01rev. 0 to rev. a addition of adr423 and adr425 to adr420/adr421...............................................................universal 5/01revision 0: initial version
adr420/adr421/adr423/adr425 rev. i | page 3 of 24 specifications adr420 electrical specifications v in = 5.0 v to 15.0 v, t a = 25c, unless otherwise noted. table 2. parameter symbol conditions min typ max unit output voltage v out a grade 2.045 2.048 2.051 v b grade 2.047 2.048 2.049 v initial accuracy 1 v outerr a grade ?3 +3 mv ?0.15 +0.15 % b grade ?1 +1 mv ?0.05 +0.05 % temperature coefficient tcv out ?40c < t a < +125c a grade 2 10 ppmc b grade 1 3 ppm/c supply voltage headroom v in ? v out 2 v line regulation ?v out /?v in v in = 5 v to 18 v, ?40c < t a < +125c 10 35 ppm/v load regulation ?v out /?i l i l = 0 ma to 10 ma, ?40c < t a < +125c 70 ppm/ma quiescent current i in no load 390 500 a ?40c < t a < +125c 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 out 1000 hours 50 ppm output voltage hysteresis v out_hys 40 ppm ripple rejection ratio rrr f in = 1 khz ?75 db short circuit to gnd i sc 27 ma 1 initial accuracy does not include shift due to solder heat effect.
adr420/adr421/adr423/adr425 rev. i | page 4 of 24 adr421 electrical specifications v in = 5.0 v to 15.0 v, t a = 25c, unless otherwise noted. table 3. parameter symbol conditions min typ max unit output voltage v out a grade 2.497 2.500 2.503 v b grade 2.499 2.500 2.501 v initial accuracy 1 v outerr a grade ?3 +3 mv ?0.12 +0.12 % b grade ?1 +1 mv ?0.04 +0.04 % temperature coefficient tcv out ?40c < t a < +125c a grade 2 10 ppm/c b grade 1 3 ppm/c supply voltage headroom v in ? v out 2 v line regulation ?v out /?v in v in = 5 v to 18 v, ?40c < t a < +125c 10 35 ppm/v load regulation ?v out /?i l i l = 0 ma to 10 ma, ?40c < t a < +125c 70 ppm/ma quiescent current i in no load 390 500 a ?40c < t a < +125c 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 out 1000 hours 50 ppm output voltage hysteresis v out_hys 40 ppm ripple rejection ratio rrr f in = 1 khz ?75 db short circuit to gnd i sc 27 ma 1 initial accuracy does not include shift due to solder heat effect.
adr420/adr421/adr423/adr425 rev. i | page 5 of 24 adr423 electrical specifications v in = 5.0 v to 15.0 v, t a = 25c, unless otherwise noted. table 4. parameter symbol conditions min typ max unit output voltage v out a grade 2.996 3.000 3.004 v b grade 2.9985 3.000 3.0015 v initial accuracy 1 v outerr a grade ?4 +4 mv ?0.13 +0.13 % b grade ?1.5 +1.5 mv ?0.04 +0.04 % temperature coefficient tcv out ?40c < t a < +125c a grade 2 10 ppm/c b grade 1 3 ppm/c supply voltage headroom v in ? v out 2 v line regulation ?v out /?v in v in = 5 v to 18 v, ?40c < t a < +125c 10 35 ppm/v load regulation ?v out /?i l i l = 0 ma to 10 ma, ?40c < t a < +125c 70 ppm/ma quiescent current i in no load 390 500 a ?40c < t a < +125c 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 out 1000 hours 50 ppm output voltage hysteresis v out_hys 40 ppm ripple rejection ratio rrr f in = 1 khz ?75 db short circuit to gnd i sc 27 ma 1 initial accuracy does not include shift due to solder heat effect.
adr420/adr421/adr423/adr425 rev. i | page 6 of 24 adr425 electrical specifications v in = 7.0 v to 15.0 v, t a = 25c, unless otherwise noted. table 5. parameter symbol conditions min typ max unit output voltage v out a grade 4.994 5.000 5.006 v b grade 4.998 5.000 5.002 v initial accuracy 1 v outerr a grade ?6 +6 mv ?0.12 +0.12 % b grade ?2 +2 mv ?0.04 +0.04 % temperature coefficient tcv out a grade ?40c < t a < +125c 2 10 ppm/c b grade 1 3 ppm/c supply voltage headroom v in ? v o 2 v line regulation ?v o /?v in v in = 7 v to 18 v, ?40c < t a < +125c 10 35 ppm/v load regulation ?v o /?i l i l = 0 ma to 10 ma, ?40c < t a < +125c 70 ppm/ma quiescent current i in no load 390 500 a ?40c < t a < +125c 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 1000 hours 50 ppm output voltage hysteresis v o_hys 40 ppm ripple rejection ratio rrr f in = 1 khz ?75 db short circuit to gnd i sc 27 ma 1 initial accuracy does not include shift due to solder heat effect.
adr420/adr421/adr423/adr425 rev. i | page 7 of 24 absolute maximum ratings these ratings apply at 25c, unless otherwise noted. table 6. parameter rating supply voltage 18 v output short-circuit duration to gnd indefinite storage temperature range ?65c to +150c operating temperature range ?40c to +125c junction temperature range ?65c to +150c lead temperature (soldering, 60 sec) 300c 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. thermal resistance ja is specified for the worst-case conditions, that is, ja is specified for devices soldered in the circuit board for surface- mount packages. table 7. package type ja unit 8-lead msop (rm) 190 c/w 8-lead soic (r) 130 c/w esd caution
adr420/adr421/adr423/adr425 rev. i | page 8 of 24 pin configurations and function descriptions 02432-002 nic = no internal connection tp = test pin (do not connect) adr420/ adr421/ adr423/ adr425 top view (not to scale) tp 1 v in 2 nic 3 gnd 4 tp 8 nic 7 v out 6 trim 5 figure 2. 8-lead soic, 8-lead msop pin configuration table 8. pin function descriptions pin no. mnemonic description 1, 8 tp test pin. there are actual connections in tp pins, but they are reserved for factory testing purposes. users should not connect anything to tp pins; otherwise, the device may not function properly. 2 v in input voltage. 3, 7 nic no internal connect. nics have no internal connections. 4 gnd ground pin = 0 v. 5 trim trim terminal. it can be used to adjust the output volt age over a 0.5% range without affecting the temperature coefficient. 6 v out output voltage.
adr420/adr421/adr423/adr425 rev. g | page 9 of 24 typical performance characteristics ?40 ?10 20 50 80 125 110 02432-004 temperature (c) v out (v) 2.0495 2.0493 2.0491 2.0489 2.0487 2.0485 2.0483 2.0481 2.0479 2.0477 2.0475 figure 3. adr420 typical output voltage vs. temperature ?40 ?10 20 50 80 125 110 02432-005 temperature (c) v out (v) 2.4995 2.4997 2.4999 2.5001 2.5003 2.5005 2.5007 2.5009 2.5011 2.5013 2.5015 figure 4. adr421 typical output voltage vs. temperature ?40 ?10 20 50 80 125 110 02432-006 temperature (c) 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 figure 5. adr423 typical output voltage vs. temperature ?40 ?10 20 50 80 125 110 02432-007 temperature (c) 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 figure 6. adr425 typical output voltage vs. temperature 4681012 14 02432-008 input voltage (v) supply current (ma) 0.55 0.50 0.45 0.40 0.35 0.30 0.25 15 +125c +25c ?40c figure 7. adr420 supply current vs. input voltage 4681012 14 02432-009 input voltage (v) supply current (ma) 0.55 0.50 0.45 0.40 0.35 0.30 0.25 +125c +25c ?40c 15 figure 8. adr421 supply current vs. input voltage
adr420/adr421/adr423/adr425 rev. i | page 10 of 24 4 6 8 10 12 1514 02432-010 input voltage (v) supply current (ma) 0.55 0.50 0.45 0.40 0.35 0.30 0.25 +125c +25c ?40c figure 9. adr423 supply current vs. input voltage 6 8 10 12 15 14 02432-011 input voltage (v) supply current (ma) 0.55 0.50 0.45 0.40 0.35 0.30 0.25 +125c +25c ?40c figure 10. adr425 supply current vs. input voltage ?40 ?10 20 50 80 110 125 02432-012 temperature (c) load regulation (ppm/ma) 70 50 60 40 30 20 10 0 i l = 0ma to 5ma v in = 4.5v v in = 6v figure 11. adr420 load regulation vs. temperature ?40 ?10 20 50 80 110 125 02432-013 temperature (c) load regulation (ppm/ma) 70 50 60 40 30 20 10 0 i l = 0ma to 5ma v in = 6.5v v in = 5v figure 12. adr421 load regulation vs. temperature ?40 ?10 20 50 80 110 125 02432-014 temperature (c) load regulation (ppm/ma) 70 50 60 40 30 20 10 0 i l = 0ma to 10ma v in = 15v v in = 7v figure 13. adr423 load regulation vs. temperature ?40 ?10 20 50 80 110 125 02432-015 temperature (c) load regulation (ppm/ma) 35 25 30 20 15 10 5 0 v in = 15v i l = 0ma to 10ma figure 14. adr425 load regulation vs. temperature
adr420/adr421/adr423/adr425 rev. i | page 11 of 24 ?40 ?10 20 50 80 110 125 02432-016 temperature (c) line regulation (ppm/v) 6 4 5 3 2 1 0 v in = 4.5v to 15v figure 15. adr420 line regulation vs. temperature ?40 ?10 20 50 80 110 125 02432-017 temperature (c) line regulation (ppm/v) 6 4 5 3 2 1 0 v in = 5v to 15v figure 16. adr421 line regulation vs. temperature ?40 ?10 20 50 80 110 02432-018 temperature (c) line regulation (ppm/v) 9 6 8 4 5 7 3 2 1 0 v in = 5v to 15v figure 17. adr423 line regulation vs. temperature ?40 ?10 20 50 80 110 125 02432-019 temperature (c) line regulation (ppm/v) 14 10 12 8 6 4 2 0 v in = 7.5v to 15v figure 18. adr425 line regulation vs. temperature 01234 02432-020 load current (ma) differential voltage (v) 2.5 2.0 1.5 1.0 0.5 0 ?40c +85c +25c 5 5 figure 19. adr420 minimum input/output voltage differential vs. load current 01234 02432-021 load current (ma) differential voltage (v) 2.5 2.0 1.5 1.0 0.5 0 ?40c +125c +25c figure 20. adr421 minimum input/output voltage differential vs. load current
adr420/adr421/adr423/adr425 rev. i | page 12 of 24 5 01234 02432-022 load current (ma) differential voltage (v) 2.5 2.0 1.5 1.0 0.5 0 ?40c +125c +25c figure 21. adr423 minimum input/output voltage differential vs. load current 01234 02432-023 load current (ma) differential voltage (v) 2.5 2.0 1.5 1.0 0.5 0 ?40c +125c +25c 5 figure 22. adr425 minimum input/output voltage differential vs. load current ?100 ?90 ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 more 02432-024 deviation (ppm) number of parts 30 20 25 15 10 5 0 sample size ? 160 temperature +25c ?40c +125c +25c figure 23. adr421 typical hysteresis 02432-025 time (1s/div) 1v/div figure 24. adr421 typical noise voltage 0.1 hz to 10 hz 02432-026 time (1s/div) 50v/div figure 25. typical noise voltage 10 hz to 10 khz 02432-027 frequency (hz) voltage noise density (nv/ hz) adr423 adr421 adr420 adr425 10 100 10 100 1k 1k 10k figure 26. voltage noise density vs. frequency
adr420/adr421/adr423/adr425 rev. i | page 13 of 24 02432-028 time (100s/div) 500mv/div line interruption 500mv/div c bypass = 0f v in v out figure 27. adr421 line transient response, no c bypass 02432-029 time (100s/div) 500mv/div line interruption 500mv/div c bypass = 0.1f v in v out figure 28. adr421 line transient response, c bypass = 0.1 f 02432-030 time (100s/div) 2v/div 1v/div c l = 0f load on load off v out 1ma load figure 29. adr421 load transient response, no c l 02432-031 time (100s/div) 2v/div 1v/div c l = 100nf load on load off v out 1ma load figure 30. adr421 load transient response, c l = 100 nf 02432-032 time (4s/div) 2v/div v in 2v/div v out c in = 0.01f no load figure 31. adr421 turn-off response 02432-033 time (4s/div) 2v/div 2v/div c in = 0.01f no load v in v out figure 32. adr421 turn-on response
adr420/adr421/adr423/adr425 rev. i | page 14 of 24 02432-034 time (4s/div) 2v/div 2v/div c l = 0.01f no input cap v in v out figure 33. adr421 turn-off response 02432-035 time (4s/div) 2v/div 2v/div c l = 0.01f no input cap v in v out figure 34. adr421 turn-on response 02432-036 time (100s/div) 2v/div 5v/div v in v out c bypass = 0.1f r l = 500 ? c l = 0 figure 35. adr421 turn-on/turn-off response adr425 adr420 adr421 adr423 10 100 1k 10k 100k 02432-037 frequency (hz) output impedance ( ? ) 50 45 40 35 30 25 20 15 10 5 0 figure 36. output im pedance vs. frequency 10 100 10k 1k 100k 1m 02432-038 frequency (hz) ripple rejection (db) 0 ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 ?100 figure 37. ripple rejection vs. frequency
adr420/adr421/adr423/adr425 rev. i | page 15 of 24 terminology temperature coefficient the change of output voltage over the operating temperature range is normalized by the output voltage at 25c, and expressed in ppm/c as () () () () () 6 10 / ? ? = 12 out 1 out 2 out out ttc25v tvtv cppm tcv where: v out ( 25c ) = v out at 25c. v out ( t 1 ) = v out at temperature 1. v out ( t 2 ) = v out 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 million per milliampere, or ohms of dc output resistance. long-term stability typical shift of output voltage at 25c on a sample of parts subjected to operation life test of 1000 hours at 125c. () () 1 out 0 out out tvtvv ? = () () () () 6 10 ? = 0 out 1 out 0 out out tv tvtv ppmv where: v out ( t 0 ) = v out at 25c at time 0. v out ( t 1 ) = v out at 25c after 1000 hours operation at 125c. thermal hysteresis the change of output voltage after the device is cycled through temperatures from +25c to ?40c to +125c and back to +25c. this is a typical value from a sample of parts put through such a cycle. ( ) tcout out hysout vc25v v _ _ ? = () () () 6 _ _ 10 ? = c25v vc25v ppm v out tcout out hysout where: v out ( 25c ) = v out at 25c. v out_tc = v out at 25 c after temperature cycle at +25c to ?40c to +125c and back to +25c. 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 improves transient response in applications where the supply suddenly changes. an addi- tional 0.1 f capacitor in parallel also helps to reduce noise from the supply. output capacitor the adr42x do not need output capacitors for stability under any load condition. an output capacitor, typically 0.1 f, filters out any low level noise voltage and does not affect the operation of the part. on the other hand, the load transient response can be improved with an additional 1 f to 10 f output capacitor in parallel. a capacitor here acts as a source of stored energy for sudden increase in load current. the only parameter that degrades by adding an output capacitor is the turn-on time, which depends on the size of the selected capacitor.
adr420/adr421/adr423/adr425 rev. i | page 16 of 24 theory of operation the adr42x series of references uses a reference generation 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 having 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 about 0.5 v with a negative temperature coefficient of about ?120 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 primary advantage over a band gap reference is that the intrinsic tem- perature coefficient is approximately 30 times lower (therefore requiring less correction). this results in much lower noise because most of the noise of a band gap reference comes from the temperature compensation circuitry. figure 38 shows the basic topology of the adr42x series. the temperature correction term is provided by a current source with a value designed to be proportional to absolute tempera- ture. the general equation is v out = g ( v p ? r1 i ptat ) (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. i ptat is the positive temperature coefficient correction current. each adr42x device is created by on-chip adjustment of r2 and r3 to achieve the specified reference output. 02432-039 * r3 gnd *extra channel implant v out = g( ? v p ? r1 i ptat ) r2 i ptat ? v p r1 v in v out adr420/adr421/ adr423/adr425 i 1 i 1 figure 38. simpli fied 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, the following equation should be used to account for the temperature effects due to power dissipation increases: t j = p d ja + t a (2) where: t j and t a are the junction temperature and the ambient temperature, respectively. p d is the device power dissipation. ja 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 39 illustrates 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. 02432-040 nic = no internal connection tp = test pin (do not connect) adr420/ adr421/ adr423/ adr425 top view (not to scale) tp 1 v in 2 nic 3 4 tp 8 nic 7 output 6 trim 5 0.1f 0.1f 10f + figure 39. basic voltage reference configuration noise performance the noise generated by adr42x references is typically less than 2 v p-p over the 0.1 hz to 10 hz band for the adr420, adr421, and adr423. figure 24 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 at power-up (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 typi- cally associated with this are the time for the active circuits to settle and the time for the thermal gradients on the chip to stabilize. figure 31 to figure 35 show the turn-on settling time for the adr421.
adr420/adr421/adr423/adr425 rev. i | page 17 of 24 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 a 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. 02432-041 adr420/ adr421/ adr423/ adr425 r2 v in input gnd trim r1 470k ? r p 10k ? 10k ? (adr420) 15k ? (adr421) output v out = 0.5% v out 2 4 5 6 figure 40. output trim adjustment reference for converters in optical network control circuits in the high capacity, all optical router network of figure 41 , arrays of micromirrors direct and route optical signals from fiber to fiber, without first converting them to electrical form, which reduces the communication speed. the tiny micro- mechanical 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 analog-to-digital converters (adcs) and digital-to-analog converters (dacs) within the system. due to the microscopic movement of the mirrors, not only is the precision of the converters important, but the noise associated with these controlling converters is extremely critical, because total noise within the system can be multiplied by the numbers of converters used. consequently, the exceptional low noise of the adr42x is necessary to maintain the stability of the control loop for this application. 02432-042 dac dac adc dsp control electronics activator left laser beam source fiber gimbal + sensor destination fiber activator right mems mirror ampl preamp ampl adr421 adr421 adr421 figure 41. all optical router network high voltage floating current source the circuit in figure 42 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. 0 2432-044 + v s ?v s sst111 vishay v in gnd v out adr420/ adr421/ adr423/ adr425 2n3904 r l 2.10k ? op09 2 4 6 figure 42. high voltage floating current source
adr420/adr421/adr423/adr425 rev. i | page 18 of 24 kelvin connections in many portable instrumentation applications where pc board cost and area are important considerations, circuit intercon- nects are often narrow. these narrow lines can cause large voltage drops if the voltage reference is required to provide load currents to various functions. in fact, a circuits 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 flow- ing through wiring resistance produce an error (v error = r i l ) at the load. however, the kelvin connection in figure 43 overcomes the problem by including the wiring resistance within the forcing loop of the op amp. because 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. 02432-045 a1 v in v in r lw a1 = op191 r lw r l v out sense v out force gnd v out adr420/ adr421/ adr423/ adr425 2 4 6 figure 43. advantage of kelvin connection dual-polarity references dual-polarity references can easily be made with an op am p and a pair of resistors. in order not to defeat the accuracy obtained by the adr42x, it is imperative to match the resistance toler- ance and the temperature coefficient of all components. 02432-046 v in 1f 0.1f r1 10k ? r3 5k ? r2 10k ? +5v ?5v +10v ?10v 6 2 4 5 v+ v? u1 adr425 v out v in trim gnd figure 44. +5 v and ?5 v reference using adr425 u2 op1177 02432-047 r1 5.6k ? r2 5.6k ? +2.5 v + 10 v ?10v ?2.5v u1 adr425 6 2 4 5 v+ v? v out v in trim gnd u2 op1177 figure 45. +2.5 v and ?2.5 v reference using adr425
adr420/adr421/adr423/adr425 rev. i | page 19 of 24 programmable current source together with a digital potentiometer and a howland current pump, the adr425 forms the reference source for a program- mable current as w b b a l v r2 r1 r2r2 i ? ? ? ? ? ? + = (3) and ref n v d vw = 2 (4) where: d is the decimal equivalent of the input code. n is the number of bits. 02432-048 u1 adr425 v out v in v dd v dd v ss trim gnd a wb u2 ad5232 u2 digital pot il v+ v? 2 5 6 4 a1 op2177 v dd v ss v+ v? a2 op2177 load vl r1 50k ? r2 a 1k ? r2 b 10 ? c2 10pf r2' 1k ? r1' 50k ? c1 10pf figure 46. programmable current source r1' and r2' must be equal to r1 and r2 a + r2 b , respectively. theoretically, r2 b can be made as small as needed to achieve the current needed within a2 output current driving capability. in the example shown in figure 46 , op2177 is able to deliver a maximum of 10 ma. because the current pump uses both positive and negative feedback, capacitors c1 and c2 are needed to ensure that negative feedback prevails and, therefore, avoiding 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 previously shown. programmable dac reference voltage with a multichannel dac, such as the quad, 12-bit voltage output ad7398 , one of its internal dacs, and an adr42x voltage reference can be used as a common programmable v ref x for the rest of the dacs. the circuit configuration is shown in figure 47 . the relationship of v ref x to v ref depends on the digital code and the ratio of r1 and r , and is given by ? ? ? ? ? ? + ? ? ? ? ? ? + = r1 r2d r1 r2 v xv n ref ref 2 1 1 (5) where: d is the decimal equivalent of input code. n is the number of bits. v ref is the applied external reference. v ref x is the reference voltage for dacs a to d. table 9. v ref x vs. r1 and r2 r1, r2 digital code v ref r1 = r2 0000 0000 0000 2 v ref r1 = r2 1000 0000 0000 1.3 v ref r1 = r2 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 02432-049 v in daca dacb dacc dacd ad7398 adr425 v ref v ref a v out a r1 0.1% r2 0.1% v ob = v ref x (d b ) v oc = v ref x (d c ) v od = v ref x (d d ) v out b v out c v out d v ref b v ref c v ref d figure 47. programmable dac reference
adr420/adr421/adr423/adr425 rev. i | page 20 of 24 precision voltage reference for data converters precision boosted output regulator a precision voltage output with boosted current capability can be realized with the circuit shown in figure 49 . in this circuit, u2 forces v out to be equal to v ref by regulating the turn on of n1. therefore, the load current is furnished by v in . in this configuration, a 50 ma load is achievable at v in of 5 v. moderate heat is generated on the mosfet, and higher current can be achieved by replacing the larger device. in addition, for a heavy capacitive load with step input, a buffer may be added at the output to enhance the transient response. the adr42x family has a number of features that make it ideal for use with adcs and dacs. the exceptionally low noise, tight temperature coefficient, and high accuracy characteristics make the adr42x ideal for low noise applications such as cellular base station applications. ad7701 is an example of an adc that is well suited for the adr42x. the adr421 is used as the precision reference for the converter in figure 48 . the ad7701 is a 16-bit adc with on-chip digital filtering intended for measuring wide dynamic range and low frequency signals, such as those representing chemical, physical, or biological processes. it contains a charge- balancing (-) adc, calibration microcontroller with on-chip static ram, clock oscillator, and serial communications port. 02432-051 v in v out r l 25 ? n1 5 6 u1 2 4 u2 ad8601 5v 2n7002 v+ v? + ? adr421 v in v out trim gnd 02432-050 ad7701 adr420/ adr421/ adr423/ adr425 v in av dd dv dd sleep mode drdy cs sclk sdata data ready read (transmit) serial clock serial clock clkin clkout sc1 sc2 dgnd dv ss v ref bp/up cal a in agnd av ss 0.1f 0.1f 10f +5v analog supply ranges select calibrate analog input analog ground ?5v analog supply gnd v out 0.1f 0.1f 0.1f 0.1f 10f figure 49. precision bo osted output regulator figure 48. voltage reference for 16-bit adc ad7701
adr420/adr421/adr423/adr425 rev. i | page 21 of 24 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-012-aa 012407-a 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 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) 4 1 85 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2441) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 figure 50. 8-lead standard small outline package [soic_n] narrow body (r-8) dimensions shown in millimeters and (inches) compliant to jedec standards mo-187-aa 6 0 0.80 0.55 0.40 4 8 1 5 0.65 bsc 0.40 0.25 1.10 max 3.20 3.00 2.80 coplanarity 0.10 0.23 0.09 3.20 3.00 2.80 5.15 4.90 4.65 pin 1 identifier 15 max 0.95 0.85 0.75 0.15 0.05 10-07-2009-b figure 51. 8-lead mini small outline package [msop] (rm-8) dimensions shown in millimeters
adr420/adr421/adr423/adr425 rev. i | page 22 of 24 ordering guide initial accuracy model 1 output voltage, v out (v) mv % temperature coefficient (ppm/c) temperature range package description package option branding adr420arz 2.048 3 0.15 10 ?40c to +125c 8-lead soic_n r-8 adr420arz-reel7 2.048 3 0.15 10 ?40c to +125c 8-lead soic_n r-8 adr420armz 2.048 3 0.15 10 ?40c to +125c 8-lead msop rm-8 l0c adr420armz-reel7 2.048 3 0.15 10 ?40c to +125c 8-lead msop rm-8 l0c adr420brz 2.048 1 0.05 3 ?40c to +125c 8-lead soic_n r-8 adr420brz-reel7 2.048 1 0.05 3 ?40c to +125c 8-lead soic_n r-8 adr421ar 2.50 3 0.12 10 ?40c to +125c 8-lead soic_n r-8 adr421arz 2.50 3 0.12 10 ?40c to +125c 8-lead soic_n r-8 adr421arz-reel7 2.50 3 0.12 10 ?40c to +125c 8-lead soic_n r-8 adr421armz 2.50 3 0.12 10 ?40c to +125c 8-lead msop rm-8 r06 adr421armz-reel7 2.50 3 0.12 10 ?40c to +125c 8-lead msop rm-8 r06 adr421br 2.50 1 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr421br-reel7 2.50 1 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr421brz 2.50 1 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr421brz-reel7 2.50 1 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr423arz 3.00 4 0.13 10 ?40c to +125c 8-lead soic_n r-8 adr423arz-reel7 3.00 4 0.13 10 ?40c to +125c 8-lead soic_n r-8 adr423armz 3.00 4 0.13 10 ?40c to +125c 8-lead msop rm-8 r0u adr423armz-reel7 3.00 4 0.13 10 ?40c to +125c 8-lead msop rm-8 r0u adr423brz 3.00 1.5 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr423brz-reel7 3.00 1.5 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr425arz 5.00 6 0.12 10 ?40c to +125c 8-lead soic_n r-8 ADR425ARZ-REEL7 5.00 6 0.12 10 ?40c to +125c 8-lead soic_n r-8 adr425armz 5.00 6 0.12 10 ?40c to +125c 8-lead msop rm-8 r7a# adr425armz-reel7 5.00 6 0.12 10 ?40c to +125c 8-lead msop rm-8 r7a# adr425br 5.00 2 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr425br-reel7 5.00 2 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr425brz 5.00 2 0.04 3 ?40c to +125c 8-lead soic_n r-8 adr425brz-reel7 5.00 2 0.04 3 ?40c to +125c 8-lead soic_n r-8 1 z = rohs compliant part. # denotes rohs-compliant product may be top or bottom marked.
adr420/adr421/adr423/adr425 rev. i | page 23 of 24 notes
adr420/adr421/adr423/adr425 rev. i | page 24 of 24 notes ?2001C2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d02432-0-5/11(i) ?2001C2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d02432-0-5/11(i)

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