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low noise, micropower 5.0 v precision voltage reference adr293 rev. b 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 ?2007 analog devices, inc. all rights reserved. features 6.0 v to 15 v supply range supply current: 15 a maximum low noise: 15 v p-p typical (0.1 hz to 10 hz) high output current: 5 ma temperature range: ?40c to +125c pin-compatible with the ref02/ref19x applications portable instrumentation precision reference for 5 v systems adc and dac reference solar-powered applications loop-current powered instruments pin configurations nc 1 v in 2 nc 3 gnd 4 nc 8 nc 7 v out 6 nc 5 nc = no connect adr293 top view (not to scale) 00164-001 figure 1. 8-lead narrow body soic (r-8) top view (not to scale) 1 2 3 4 adr293 v in nc gnd nc 8 7 6 5 nc v out nc nc nc = no connect 00164-002 figure 2. 8-lead tssop (ru-8) general description the adr293 is a low noise, micropower precision voltage reference that utilizes an xfet? (extra implanted junction fet) reference circuit. the xfet architecture offers significant performance improvements over traditional band gap and buried zener-based references. improvements include one quarter the voltage noise output of band gap references operating at the same current, very low and ultralinear temperature drift, low thermal hysteresis, and excellent long- term stability. the adr293 is a series voltage reference providing stable and accurate output voltage from a 6.0 v supply. quiescent current is only 15 a maximum, making this device ideal for battery powered instrumentation. three electrical grades are available offering initial output accuracy of 3 mv, 6 mv, and 10 mv. temperature coefficients for the three grades are 8 ppm/c, 15 ppm/c, and 25 ppm/c maximum. line regulation and load regulation are typically 30 ppm/v and 30 ppm/ma, respectively, maintaining the references overall high performance. the adr293 is specified over the extended industrial temperature range of C40c to +125c. this device is available in the 8-lead soic and 8-lead tssop packages. table 1. adr29x products device output voltage (v) initial accuracy (%) temperature coefficient (ppm/c max) adr291 2.500 0.08, 0.12, 0.24 8, 15, 25 adr292 4.096 0.07, 0.10, 0.15 8, 15, 25 adr293 5.000 0.06, 0.12, 0.20 8, 15, 25
adr293 rev. b | page 2 of 16 table of contents features .............................................................................................. 1 applications....................................................................................... 1 pin configurations ........................................................................... 1 general description ......................................................................... 1 revision history ............................................................................... 2 specifications..................................................................................... 3 electrical specificiations.............................................................. 3 absolute maximum ratings............................................................ 5 thermal resistance ...................................................................... 5 esd caution.................................................................................. 5 typical performance characteristics ............................................. 6 terminology ...................................................................................... 9 theory of operation ...................................................................... 10 device power dissipation considerations.............................. 10 basic voltage reference connections ..................................... 10 noise performance ..................................................................... 10 turn-on time ............................................................................ 10 applications..................................................................................... 11 a negative precision reference without precision resistors....................................................................................... 11 a precision current source ...................................................... 11 kelvin connections.................................................................... 11 voltage regulator for portable equipment ............................. 12 outline dimensions ....................................................................... 13 ordering guide .......................................................................... 14 revision history 6/07rev. a to rev. b updated format..................................................................universal changes to table 1............................................................................ 1 updated outline dimensions ....................................................... 13 changes to ordering guide .......................................................... 13 3/01rev. 0 to rev. a
adr293 rev. b | page 3 of 16 specifications electrical specificiations v s = 6.0 v, t a = 25c, unless otherwise noted. table 2. parameter symbol conditions min typ max unit output voltage v out i out = 0 ma e grade 4.997 5.000 5.003 v f grade 4.994 5.000 5.006 v g grade 4.990 5.000 5.010 v initial accuracy i out = 0 ma e grade C3 +3 mv 0.06 % f grade C6 +6 mv 0.12 % g grade C10 +10 mv 0.20 % line regulation v out /v in 6.0 v to 15 v, i out = 0 ma e, f grades 30 100 ppm/v g grade 40 150 ppm/v load regulation v out /i load v s = 6.0 v, 0 ma to 5 ma e, f grades 30 100 ppm/ma g grade 40 150 ppm/ma long-term stability v out after 1000 hours of operation @ 125c 50 ppm noise voltage e n 0.1 hz to 10 hz 15 v p-p wideband noise density e n at 1 khz 640 nv/hz v s = 6.0 v, t a = ?25c to +85c, unless otherwise noted. table 3. parameter symbol conditions min typ max unit temperature coefficient tcv out i out = 0 ma e grade 3 8 ppm/c f grade 5 15 ppm/c g grade 10 25 ppm/c line regulation v out /v in 6.0 v to 15 v, i out = 0 ma e, f grades 35 150 ppm/v g grade 50 200 ppm/v load regulation v out /i load v s = 6.0 v, 0 ma to 5 ma e, f grades 20 150 ppm/ma g grade 30 200 ppm/ma
adr293 rev. b | page 4 of 16 v s = 6.0 v, t a = ?40c to +125c, unless otherwise noted. table 4. parameter symbol conditions min typ max unit temperature coefficient tcv out i out = 0 ma e grade 3 10 ppm/c f grade 5 20 ppm/c g grade 10 30 ppm/c line regulation v out /v in 6.0 v to 15 v, i out = 0 ma e, f grades 40 200 ppm/v g grade 70 250 ppm/v load regulation v out /i load v s = 6.0 v, 0 ma to 5 ma e, f grades 20 200 ppm/ma g grade 30 300 ppm/ma supply current i s @ 25c 11 15 a 15 20 a thermal hysteresis v out-hys 8-lead soic_n 72 ppm 8-lead tssop 157 ppm
adr293 rev. b | page 5 of 16 absolute maximum ratings table 5. 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 worst-case conditions; that is, ja is specified for device in socket testing. in practice, ja is specified for a device soldered in circuit board. table 6. thermal resistance package type ja jc unit 8-lead soic_n (r-8) 158 43 c/w 8-lead tssop (ru-8) 240 43 c/w esd caution
adr293 rev. b | page 6 of 16 typical performance characteristics 5.006 5.004 5.002 5.000 4.998 4.996 4.994 output vol t age (v) ?50 ?25 0 25 50 75 100 125 temperature (c) v s = 6v 3 typical parts 00164-003 figure 3. v out vs. temperature 16 14 12 10 8 6 4 2 0 supply current (a) 0 2 4 6 8 10 12 14 16 input voltage (v) t a = +125c t a = +25c t a = ?40c 00164-004 figure 4. supply current vs. input voltage v s = 6v 16 14 12 10 8 6 supply current (a) ?50 ?25 0 25 50 75 100 125 temperature (c) 00164-005 figure 5. supply current vs. temperature 100 80 60 40 20 0 line regul a tion (ppm/v) ?50 ?25 0 25 50 75 100 125 temperature (c) v s = 6v to 15v 00164-006 figure 6. line regulation vs. temperature 100 80 60 40 20 0 line regul a tion (ppm/v) ?50 ?25 0 25 50 75 100 125 temperature (c) v s = 6v to 9v 00164-007 i out = 0ma figure 7. line regulation vs. temperature 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 differenti a l voltage (v) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 load current (ma) 00164-008 t a = +125c t a = +25c t a = ?40c figure 8. minimum input/output vo ltage differential vs. load current
adr293 rev. b | page 7 of 16 200 160 120 80 40 0 load regul a tion (ppm/ma) ?50 ?25 0 25 50 75 100 125 temperature (c) 00164-009 v s = 6v i out = 5ma i out = 1ma figure 9. load regulation vs. temperature 2 1 0 ?1 ?2 ?3 ?4 v out from nomin a l (mv) 10 100 1k sourcing load current (ma) 00164-010 t a = +125c t a = +25c t a = ?40c figure 10. v out from nominal vs. load current 1200 1000 800 600 400 200 0 10 100 1k frequency (hz) 00164-011 voltage noise density (nv/ hz) v in = 15v t a = 25c figure 11. voltage noise density 120 100 80 60 40 20 0 ripple rejection (db) 10 100 1k frequency (hz) 00164-012 v s = 6v figure 12. ripple rejection vs. frequency 50 40 30 20 10 0 output impedance ( ? ) v s = 6v i l = 0ma 10 100 1k 10k frequency (hz) 00164-013 figure 13. output im pedance vs. frequency 10v p-p 00164-014 1s/div figure 14. 0.1 hz to 10 hz noise
adr293 rev. b | page 8 of 16 0 0164-015 50s/div i l = 5ma 2v/div 5v/div figure 15. turn-on time 00164-016 50s/div i l = 5ma 2v/div 5v/div figure 16. turn-off time 00164-017 1ms/div i l = 5ma figure 17. load transient 00164-018 1ms/div i i = 5ma c l = 1nf figure 18. load transient 00164-019 1ms/div i i = 5ma c l = 100nf figure 19. load transient 18 16 14 12 10 8 6 4 2 0 frequency in number of units ?200 ?160 ?120 ?80 ?40 0 40 80 120 160 200 240 v out deviation (ppm) temperature +25c ?40c +85c +25c 00164-020 figure 20. typical hyster esis for adr29x product
adr293 rev. b | page 9 of 16 terminology 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 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 microvolts per milliampere, parts per million per milliampere, or ohms of dc output resistance. long-term stability typical shift of output voltage of 25c on a sample of parts subjected to high temperature operating life test of 1000 hours at 125c. ( ) () 1 out 0 out out tvtvv ? = [] () () () 6 10 ppm ? = 0 out 1 out 0 out out tv tvtv v where: v out (t 0 ) = v o ut at 25c at time 0. v out (t 1 ) = v o ut at 25c after 1000 hours operation at 125c. nc = no connect there are in fact connections at nc pins, which are reserved for manufacturing purposes. users should not connect anything at nc pins. temperature coefficient the change of output voltage over the operating temperature change and normalized by the output voltage at 25c, expressed in ppm/c. [] () ( ) () () 6 10 cppm/ ? ? = 12 out 1 out 2 out out ttc25v tvv vtc where: v out (25c) = v out at 25c. v out (t 1 ) = v o ut at temperature 1. v out (t 2 ) = v o ut at temperature 2. thermal hysteresis thermal hysteresis is defined as the change of output voltage after the device is cycled through temperatures from +25c to C40c to +85c 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 ppm ? = ? ? c25v vc25v v out tcout out hysout where: v out (25c) = v out at 25c. v out-tc = v out (25c) after temperature cycle at +25c to C40c to +85c and back to +25c.
adr293 rev. b | page 10 of 16 theory of operation the adr293 uses a new reference generation technique known as xfet, which yields a reference with low noise, low supply current, and very low thermal hysteresis. the core of the xfet reference consists of two junction field effect transistors, 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 C120 ppm/k. this slope is essentially locked to the dielectric constant of silicon and can be closely compen- sated 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 advantage over a band gap reference is that the intrinsic temperature coefficient is some 30 times lower (therefore, less correction is needed) and this results in much lower noise, because most of the noise of a band gap reference comes from the temperature compensation circuitry. the simplified schematic in figure 21 shows the basic topology of the adr293. the temperature correction term is provided by a current source with value designed to be proportional to absolute temperature. the general equation is () () r3i r1 r3r2r1 vv ptat p out + ? ? ? ? ? ? ++ = where: v p is the difference in pinch-off voltage between the two fets. i ptat is the positive temperature coefficient correction current. the process used for the xfet reference also features vertical npn and pnp transistors, the latter of which are used as output devices to provide a very low dropout voltage. v out v in i ptat gnd r1 r2 r3 i 1 i 1 1 1 extra channel implant v out = ? v p + i ptat r3 r1 + r2 + r3 r1 ? v p 00164-021 figure 21. simpli fied schematic device power dissipation considerations the adr293 is guaranteed to deliver load currents to 5 ma with an input voltage that ranges from 5.5 v to 15 v. when this device is used in applications with large input voltages, care should be exercised to avoid exceeding the published specifications for maximum power dissipation or junction temperature that could result in premature device failure. the following formula should be used to calculate a devices maximum junction temperature or dissipation: ja a j d tt p ? = where: t j and t a are the junction temperature and ambient temperature, respectively. p d is the device power dissipation. ja is the device package thermal resistance. basic voltage reference connections references, in general, require a bypass capacitor connected from the v out pin to the gnd pin. the circuit in figure 22 illustrates the basic configuration for the adr293. note that the decoupling capacitors are not required for circuit stability. nc nc nc nc v out nc 0.1f 0.1f 10f + nc = no connect 1 2 3 4 8 7 6 5 00164-022 adr293 figure 22. basic voltage reference configuration noise performance the noise generated by the adr293 is typically less than 15 v p-p over the 0.1 hz to 10 hz band. the noise measure- ment 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. figure 15 shows the typical turn-on time for the adr293.
adr293 rev. b | page 11 of 16 applications 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 reference voltage, it is often required to reconfigure a current- switching dac into a voltage-switching dac by using 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. therefore, a negative voltage reference is 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 by using an operational amplifier and a pair of matched resistors in an inverting configuration. the disadvantage to that approach is that the largest single source of error in the circuit is the relative matching of the resistors used. the circuit illustrated in figure 23 avoids the need for tightly matched resistors with the use of an active integrator circuit. in this circuit, the output of the voltage reference provides the input drive for the integrator. to maintain circuit equilibrium, the integrator adjusts its output to establish the proper relationship between the references v out and gnd. one caveat with this approach should be mentioned. although rail-to-rail output amplifiers work best in the application, these operational amplifiers require a finite amount (mv) of headroom when required to provide any load current. the choice for the circuits negative supply should take this issue into account. a1 100 ? +5v ?5v 1k? 1f 100k ? ?v ref 1f v out gnd v in adr293 2 6 4 00164-023 a1 = 1/2 op291, 1/2 op295 figure 23. a negative precision voltage reference uses no precision resistors a precision current source many times in low power applications, the need arises for a precision current source that can operate on low supply voltages. as shown in figure 24 , the adr293 is configured as a precision current source. the circuit configuration illustrated is a floating current source with a grounded load. the output voltage of the reference is bootstrapped across r set , which sets the output current into the load. with this configuration, circuit precision is maintained for load currents in the range from the references supply current, typically 15 a to approximately 5 ma. 1f v out gnd v in adr293 i out r l i sy adjust r1 p1 r set 2 6 4 00164-024 figure 24. a precision 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 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 flowing through wiring resistance produce an error (v error = r i l ) at the load. however, the kelvin connection in figure 25 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. a1 1f 100k ? +v out sense v in r lw r l r lw +v out force v out gnd v in adr293 2 6 4 0 0164-025 figure 25. advantage of kelvin connection
adr293 rev. b | page 12 of 16 voltage regulator for portable equipment the adr293 is ideal for providing a stable, low cost, and low power reference voltage in portable equipment power supplies. figure 26 shows how the adr293 can be used in a voltage regulator that not only has low output noise (as compared to switch mode design) and low power, but also a very fast recovery after current surges. some precautions should be taken in the selection of the output capacitors. too high an esr (effective series resistance) could endanger the stability of the circuit. a solid tantalum capacitor, 16 v or higher, and an aluminum electrolytic capacitor, 10 v or higher, are recom- mended for c1 and c2, respectively. in addition, the path from the ground side of c1 and c2 to the ground side of r1 should be kept as short as possible. adr293 v out gnd v in 0.1f lead-acid battery + 6v charger input r1 402k ? 1% c1 68f tant c2 1000f elect r2 402k ? 1% ++ 5v, 100ma irf9530 r3 510k ? op20 2 6 2 7 6 4 3 4 00164-026 figure 26. voltage regulator for portable equipment
adr293 rev. b | page 13 of 16 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-a a 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 27. 8-lead standard small outline package [soic_n] narrow body (r-8) dimensions shown in millimeters and (inches) 8 5 41 pin 1 0.65 bsc seating plane 0.15 0.05 0.30 0.19 1.20 max 0.20 0.09 8 0 6.40 bsc 4.50 4.40 4.30 3.10 3.00 2.90 coplanarit y 0.10 0.75 0.60 0.45 compliant to jedec standards mo-153-aa figure 28. 8-lead thin shrink small outline package [tssop] (ru-8) dimensions shown in millimeters
adr293 rev. b | page 14 of 16 ordering guide model output voltage (v) initial accuracy (%) temperature coefficient (ppm/c max) temperature range package description package option ordering quantity adr293er 5.00 0.06 8 ?40c to +125c 8-lead soic_n r-8 98 adr293er-reel 5.00 0.06 8 ?40c to +125c 8-lead soic_n r-8 2,500 adr293erz 1 5.00 0.06 8 ?40c to +125c 8-lead soic_n r-8 98 adr293erz-reel 1 5.00 0.06 8 ?40c to +125c 8-lead soic_n r-8 2,500 adr293fr 5.00 0.12 15 ?40c to +125c 8-lead soic_n r-8 98 adr293frz 1 5.00 0.12 15 ?40c to +125c 8-lead soic_n r-8 98 adr293gr 5.00 0.20 25 ?40c to +125c 8-lead soic_n r-8 98 adr293gr-reel7 5.00 0.20 25 ?40c to +125c 8-lead soic_n r-8 1,000 adr293grz 1 5.00 0.20 25 ?40c to +125c 8-lead soic_n r-8 98 adr293grz-reel7 1 5.00 0.20 25 ?40c to +125c 8-lead soic_n r-8 1,000 adr293gru 5.00 0.20 25 ?40c to +125c 8-lead tssop ru-8 96 adr293gru-reel 5.00 0.20 25 ?40c to + 125c 8-lead tssop ru-8 2,500 adr293gru-reel7 5.00 0.20 25 ?40c to +125c 8-lead tssop ru-8 1,000 adr293gruz 1 5.00 0.20 25 ?40c to +125c 8-lead tssop ru-8 96 adr293gruz-reel 1 5.00 0.20 25 ?40c to +125c 8-lead tssop ru-8 2,500 adr293gruz-reel7 1 5.00 0.20 25 ?40c to +125c 8-lead tssop ru-8 1,000 1 z = rohs compliant part.
adr293 rev. b | page 15 of 16 notes
adr293 rev. b | page 16 of 16 notes ?2007 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. c00164-0-6/07(b)

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