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rev. a adr370 * precision low power 2.048 v sot-23 voltage reference 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. * protected by u.s.patent no. 5,969,657; other patents pending. pin configuration 3-lead sot-23 1 3 2 v in v out adr370 gnd table i. adr370 products output initial temperature voltage accuracy coefficent products (v o ) (mv) (%) (ppm/ c) adr370brt-reel7 2.048 4 0.2 50 adr370art-reel7 2.048 10 0.5 100 features initial accuracy: 4 mv max initial accuracy error: 0.2% low tcvo: 50 ppm/ c max from ?0 c to +125 c, 30 ppm/ c max from +25 c to +70 c load regulation: 200 v/ma, 100 ppm/ma line regulation: 25 v/v, 20 ppm/v wide operating range: v in = 2.3 v to 15 v low power: 72 a max high output sink/source current: 5 ma min wide temperature range: ?0 c to +125 c tiny 3-lead sot-23 package with standard pinout applications battery-powered instrumentation portable medical instruments data acquisition systems industrial process control systems automotive general description the adr370 is a low cost, 3-terminal (series) band-gap voltage reference featuring high accuracy, high stability, and low power consumption packaged in a tiny 3-lead sot-23 package. precise matching and thermal tracking of on-chip components, as well as patented temperature drift curvature correction design techniques, have been employed to ensure that the adr370 provides an accurate 2.048 v output. this micropowered, low dropout voltage device will source or sink up to 5 ma of load current while providing a stable 2.048 v output. the compact footprint, high accuracy, and an operating range of 2.3 v to 12 v make the adr370 ideal for use in 3 v and 5 v systems where there may be wide variations in supply voltage and a need to minimize power dissipation. the adr370 is offered in a and b grades; all devices are specified over the extended industrial range of C 40 c to +125 c.
rev. a ? adr370?pecifications electrical characteristics parameter symbol conditions min typ max unit output voltage (@ 25 c) v o 2.044 2.048 2.052 v initial accuracy error a grade v oerr C 10 +10 mv v oerr C 0.5 +0.5 % b grade v oerr C 4+4mv v oerr C 0.2 +0.2 % output voltage temperature drift a grade tcv o C 40 c to +125 c 100 ppm/ c b grade tcv o C 40 c to +125 c50 ppm/ c tcv o 25 c to 70 c30 ppm/ c supply headroom v in C v out 200 mv load regulation 0 ma < i out < 5 ma @ 25 c C 0.200 +0.200 mv/ma C 3 ma < i out < 0 ma @ 25 c C 0.480 +0.480 mv/ma C 0.1 ma < i out < +0.1 ma C 0.425 +0.425 mv/ma line regulation v out 200 mv < v in < 15 v 20 ppm/v i out = 0 ma ripple rejection ? v out / ? v in v in = 5 v 100 mv (f = 120 hz) 80 db quiescent current 72 a short-circuit current to ground 15 a noise voltage (@ 25 c) 0.1 hz to 10 hz 70 v p-p 10 hz to 10 khz 50 v rms turn-on settling time c l = 0.2 f 100 s long term stability 1,000 hours @ 25 c 100 ppm/1,000 hrs output voltage hysteresis 115 ppm temperature range C 40 +125 c * guaranteed by characterization. specifications subject to change without notice. (t a = t min to t max , v in = 5 v, unless otherwise noted.)
rev. a adr370 ? absolute maximum ratings * supply voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 v storage temperature range rt package . . . . . . . . . . . . . . . . . . . . . . . . C 65 c to +125 c operating temperature range . . . . . . . . . . . C 40 c to +125 c lead temperature range soldering, 60 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 c infrared, 15 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 c * absolute maximum ratings apply at 25 c, unless otherwise noted. 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 adr370 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. ordering guide output initial temperature number voltage accuracy coefficient package package of parts temperature model (v o )( mv) (%) (ppm/ c) description option branding per reel range ADR370BRT-R2 2.048 4 0.5 50 sot-23 3-lead rpb 250 C 40 c to +125 c adr370brt-reel7 2.048 4 0.2 50 sot-23 3-lead rpb 3,000 C 40 c to +125 c adr370art-r2 2.048 10 0.5 100 sot-23 3-lead rpa 250 C 40 c to +125 c adr370art-reel7 2.048 10 0.5 100 sot-23 3-lead rpa 3,000 C 40 c to +125 c package type ja jc unit 3-sot-23 (rt) 220 102 c/w
rev. a ? adr370?ypical performance characteristics load ?ma 12 ? ? 5 ? ? v o mv ? ? 01234 10 4 2 0 ? 8 6 ?0 c +125 c +25 c tpc 1. load regulation vs. load current temperature ? c 2.048 2.036 ?0 output voltage ?v 45 125 2.038 2.040 2.042 2.044 2.046 v in = 5v v in = 15v tpc 2. output voltage vs. temperature temperature ? c 80 20 ?0 supply current a 45 125 30 40 50 60 70 v in = 5v v in = 15v tpc 3. supply current vs. temperature temperature ? c 6 ?0 ?0 line regulation ?ppm/v 45 125 ? 0 4 v in 5v to 15v ? ? ? 2 tpc 4. line regulation vs. temperature time ?0.1s/div 0 0 0 00 0 vo ltag e ?10 v/div 00000000 0 0 0 0 0 0 tpc 5. voltage noise 0.1 hz to 10 hz time ?0.1s/div 0 0 0 00 0 vo ltag e ?200 v/div 00000000 0 0 0 0 0 0 tpc 6. voltage noise 10 hz to 100 khz
rev. a adr370 ? time ?100 s/div 0 0 0 00 0 vo ltag e v 00000000 0 0 0 0 0 0 v out = 1v/div v in = 5v/div c by = 0.1 f c load = 0.22 f tpc 7. turn-on response time ?100 s/div 0 0 0 00 0 vo ltag e v 00000000 0 0 0 0 0 0 v out = 1v/div v in = 5v/div r load = 1k tpc 8. turn-off response time ?100 s/div 0 0 0 00 0 vo ltag e v 00000000 0 0 0 0 0 0 v in = 1v/div v out = 1v/div c l = 0.1 f tpc 9. line transient response time ?100ms/div 0 0 0 00 0 vo ltag e v 00000000 0 0 0 0 0 0 v out = 20mv/div v in = 2v/div c by = 0.1 f c load = 0.1 f tpc 10. load transient response
rev. a ? adr370 parameter definitions temperature coefficient temperature coefficient is the change of output voltage with respect to operating temperature changes, normalized by the output voltage at 25 c. this parameter is expressed in ppm/ c and can be determined with the following equation tcv ppm c vt vt vctt o oo o ? ? ? ? ? ? = () ? () () ? () 21 21 6 25 10 (1) 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 line regulation is the change in output voltage due to a specified change in input voltage. this parameter accounts for 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 load regulation is the change in output voltage due to a specified change in load current. this parameter accounts for 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 long term stability is the typical shift of output voltage at 25 c on a sample of parts subjected to a test of 1,000 hours at 25 c. ? ? vvtvt v ppm vt vt vt oo o o oo o = () ? () [] = () ? () () 01 01 0 6 10 (2) where: v o (t 1 ) = v o at 25 c at time 0. v o (t 2 ) = v o at 25 c after 1,000 hours operation at 25 c. thermal hysteresis thermal hysteresis is defined as the change of output voltage after the device is cycled through temperature from +25 c to C 40 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 (3) w here: v o ( 25 c) = v o at 25 c. v o_tc = v o at 25 c after temperature cycle at +25 c to C 40 c to +125 c and back to +25 c. theory of operation the adr370 uses the band-gap concept to produce a stable, low temperature coefficient voltage reference suitable for high accuracy data acquisition components and systems. this device makes use of underlying temperature characteristics of a silicon transistor s base-emitter voltage (v be ) in the forward biased operating region. under this condition, all such transistors have a C 2 mv/ c temperature coefficient (tc) and a v be that, when extrapolated to absolute zero, 0 k, (with collector current pro- portional to absolute temperature) approximates the silicon band-gap voltage. by summing a voltage that has an equal and opposite temperature coefficient of 2 mv/ c with a v be of a forward biased transistor, an almost zero tc reference can be developed. the simplified circuit diagram in figure 1 shows how a compensating voltage, v1, is achieved by driving two transistors at different current densities and amplifying the resultant v be difference ( ? v be , which has a positive tc). the sum (v bg ) of v be and v1 is then buffered and amplified to produce a stable reference voltage of 2.048 v at the output. v in v out gnd v ds r5 r6 r4 r3 r2 r1 v1 figure 1. simplified schematic applying the adr370 in order to achieve the specified performance, two external components should be used in conjunction with the adr370, a 4.7 f capacitor and a 1 f capacitor should be applied to the input and output, respectively. figure 2 shows the adr370 with both the input and output capacitors attached. for further transient response optimization, an additional 0.1 f capacitor in parallel with the 4.7 f input capacitor can be used. a 1 f output capacitor will provide stable performance for all loading conditions. the adr370 can, however, operate under low ( C 100 a < i out < +100 a) current conditions with just a 0.2 f output capacitor and a 1 f input capacitor. c in v in adr370 gnd 4.7 f c out v out 1 f figure 2. typical connection diagram
rev. a adr370 ? applications low cost negative reference a low cost negative reference can be obtained by leveraging the current sinking capability of the adr370. simply tying the v out terminal to ground and adding a bias resistor, r set , to the gnd pin of the device, a negative voltage reference can be obtained as shown in figure 3. r set should be chosen such that i set remains between 1 ma to 5 ma. v in v dd v ss r set i set adr370 v out gnd ?ref figure 3. low cost negative reference precision negative reference without using any matching resistors, a precision negative reference can be obtained using the configuration shown in figure 4. the voltage difference between v out and gnd of the adr370 is 2.048 v. since v out is at virtual ground, u2 will close the loop by forcing the gnd pin to be the negative reference node. u2 should be a low offset voltage precision op amp, such as the op1177. v in +15v u2 u1 2.3v to 12v op1177 ?5v adr370 v out gnd ?ref figure 4. precision negative reference low cost current source figure 5 illustrates how a simple, low cost current source can be configured using the adr370. the load current, i l , is simply the sum of i set and the quiescent current, i q . i set is simply the reference voltage generated by the adr370 divided by r set . i v r set set = 2 048 . (4) the quiescent current, i q , varies slightly with load. the variation in i q limits the use of this circuit to general-purpose applications. v in v l + 2.5v < v dd < v l + 12v adr370 v out gnd i set = r set r set v l r l i l i q = 65 a 2.048v figure 5. low cost current source precision current source with adjustable output a precision current source can be implemented with the circuit shown in figure 6. by adding a mechanical or digital potenti- ometer, this circuit becomes an adjustable current source. if a digital potentiometer like the ad5201 is used, the load current is simply the voltage across terminals b-to-w of the digital potentiometer divided by r set . i vd r l ref set = 256 (5) where d is the decimal equivalent of the digital potentiometer input code. v in +12v a b w ?.048v to v l 0v to (2.048v + v l ) 12v op1177 ad5201 ?2v adr370 v out gnd v l r l r set i l figure 6. programmable 0 ma to 5 ma current source to optimize the resolution of this circuit, dual supply op amps should be used because the ground potential of adr370 can swing from C 2.048 v at zero scale to v l at full scale of the po tentiometer setting.
rev. a ? adr370 12-bit precision programmable current source by replacing the potentiometer in figure 6 with a 12-bit precision dac like the ad5322, a higher precision programmable current source can be achieved. figure 7 illustrates the implementation of this circuit. the load current can be determined with the following equation. i vd r l ref set = ? () 1 4096 (6) the compliance voltage should be kept low so that the supply voltage to u2, between v dd and gnd, does not fall below 2.5 v. v in u1 u2 +5v v+ v 1 11 u3 2 3 vref (1 ?d2/n) +5v op1177 ad5322 ?v adr370 v out gnd +5v v l r l r set t ol 0.05% i l v in v dd v o gnd figure 7. 12-bit programmable current source precision boosted output regulator a precision voltage output with boosted current can be realized with the circuit shown in figure 8. in this circuit, v o is maintained by the adr370 at 2.048 v. the adr370 sources a maximum of 5 ma if the load current, i l , is more than 5 ma, current is furnished by the transistor, q1, and the input voltage supply v dd . v in r1 10k r l i l adr370 v out gnd v dd q1 2n3906 4v to 12v figure 8. precision boosted output regulator q1 will be turned on to regulate current as needed. r1 is required to bias the base of q1 and must be large enough to comply with the supply current requirements of the adr370. the supply voltage can be as low as 4 v. the maximum current output of this circuit is limited by the power dissipation of the bipolar transistor, q1. pv i diss dd l =? () 2 048 . (7) using the 2n3906 pnp transistor shown in figure 8 and a 4 v power supply, r l should be chosen so that a maximum of 100 ma is drawn from the circuit, which limits the power dissipation of q1 to ~200 mw.
rev. a adr370 ? tape and reel dimensions dimensions shown in millimeters. 2.80 2.70 2.60 1.10 1.00 0.90 0.35 0.30 0.25 4.10 4.00 3.90 1.55 1.50 1.50 8.30 8.00 7.70 3.20 3.10 2.90 2.05 2.00 1.95 1.85 1.75 1.65 3.55 3.50 3.45 0.75 min direction of unreeling 1.00 min 13.20 13.00 12.80 9.90 8.40 8.40 20.20 min 1.50 min 7" reel 100.00 or 13" reel 330.00 7" reel 50.00 min or 13" reel 100.00 min 14.40 max outline dimensions 3-lead small outline transistor package [sot-23-3] (rt-3) dimensions shown in millimeters. 3.04 2.90 2.80 pin 1 1.40 1.30 1.20 2.64 2.10 1.90 bsc 1 2 3 seating plane 1.12 0.89 0.10 0.01 0.50 0.30 0.20 0.08 0.60 0.50 0.40 0.95 bsc compliant to jedec standards to-236ab
rev. a ?0 adr370 revision history location page 7/03?ata sheet changed from rev. 0 to rev. a. updated features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 updated table i . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 updated electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 updated absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 updated ordering guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 updated parameter definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 updated outline dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
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