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1.25 v micropower, precision shunt voltage reference adr1581 rev. 0 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. pin configuration features wide operating range: 60 a to 10 ma nc = no connect top view v + 1 v ? 2 nc (or v?) 3 adr1581 06672-001 initial accuracy: 0.12% maximum temperature drift: 50 ppm/c maximum output impedance: 0.5 maximum wideband noise (10 hz to 10 khz): 20 v rms operating temperature range: ?40c to +85c high esd rating figure 1. sot-23 4 kv human body model 0 2 4 6 8 10 12 14 16 18 20 temperature drift (ppm/c) quantity ?20 ?10 0 10 20 06672-002 400 v machine model compact, surface-mount sot-23 package applications portable, battery-powered equipment cellular phones, notebook computers, pdas, gpss, and dmms computer workstations suitable for use with a wide range of video ramdacs smart industrial transmitters pcmcia cards automotive 3 v/5 v, 8-bit to 12-bit data converters general description figure 2. reverse voltage temperature drift distribution the adr1581 1 is a low cost, 2-terminal (shunt), precision band gap reference. it provides an accurate 1.250 v output for input currents between 60 a and 10 ma. 0 10 20 30 40 50 60 70 80 90 100 output error (mv) quantity ?5 ?4 ?3 ?2 ?1 0 1 2 3 4 5 06672-003 the superior accuracy and stability of the adr1581 is made possible by the precise matching and thermal tracking of on- chip components. proprietary curvature correction design techniques have been used to minimize the nonlinearities in the voltage output temperature characteristics. the adr1581 is stable with any value of capacitive load. the low minimum operating current makes the adr1581 ideal for use in battery-powered 3 v or 5 v systems. however, the wide operating current range means that the adr1581 is extremely versatile and suitable for use in a wide variety of high current applications. figure 3. reverse voltage error distribution the adr1581 is available in two grades, a and b, both of which are provided in the sot-23 package. both grades are specified over the industrial temperature range of ?40c to +85c. 1 protected by u.s. patent no. 5,969,657; other patents pending.
adr1581 rev. 0 | page 2 of 12 table of contents features .............................................................................................. 1 applications....................................................................................... 1 general description ......................................................................... 1 pin configuration............................................................................. 1 revision history ............................................................................... 2 specifications..................................................................................... 3 absolute maximum ratings............................................................ 4 esd caution.................................................................................. 4 typical performance characteristics ............................................. 5 theory of operation ........................................................................ 6 applying the adr1581................................................................ 6 temperature performance............................................................6 voltage output nonlinearity vs. temperature ..........................7 reverse voltage hysteresis...........................................................7 output impedance vs. frequency ...............................................8 noise performance and reduction .............................................8 turn-on time ...............................................................................8 transient response .......................................................................9 precision micropower low dropout reference .......................9 using the adr1581 with 3 v data converters ..................... 10 outline dimensions ....................................................................... 11 ordering guide .......................................................................... 12 revision history 5/07revision 0: initial version
adr1581 rev. 0 | page 3 of 12 specifications t a = 25c, i in = 100 a, unless otherwise noted. table 1. adr1581a adr1581b parameter min typ max min typ max unit reverse voltage output (sot-23) 1.240 1.250 1.260 1.2485 1.250 1.2515 v reverse voltage temperature drift ?40c to +85c 100 50 ppm/c minimum operating current, t min to t max 60 60 a reverse voltage change with reverse current 60 a < i in < 10 ma, t min to t max 2.5 6 2.5 6 mv 60 a < i in < 1 ma, t min to t max 0.8 0.8 mv dynamic output impedance (?v r /i r ) i in = 1 ma 100 a (f = 120 hz) 0.4 1 0.4 0.5 output noise rms noise voltage: 10 hz to 10 khz 20 20 v rms low frequency noise voltage: 0.1 hz to 10 hz 4.5 4.5 v p-p turn-on settling time to 0.1% 1 5 5 s output voltage hysteresis 2 80 80 v temperature range specified performance, t min to t max ?40 +85 ?40 +85 c operating range 3 ?55 +125 ?55 +125 c 1 measured with a no load capacitor. 2 output hysteresis is defined as the change in the +25c output voltage after a temperature excursion to ?40c, then to +85c, and back to +25c. 3 the operating temperature range is defined as the temperature extremes at which the device continues to function. parts may de viate from their specified performance.
adr1581 rev. 0 | page 4 of 12 absolute maximum ratings table 2. parameter rating 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. reverse current 25 ma forward current 20 ma internal power dissipation 1 sot-23 (rt) 0.3 w storage temperature range ?65c to +150c operating temperature range adr1581/rt ?55c to +125c esd caution lead temperature, soldering vapor phase (60 sec) 215c infrared (15 sec) 220c esd susceptibility 2 human body model 4 kv machine model 400 v 1 specification is for device (sot- 23 package) in free air at 25c: ja = 300c/w. 2 the human body model is a 100 pf ca pacitor discharged through 1.5 k. for the machine model, a 200 pf capacitor is discharged directly into the device.
adr1581 rev. 0 | page 5 of 12 typical performance characteristics 2000 1500 1000 500 0 ?500 ?1000 ?1500 reverse voltage change (ppm) ?55 ?35 ?15 5 25 45 65 85 105 125 temperature (c) 20ppm/c 5ppm/c 06672-004 100 80 60 40 20 0 reverse current (a) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 reverse voltage (v) +125c +25c ?40c 06672-007 figure 7. reverse current vs. reverse voltage figure 4. output drift for different temperature characteristics 7 6 5 4 3 2 1 0 ?1 reverse voltage change (mv) 0.01 0.10 1.00 10 reverse current (ma) +85c +25c ?40c 06672-005 1 0.8 0.6 0.4 0.2 0 forward voltage (a) 0.01 0.1 1 10 100 forward current (ma) 06672-008 +85c +25c ?40c figure 8. forward voltage vs. forward current figure 5. output voltage error vs. reverse current frequency (hz) 600 200 400 noise voltage (nv/ hz) 1.0 10 100 1k 10k 100k 1m 06672-006 figure 6. noise spectral density
adr1581 rev. 0 | page 6 of 12 theory of operation the adr1581 uses the band gap concept to produce a stable, low temperature coefficient voltage reference suitable for high accuracy data acquisition components and systems. the device makes use of the underlying physical nature of a silicon transistor base emitter voltage in the forward-biased operating region. all such transistors have an approximately ?2 mv/c temperature coefficient, which is unsuitable for use directly as a low tc reference; however, extrapolation of the temperature characteristic of any one of these devices to absolute zero (with collector current proportional to absolute temperature) reveals that its v be goes to approximately the silicon band gap voltage. therefore, if a voltage could be developed with an opposing temperature coefficient to sum with v be , a zero tc reference would result. the adr1581 circuit in figure 11 shows a typical connection of the adr1581brt operating at a minimum of 100 a. this connection can provide 1 ma to the load while accommodating 10% power supply variations. v s i r + i l r s v out i l v r i r 0 6672-010 figure 10. typical connection diagram figure 9 provides such a compensating voltage, v1, by driving two transistors at different current densities and amplifying the resultant v be difference (v be ), which has a positive tc. the sum of v be and v1 provides a stable voltage reference. +5v(+3v) 10% 2.94k ? (1.30k ? ) r s v r v out 0 6672-011 v + v? v1 v be v be 06672-009 figure 11. typical connection diagram temperature performance the adr1581 is designed for reference applications where stable temperature performance is important. extensive temperature testing and characterization ensure that the devices performance is maintained over the specified temperature range. some confusion exists in the area of defining and specifying refer- ence voltage error over temperature. historically, references have been characterized using a maximum deviation per degree celsius, for example, 50 ppm/c. however, because of nonlinearities in temperature characteristics that originated in standard zener references (such as s type characteristics), most manufacturers now use a maximum limit error band approach to specify devices. this technique involves the measurement of the output at three or more temperatures to guarantee that the voltage falls within the given error band. the proprietary curvature correction design techniques used to minimize the adr1581 nonlinearities allow the temperature performance to be guaranteed using the maximum deviation method. this method is more useful to a designer than one that simply guarantees the maximum error band over the entire temperature change. figure 9. sche matic diagram applying the adr1581 the adr1581 is simple to use in virtually all applications. to operate the adr1581 as a conventional shunt regulator (see figure 10 ), an external series resistor is connected between the supply voltage and the adr1581. for a given supply voltage, the series resistor, r s , determines the reverse current flowing through the adr1581. the value of r s must be chosen to accommodate the expected variations of the supply voltage (v s ), load current (i l ), and the adr1581 reverse voltage (v r ) while maintaining an acceptable reverse current (i r ) through the adr1581. figure 12 shows a typical output voltage drift for the adr1581 and illustrates the methodology. the maximum slope of the two diagonals drawn from the initial output value at +25c to the output values at +85c and ?40c determines the performance grade of the device. for a given grade of the adr1581, the designer can easily determine the maximum total error from the initial tolerance plus the temperature variation. the minimum value for r s should be chosen when v s is at its minimum and i l and v r are at their maximum while maintaining the minimum acceptable reverse current. the value of r s should be large enough to limit i r to 10 ma when v s is at its maximum and i l and v r are at their minimum. the equation for selecting r s is as follows: r s = ( v s ? v r )/( i r + i l )
adr1581 rev. 0 | page 7 of 12 output voltage (v) 1.2488 1.2498 1.2500 1.2502 1.2504 1.2506 1.2508 1.2494 1.2496 1.2490 1.2492 v max v min slope = tc = (v max ? v o ) (+85c ? +25c) 1.250v 10 ?6 slope = tc = (v min ? v o ) (?40c ? +25c) 1.250v 10 ?6 v o ?55 ?35 ?15 5 25 45 65 85 105 125 temperature (c) 06672-012 600 300 0 residual drift error (ppm) 500 400 200 100 ?55 ?35 ?15 5 25 45 65 85 105 125 temperature (c) 06672-013 figure 12. output vo ltage vs. temperature figure 13. residual drift error reverse voltage hysteresis for example, the adr1581brt initial tolerance is 1.5 mv; a 50 ppm/c temperature coefficient corresponds to an error band of 4.1 mv (50 10 ?6 1.250 v 65c). therefore, the unit is guaranteed to be 1.250 v 5.6 mv over the operating temperature range. a major requirement for high performance industrial equipment manufacturers is a consistent output voltage at nominal temperature following operation over the operating temperature range. this characteristic is generated by measuring the difference between the output voltage at +25c after operating at +85c and the output voltage at +25c after operating at ?40c. duplication of these results requires a combination of high accuracy and stable temperature control in a test system. evaluation of the adr1581 produces curves similar to those in figure 14 displays the hysteresis associated with the adr1581. this characteristic exists in all references and has been minimized in the adr1581. figure 4 and figure 12 . voltage output nonlinearity vs. temperature quantity 0 15 20 25 30 35 40 5 10 hysteresis voltage (v) ?400 ?300 ?200 ?100 0 100 200 300 400 06672-014 when a reference is used with data converters, it is important to understand how temperature drift affects the overall converter performance. the nonlinearity of the reference output drift represents additional error that is not easily calibrated out of the system. the usual way of showing the reference output drift is to plot the reference voltage vs. temperature (see figure 12 ). an alternative method is to draw a straight line between the temperature endpoints and measure the deviation of the output from the straight line. this shows the same data in a different format. this characteristic (see figure 13 ) is generated by normalizing the measured drift characteristic to the endpoint average drift. the residual drift error of approximately 500 ppm shows that the adr1581 is compatible with systems that require 10-bit accurate temperature performance. figure 14. reverse voltage hysteresis distribution
adr1581 rev. 0 | page 8 of 12 40v/div 21v rms 20v/div 10v/div 10ms/div 6.5v rms, t = 0.2ms (a) (b) (c) 2.90v rms, t = 960ms 06672-017 output impedance vs. frequency understanding the effect of the reverse dynamic output impedance in a practical application is important to successfully applying the adr1581. a voltage divider is formed by the adr1581 output impedance and the external source impedance. when an external source resistor of about 30 k (i r = 100 a) is used, 1% of the noise from a 100 khz switching power supply is developed at the output of the adr1581. figure 15 shows how a 1 f load capacitor connected directly across the adr1581 reduces the effect of power supply noise to less than 0.01%. 1k 10 0.1 1 100 frequency (hz) c l = 0 c l = 1f i r = 0.1i r i r = 100a i r = 1ma output impedance ( ? ) 10 100 1k 10k 100k 1m 06672-015 figure 17. total rms noise turn-on time many low power instrument manufacturers are becoming increasingly concerned with the turn-on characteristics of the components in their systems. fast turn-on components often enable the end user to keep power off when not needed, and yet those components respond quickly when the power is turned on for operation. figure 18 displays the turn-on characteristics of the adr1581. upon application of power (cold start), the time required for the output voltage to reach its final value within a specified error is the turn-on settling time. two components normally associated with this are time for active circuits to settle and time for thermal gradients on the chip to stabilize. this characteristic is generated from cold start operation and represents the true turn-on wave- form after power-up. figure 15. output im pedance vs. frequency noise performance and reduction the noise generated by the adr1581 is typically less than 5 v p-p over the 0.1 hz to 10 hz band. figure 20 shows both the coarse and fine turn-on settling characteristics of the device; the total settling time to within 1.0 mv is about 6 s, and there is no long thermal tail when the horizontal scale is expanded to 2 ms/div. figure 16 shows the 0.1 hz to 10 hz noise of a typical adr1581. noise in a 10 hz to 10 khz bandwidth is approximately 20 v rms (see figure 17 a). if further noise reduction is desired, a one-pole low-pass filter can be added between the output pin and ground. a time constant of 0.2 ms has a ?3 db point at about 800 hz and reduces the high frequency noise to about 6.5 v rms (see 250mv/div 5s/div c l = 200pf v in 0v 2.4v 06672-018 figure 17 b). a time constant of 960 ms has a ?3 db point at 165 hz and reduces the high frequency noise to about 2.9 v rms (see figure 17 c). 1v/div time (1s/div) 4.48v p-p 06672-016 figure 18. turn-on response time + ? r s = 11.5k ? r l c l v out v r v in 006672-010 figure 19. turn-on, settling, and transient test circuit figure 16. 0.1 hz to 10 hz voltage noise
adr1581 rev. 0 | page 9 of 12 output turn-on time is modified when an external noise-reduction filter is used. when present, the time constant of the filter dom- inates the overall settling. attempts to drive a large capacitive load (in excess of 1000 pf) may result in ringing, as shown in the step response (see figure 22 ). this is due to the additional poles formed by the load capacitance and the output impedance of the reference. a recommended method of driving capacitive loads of this magnitude is shown in 0v v in 2.4v output error 1mv/div, 2s/div output 0.5mv/div, 2ms/div 0 6672-020 figure 19 . a resistor isolates the capacitive load from the output stage, whereas the capacitor provides a single-pole low-pass filter and lowers the output noise. 1.8v 2.0v v in c l = 0.01f 50s/div 10mv/div 06672-022 figure 20. turn-on settling transient response many adcs and dacs present transient current loads to the reference. poor reference response can degrade the converters performance. figure 22. transient response with capacitive load figure 21 displays both the coarse and fine settling characteristics of the device to load transients of 50 a. precision micropower low dropout reference 1mv/div 20mv/div 1s/div 1mv/div 20mv/div (a) (b) i r = 150a ? 50a step i r = 150a + 50a step 06672-021 the circuit in figure 23 provides an ideal solution for creating a stable voltage reference with low standby power consumption, low input/output dropout capability, and minimum noise output. the amplifier both buffers and optionally scales up the adr1581 output voltage. output voltages as high as 2.1 v can supply 1 ma of load current. a one-pole filter connected between the adr1581 and the op193 input can be used to achieve low output noise. the nominal quiescent power consumption is 250 w. 3 v 28.7k ? adr1581 op193 v out = 1.250v or v out = 1.250 (1 + r2/r3) r3 r2 4.7f 205 ? 06672-023 figure 21. transient settling figure 21 a shows the settling characteristics of the device for an increased reverse current of 50 a. figure 21 b shows the response when the reverse current is decreased by 50 a. the transients settle to 1 mv in about 3 s. figure 23. micropower buffered reference
adr1581 rev. 0 | page 10 of 12 using the adr1581 with 3 v data converters the adr1581 is ideal for creating the reference level to use with 12-bit multiplying dacs, such as the ad7943, ad7945, and ad7948. in the single-supply bias mode (see figure 25 ), the impedance seen looking into the i out2 terminal changes with dac code. if the adr1581 drives i out2 and agnd directly, less than 0.2 lsbs of additional linearity error results. the buffer amp eliminates linearity degradation resulting from variations in the reference level. the adr1581 low output drift (50 ppm/c) and compact subminiature sot-23 package make it ideally suited for todays high performance converters in space-critical applications. one family of adcs for which the adr1581 is well suited is the ad7714-3 and ad7715-3 . the ad7714 / ad7715 are charge- balancing (-) adcs with on-chip digital filtering intended for the measurement of wide dynamic range, low frequency signals, such as those representing chemical, physical, or biological processes. dac r fb agnd dgnd a1 c1 3.3 v 29.4k ? 3.3v adr1581 signal ground a1: op295 ad822 op2283 a1 v ref v in v dd i out1 i out2 v out ad7943 06672-025 figure 24 shows the adr1581 connected to the ad7714 / ad7715 for 3 v operation. ad7714-3/ad7715-3 a dr1581 3 v 28.7k ? ref in(+) ref in(?) high impedance >1g ? r sw 5k ? (typ) c ref (3pf to 8pf) switching frequency depends on f clkin 06672-024 figure 24. reference circuit for the ad7714-3 / ad7715-3 figure 25. single-supply system
adr1581 rev. 0 | page 11 of 12 outline dimensions 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-236-ab figure 26. 3-lead small outline transistor package [sot-23-3] (rt-3) dimensions shown in millimeters 053006-0 20.20 min 1.00 min 0.75 min 1.10 1.00 0.90 1.50 min 7? reel 100.00 or 13? reel 330.00 7? reel 50.00 min or 13? reel 100.00 min direction of unreeling 0.35 0.30 0.25 2.80 2.70 2.60 1.55 1.50 1.45 4.10 4.00 3.90 1.10 1.00 0.90 2.05 2.00 1.95 8.30 8.00 7.70 3.20 3.10 2.90 3.55 3.50 3.45 13.20 13.00 12.80 14.40 min 9.90 8.40 6.90 figure 27. tape and reel dimensions (rt-3) dimensions shown in millimeters
adr1581 rev. 0 | page 12 of 12 ordering guide temperature range initial output error temperature coefficient package option model package description branding adr1581artz-reel7 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 r2m 1 adr1581artz-r2 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 r2m 1 adr1581brtz-reel7 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 r2k 1 ADR1581BRTZ-R2 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 r2k 1 1 z = rohs compliant part. ?2007 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d06672-0-5/07(0)

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