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1.2 v micropower, precision shunt voltage reference ad1580 rev. d 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 ?2008 analog devices, inc. all rights reserved. features wide operating range: 50 a to 10 ma initial accuracy: 0.1% 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 4 kv human body model 400 v machine model compact, surface-mount sot-23 and sc70 packages 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 the ad1580 1 is a low cost, 2-terminal (shunt), precision band gap reference. it provides an accurate 1.225 v output for input currents between 50 a and 10 ma. the superior accuracy and stability of the ad1580 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 nonli- nearities in the voltage output temperature characteristics. the ad1580 is stable with any value of capacitive load. the low minimum operating current makes the ad1580 ideal for use in battery-powered 3 v or 5 v systems. however, the wide operating current range means that the ad1580 is extremely versatile and suitable for use in a wide variety of high current applications. the ad1580 is available in two grades, a and b, both of which are provided in the sot-23 and sc70 packages, the smallest surface-mount packages available. both grades are specified over the industrial temperature range of ?40c to +85c. 1 protected by u.s. patent no. 5,969,657. pin configurations nc = no connect top view v+ 1 v? 2 nc (or v?) 3 ad1580 00700-001 nc = no connect top view v? 1 v+ 2 nc (or v?) 3 ad1580 00700-002 figure 1. sot-23 figure 2. sc70 50 0 quantity 45 40 35 30 25 20 15 10 5 temperature drift (ppm/c) ?40 ?30 ?20 ?10 0 10 20 30 40 00700-003 figure 3. reverse voltage temperature drift distribution output error (mv) 300 0 quantity 250 200 150 100 50 ?10 ?8 ?6 ?4 ?2 0 2 4 6 8 10 00700-004 figure 4. reverse voltage error distribution
ad1580 rev. d | page 2 of 12 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 general description ......................................................................... 1 pin configurations ........................................................................... 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 esd caution .................................................................................. 4 typical performance characteristics ............................................. 5 theory of operation ........................................................................ 6 applying the ad1580 .................................................................. 6 temperature performance ........................................................... 6 voltage output nonlinearity vs. temperature ..........................7 reverse voltage hysteresis ...........................................................7 output impedance vs. frequency ...............................................7 noise performance and reduction .............................................8 turn-on time ...............................................................................8 transient response .......................................................................9 precision micropower low dropout reference .......................9 using the ad1580 with 3 v data converters ...........................9 outline dimensions ....................................................................... 11 ordering guide .......................................................................... 12 package branding information ................................................ 12 revision history 1/08rev. c to rev. d changes to figure 5 .......................................................................... 5 changes to figure 6 caption ........................................................... 5 changes to ordering guide .......................................................... 12 7/06rev. b to rev. c updated format .................................................................. universal changes to figure 13 ........................................................................ 7 changes to figure 16 ........................................................................ 8 updated outline dimensions ....................................................... 11 changes to ordering guide .......................................................... 12 7/04rev. a to rev. b changes to ordering guide .............................................................2 10/03rev. 0 to rev. a renumbered figures and tpcs ........................................ universal edits to features .................................................................................1 edits to general description ...........................................................1 edits to ordering guide ...................................................................2 updated figures 5 through 7 ..........................................................4 updated outline dimensions ..........................................................8
ad1580 rev. d | page 3 of 12 specifications t a = 25c, i in = 100 a, unless otherwise noted. table 1. model ad1580a ad1580b unit min typ max min typ max reverse voltage output (sot-23) 1.215 1.225 1.235 1.224 1.225 1.226 v reverse voltage output (sc70) 1.2225 1.225 1.2275 v reverse voltage temperature drift ?40c to +85c 100 50 ppm/c minimum operating current, t min to t max 50 50 a reverse voltage change with reverse current 50 a < i in < 10 ma, t min to t max 2.5 6 2.5 6 mv 50 a < i in < 1 ma, t min to t max 0.5 0.5 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 5 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 no load capacitor. 2 output hysteresis is defined as the change in the +25c outp ut voltage after a temperature ex cursion to +85c and then to ?40 c. 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.
ad1580 rev. d | page 4 of 12 absolute maximum ratings table 2. parameter rating 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 ad1580/rt ?55c to +125c 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 in fr ee air at 25c, sot-23 package. 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. 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. esd caution
ad1580 rev. d | page 5 of 12 typical performance characteristics reverse voltage change (ppm) ?2000 ?1000 ?500 0 500 1000 ?1500 temperature (c) ?55 ?35 ?15 5 25 45 65 85 105 125 00700-005 figure 5. output drift for different temperature characteristics 4 3 ?1 2 1 0 reverse voltage change (mv) reverse current (ma) 0.01 0.1 1 10 t a = +125c t a = ?40c to +85c 00700-006 figure 6. reverse voltage change vs. reverse current frequency (hz) 600 200 400 noise voltage (nv/ hz) 1.0 10 100 1k 10k 100k 1m 00700-007 figure 7. noise spectral density reverse voltage (v) 100 0 40 20 80 60 ?40c +85c +25c reverse current (a) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 00700-008 figure 8. reverse current vs. reverse voltage forward current (ma) 1.0 0 forward voltage (v) 0.4 0.2 0.8 0.6 +25c +85c ?40c 0.01 0.1 1 10 100 00700-009 figure 9. forward voltage vs. forward current
ad1580 rev. d | page 6 of 12 theory of operation the ad1580 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 tran- sistor base emitter voltage in the forward biased operating region. all such transistors have an approximately ?2 mv/c temperature coefficient (tc), 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. thus, if a voltage could be developed with an opposing temperature coefficient to sum with v be , a zero tc reference would result. the ad1580 circuit in figure 10 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. v + v? v1 v be v be 00700-010 figure 10. schematic diagram applying the ad1580 the ad1580 is simple to use in virtually all applications. to operate the ad1580 as a conventional shunt regulator (see figure 11 ), an external series resistor is connected between the supply voltage and the ad1580. for a given supply voltage, the series resistor, r s , determines the reverse current flowing through the ad1580. 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 ad1580 reverse voltage, v r ; while maintaining an acceptable reverse current, i r , through the ad1580. 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 ) figure 12 shows a typical connection of the ad1580brt 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 00700-011 figure 11. typical connection diagram +5 v (+3 v )10 % 2.94k ? (1.30k ? ) r s v r v out 00700-012 figure 12. typical connection diagram temperature performance the ad1580 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 reference voltage error over temperature. historically, references have been characterized using a maximum deviation per degree celsius, for example, 50 ppm/c. however, because of nonlinear- ities in temperature characteristics that originated in standard zener references (such as s type characteristics), most manufac- turers now use a maximum limit error band approach to specify devices. this technique involves the measurement of the output at three or more different temperatures to guarantee that the voltage falls within the given error band. the proprietary curvature correction design techniques used to minimize the ad1580 nonlinearities allow the temperature performance to be guaranteed using the maximum deviation method. this method is of more use to a designer than the one that simply guarantees the maximum error band over the entire temper- ature change. figure 13 shows a typical output voltage drift for the ad1580 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 ad1580, the designer can easily determine the maximum total error from the initial tolerance plus temperature variation.
ad1580 rev. d | page 7 of 12 output voltage (v) 1.2238 1.2248 1.2250 1.2252 1.2254 1.2256 1.2258 1.2244 1.2246 1.2240 1.2242 v max v min slope = tc = (v max ?v o ) (+85c ? +25c) 1.225 10 ?6 slope = tc = (v min ?v o ) (?40c ? +25c) 1.225 10 ?6 v o ?55 ?35 ?15 5 25 45 65 85 105 125 temperature (c) 00700-013 figure 13. output voltage vs. temperature for example, the ad1580brt initial tolerance is 1 mv; a 50 ppm/c temperature coefficient corresponds to an error band of 4 mv (50 10 ?6 1.225 v 65c). thus, the unit is guaranteed to be 1.225 v 5 mv over the operating temperature range. duplication of these results requires a combination of high accuracy and stable temperature control in a test system. evaluation of the ad1580 produces a curve similar to that in figure 5 and figure 13 . voltage output nonlinearity vs. temperature 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 an additional error that is not easily calibrated out of the system. this characteristic (see figure 14 ) is generated by normalizing the measured drift characteristic to the end point average drift. the residual drift error of approximately 500 ppm shows that the ad1580 is compatible with systems that require 10-bit accurate temperature performance. 600 300 0 residual drift error (ppm) 500 400 200 100 ?55 ?35 ?15 5 25 45 65 85 105 125 temperature (c) 00700-014 figure 14. residual drift error reverse voltage hysteresis 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 measur- ing the difference between the output voltage at +25c after operation at +85c and the output, at +25c after operation at ?40c. figure 15 displays the hysteresis associated with the ad1580. this characteristic exists in all references and has been minimized in the ad1580. quantity 0 15 20 25 30 35 40 5 10 hysteresis voltage (v) ?400 ?300 ?200 ?100 0 100 200 300 400 00700-015 figure 15. reverse voltage hysteresis distribution output impedance vs. frequency understanding the effect of the reverse dynamic output imped- ance in a practical application may be important to successfully apply the ad1580. a voltage divider is formed by the ad1580 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 devel- oped at the output of the ad1580. figure 16 shows how a 1 f load capacitor connected directly across the ad1580 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 00700-016 figure 16. output im pedance vs. frequency
ad1580 rev. d | page 8 of 12 noise performance and reduction the noise generated by the ad1580 is typically less than 5 v p-p over the 0.1 hz to 10 hz band. figure 17 shows the 0.1 hz to 10 hz noise of a typical ad1580. noise in a 10 hz to 10 khz bandwidth is approximately 20 v rms (see figure 18 a). if further noise reduction is desired, a 1-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 figure 18 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 18 c). 1s/div 1v/div 4.5v p-p 00700-017 figure 17. 0.1 hz to 10 hz voltage noise 40v/div 21v rms 20v/div 10v/div 10ms/div 6.5v rms, =0.2ms (a) (b) (c) 2.90v rms, = 960ms 00700-018 figure 18. total rms noise turn-on time many low power instrument manufacturers are becoming increasingly concerned with the turn-on characteristics of components being used in their systems. fast turn-on compo- nents 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 19 displays the turn-on characteristic of the ad1580. 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 waveform after power-up. figure 21 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. 250mv/div 5s/div c l = 200pf v in 0v 2.4v 00700-019 figure 19. turn-on response time + ? r s =11.5k ? r l c l v out v r v in 00700-020 figure 20. turn-on, settling, and transient test circuit output turn-on time is modified when an external noise reduction filter is used. when present, the time constant of the filter dominates overall settling. 0v v in 2.4v output error 1mv/div, 2s/div output 0.5mv/div, 2ms/div 00700-021 figure 21. turn-on settling
ad1580 rev. d | page 9 of 12 transient response many adc and dac converters present transient current loads to the reference. poor reference response can degrade the converters performance. figure 22 displays both the coarse and fine settling characteristics of the device to load transients of 50 a. (a) (b) 1s/div 1mv/div 20mv/div i r = 100a ? 50a step i r = 100a + 50a step 1mv/div 20mv/div 00700-022 figure 22. transient settling figure 22 a shows the settling characteristics of the device for an increased reverse current of 50 a. figure 22 b shows the response when the reverse current is decreased by 50 a. the transients settle to 1 mv in about 3 s. attempts to drive a large capacitive load (in excess of 1000 pf) may result in ringing, as shown in the step response (see figure 23 ). this is due to the additional poles formed by the load capacit- ance and the output impedance of the reference. a recommended method of driving capacitive loads of this magnitude is shown in figure 20 . a resistor isolates the capacitive load from the output stage, while 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 0 0700-023 figure 23. transient respon se with capacitive load precision micropower low dropout reference the circuit in figure 24 provides an ideal solution for making 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 ad1580 output voltage, v r . output voltages as high as 2.1 v can supply 1 ma of load current. a one-pole filter connected between the ad1580 and the op193 input can be used to achieve low output noise. the nominal quiescent power consumption is 200 w. 3 v 34.8k ? ad1580 op193 v out = +1.225v or v out = +1.225 (1 + r2/r3) r3 r2 4.7f 205? 00700-024 figure 24. micropower buffered reference using the ad1580 with 3 v data converters the ad1580 low output drift (50 ppm/c) and compact submi- niature sot-23 package make it ideally suited for todays high performance converters in space critical applications. one family of adcs for which the ad1580 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. figure 25 shows the ad1580 connected to the ad7714-3/ad7715-3 for 3 v operation. ad7714-3 and ad7715?3 ad1580 3 v 34.8k ? refin(+) refin(?) high impedance >1g ? r sw 5k? (typ) c ref (3pf to 8pf) switching frequency depends on f clkin 00700-025 figure 25. reference circuit for the ad7714-3 and ad7715-3
ad1580 rev. d | page 10 of 12 dac rbf agnd dgnd a1 c1 3.3 v 41.2k ? 3.3v ad1580 signal ground a1: op295 ad822 op2283 a1 v ref v in v dd i out1 i out2 v out ad7943/ ad7945/ ad7948 00700-026 the ad1580 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 26 ), the impedance seen looking into the i out2 terminal changes with dac code. if the ad1580 drives i out2 and agnd directly, less than 0.2 lsbs of additional linearity error results. the buffer amp eliminates any linearity degradation that could result from variations in the reference level. figure 26. single-supply system
ad1580 rev. d | 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 all dimensions compliant with eiaj sc70 0.40 0.25 0.10 max 1.00 0.80 seating plane 1.10 0.80 0.40 0.10 0.26 0.10 0.30 0.20 0.10 2 1 3 pin 1 0.65 bsc 2.20 2.00 1.80 2.40 2.10 1.80 1.35 1.25 1.15 0.10 coplanarity 111505-0 figure 27. 3-lead small outline transistor package [sot-23-3] (rt-3) dimensions shown in millimeters figure 28. 3-lead thin shrink small outline transistor package [sc70] (ks-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 29. tape an d reel dimensions (rt-3 and ks-3) dimensions shown in millimeters
ad1580 rev. d | page 12 of 12 ordering guide model temperature range initial output error temperature coefficient package description package option branding ad1580art-r2 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 0axx ad1580art-reel ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 0axx ad1580art-reel7 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 0axx ad1580artz-reel 1 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 r0y ad1580artz-reel7 1 ?40c to +85c 10 mv 100 ppm/c 3-lead sot-23-3 rt-3 r0y AD1580BRT-R2 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 0bxx ad1580brt-reel7 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 0bxx ad1580brtz-r2 1 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 0bxx ad1580brtz-reel7 1 ?40c to +85c 1 mv 50 ppm/c 3-lead sot-23-3 rt-3 r2e ad1580bksz-reel 1 ?40c to +85c 2.5 mv 50 ppm/c 3-lead sc70 ks-3 r2e ad1580bksz-reel7 1 ?40c to +85c 2.5 mv 50 ppm/c 3-lead sc70 ks-3 r2e 1 z = rohs compliant part. package branding information in the sot-23 package (rt), four marking fields identify the device generic, grade, and date of processing. the first field is the product identifier. a 0 identifies the generic as the ad1580. the second field indicates the device grade: a or b. in the third field, a numeral or letter i ndicates a calendar year: 5 for 1995, a for 2001. in the fourth field, letters a through z represent a two-week window within the calendar year, starting with a for the first tw o weeks of january. ?2008 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. d00700-0-1/08(d)

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