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low power, low cost 2.5 v reference ad680 rev. h 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 chan ge without notice. no license is granted by implication or otherwise under any patent or patent ri ghts 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 ?2005 analog devices, inc. all rights reserved. features low quiescent current at 250 a max laser trimmed to high accuracy 2.5 v 5 mv max (an, ar grades) trimmed temperature coefficient 20 ppm/c max (an, ar grades) low noise at 8 v p-p from 0.1 hz to 10 hz 250 nv/hz wideband temperature output pin (n, r packages) available in three package styles 8-lead pdip, 8-lead soic, and 3-pin to-92 general description the ad680 is a band gap voltage reference that provides a fixed 2.5 v output from inputs between 4.5 v and 36 v. the architecture of the ad680 enables the reference to be operated at a very low quiescent current while still realizing excellent dc characteristics and noise performance. trimming of the high stability thin-film resistors is performed for initial accuracy and temperature coefficient, resulting in low errors over temperature. the precision dc characteristics of the ad680 make it ideal for use as a reference for dacs that require an external precision reference. the device is also ideal for adcs and, in general, can offer better performance than the standard on-chip references. based upon its low quiescent current, which rivals that of many incomplete 2-terminal references, the ad680 is recommended for low power applications, such as hand-held, battery-operated equipment. a temperature output pin is provided on the 8-lead package versions of the ad680. the temperature output pin provides an output voltage that varies linearly with temperature and allows the ad680 to be configured as a temperature transducer while providing a stable 2.5 v output. the ad680 is available in five grades. the ad680an is speci- fied for operation from ?40c to +85c, while the ad680jn is specified for 0c to 70c operation. both the ad680an and ad680jn are available in 8-lead pdip packages. the ad680ar is specified for operation from ?40c to +85c, while the ad680jr is specified for 0c to 70c operation. both are available in 8-lead soic packages. the ad680jt is specified for 0c to 70c operation and is available in a 3-pin to-92 package. connection diagrams * tp denotes factory test point. no connections should be made to these pins. nc = no connect ad680 top view (not to scale) tp* 1 +v in 2 temp 3 gnd 4 tp* tp* v out nc 8 7 6 5 00813-003 figure 1. 8-lead pdip and 8-lead soic pin configuration 00813-004 ad680 bottom view (not to scale) 32 1 +v in v out gnd figure 2. connection diagram to-92 product highlights 1. high accuracy. the ad680 band gap reference operates on a very low quiescent current which rivals that of many 2-terminal references. this makes the complete, higher accuracy ad680 ideal for use in power-sensitive applications. 2. low errors. laser trimming of both initial accuracy and temperature coef- ficients results in low errors over temperature without the use of external components. the ad680an and ad680ar have a maximum variation of 6.25 mv between ?40c and +85c. 3. low noise. the ad680 noise is low, typically 8 v p-p from 0.1 hz to 10 hz. spectral density is also low, typically 250 nv/hz. 4. temperature transducer. the temperature output pin on the 8-lead package versions enables the ad680 to be configured as a temperature transducer. 5. low cost. pdip packaging provides machine insertability, while soic packaging provides surface-mount capability. to-92 packaging offers a cost-effective alternative to 2-terminal references, offering a complete solution in the same package in which 2-terminal references are usually found.
ad680 rev. h | page 2 of 12 table of contents specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 4 output protection ........................................................................ 4 esd caution .................................................................................. 4 pin configuration and connection diagram ............................... 5 theory of operation ........................................................................ 6 applying the ad680 .................................................................... 6 noise performance ....................................................................... 6 tur n-on ti me ................................................................................ 7 dynamic performance ................................................................. 7 load regulation ............................................................................8 temperature performance ............................................................8 temperature output pin ..............................................................9 differential temperature transducer .........................................9 low power, low voltage reference for data converters ........9 4.5 v reference from a 5 v supply .......................................... 10 voltage regulator for portable equipment ............................. 10 outline dimensions ....................................................................... 11 ordering guide .......................................................................... 12 revision history 8/05rev. g to rev. h changes to ordering guide ..........................................................11 12/04rev. f to rev. g u pdated format ................................................................. universal changes to ordering guide ..........................................................11 5/04rev. e to rev. f c hanges to ordering guide ...................................................3 5/03rev. d to rev. e c hanges to ordering guide ...................................................3 added esd caution ..........................................................................3 changes to figure 20.........................................................................7 updated outline dimensions ...............................................8 7/01rev. c to rev. d c hanges to specifications........................................................2 changes to ordering guide ....................................................3 table i added ......................................................................................6
ad680 rev. h | page 3 of 12 specifications t a = 25c, v in = 5 v, unless otherwise noted. specifications in boldface are tested on all production units at final electrical test. results from these tests are used to calculate outgoing quality levels. all minimum and maximum specifications are guaranteed. table 1. ad680an/ad680ar ad680jn/ad680jr ad680jt parameter min typ max min typ max min typ max unit output voltage output voltage, v o 2.495 2.500 2.505 2.490 2.500 2.510 2.490 2.500 2.510 v initial accuracy, v oerr ?5 +5 ?10 +10 ?10 +10 mv ?0.20 +0.20 ?0.40 +0.40 ?0.40 +0.40 % output voltage drift 1 0c to 70c 10 10 25 10 30 ppm/c ?40c to +85c 20 25 25 ppm/c line regulation 4.5 v +v in 15 v 40 40 40 v/v (@ t min to t max ) 40 40 40 v/v 15 v +v in 36 v 40 40 40 v/v (@ t min to t max ) 40 40 40 v/v load regulation 0 < i out < 10 ma 80 100 80 100 80 100 v/ma (@ t min to t max ) 80 100 80 100 80 100 v/ma quiescent current 195 250 195 250 195 250 a (@ t min to t max ) 280 280 280 a power dissipation 1 1.25 1 1.25 1 1.25 mw output noise 0.1 hz to 10 hz 8 10 8 10 8 10 v p-p spectral density, 100 hz 250 250 250 nv/hz capacitive load 50 50 50 nf long-term stability 25 25 25 ppm/1,000 hr short-circuit current to ground 25 50 25 50 25 50 ma temperature pin voltage output @ 25c 540 596 660 540 596 660 mv temperature sensitivity 2 2 mv/c output current ?5 +5 ?5 +5 a output resistance 12 12 k temperature range specified performance ?40 +85 0 70 0 70 c operating performance 2 ?40 +85 ?40 +85 ?40 +85 c 1 maximum output voltage drift is guaranteed for all packages. 2 the operating temperature range is define d as the temperature extremes at which the device will still function. parts may devi ate from their specified performance outside their specified temperature range.
ad680 rev. h | page 4 of 12 absolute maximum ratings table 2. parameter rating v in to ground 36 v power dissipation (25c) 500 mw storage temperature ?65c to +125c lead temperature (soldering, 10 sec) 300c package thermal resistance ja (all packages) 120c/w stresses above those listed under absolute maximum ratings ma y 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. output protection output safe for indefinite short to gnd and momentary short to ?v in . esd caution esd (electrostatic discharge) sensitive device. electros tatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge wi thout detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
ad680 rev. h | page 5 of 12 pin configurations and function descriptions * tp denotes factory test point. no connections should be made to these pins. nc = no connect ad680 top view (not to scale) tp* 1 +v in 2 temp 3 gnd 4 tp* tp* v out nc 8 7 6 5 00813-003 figure 3. 8-lead pdip and 8-lead soic pin configuration 00813-004 ad680 bottom view (not to scale) 32 1 +v in v out gnd figure 4. connection diagram table 3. pin function descriptions pin o. mnemonic descriptions 1, 7, 8 tp test point. a factory test poi nt. no connectio ns are made to these pins. 2 +v in input voltage. 3 temp temperature output. 4 gnd ground. 5 nc no connect. 6 v out output voltage.
ad680 rev. h | page 6 of 12 theory of operation band gap references are the high performance solution for low supply voltage operation. a typical precision band gap consists of a reference core and buffer amplifier. based on a new, pat- ented band gap reference design ( figure 5 ), the ad680 merges t he amplifier and the core band gap function to produce a compact, complete precision reference. central to the device is a high gain amplifier with an intentionally la rge proportional to absolute temperature (ptat) input offset. this offset is controlled by the area ratio of the amplifier input pair, q1 and q2, and is developed across resistor r1. transistor q12s base emitter voltage has a complementary to absolute temperature (ctat) characteristic. resistor r2 and the parallel combination of resistor r3 and resistor r4 multiply the ptat voltage across the r1 resistor. trimming the r3 and r4 resistors to the proper ratio produces a temperature invariant of 2.5 v at the output. the result is an accurate, stable output voltage accomplished with a minimum number of components. 00813-005 +v in q11 temp q12 r2 r1 q5 q4 q1 1 q2 8 q9 r5 q8 q3 q7 q6 q10 gnd c1 r6 r7 r4 r3 v out figure 5. schematic diagram applying the ad680 the ad680 is simple to use in virtually all precision reference applications. when power is applied to +v in and the gnd pin is tied to ground, v out provides a 2.5 v output. the ad680 typically requires less than 250 a of current when operating from a supply of 4.5 v to 36 v. to operate the ad680, the +v in pin must be bypassed to the gnd pin with a 0.1 f capacitor tied as close to the ad680 as possible. although the ground current for the ad680 is small, typically 195 a, a direct connection should be made between the ad680 gnd pin and the system ground plane. reference outputs are frequently required to handle fast t ransients caused by input switching networks, commonly found in adcs and measurement instrumentation equipment. many of the dynamic problems associated with this situation can be minimized with a few simple techniques. using a series resistor between the reference output and the load tends to decouple the reference output from the transient source, or a relatively large capacitor connected from the reference output to ground can serve as a charge storage element to absorb and deliver charge as required by the dynamic load. a 50 nf capaci- tor is recommended for the ad680 in this case; this is large enough to store the required charge, but small enough not to disrupt the stability of the reference. the 8-lead pdip and 8-lead soic packaged versions of the ad680 als o provide a temperature output pin. the voltage on this pin is nominally 596 mv at 25c. this pin provides an output linearly proportional to temperature with a characteristic of 2 mv/c. noise performance the noise generated by the ad680 is typically less than 8 v p-p over the 0.1 hz to 10 hz band. figure 6 shows the 0.1 hz to 10 hz n oise of a typical ad680. the noise measurement is made with a band-pass filter made of a 1-pole high-pass filter, with a corner frequency at 0.1 hz, and a 2-pole low-pass filter, with a corner frequency at 12.6 hz, to create a filter with a 9.922 hz bandwidth. 00813-006 5 v 1s 100 90 0% 10 figure 6. 0.1 hz to 10 hz noise noise in a 300 khz bandwidth is approximately 800 v p-p. figure 7 shows the broadband noise of a typical ad680.
ad680 rev. h | page 7 of 12 00813-007 500 v 100 90 0% 10 50 s 500 v figure 7. broadband noise at 300 khz 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. the turn-on settling time of the ad680 is about 20 s to within 0.025% of its final value, as shown in figure 8 . 00813-008 v in v out 100 90 0% 10 10 s 5v 1mv figure 8. turn-on settling time the ad680 thermal settling characteristic benefits from its compact design. once initial turn-on is achieved, the output linearly approaches its final value; the output is typically within 0.01% of its final value after 25 ms. dynamic performance the output stage of the amplifier is designed to provide the ad680 with static and dynamic load regulation superior to less complete references. figure 9 to figure 11 display the char- ac teristics of the ad680 output amplifier driving a 0 ma to 10 ma load. longer settling times result if the reference is forced to sink any transient current. in some applications, a varying load may be both resistive and c apacitive in nature, or the load may be connected to the ad680 by a long capacitive cable. 00813-009 ad680 +v in v out v out v out 0v v l 249 0.1 f figure 9. transient load test circuit 00813-010 v out v l 100 90 0% 10 5 s 50mv 2v figure 10. large scale transient response 00813-011 v out v in 100 90 0% 10 5 s 5mv 2v figure 11. fine scale settling for transient load
ad680 rev. h | page 8 of 12 00813-012 ad680 +v in v out v out v out 0v v l 249 0.1 f c l 1000pf figure 12. capacitive load transient response test circuit figure 13 displays the output amplifier characteristics driving a 1,000 pf , 0 ma to 10 ma load. 00813-013 v out v l 100 90 0% 10 5 s 5mv 2v figure 13. output response with capacitive load load regulation figure 14 depicts the load regulation characteristics of th e ad680. 00813-014 v out v l 100 90 0% 10 100 s 1mv 1v figure 14. typical load regulation characteristics temperature performance the ad680 is designed for reference applications where tem- perature 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 r eference voltage error over temperature. historically, references have been characterized using a maximum deviation per degree centigrade, that is, ppm/c. however, because of nonlinearities 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 measuring the output at three or more different temperatures to specify an output voltage error band. 00813-015 2.501 2.500 2.498 temperature ( c) ?50 60 02040 2.499 ?10?30 80 100 slope = tc = v max ? v min (t max ? t min ) 2.5v 10 ?6 = 2.501 ? 2.498 (85 c ? (?40 c)) 2.5v 10 ?6 = 9.6ppm/ c volts (v) figure 15. typical ad680an/ad680ar temperature drift figure 15 shows a typical output voltage drift for the ad680an/ ad680ar and i llustrates the test methodology. the box in figure 15 is bounded on the left and right sides by the operat- in g temperature extremes, and on the top and bottom by the maximum and minimum output voltages measured over the operating temperature range. the maximum height of the box for the appropriate temperature r ange and device grade is shown in table 4 . duplication of these r esults requires a combination of high accuracy and stable tem- perature control in a test system. evaluation of the ad680 will produce a curve similar to that in figure 15 , but output readings co uld vary depending upon the test equipment used. table 4. maximum output change in mv maximum output change (mv) device grade 0c to 70c ?40c to +85c ad680jn/ad680jr 4.375 not applicable ad680jt 5.250 not applicable ad680an not applicable 6.250
ad680 rev. h | page 9 of 12 temperature output pin the 8-lead package versions of the ad680 provide a tempera- ture output pin on pin 3 of each device. the output of pin 3 (temp) is a voltage that varies linearly with temperature. v temp at 25 c is 596 mv, and the temperature coefficient is 2 mv/ c. figure 16 shows the output of this pin over temperature. the temperature pin has an output resistance of 12 k and is c apable of sinking or sourcing currents of up to 5 a without disturbing the reference output. this enables the temp pin to be buffered by many inexpensive operational amplifiers that have bias currents below this value. 760 720 680 640 600 560 520 480 440 ?50 ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 00813-016 temperature ( c) temp pin voltage (mv) figure 16. temp pin transfer characteristics differential temperature transducer figure 17 shows a differential temperature transducer that can be us ed to measure temperature changes in the environment of the ad680. this circuit operates from a 5 v supply. the temperature-dependent voltage from the temp pin of the ad680 is amplified by a factor of 5 to provide wider full-scale range and more current sourcing capability. an exact gain of 5 can be achieved by adjusting the trim potentiometer until the output varies by 10 mv/c. to minimize resistance changes with temperature, use resistors with low temperature coefficients, such as metal film resistors. 00813-017 6 3 2 7 4 op90 5v + ? r f 6.98k 1% r b 1.69k 1% r bp 100 2 3 4 ad680 temp gnd v in 0.1 f 5v v out t = 10mv/ c figure 17. differential temperature transducer low power, low voltage reference for data converters the ad680 has a number of features that make it ideally suited for use with adcs and dacs. the low supply voltage required makes it possible to use the ad680 with todays converters that run on 5 v supplies without having to add a higher supply voltage for the reference. the low quiescent current (195 a), combined with the completeness and accuracy of the ad680, make it ideal for low power applications, such as hand-held, battery-operated meters. the ad7701 is an adc that is well-suited for the ad680. figure 18 shows the ad680 used as the reference for this con verter. the ad7701 is a 16-bit adc with on-chip digital f iltering intended for the measurement of wide dynamic range and low frequency signals, such as those representing chemical, physical, or biological processes. it contains a charge balancing (?C) adc, a calibration microcontroller with on-chip static ram, a clock oscillator, and a serial communications port. this entire circuit runs on 5 v supplies. the power dissipation of the ad7701 is typically 25 mw and, when combined with th e power dissipation of the ad680 (1 mw), the entire circuit consumes just 26 mw of power. 00813-018 ad680 gnd 0.1 f ad7701 cal agnd dgnd sc2 sc1 clkout clkin sclk sdata cs drdy mode data ready read (transmit) serial clock serial data sleep 0.1 f 10 f 0.1 f 0.1 f +5v a nalo g supply range select calibrate analog input analog gnd ?5v analog supply 0.1 f 0.1 f1 0 f v in v out av dd dv dd dv ss v ref a in av ss bp/up figure 18. low power, low voltage supply reference fo r the ad7701 16-bit adc
ad680 rev. h | page 10 of 12 4.5 v reference from a 5 v supply the ad680 can be used to provide a low power, 4.5 v reference, as shown in figure 19 . in addition to the ad680, the circuit us es a low power op amp and a transistor in a feedback con- figuration that provides a regulated 4.5 v output for a power supply voltage as low as 4.7 v. the high quality tantalum 10 f capacitor (c1) in parallel with the ceramic 0.1 f capacitor (c2) and the 3.9 resistor (r5) ensure a low output impedance up to approximately 50 mhz (see figure 19 ). 00813-019 6 3 2 7 4 op90 +in v+ v? out ?in r1 2k 1% cf 0.1 f r4 3.57k r2 2.5k 1% ad680 v out gnd v in 0.1 f r3 1k cc 3.3 f 2n2907a 4.7v to 15v c1 10 f + c2 0.1 f r5 3.9 figure 19. 4.5 v reference running from a single 5 v supply voltage regulator for portable equipment the ad680 is ideal for providing a stable, low cost, low power reference voltage in portable equipment power supplies. figure 20 shows how the ad680 can be used in a voltage r egulator that not only has low output noise (as compared to a switch mode design) and low power, but it also has a very fast recovery after current surges. some caution 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 electro- lytic capacitor, 10 v or higher, are recommended for c1 and c2, respectively. also, the path from the ground side of c1 and c2 to the ground side of r1 should be kept as short as possible. 00813-020 2 3 7 6 4 op777 + ? r3 510k irf9530 ad680 v out gnd v in c1 68 f tant + c2 1000 f elect + 2 6 temp 3 4 0.1 f charge r input 6v lead-acid battery + r2 402k 1% r1 402k 1% figure 20. voltage regulator for portable equipment
ad680 rev. h | page 11 of 12 outline dimensions 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 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 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-012aa figure 21. 8-lead standard small outline package [soic] nar row body (r-8) dimensions show in millimeters and (inches) compliant to jedec standards ms-001-ba 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) seating plane 0.015 (0.38) min 0.210 (5.33) max pin 1 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) 0.070 (1.78) 0.060 (1.52) 0.045 (1.14) 8 1 4 5 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 0.100 (2.54) bsc 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 0.060 (1.52) max 0.430 (10.92) max 0.014 (0.36) 0.010 (0.25) 0.008 (0.20) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 0.015 (0.38) gauge plane 0.005 (0.13) min controlling dimensions are in inches; millimeter dimensions (in parentheses) are rounded-off inch equivalents for reference only and are not appropriate for use in design. corner leads may be configured as whole or half leads. figure 22. 8-lead plastic dual in-line package [pdip] nar row body (n-8) dimensions shown in inches and (millimeters) controlling dimensions are in inches; millimeter dimensions (in parentheses) are rounded-off equivalents for reference only and are not appropriate for use in design compliant to jedec standards to-226aa 0.115 (2.92) 0.080 (2.03) 0.115 (2.92) 0.080 (2.03) 0.165 (4.19) 0.125 (3.18) 1 2 3 bottom view sq 0.019 (0.482) 0.016 (0.407) 0.105 (2.66) 0.095 (2.42) 0.055 (1.40) 0.045 (1.15) seating plane 0.500 (12.70) min 0.205 (5.21) 0.175 (4.45) 0.210 (5.33) 0.170 (4.32) 0.135 (3.43) min 0.050 (1.27) max figure 23. 3-pin plastic header-style package [to-92] (t -3) dimensions shown in inches and (millimeters)
ad680 rev. h | page 12 of 12 ordering guide initial accuracy model output voltage v o (v) (mv) (%) temperature coefficient (ppm/c) package description package option parts per reel temperature range (c) ad680ar 2.5 5 0.20 20 soic r-8 ?40 to +85 AD680AR-REEL 2.5 5 0.20 20 soic r-8 2,500 ?40 to +85 AD680AR-REEL7 2.5 5 0.20 20 soic r-8 1,000 ?40 to +85 ad680arz 1 2.5 5 0.20 20 soic r-8 ?40 to +85 ad680arz-reel7 1 2.5 5 0.20 20 soic r-8 1,000 ?40 to +85 ad680jr 2.5 10 0.40 25 soic r-8 0 to 70 ad680jr-reel7 2.5 10 0.40 25 soic r-8 1,000 0 to 70 ad680jrz 1 2.5 10 0.40 25 soic r-8 0 to 70 ad680jrz-reel7 1 2.5 10 0.40 25 soic r-8 1,000 0 to 70 ad680an 2.5 5 0.20 20 pdip n-8 ?40 to +85 ad680anz 1 2.5 5 0.20 20 pdip n-8 ?40 to +85 ad680jn 2.5 10 0.40 25 pdip n-8 0 to 70 ad680jnz 1 2.5 10 0.40 25 pdip n-8 0 to 70 ad680jt 2.5 10 0.40 30 to-92 t-3 0 to 70 ad680jtz 1 2.5 10 0.40 30 to-92 t-3 0 to 70 1 z = pb-free part. ?2005 analog devices, inc. all rights reserved. trademarks and registered trademarks are the prop erty of their respective owners. c00813C0C8/05(h)

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