AD780-2.5V電壓基準(zhǔn)解析

1、REV. AIn formati on furni shed by An alog Devices is believed to be accurate an dreliable.However, no responsibility is assumed by Analog Devices for itsuse, nor for any infringements of patents or other rights of third partieswhich may result from its use. No lice nse is gran ted by implicati on or

2、otherwise un der any pate nt or pate nt rights of An alog Devices.a2.5 V/3.0 VHigh Precisio n Refere neeAD780One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.Tel: 617/329-4700Fax: 617/326-8703FUNCTIONAL BLOCK DIAGRAMNC TEMP +VIN V OUTTRIMGND2.5V - NC3.0V - GNDNC = NO CONNECTPRODUCT D

3、ESCRIPTIONThe AD780 is an ultrahigh precisi on ban dgap refere nee voltagewhich provides a 2.5V or 3.0 V output from in puts betwee n4.0 V and 36 V. Low in itial error and temperature drift com-bined with low output noise and the ability to drive any value ofcapacitanee make the AD780 the ideal choi

4、ce for enhancing theperforma nee of high resoluti on ADCs and DACs and for an yge neral purpose precisi on refere nee applicati on. A unique lowheadroom desig n facilitates a 3.0 V output from a 5.0 V 10% in put, provii ng a 20% boost to the dyn amic range of an ADC,over performa nee with exist ing

5、2.5 V refere nces.The AD780 can be used to source or sink up to 10 mA and canbe used in series orshunt mode, thus allowi ng positive or n ega-tive output voltages without exter nalcomp onen ts. This makes itsuitable for virtually any high performa nee refere nee applicatio n.U nlike some compet ing

6、refere nces, the AD780 has no“regio n of possiblein stability.” The part is stable un der all load coods whe n a 1 F bypass capacitor is used on the supply.A temperature output pin is provided on the AD780. This pro-vides an output voltage that varies linearly with temperature, al-lowing the AD780 t

7、o becon figured as a temperature tran sducerwhile provid ing a stable 2.5 V or 3.0 V output.The AD780 is a pin-compatible performa nee upgrade for theLT1019(A2.5 and the AD680. The latter is targeted towardlow power applicati ons.The AD780 is available in two grades in plastic DIP, SOIC an dcerdip p

8、ackages. The AD780AN, AD780AR, AD780BN an dAD780BR are specified for operatio n from F0C to +85 C.The AD780SQ and AD780SQ/883B are specified for -55C to+125 C operati on.FEATURESPin-Programmable 2.5 V or 3.0 V OutputUltralow Drift: 3 ppm/? C maxHigh Accuracy: 2.5 V or 3.0 V ? 1 mV maxLow Noise: 100

9、nV/V Hz NoiseReducti on CapabilityLow Quiesce nt Curre nt: 1 mA maxOutput Trim CapabilityPlug-I n Upgrade for Prese nt Refere ncesTemperature Output PinSeries or Shu nt Mode Operation ? 2.5 V, ? 3.0 VPRODUCT HIGHLIGHTS1. The AD780 provides a pin-programmable 2.5 V or 3.0 Voutput from a 4 V to 36V in

10、put.2. Laser trimming of both initial accuracy and temperaturecoefficients results in low errors over temperature without theuse of exter nal comp onen ts. The AD780BN has a maximumvariation of 0.8 mV from F0C to +85 C.3. For applications requiring even higher accuracy, an optionalfine-trim connecti

11、on is provided.4. The AD780 noise is extremely low, typically 4 V p-p from0.1 Hz to 10 Hz and a wideba nd spectral no ise den sity oftypically 100 nV/V by simply using two exter nal capacitors.5. The temperature output pin en ables the AD780 to be con fig-ured as a temperature tran sducer while prov

12、id ing a stableoutput refere nee voltage.AD780 SPECIFICATIONSAD780AN/AR/SQAD780BN/BRParameterMinTypMaxMinTypMaxUnitsOUTPUT VOLTAGE2.5 V Out2.4952.5052.4992.501Volts 3.0 V Out2.9953.0052.9993.001Volts OUTPUT VOLTAGE DRIFT1 -40C to +85 C 73ppm/C -55C to +125 C20ppm/CLINE REGULATION2.5 V Output, 4 V +V

13、IN 36 VT MIN to TMAX10* 卩 V/V3.0 V Output, 4.5 V +VIN 36 VT MIN to TMAX 10* 卩 V/VLOAD REGULATION, SERIES MODESourci ng 0 IOUT 10 mA50* V/mAT MIN to TMAX75* N/mASinking -0 IOUT 0 mA75* V/mA -40C to +85 C 75* M/mA -55C to +125 C 150* jV/mALOAD REGULATION, SHUNT MODEI ISHUNT UED ATMC7/1REV. A 七NOISE CO

14、MPARISONThe wideba nd no ise performa nee of the AD780 can also be ex-pressed in ppm. The typical performanee with C1, C2 is0.6 ppm and without external capacitors is 1.2 ppm.This performa nee is respectively 7? and 3? lower tha n thespecified performa nee of the LT1019.10Hz TO 10kHzFigure 6. Reduce

15、d Noise Performa nee with C1 = 100 F, C2 = 10QnFTEMPERATURE PERFORMANCEThe AD780 provides superior performa nee over temperature bymea ns of a comb in ati on of pate nted circuit desig n tech niq ues,precisi on thi n film resistors and drift trimming. Temperatureperforma nee is specified in terms of

16、 ppm/C, but because ofnon li nearity in the temperature characteristic, the Box-Testmethod is used to test and specify the part. The non li nearitytakes the form of the characteristic S-shaped curve show n inF igure 7. The Box-Test method forms a recta ngular box aroun dthis curve, enclosing the max

17、imum and minimum output volt-ages over the specified temperature ran ge. The specified drift isequal to the slope of the diago nal of this box.2.0-0.81400.4-0.4 -400-601.60.81.21201008060402020TEMPERATURE - E R R O R -m VFigure 7. Typical AD780BN Temperature DriftTEMPERATURE OUTPUT PINThe AD780 prov

18、ides a “TEMP output (Pin 3 that variesriy with temperature. This output can be used to mon itorcha nges in system ambie nt temperature and to in itiate calibra-tion of the system if desired.The voltage VTEMP is 560 mV at 25 C, anthe temperature co-efficient is approximately 2 mV/ C. Figure 8 followi

19、ng showsthe typical VTEMP characteristic curve over temperature.4.252.001502.502.25 H50 -52.753.003.253.503.754.001251007550250-5TEMPERATURE - CV O L T A G E O U TFigure 8. Temperature Pin Tran sfer CharacteristicSince the TEMP voltage is acquired from the bandgap core cir-cuit, current pulled from

20、this pin will have an effect on VOUT . Care must be taken to buffer the TEMP output with a suitableop amp, e.g., an AD OP07, AD820 or AD711 (all of whichwould result in less than a 100 V cha ng甲 in VOUT . The rela-tio nship between ITEMP and VOUT is as follows:?V OUT 5.8 mV/ 皿MP (2.5 V ran geor?V OU

21、T = 6.9 mV/ 甩? ITEMP (3.0 V rangeTEMPERATURE TRANSDUCER CIRCUITThe circuit shown in Figure 9 is a temperature transducer whicha amplifies theTEMP output voltage by a gain of a little over 5to provide a wider full scale output range. The trimpot can beused to adjust the output so it varies exactly by

22、 10 mVC. To mi ni mize resista nee cha nges with temperature, resistors withlow temperature coefficie nts, such as metal film resistors shouldbe used.10mV/ CFigure 9. Differe ntial Temperature Tran sducerAD780 SUPPLY CURRENT OVER TEMPERATURE +VIN The AD780quiesce nt curre nt will vary slightly over

23、temperature and in put supply ran ge. The test limit is 1 mA over the in dustrial and 1.3 mA over the military temperature ran ge. Typical performa nce with in put voltage and temperature variati on is show n in Figure 10 followi ng. 1 F Qi85 吒5C 2 AD780 6 VOUT 249 ? QUIESCENT CURRENT- mA 0.80 25 C4

24、 0.75 125 C 0.70 VL VOUT 0V Figure 12a. Transient Resistive Load Test Circuit 0.65 0.60 4 INPUT VOLTAGE -Volts 36 0mA 10mA OUTPUT CHANGE - 50mV/DIV ILOAD Figure 10. Typical Supply Curre nt over Temperature TURN-ONTIME VOUT (CL = OpF The time required for the output voltage to reach its final value w

25、ith in a specified error band is defi ned as the turn-on settli ng time. The two major factors that affect this are the active circuit settling time and the time for the thermal gradients on the chip to stabilize. Typical settling performanee is shown in Figure 11 following. The AD780 settles to wit

26、hin 0.1% of its fin al value within 10 s. 10 s/DIV Figur甲 12b.Settli ng Un der Tran sie nt Resistive Load VIN 5V 0V The dyn amic load may be resistive and capacitive. For example the load may be connected via a long capacitive cable. Figure 13 following shows the performance of the AD780 driving a 1

27、000 pF, 0 mA to 10 mA load. +VIN VOUT 2.500V 2.499V 2.498V 2 1 F 10/b/DIV AD780 6 CL VOUT Figure 11. Turn-O n Settli ng Time Performa nce DYNAMIC PERFORMANCE 4 1000pF 249 ? The output stage of the AD780 has bee n desig ned to provide superior static and dyn amic load regulatio n. Figure 12 shows the

28、 performa nce of the AD780 while driv ing a 0 mA to 10 mA load. VL VOUT 0V Figure 13a. Cap acitive Load Tran sie nt Respo nse Test Circuit -6-REV. AAD780 +5V 0mA 10mA OUTPUT CHANGE -50mV/DIV ILOAD 2 VIN VOUT(CL = 1000pF 1 F/OUT 6 VREF +F AD780 VREF +S GND 4 2.5/3.0V SELECT 8 AD7884 10(js/DIV Figure

29、13b. Settling Under Dynamic Capacitive Load LINE REGULATION Figure 15. Precision 3.0 V Reference for the AD7884 16-Bit, High Speed ADC Line regulation is a measure of the change in output voltage due to a specified cha nge in in put voltage. It is inten ded to simulate worst case un regulated supply

30、 con diti ons and is measured in V/V. Fig/re 14 shows typical performa nce with 4.0 V VIN 15.0 V. 200 T = 25 C The AD780 is also ideal for use with higher resolution conv erters such as the AD7710/AD7711/AD7712. (See Figure 16. While these parts are specified with a 2.5 V internal reference, the AD7

31、80 in 3 V mode can be used to improve the absolute accuracy, temperature stability and dyn amic ran ge. It is show n followi ng with the two optional noise reduction capacitors. +5V OUTPUT CHANGE - / 100 2 VIN 0 1 F VOUT 6 REFIN+ -00 AD780 3 100nF GND 4 4 10 INPUT VOLTAGE - Volts 15 100 F 2.5/3.0V S

32、ELECT 8 AD7710 -00 REFIN -Figure 14. Output VoltageChange vs. I nput Voltage PRECISION REFERENCE FOR HIGH RESOLUTION +5 VDATA CONVERTERS Figure 16. Precisi on 2.5 V or 3.0 V Refere nee for the AD7710High Resolutio n, Sigma-Delta ADC +4.5 V REFERENCE FROM +5 V SUPPLY TheAD780 is ideally suited to be

33、the referenee for most +5 V high resolution ADCs. TheAD780 is stable under any capacitive load, it has superior dynamic load performanee, and the 3.0 V output provides the conv erter with maximum dyn amic range without requiring an additional and expensive buffer amplifier. One of the many ADCs that theAD780 is suited for is the AD7884, a 16-bit, high speed sampling