High Precision Voltage Reference AD588* NOISE REDUCTION VHIGH SEN

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High Precision Voltage Reference AD588* NOISE REDUCTION VHIGH SEN

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FEATURES Drift: ppm/ Initial Error: Pin-Programmable Output Tracking, Flexible Output Force Sense Terminals High Impedance Ground Sense Machine-lnsertable Packaging MIL-STD-883 Compliant Versions Available
High Precision Voltage Reference AD588*
NOISE REDUCTION VHIGH SENSE
FORCE SENSE FORCE
PRODUCT DESCRIPTION
AD588 represents major advance state-of-the-art monolithic voltage references. initial error temperature drift give AD588 absolute accuracy performance previously available monolithic form. AD588 uses proprietary ion-implanted buried Zener diode, laser-waferdrift trimming high stability thin-film resistors provide outstanding performance cost. AD588 includes basic reference cell three additional amplifiers which provide pin-programmable output ranges. amplifiers laser-trimmed offset drift maintain accuracy reference. amplifiers configured allow Kelvin connections load and/or boosters driving long lines high-current loads, delivering full accuracy AD588 where required application circuit. initial error allows AD588 used system reference precision measurement applications requiring 12-bit absolute accuracy. such systems, AD588 provide known voltage system calibration software drift allows compensation drift other components system. Manual system calibration cost periodic recalibration therefore eliminated. Furthermore, mechanical instability trimming potentiometer potential improper calibration eliminated using AD588 conjunction autocalibration software. AD588 available seven versions. AD588 grades packaged 16-pin cerdip specified +70°C operation. AD588AQ grades packaged 16-pin cerdip specified -25°C +85°C industrial temperature range. ceramic AD588SQ grades specified full military/aerospace temperature range. military surface mount applications, AD588SE grades also available 20-pin packages.
*Covered Patent Number 4,644,253.
AD588
GAIN
SENSE
SENSE
VLOW
PRODUCT HIGHLIGHTS
AD588 offers 12-bit absolute accuracy without user adjustments. Optional fine-trim connections provided applications requiring higher precision. fine-trimming does alter operating conditions Zener buffer amplifiers thus does increase temperature drift. Output noise AD588 very low-typically p-p. provided additional noise filtering using external capacitor. precision tracking mode with Kelvin output connections available with external components. Tracking error less than millivolt fine-trim available applications requiring exact symmetry between outputs. strapping capability allows configuration wide variety outputs: dual outputs single outputs. Extensive temperature testing -55°C, -25°C, 0°C, +25°C, +50°C, +70°C, +85°C +125°C ensures that specified temperature coefficient truly representative device performance.
REV.
Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Analog Devices.
Technology Way, P.O. 9106, Norwood, 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AD588-SPECIFICATIONS
OUTPUT VOLTAGE ERROR Outputs Outputs TRACKING MODE Symmetry Error OUTPUT VOLTAGE DRIFT +70°C -25°C +85°C -55°C +125°C GAIN ADJ2 Trim Range Input Resistance LINE REGULATION TMIN TMAX3 LOAD REGULATION TMIN TMAX Output, IOUT Output, IOUT SUPPLY CURRENT TMIN TMAX Power Dissipation OUTPUT NOISE (Any Output) Spectral Density, LONG-TERM STABILITY +25°C) BUFFER AMPLIFIERS Offset Voltage Offset Voltage Drift Bias Current Open Loop Gain Output Current Common-Mode Rejection (A3, Short-Circuit Current TEMPERATURE RANGE Specified Performance Grades Grades Grades -1.5
(typical output,
unless otherwise noted1)
AD588KQ/BQ -0.75 -1.5 +0.75 +1.5 Units ppm/°C ppm/°C ppm/°C µV/V
AD588SQ +1.5
AD588JQ/AQ/TQ -1.5 +1.5
µV/mA µV/mA nV/Hz ppm/1000 µV/°C
+125
+125
NOTES Output Configuration Figure Figure Figure Specifications tested using configuration unless otherwise indicated. Gain balance adjustments guaranteed capable trimming output voltage error symmetry error zero. Test Conditions: Output 13.5 Output -13.5 Output +10.8 -10.8 Specifications subject change without notice Specifications shown boldface tested production units final electrical test. Results from those tests used calculate outgoing quality levels. specifications guaranteed, although only those shown boldface tested production units.
ORDERING GUIDE
Part Number1 AD588AQ AD588BQ AD588SQ AD588TQ AD588JQ AD588KQ
NOTES
Initial Error
Temperature Temperature Package Coefficient Range Option ppm/°C ppm/°C ppm/°C ppm/°C ppm/°C ppm/°C +852 +125 +125 Cerdip (Q-16) Cerdip (Q-16) Cerdip (Q-16) Cerdip (Q-16) Cerdip (Q-16) Cerdip (Q-16)
details grade package offerings screened accordance with MIL-STD-883, refer Analog Devices Military Products Databook current AD588/883B. Temperature coefficient specified from +70°C.
REV.
AD588
ABSOLUTE MAXIMUM RATINGS*
Power Dissipation (+25°C) Package Storage Temperature Range -65°C +150°C Lead Temperature Range (Soldering sec) +300°C Package Thermal Resistance (JA/JC) .90/25°C/W Output Protection: Outputs Safe Shorted Ground
*Stresses above those listed under "Absolute Maximum Ratings" cause permanent damage device. This stress rating only functional operation device these other conditions above those indicated operational sections this specification implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
REDUCTION (Pin form low-pass filter reduce noise contribution Zener circuit. matched nominal thin-film resistors divide output half. (Pin provides access center voltage span (BALANCE ADJUST) used fine adjustment this division. Ground sensing circuit provided amplifier noninverting input (Pin senses system ground which will transferred point circuit where inverting input (Pin connected. This output drives appropriate voltage. Thus, connected VLOW will same voltage system ground. Alternatively, connected pin, will ground will respectively. Amplifiers internally compensated used buffer voltages Pins well provide full Kelvin output. Thus, AD588 full Kelvin capability providing means sense system ground provide forced sensed outputs referenced that ground.
APPLYING AD588
CONFIGURATIONS
AD588 configured provide reference outputs shown Figures respectively. also used provide tracking reference shown Figure Table details appropriate connections each output range. each case, connected system ground power applied Pins
THEORY OPERATION
AD588 consists buried Zener diode reference, amplifiers used provide programmable output ranges, associated thin-film resistors shown block diagram Figure temperature compensation circuitry provides device with temperature coefficient ppm/°C less.
architecture AD588 provides ground sense uncommitted output buffer amplifiers which offer user great deal functional flexibility. AD588 specified tested configurations shown Figure user choose take advantage many other configuration options available with AD588. However, performance these configurations guaranteed meet extremely stringent data sheet specifications. indicated Table buffered output provided using amplifier configuration (Figure 2a). buffered output provided using amplifier configuration (Figure 2c). Specifications guaranteed outputs these configurations. Performance will similar that specified outputs. indicated Table unbuffered outputs available Pins Loading these unbuffered outputs will impair circuit performance. Amplifiers used interchangeably. However, AD588 tested (and specifications guaranteed) with amplifiers connected indicated Figure Table When either unused, output force sense pins should connected input tied ground.
Figure AD588 Functional Block Diagram
Amplifier performs several functions. primarily acts amplify Zener voltage from required output. addition, also provides external adjustment output through GAIN ADJUST. Using bias compensation resistor between Zener output noninverting input capacitor added NOISE REV.
outputs same voltage obtained connecting both appropriate unbuffered output Pins Performance these dual output configurations will typically meet data sheet specifications.
CALIBRATION
Generally, AD588 will meet requirements precision system without additional adjustment. Initial output voltage error output noise specs allow
AD588
Table AD588 Connections
Range
Connect Unbuffered1 Output Pins Pin:
Buffered Output Connections
Buffered Output Pins
11-13 14-15 8-13 14-15 8-13 14-15 11-4 8-13 14-15
"Unbuffered" outputs should loaded.
accuracies 12-16 bits. However, applications where even greater level accuracy required, additional calibration called for. Provision trimming been made through GAIN ADJUST BALANCE ADJUST pins (Pins respectively). AD588 provides precision span with center (VCT) which used with buffer ground sense amplifiers achieve voltage output configurations Table GAIN ADJUST BALANCE ADJUST used these configurations trim magnitude span voltage position center within span. GAIN ADJUST should performed first. Although trims interactive within device, GAIN trim will move BALANCE trim point changes magnitude span. Figure shows GAIN BALANCE trims tracking configuration. 20-turn potentiometer used each trim. potentiometer GAIN trim connected between Pins (VHIGH) (VLOW) with wiper connected (GAIN ADJ). potentiometer adjusted produce exactly between Pins amplifier outputs. BALANCE potentiometer, also connected between Pins with wiper (BAL ADJ), then adjusted center span from Trimming other configurations works exactly same manner. When producing GAIN used trim used trim configuration, GAIN again used trim magnitude span, while used trim center tap, single output configurations, GAIN used trim outputs utilizing full span (+10 while used trim outputs using half span Input impedance both GAIN ADJUST BALANCE ADJUST pins approximately GAIN ADJUST trim network effectively attenuates across trim potentiometer factor about 1500 provide trim range -3.5 +7.5 with resolution approximately µV/turn turn potentiometer). BALANCE ADJUST trim network attenuates trim voltage factor about 1400, providing trim range with resolution µV/turn. REV.
Figure Output
Figure Outputs
AD588
Figure Effect Noise Reduction Capacitor Broadband Noise
TURN-ON TIME
Figure Output
Trimming AD588 introduces additional errors over temperature precision potentiometers required. single output voltage ranges, cases when BALANCE ADJUST required, should connected GAIN ADJUST required, should left floating.
NOISE PERFORMANCE REDUCTION
Upon application power (cold start), time required output voltage reach final value within specified error band turn-on settling time. components normally associated with this are: time active circuits settle time thermal gradients chip stabilize. Figure shows turn-on characteristics AD588. shows settling about Note absence thermal tails when horizontal scale expanded ms/cm Figure
noise generated AD588 typically less than over band. Noise bandwidth approximately p-p. dominant source this noise buried Zener which contributes approximately nV/Hz. comparison, amp's contribution negligible. Figure shows noise typical AD588.
Electrical Turn-On
Figure Noise
further noise reduction desired, optional capacitor added between NOISE REDUCTION ground shown Figure This will form low-pass filter with output Zener cell. capacitor will have point will reduce high frequency MHz) noise about p-p. Figure shows noise typical AD588 both with without capacitor. Note that second capacitor needed order implement NOISE REDUCTION feature when using AD588 mode (Figure 2c.). NOISE REDUCTION capacitor limited maximum this mode. REV.
Extended Time Scale Figure Turn-On Characteristics
Output turn-on time modified when external noise reduction capacitor used. When present, this capacitor presents additional load internal Zener diode's current source, resulting somewhat longer turn-on time. case capacitor, initial turn-on time approximately (see Figure Note: NOISE REDUCTION feature used configuration, resistor between Pins required proper start
AD588
Figure Maximum Output Change-mV
KELVIN CONNECTIONS
Figure Turn-On with
TEMPERATURE PERFORMANCE
AD588 designed precision reference applications where temperature performance critical. Extensive temperature testing ensures that device's high level performance maintained over operating temperature range. Figure shows typical output voltage drift AD588BD illustrates test methodology. Figure bounded sides operating temperature extremes bottom maximum minimum output voltages measured over operating temperature range. slope diagonal drawn from lower left corner determines performance grade device.
Force sense connections, also referred Kelvin connections, offer convenient method eliminating effects voltage drops circuit wires. seen Figure load current wire resistance produce error (VERROR load. Kelvin connection Figure overcomes problem including wire resistance within forcing loop amplifier sensing load voltage. amplifier corrects errors load voltage. circuit shown, output amplifier would actually volts VERROR voltage load would desired volts. AD588 three amplifiers which used implement Kelvin connections. Amplifier dedicated ground force-sense function while uncommitted amplifiers free other force-sense chores. some single-output applications, amplifier unused.
Figure Typical AD588BD Temperature Drift
Each AD588A grade unit tested -25°C, 0°C, +25°C, +50°C, +70°C +85°C. Each AD588S grade unit tested -55°C, -25°C, 0°C, +25°C, +50°C, +70°C +125°C. This approach ensures that variations output voltage that occur temperature changes within specified range will contained within whose diagonal slope equal maximum specified drift. position vertical scale will change from device device initial error shape curve vary. Maximum height appropriate temperature range shown Figure Duplication these results requires combination high accuracy stable temperature control test system. Evaluation AD588 will produce curve similar that Figure output readings vary depending test methods equipment utilized.
Open Loop Frequency Response (A3,
Power Supply Rejection Frequency (A3,
REV.
AD588
Unity Gain Follower Pulse Response (Large Signal)
Unity Gain Follower Pulse Response (Small Signal)
DYNAMIC PERFORMANCE
output buffer amplifiers designed provide AD588 with static dynamic load regulation superior less complete references. Many converters present transient current loads reference, poor reference response degrade converter's performance.
Figure Advantage Kelvin Connection
Figure displays characteristics AD588 output amplifier driving load.
such cases, unused amplifier should connected unity-gain follower (force sense tied together) input should connected ground. unused amplifier section used other circuit functions well. curves this page show typical performance
Figure 10a. Transient Load Test Circuit
Common-Mode Rejection Frequency (A3, Figure 10b. Large-Scale Transient Response
NOISE REDUCTION VHIGH SENSE
FORCE SENSE FORCE
AD588
GAIN
SENSE
SENSE
VLOW
Input Noise Voltage Spectral Density
REV.
Figure 10c. Fine Scale Settling Transient Load
AD588
Figure displays output amplifier characteristics driving load, common situation found when reference shared among multiple converters used provide bipolar offset current. Figure displays crosstalk between output amplifiers. trace shows output dc-coupled offset volts, while output subjected mA-to-10 load current step. transient settles about load-induced offset about
Figure 11a. Transient Constant Load Test Circuit Figure 13a. Load Crosstalk Test Circuit
Figure 11b. Transient Response mA-10 Load
some applications, varying load both resistive capacitive nature, connected AD588 long capacitive cable. Figure displays output amplifier characteristics driving 1,000 mA-to-10 load.
Figure 13b. Load Crosstalk
Attempts drive large capacitive load excess 1,000 result ringing oscillation, shown step response photo (Figure 14a). This additional pole formed load capacitance output impedance amplifier, which consumes phase margin. recommended method driving capacitive loads this magnitude shown Figure 14b. resistor isolates capacitive load from output stage, while resistor provides feedback path preserves output accuracy capacitor provides high frequency feedback loop. performance this circuit shown Figure 14c.
Figure 12a. Capacitive Load Transient Response Test Circuit
Figure 14a. Output Amplifier Step Response,
Figure 12b. Output Response with Capacitive Load
REV.
AD588
USING AD588 WITH CONVERTERS
AD588 ideal reference wide variety converters. Several representative examples follow.
14-Bit Digital-to-Analog Converter-AD7535
High resolution CMOS converters require reference voltage high precision maintain rated accuracy. combination AD588 AD7535 takes advantage initial accuracy, drift full Kelvin output capability AD588 well resolution, monotonicity accuracy AD7535 produce subsystem with outstanding characteristics.
Figure 14b. Compensation Capacitive Loads
16-Bit Digital-to-Analog Converter-AD569
Another application which fully utilizes capabilities AD588 supplying reference AD569, shown Figure Amplifier senses system common forces assume this value, producing Pins respectively. Amplifiers buffer these voltages appropriate reference force-sense pins AD569. full Kelvin scheme eliminates effect circuit traces wires wire bonds AD588 AD569 themselves, which would otherwise degrade system performance.
SUBSTITUTING INTERNAL REFERENCES
Figure 14c. Output Amplifier Step Response Using Figure Compensation
Many converters include built-in references. Unfortunately, such references major source drift these converters. using more stable external reference like AD588, drift performance improved dramatically.
Figure AD588/AD7535 Connections
REV.
AD588
Figure High Accuracy Tracking Reference AD569
12-Bit Analog-to-Digital Converter-AD574A
AD574A specified gain drift from ppm/°C ppm/°C, (depending grade) using on-chip reference. reference contributes typically this drift. Therefore, total drift using AD588 supply reference improved factor Using this combination result apparent increases fullscale error difference between on-board reference which device laser trimmed external reference
with which device actually applied. on-board reference specified while external reference specified This result apparent full-scale error beyond specified AD574 gain error. Resistors allow this error nulled. Their contribution full-scale drift negligible. high output drive capability allows AD588 drive converters multi-converter system. converters will have gain errors that track better than ppm/°C.
Figure AD588/AD574A Connections
REV.
-10-
AD588
EXCITATION
Resistance Temperature Detector (RTD) circuit element whose resistance characterized positive temperature coefficient. measurement resistance indicates measured temperature. Unfortunately, resistance wires leading often adds error this measurement. 4-wire ohms measurement overcomes this problem. This method uses wires bring excitation current additional wires resulting voltage. these additional wires high input impedance measurement circuit, effect their resistance negligible. Therefore, they transmit true voltage.
Figure Boosted Precision Current Source
BRIDGE DRIVER CIRCUITS
Figure 4-Wire Ohms Measurement
practical consideration when using 4-wire ohms technique with self-heating effect that excitation current temperature RTD. designer must choose smallest practical excitation current that still gives desired resolution. manufactures usually specify self-heating, effect each their models types RTDs. Figure shows AD588 providing precision excitation current RTD. small excitation current dissipates mere power RTD.
Wheatstone bridge common transducer. simplest form, bridge consists terminal elements connected form quadrilateral, source excitation connected along diagonals detector comprising other diagonal. Figure shows simple bridge driven from unipolar excitation supply. differential voltage, proportional deviation element from initial bridge values. Unfortunately, this bridge output voltage riding common-mode voltage equal approximately VIN/2. Further processing this signal necessarily limited high common-mode rejection techniques such instrumentation isolation amplifiers. Figure shows same bridge transducer, this time driven from pair bipolar supplies. This configuration ideally eliminates common-mode voltage relaxes restrictions processing elements that follow.
Unipolar Drive
Figure Precision Current Source
BOOSTED PRECISION CURRENT SOURCE
current-source application load current limited output drive capability amplifier event that more drive current needed, series pass transistor inserted inside feedback loop provide higher current. Accuracy drift performance unaffected pass transistor.
Bipolar Drive Figure Bridge Transducer Excitation
REV.
-11-
AD588
shown Figure AD588 excellent choice control element bipolar bridge driver scheme. Transistors serve series pass elements boost current drive capability required typical bridge. differential gain stage still required bridge balance perfect. Such gain stages expensive. Additional common-mode voltage reduction realized using circuit illustrated Figure ground sense amplifier, servo's supplies bridge maintain virtual ground center tap. voltage which appears opposite center single-ended (referred ground) amplified less expensive circuit.
C1016b-10-10/86 PRINTED U.S.A.
Figure Bipolar Bridge Drive
Figure Floating Bipolar Bridge Drive with Minimum
OUTLINE DIMENSIONS
Dimensions shown inches (mm).
Cerdip Package
REV.
-12-

High Precision Voltage Reference AD588* NOISE REDUCTION VHIGH SEN

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