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1.25 V Micropower, Precision Shunt Voltage Reference ADR1581
FEATURES
Wide operating range: 60 A to 10 mA 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 4 kV human body model 400 V machine model Compact, surface-mount SOT-23 package
PIN CONFIGURATION
V+ 1
ADR1581
3
NC (OR V-)
V- 2 NC = NO CONNECT
06672-001
TOP VIEW
Figure 1. SOT-23
20 18 16
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
QUANTITY
14 12 10 8 6 4 2 -10 0 10 TEMPERATURE DRIFT (ppm/C) 20
06672-002
0 -20
GENERAL DESCRIPTION
The ADR1581 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. The superior accuracy and stability of the ADR1581 is made possible by the precise matching and thermal tracking of onchip 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. 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
Figure 2. Reverse Voltage Temperature Drift Distribution
100 90 80 70
QUANTITY
1
60 50 40 30 20 10
-5 -4 -3 -2 -1 0 1 2 OUTPUT ERROR (mV) 3 4 5
06672-003
0
Figure 3. Reverse Voltage Error Distribution
Protected by U.S. Patent No. 5,969,657; other patents pending.
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 (c)2007 Analog Devices, Inc. All rights reserved.
ADR1581 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
5/07--Revision 0: Initial Version
Rev. 0 | Page 2 of 12
ADR1581 SPECIFICATIONS
TA = 25C, IIN = 100 A, unless otherwise noted. Table 1.
Parameter REVERSE VOLTAGE OUTPUT (SOT-23) REVERSE VOLTAGE TEMPERATURE DRIFT -40C to +85C MINIMUM OPERATING CURRENT, TMIN to TMAX REVERSE VOLTAGE CHANGE WITH REVERSE CURRENT 60 A < IIN < 10 mA, TMIN to TMAX 60 A < IIN < 1 mA, TMIN to TMAX DYNAMIC OUTPUT IMPEDANCE (VR/IR) IIN = 1 mA 100 A (f = 120 Hz) OUTPUT NOISE RMS Noise Voltage: 10 Hz to 10 kHz Low Frequency Noise Voltage: 0.1 Hz to 10 Hz TURN-ON SETTLING TIME TO 0.1% 1 OUTPUT VOLTAGE HYSTERESIS 2 TEMPERATURE RANGE Specified Performance, TMIN to TMAX Operating Range 3
1 2 3
Min 1.240
ADR1581A Typ Max 1.250 1.260 100 60 2.5 0.8 0.4 20 4.5 5 80 6
Min 1.2485
ADR1581B Typ Max 1.250 1.2515 50 60 2.5 0.8 0.4 20 4.5 5 80 6
Unit V ppm/C A mV mV V rms V p-p s V
1
0.5
-40 -55
+85 +125
-40 -55
+85 +125
C C
Measured with a no load capacitor. 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. The operating temperature range is defined as the temperature extremes at which the device continues to function. Parts may deviate from their specified performance.
Rev. 0 | Page 3 of 12
ADR1581 ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Reverse Current Forward Current Internal Power Dissipation1 SOT-23 (RT) Storage Temperature Range Operating Temperature Range ADR1581/RT Lead Temperature, Soldering Vapor Phase (60 sec) Infrared (15 sec) ESD Susceptibility2 Human Body Model Machine Model
1 2
Rating 25 mA 20 mA 0.3 W -65C to +150C -55C to +125C 215C 220C 4 kV 400 V
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
Specification is for device (SOT-23 package) in free air at 25C: JA = 300C/W. The human body model is a 100 pF capacitor discharged through 1.5 k. For the machine model, a 200 pF capacitor is discharged directly into the device.
Rev. 0 | Page 4 of 12
ADR1581 TYPICAL PERFORMANCE CHARACTERISTICS
2000 1500
80 100
REVERSE VOLTAGE CHANGE (ppm)
1000 20ppm/C 500 0 5ppm/C -500 -1000
REVERSE CURRENT (A)
60
40
+125C -40C
20 +25C
06672-004
-35
-15
5 25 45 65 TEMPERATURE (C)
85
105
125
0
0.2
0.4
0.6 0.8 1.0 REVERSE VOLTAGE (V)
1.2
1.4
Figure 4. Output Drift for Different Temperature Characteristics
Figure 7. Reverse Current vs. Reverse Voltage
7 6
1 -40C 0.8
FORWARD VOLTAGE (A)
REVERSE VOLTAGE CHANGE (mV)
5 4 3 2 1 0
06672-005
+85C
0.6
+25C +85C
0.4
+25C
-40C
0.2
0.10 1.00 REVERSE CURRENT (mA)
10
0.1
1 10 FORWARD CURRENT (mA)
100
Figure 5. Output Voltage Error vs. Reverse Current
Figure 8. Forward Voltage vs. Forward Current
600
NOISE VOLTAGE (nV/ Hz)
400
200
1.0
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 6. Noise Spectral Density
06672-006
Rev. 0 | Page 5 of 12
06672-008
-1 0.01
0 0.01
06672-007
-1500 -55
0
ADR1581 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 VBE goes to approximately the silicon band gap voltage. Therefore, if a voltage could be developed with an opposing temperature coefficient to sum with VBE, a zero TC reference would result. The ADR1581 circuit in Figure 9 provides such a compensating voltage, V1, by driving two transistors at different current densities and amplifying the resultant VBE difference (VBE), which has a positive TC. The sum of VBE and V1 provides a stable voltage reference.
V+
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.
VS RS VR IR VOUT
06672-010
IR + IL IL
Figure 10. Typical Connection Diagram
+5V(+3V) 10% RS VR VOUT
06672-011
2.94k (1.30k)
Figure 11. Typical Connection Diagram
V1
TEMPERATURE PERFORMANCE
The ADR1581 is designed for reference applications where stable temperature performance is important. Extensive temperature testing and characterization ensure that the device's 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 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 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.
VBE
VBE V-
Figure 9. Schematic 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, RS, determines the reverse current flowing through the ADR1581. The value of RS must be chosen to accommodate the expected variations of the supply voltage (VS), load current (IL), and the ADR1581 reverse voltage (VR) while maintaining an acceptable reverse current (IR) through the ADR1581. The minimum value for RS should be chosen when VS is at its minimum and IL and VR are at their maximum while maintaining the minimum acceptable reverse current. The value of RS should be large enough to limit IR to 10 mA when VS is at its maximum and IL and VR are at their minimum. The equation for selecting RS is as follows: RS = (VS - VR)/(IR + IL)
Rev. 0 | Page 6 of 12
06672-009
ADR1581
1.2508 (VMAX - VO) 1.2506 SLOPE = TC = (+85C - +25C) x 1.250V x 10 -6 1.2504
600 500
1.2502 1.2500 1.2498 1.2496 1.2494 1.2492 1.2490
06672-012
RESIDUAL DRIFT ERROR (ppm)
VMAX
OUTPUT VOLTAGE (V)
400
VO
300
200
SLOPE = TC = VMIN -35 -15 5 25
(VMIN - VO) (-40C - +25C) x 1.250V x 10 -6
100
45
65
85
105
125
-35
-15
5
25
45
65
85
105
125
TEMPERATURE (C)
TEMPERATURE (C)
Figure 12. Output Voltage vs. Temperature
Figure 13. Residual Drift Error
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 x 10-6 x 1.250 V x 65C). Therefore, the unit is guaranteed to be 1.250 V 5.6 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 ADR1581 produces curves similar to those in Figure 4 and Figure 12.
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 measuring the difference between the output voltage at +25C after operating at +85C and the output voltage at +25C after operating at -40C. Figure 14 displays the hysteresis associated with the ADR1581. This characteristic exists in all references and has been minimized in the ADR1581.
40 35 30 25 20 15 10 5
06672-014
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 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.
QUANTITY
0 -400
-300
-200
-100
0
100
200
300
400
HYSTERESIS VOLTAGE (V)
Figure 14. Reverse Voltage Hysteresis Distribution
Rev. 0 | Page 7 of 12
06672-013
1.2488 -55
0 -55
ADR1581
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 (IR = 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
40V/DIV 21V rms
(a)
20V/DIV
6.5V rms, t = 0.2ms
(b)
10V/DIV
2.90V rms, t = 960ms
10ms/DIV
Figure 17. Total RMS Noise
OUTPUT IMPEDANCE ()
100
CL = 0
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.
1M
10 IR = 0.1IR IR = 100A 1 IR = 1mA
CL = 1F
100
1k
10k
100k
FREQUENCY (Hz)
Figure 15. Output Impedance 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 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 17a). 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 Figure 17b). 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 17c).
4.48V p-p
06672-015
0.1 10
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 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.
2.4V 0V VIN
CL = 200pF
1V/DIV
250mV/DIV
5s/DIV
Figure 18. Turn-On Response Time
RS = 11.5k RL
+
06672-016
-
Figure 19. Turn-On, Settling, and Transient Test Circuit
TIME (1s/DIV)
Figure 16. 0.1 Hz to 10 Hz Voltage Noise
Rev. 0 | Page 8 of 12
006672-010
VIN
VR
CL
VOUT
06672-018
06672-017
(c)
ADR1581
Output turn-on time is modified when an external noise-reduction filter is used. When present, the time constant of the filter dominates the overall settling.
2.4V VIN 0V OUTPUT ERROR 1mV/DIV, 2s/DIV
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 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.
2.0V 1.8V VIN
Figure 20. Turn-On Settling
CL = 0.01F
TRANSIENT RESPONSE
Many ADCs and DACs present transient current loads to the reference. Poor reference response can degrade the converter's performance. Figure 21 displays both the coarse and fine settling characteristics of the device to load transients of 50 A.
20mV/DIV 1mV/DIV 10mV/DIV 50s/DIV
06672-022
06672-020
OUTPUT 0.5mV/DIV, 2ms/DIV
Figure 22. Transient Response with Capacitive Load
PRECISION MICROPOWER LOW DROPOUT REFERENCE
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.
3V 28.7k
IR = 150A + 50A STEP
(a)
(b)
IR = 150A - 50A STEP
06672-021
205 4.7F
20mV/DIV
1mV/DIV
1s/DIV
OP193
Figure 21. Transient Settling
VOUT = 1.250V OR VOUT = 1.250 (1 + R2/R3)
Figure 21a shows the settling characteristics of the device for an increased reverse current of 50 A. Figure 21b shows the response when the reverse current is decreased by 50 A. The transients settle to 1 mV in about 3 s.
ADR1581
R3
R2
06672-023
Figure 23. Micropower Buffered Reference
Rev. 0 | Page 9 of 12
ADR1581
USING THE ADR1581 WITH 3 V DATA CONVERTERS
The ADR1581 low output drift (50 ppm/C) and compact subminiature SOT-23 package make it ideally suited for today's 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 chargebalancing (-) 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 24 shows the ADR1581 connected to the AD7714/AD7715 for 3 V operation.
3V 28.7k REF IN(+)
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 IOUT2 terminal changes with DAC code. If the ADR1581 drives IOUT2 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.
3.3V
VDD VREF
RFB IOUT1
C1 IOUT2 AGND A1 A1: OP295 AD822 OP2283 VOUT
VIN
DAC
AD7714-3/AD7715-3
RSW 5k (TYP) CREF (3pF TO 8pF) SWITCHING FREQUENCY DEPENDS ON fCLKIN HIGH IMPEDANCE >1G
AD7943
DGND
ADR1581
REF IN(-)
3.3V
06672-024
29.4k
A1
06672-025
Figure 24. Reference Circuit for the AD7714-3/AD7715-3
ADR1581
SIGNAL GROUND
Figure 25. Single-Supply System
Rev. 0 | Page 10 of 12
ADR1581 OUTLINE DIMENSIONS
3.04 2.90 2.80 1.40 1.30 1.20
1
3
2.64 2.10
2
PIN 1 0.95 BSC 1.90 BSC 1.12 0.89 0.10 0.01 SEATING PLANE 0.50 0.30 0.60 0.50 0.40 0.20 0.08
COMPLIANT TO JEDEC STANDARDS TO-236-AB
Figure 26. 3-Lead Small Outline Transistor Package [SOT-23-3] (RT-3) Dimensions shown in millimeters
1.55 1.50 1.45
4.10 4.00 3.90
2.05 2.00 1.95
1.10 1.00 0.90
1.10 1.00 0.90
7" REEL 100.00 OR 13" REEL 330.00 0.35 0.30 0.25 20.20 MIN
14.40 MIN
8.30 8.00 7.70
3.55 3.50 3.45 3.20 3.10 2.90 1.00 MIN 0.75 MIN
2.80 2.70 2.60
1.50 MIN
13.20 13.00 12.80
7" REEL 50.00 MIN OR 13" REEL 100.00 MIN
DIRECTION OF UNREELING
Figure 27. Tape and Reel Dimensions (RT-3) Dimensions shown in millimeters
Rev. 0 | Page 11 of 12
053006-0
9.90 8.40 6.90
ADR1581
ORDERING GUIDE
Model ADR1581ARTZ-REEL7 1 ADR1581ARTZ-R21 ADR1581BRTZ-REEL71 ADR1581BRTZ-R21
1
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Initial Output Error 10 mV 10 mV 1 mV 1 mV
Temperature Coefficient 100 ppm/C 100 ppm/C 50 ppm/C 50 ppm/C
Package Description 3-Lead SOT-23-3 3-Lead SOT-23-3 3-Lead SOT-23-3 3-Lead SOT-23-3
Package Option RT-3 RT-3 RT-3 RT-3
Branding R2M R2M R2K R2K
Z = RoHS Compliant Part.
(c)2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06672-0-5/07(0)
Rev. 0 | Page 12 of 12

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