1.25 V Micropower, Precision Shunt
Voltage Reference
ADR1581
Rev. 0
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2007 Analog Devices, Inc. All rights reserved.
PIN CONFIGURATION
FEATURES
Wide operating range: 60 μA to 10 mA
NC = NO CONNECT
TOP VIEW
V+
1
V–
2
NC (OR V–)
3
ADR1581
06672-001
Initial accuracy: ±0.12% maximum
Temperature drift: ±50 ppm/°C maximum
Output impedance: 0.5 Ω maximum
Wideband noise (10 Hz to 10 kHz): 20 μV rms
Operating temperature range: −40°C to +85°C
High ESD rating Figure 1. SOT-23
4 kV human body model
0
2
4
6
8
10
12
14
16
18
20
TEMPERATURE DRIFT (ppm/°C)
QUANTITY
–20 –10 0 10 20
06672-002
400 V machine model
Compact, surface-mount SOT-23 package
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 Figure 2. Reverse Voltage Temperature Drift Distribution
The ADR15811 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.
0
10
20
30
40
50
60
70
80
90
100
OUTPUT ERROR (mV)
QUANTITY
–5 –4 –3 –2 –1 0 1 2 3 4 5
06672-003
The superior accuracy and stability of the ADR1581 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 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.
Figure 3. Reverse Voltage Error Distribution
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 −40°C to +85°C.
1 Protected by U.S. Patent No. 5,969,657.
ADR1581
Rev. 0 | Page 2 of 12
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
ADR1581
Rev. 0 | Page 3 of 12
SPECIFICATIONS
TA = 25°C, IIN = 100 µA, unless otherwise noted.
Table 1.
ADR1581A ADR1581B
Parameter Min Typ Max Min Typ Max Unit
REVERSE VOLTAGE OUTPUT (SOT-23) 1.240 1.250 1.260 1.2485 1.250 1.2515 V
REVERSE VOLTAGE TEMPERATURE DRIFT
−40°C to +85°C 100 50 ppm/°C
MINIMUM OPERATING CURRENT, TMIN to TMAX 60 60 A
REVERSE VOLTAGE CHANGE WITH REVERSE CURRENT
60 A < IIN < 10 mA, TMIN to TMAX 2.5 6 2.5 6 mV
60 A < IIN < 1 mA, TMIN to TMAX 0.8 0.8 mV
DYNAMIC OUTPUT IMPEDANCE (VR/∆IR)
IIN = 1 mA ± 100 A (f = 120 Hz) 0.4 1 0.4 0.5 Ω
OUTPUT NOISE
RMS Noise Voltage: 10 Hz to 10 kHz 20 20 V rms
Low Frequency Noise Voltage: 0.1 Hz to 10 Hz 4.5 4.5 V p-p
TURN-ON SETTLING TIME TO 0.1%1 5 5 µs
OUTPUT VOLTAGE HYSTERESIS2 80 80 µV
TEMPERATURE RANGE
Specified Performance, TMIN to TMAX −40 +85 −40 +85 °C
Operating Range3−55 +125 −55 +125 °C
1 Measured with a no load capacitor.
2 Output hysteresis is defined as the change in the +25°C output voltage after a temperature excursion to −40°C, then to +85°C, and back to +25°C.
3 The operating temperature range is defined as the temperature extremes at which the device continues to function. Parts may deviate from their specified
performance.
ADR1581
Rev. 0 | Page 4 of 12
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
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.
Reverse Current 25 mA
Forward Current 20 mA
Internal Power Dissipation1
SOT-23 (RT) 0.3 W
Storage Temperature Range −65°C to +150°C
Operating Temperature Range
ADR1581/RT −55°C to +125°C ESD CAUTION
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
ESD Susceptibility2
Human Body Model 4 kV
Machine Model 400 V
1 Specification is for device (SOT-23 package) in free air at 25°C: θJA = 300°C/W.
2 The human body model is a 100 pF capacitor discharged through 1.5 kΩ. For
the machine model, a 200 pF capacitor is discharged directly into the device.
ADR1581
Rev. 0 | Page 5 of 12
TYPICAL PERFORMANCE CHARACTERISTICS
2000
1500
1000
500
0
–500
–1000
–1500
REVERSE VOLTAGE CHANGE (ppm)
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
20ppm/°C
5ppm/°C
06672-004
100
80
60
40
20
0
REVERSE CURRENT (µA)
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
REVERSE VOLTAGE (V)
+125°C
+25°C
–40°C
06672-007
Figure 7. Reverse Current vs. Reverse Voltage
Figure 4. Output Drift for Different Temperature Characteristics
7
6
5
4
3
2
1
0
–1
REVERSE VOLTAGE CHANGE (mV)
0.01 0.10 1.00 10
REVERSE CURRENT (mA)
+85°C
+25°C –40°C
06672-005
1
0.8
0.6
0.4
0.2
0
FORWARD VOLTAGE (µA)
0.01 0.1 1 10 100
FORWARD CURRENT (mA)
06672-008
+85°C
+25°C
–40°C
Figure 8. Forward Voltage vs. Forward Current
Figure 5. Output Voltage Error vs. Reverse Current
FREQUENCY (Hz)
600
200
400
NOISE VOLTAGE (nV/ Hz)
1.0 10 100 1k 10k 100k 1M
06672-006
Figure 6. Noise Spectral Density
ADR1581
Rev. 0 | Page 6 of 12
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 11 shows a typical connection of the ADR1581BRT
operating at a minimum of 100 µA. This connection can
provide ±1 mA to the load while accommodating ±10%
power supply variations.
V
S
IR + IL
RS
VOUT
IL
VR
IR
0
6672-010
Figure 10. Typical Connection Diagram
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.
+5V(+3V) ±10%
2.94kΩ
(1.30kΩ)
R
S
V
R
V
OUT
0
6672-011
V
+
V–
V1
ΔV
BE
V
BE
06672-009
Figure 11. Typical Connection Diagram
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 refer-
ence 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 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.
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 +25°C to the
output values at +85°C and −40°C 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.
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)
ADR1581
Rev. 0 | Page 7 of 12
OUTPUT VOLTAGE (V)
1.2488
1.2498
1.2500
1.2502
1.2504
1.2506
1.2508
1.2494
1.2496
1.2490
1.2492
VMAX
VMIN
SLOPE = TC = (VMAX – VO)
(+85°C – +25°C) × 1.250V × 10–6
SLOPE = TC = (VMIN – VO)
(–40°C – +25°C) × 1.250V × 10–6
VO
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
06672-012
600
300
0
RESIDUAL DRIFT ERROR (ppm)
500
400
200
100
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
06672-013
Figure 12. Output Voltage vs. Temperature Figure 13. Residual Drift Error
REVERSE VOLTAGE HYSTERESIS
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 × 10−6 × 1.250 V × 65°C). Therefore, the
unit is guaranteed to be 1.250 V ± 5.6 mV over the operating
temperature range.
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 +25°C after operating
at +85°C and the output voltage at +25°C after operating at −40°C.
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 14 displays the hysteresis associated with the ADR1581.
This characteristic exists in all references and has been minimized
in the ADR1581.
Figure 4
and Figure 12.
VOLTAGE OUTPUT NONLINEARITY VS.
TEMPERATURE
QUANTITY
0
15
20
25
30
35
40
5
10
HYSTERESIS VOLTAGE (µV)
–400 –300 –200 –100 0 100 200 300 400
06672-014
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.
Figure 14. Reverse Voltage Hysteresis Distribution
ADR1581
Rev. 0 | Page 8 of 12
40µV/DIV 21µV rms
20µV/DIV
10µV/DIV
10ms/DIV
6.5µV rms, t = 0.2ms
(a)
(b)
(c)
2.90µV rms, t = 960ms
06672-017
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 µF load
capacitor connected directly across the ADR1581 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
= 1µF
ΔI
R
= 0.1I
R
I
R
= 100µA
I
R
= 1mA
OUTPUT IMPEDANCE (Ω)
10 100 1k 10k 100k 1M
06672-015
Figure 17. Total RMS Noise
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.
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 wave-
form after power-up.
Figure 15. Output Impedance vs. Frequency
NOISE PERFORMANCE AND REDUCTION
The noise generated by the ADR1581 is typically less than
5 µV p-p over the 0.1 Hz to 10 Hz band. 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 µs, and there is no long thermal
tail when the horizontal scale is expanded to 2 ms/div.
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
250mV/DIV 5µs/DIV
C
L
= 200pF
V
IN
0V
2.4V
06672-018
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).
1µV/DIV
TIME (1s/DIV)
4.48µV p-p
06672-016
Figure 18. Turn-On Response Time
+
–
R
S
= 11.5kΩR
L
C
L
V
OUT
V
R
V
IN
006672-010
Figure 19. Turn-On, Settling, and Transient Test Circuit
Figure 16. 0.1 Hz to 10 Hz Voltage Noise
ADR1581
Rev. 0 | Page 9 of 12
Output turn-on time is modified when an external noise-reduction
filter is used. When present, the time constant of the filter dom-
inates the overall settling.
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
0V
V
IN
2.4V
OUTPUT ERROR
1mV/DIV, 2µs/DIV
OUTPUT
0.5mV/DIV, 2ms/DIV
0
6672-020
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.
1.8V
2.0V
V
IN
C
L
= 0.01µF
50µs/DIV10mV/DIV
06672-022
Figure 20. Turn-On Settling
TRANSIENT RESPONSE
Many ADCs and DACs present transient current loads to the
reference. Poor reference response can degrade the converter’s
performance.
Figure 22. Transient Response with Capacitive Load
Figure 21 displays both the coarse and fine settling characteristics
of the device to load transients of ±50 A. PRECISION MICROPOWER LOW DROPOUT
REFERENCE
1mV/DIV
20mV/DIV
1µs/DIV1mV/DIV
20mV/DIV
(a)
(b)
I
R
= 150µA – 50µA STEP
I
R
= 150µA + 50µA STEP
06672-021
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 µW.
3
V
28.7kΩ
ADR1581
OP193
V
OUT
= 1.250V
OR
V
OUT
= 1.250 (1 + R2/R3)
R3 R2
4.7µF
205Ω
06672-023
Figure 21. Transient Settling
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 µA. The transients
settle to 1 mV in about 3 µs.
Figure 23. Micropower Buffered Reference
ADR1581
Rev. 0 | Page 10 of 12
USING THE ADR1581 WITH 3 V DATA
CONVERTERS
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.
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 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.
DAC
R
FB
AGND
DGND
A1
C1
3.3
V
29.4kΩ
3.3V
ADR1581
SIGNAL GROUND
A1: OP295
AD822
OP2283
A1
V
REF
V
IN
V
DD
I
OUT1
I
OUT2
V
OUT
AD7943
06672-025
Figure 24 shows the ADR1581 connected to the
AD7714/AD7715 for 3 V operation.
AD7714-3/AD7715-3
A
DR1581
3
V
28.7kΩ
REF IN(+)
REF IN(–)
HIGH
IMPEDANCE
>1GΩ
R
SW
5kΩ (TYP)
C
REF
(3pF TO 8pF)
SWITCHING
FREQUENCY DEPENDS
ON
fCLKIN
06672-024
Figure 24. Reference Circuit for the AD7714-3/AD7715-3
Figure 25. Single-Supply System
ADR1581
Rev. 0 | 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
12
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
Figure 26. 3-Lead Small Outline Transistor Package [SOT-23-3]
(RT-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 27. Tape and Reel Dimensions
(RT-3)
Dimensions shown in millimeters
ADR1581
Rev. 0 | Page 12 of 12
ORDERING GUIDE
Temperature
Range
Initial Output
Error
Temperature
Coefficient
Package
Option Model Package Description Branding
ADR1581ARTZ-REEL7 −40°C to +85°C 10 mV 100 ppm/°C 3-Lead SOT-23-3 RT-3 R2M
1
ADR1581ARTZ-R2 −40°C to +85°C 10 mV 100 ppm/°C 3-Lead SOT-23-3 RT-3 R2M
1
ADR1581BRTZ-REEL7 −40°C to +85°C 1 mV 50 ppm/°C 3-Lead SOT-23-3 RT-3 R2K
1
ADR1581BRTZ-R2 −40°C to +85°C 1 mV 50 ppm/°C 3-Lead SOT-23-3 RT-3 R2K
1
1 Z = RoHS Compliant Part.
©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06672-0-5/07(0)
