AD ADR1581 1.25 v micropower, precision shunt voltage reference Datasheet

1.25 V Micropower, Precision Shunt
Voltage Reference
ADR1581
PIN CONFIGURATION
FEATURES
Wide operating range: 60 μA to 10 mA
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
4 kV human body model
400 V machine model
Compact, surface-mount SOT-23 package
V+ 1
ADR1581
3
NC (OR V–)
TOP VIEW
NC = NO CONNECT
06672-001
V– 2
Figure 1. SOT-23
20
18
16
APPLICATIONS
14
QUANTITY
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.
8
4
2
0
–20
–10
0
10
TEMPERATURE DRIFT (ppm/°C)
20
Figure 2. Reverse Voltage Temperature Drift Distribution
100
90
80
70
QUANTITY
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 μA and 10 mA.
10
6
GENERAL DESCRIPTION
1
12
06672-002
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
60
50
40
30
20
10
0
–5
–4
–3
–2
–1
0
1
2
OUTPUT ERROR (mV)
3
4
5
06672-003
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.
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
©2007 Analog Devices, Inc. All rights reserved.
ADR1581
TABLE OF CONTENTS
Features .............................................................................................. 1
Temperature Performance............................................................6
Applications....................................................................................... 1
Voltage Output Nonlinearity vs. Temperature ..........................7
General Description ......................................................................... 1
Reverse Voltage Hysteresis...........................................................7
Pin Configuration............................................................................. 1
Output Impedance vs. Frequency ...............................................8
Revision History ............................................................................... 2
Noise Performance and Reduction .............................................8
Specifications..................................................................................... 3
Turn-On Time ...............................................................................8
Absolute Maximum Ratings............................................................ 4
Transient Response .......................................................................9
ESD Caution.................................................................................. 4
Precision Micropower Low Dropout Reference .......................9
Typical Performance Characteristics ............................................. 5
Using the ADR1581 with 3 V Data Converters ..................... 10
Theory of Operation ........................................................................ 6
Outline Dimensions ....................................................................... 11
Applying the ADR1581................................................................ 6
Ordering Guide .......................................................................... 12
REVISION HISTORY
5/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 12
ADR1581
SPECIFICATIONS
TA = 25°C, IIN = 100 μA, unless otherwise noted.
Table 1.
Parameter
REVERSE VOLTAGE OUTPUT (SOT-23)
REVERSE VOLTAGE TEMPERATURE DRIFT
−40°C to +85°C
MINIMUM OPERATING CURRENT, TMIN to TMAX
REVERSE VOLTAGE CHANGE WITH REVERSE CURRENT
60 μA < IIN < 10 mA, TMIN to TMAX
60 μA < IIN < 1 mA, TMIN to TMAX
DYNAMIC OUTPUT IMPEDANCE (∆VR/ΔIR)
IIN = 1 mA ± 100 μA (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
Min
1.2485
ADR1581B
Typ
Max
1.250
1.2515
100
60
Unit
V
50
60
ppm/°C
μA
2.5
0.8
6
2.5
0.8
6
mV
mV
0.4
1
0.4
0.5
Ω
20
4.5
5
80
−40
−55
20
4.5
5
80
+85
+125
−40
−55
μV rms
μV p-p
μs
μV
+85
+125
Measured with a no load capacitor.
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.
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
°C
°C
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
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.
Rating
25 mA
20 mA
0.3 W
−65°C to +150°C
−55°C to +125°C
ESD CAUTION
215°C
220°C
4 kV
400 V
Specification is for device (SOT-23 package) in free air at 25°C: θJA = 300°C/W.
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.
Rev. 0 | Page 4 of 12
ADR1581
TYPICAL PERFORMANCE CHARACTERISTICS
100
1500
80
REVERSE CURRENT (µA)
REVERSE VOLTAGE CHANGE (ppm)
2000
1000
20ppm/°C
500
0
5ppm/°C
–500
60
40
+125°C
–40°C
20
–1000
5
25
45
65
TEMPERATURE (°C)
85
105
125
0
7
0.6
0.8
1.0
REVERSE VOLTAGE (V)
1.2
1.4
100
1
6
–40°C
0.8
4
FORWARD VOLTAGE (µA)
5
+85°C
3
2
1
–40°C
+25°C
+25°C
0.6
+85°C
0.4
0.2
0
–1
0.01
0.10
1.00
REVERSE CURRENT (mA)
10
0
0.01
06672-005
REVERSE VOLTAGE CHANGE (mV)
0.4
Figure 7. Reverse Current vs. Reverse Voltage
Figure 4. Output Drift for Different Temperature Characteristics
600
400
10
100
1k
10k
FREQUENCY (Hz)
100k
1M
06672-006
200
1.0
0.1
1
10
FORWARD CURRENT (mA)
Figure 8. Forward Voltage vs. Forward Current
Figure 5. Output Voltage Error vs. Reverse Current
NOISE VOLTAGE (nV/ Hz)
0.2
06672-007
–15
06672-004
–35
0
06672-008
+25°C
–1500
–55
Figure 6. Noise Spectral Density
Rev. 0 | Page 5 of 12
ADR1581
THEORY OF OPERATION
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.
VS
RS
IR + IL
IL
VR
IR
06672-010
VOUT
Figure 10. Typical Connection Diagram
+5V(+3V) ±10%
RS
2.94kΩ
(1.30kΩ)
VR
VOUT
06672-011
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 (ΔVBE), which has a
positive TC. The sum of VBE and V1 provides a stable voltage
reference.
V+
Figure 11. Typical Connection Diagram
TEMPERATURE PERFORMANCE
V1
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.
VBE
V–
06672-009
ΔVBE
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.
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 +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 equation for selecting RS is as follows:
RS = (VS − VR)/(IR + IL)
Rev. 0 | Page 6 of 12
ADR1581
1.2508
600
(VMAX – VO)
1.2506 SLOPE = TC =
(+85°C – +25°C) × 1.250V × 10 –6
OUTPUT VOLTAGE (V)
RESIDUAL DRIFT ERROR (ppm)
VMAX
1.2504
1.2502
1.2500
VO
1.2498
1.2496
1.2494
1.2492
SLOPE = TC =
(VMIN – VO)
(–40°C – +25°C) × 1.250V × 10 –6
500
400
300
200
100
VMIN
–15
5
25
45
65
85
TEMPERATURE (°C)
105
125
0
–55
–35
–15
5
25
45
65
85
105
125
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 × 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.
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 +25°C after operating
at +85°C and the output voltage at +25°C after operating at −40°C.
Figure 14 displays the hysteresis associated with the ADR1581.
This characteristic exists in all references and has been minimized
in the ADR1581.
VOLTAGE OUTPUT NONLINEARITY VS.
TEMPERATURE
40
Rev. 0 | Page 7 of 12
35
30
QUANTITY
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.
25
20
15
10
5
0
–400
–300
–200
–100
0
100
200
300
HYSTERESIS VOLTAGE (µV)
Figure 14. Reverse Voltage Hysteresis Distribution
400
06672-014
–35
06672-012
1.2488
–55
06672-013
1.2490
ADR1581
OUTPUT IMPEDANCE VS. FREQUENCY
40µV/DIV
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 kΩ (IR = 100 μA) 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%.
21µV rms
(a)
20µV/DIV
6.5µV rms, t = 0.2ms
(b)
(c)
10ms/DIV
1k
06672-017
2.90µV rms, t = 960ms
10µV/DIV
OUTPUT IMPEDANCE (Ω)
Figure 17. Total RMS Noise
100
TURN-ON TIME
CL = 0
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.
10
ΔIR = 0.1IR
IR = 100µA
CL = 1µF
1
0.1
10
100
1k
10k
100k
FREQUENCY (Hz)
1M
06672-015
IR = 1mA
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 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 μV 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 μV 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 μV rms (see Figure 17c).
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 μs, and there is no long thermal
tail when the horizontal scale is expanded to 2 ms/div.
2.4V
VIN
0V
CL = 200pF
250mV/DIV
1µV/DIV
06672-018
4.48µV p-p
5µs/DIV
Figure 18. Turn-On Response Time
RL
RS = 11.5kΩ
06672-016
TIME (1s/DIV)
VR
CL
VOUT
–
Figure 19. Turn-On, Settling, and Transient Test Circuit
Figure 16. 0.1 Hz to 10 Hz Voltage Noise
Rev. 0 | Page 8 of 12
006672-010
+
VIN
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, 2µs/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
VIN
OUTPUT
0.5mV/DIV, 2ms/DIV
06672-020
1.8V
Figure 20. Turn-On Settling
CL = 0.01µF
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 μA.
20mV/DIV
10mV/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 μW.
1mV/DIV
IR = 150µA + 50µA STEP
(a)
(b)
3V
IR = 150µA – 50µA STEP
1mV/DIV
1µs/DIV
06672-021
28.7kΩ
20mV/DIV
50µs/DIV
06672-022
TRANSIENT RESPONSE
205Ω
OP193
4.7µF
Figure 21. Transient Settling
ADR1581
R3
R2
06672-023
Figure 21a shows the settling characteristics of the device for an
increased reverse current of 50 μA. Figure 21b shows the response
when the reverse current is decreased by 50 μA. The transients
settle to 1 mV in about 3 μs.
VOUT = 1.250V
OR
VOUT = 1.250 (1 + R2/R3)
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 (∑-Δ) 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.
3.3V
REF IN(–)
CREF
(3pF TO 8pF)
IOUT2
AGND
A1
VOUT
A1: OP295
AD822
OP2283
DGND
HIGH
IMPEDANCE
>1GΩ
SWITCHING
FREQUENCY DEPENDS
ON fCLKIN
DAC
AD7943
AD7714-3/AD7715-3
RSW
5kΩ (TYP)
VREF
3.3V
29.4kΩ
A1
ADR1581
Figure 24. Reference Circuit for the AD7714-3/AD7715-3
SIGNAL GROUND
Figure 25. Single-Supply System
Rev. 0 | Page 10 of 12
06672-025
REF IN(+)
C1
IOUT1
06672-024
28.7kΩ
RFB
VDD
VIN
3V
ADR1581
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.
ADR1581
OUTLINE DIMENSIONS
3.04
2.90
2.80
1.40
1.30
1.20
3
1
2.64
2.10
2
PIN 1
0.95 BSC
1.90 BSC
1.12
0.89
0.10
0.01
0.50
0.30
SEATING
PLANE
0.20
0.08
0.60
0.50
0.40
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
2.05
2.00
1.95
8.30
8.00
7.70
1.10
1.00
0.90
1.10
1.00
0.90
3.55
3.50
3.45
3.20
3.10
2.90
1.00 MIN
2.80
2.70
2.60
7” REEL 100.00
OR
13” REEL 330.00
0.35
0.30
0.25
1.50 MIN
20.20
MIN
14.40 MIN
7” REEL 50.00 MIN
OR
13” REEL 100.00 MIN
13.20
13.00
12.80
0.75 MIN
9.90
8.40
6.90
DIRECTION OF UNREELING
Figure 27. Tape and Reel Dimensions
(RT-3)
Dimensions shown in millimeters
Rev. 0 | Page 11 of 12
053006-0
4.10
4.00
3.90
ADR1581
ORDERING GUIDE
Model
ADR1581ARTZ-REEL7 1
ADR1581ARTZ-R21
ADR1581BRTZ-REEL71
ADR1581BRTZ-R21
1
Temperature
Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
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
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)
Rev. 0 | Page 12 of 12
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