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Low Noise Micropower 2.5 V and
4.096 V Precision Voltage References
ADR291/ADR292
CONNECTION DIAGRAMS
Supply range
2.8 V to 15 V, ADR291
4.4 V to 15 V, ADR292
Supply current: 15 μA maximum
Low noise: 8 μV and 12 μV p-p (0.1 Hz to 10 Hz)
High output current: 5 mA
Temperature range: −40°C to +125°C
Pin-compatible with REF02/REF19x
NC 1
VIN 2
NC 3
ADR291/
ADR292
8
NC
7
NC
6 VOUT
TOP VIEW
GND 4 (Not to Scale) 5 NC
NC = NO CONNECT
00163-001
FEATURES
APPLICATIONS
Portable instrumentation
Precision reference for 3 V and 5 V systems
Analog-to-digital and digital-to-analog converter reference
Solar-powered applications
Loop-current-powered instruments
NC
1
VIN
2
NC
3
GND
4
ADR291/
ADR292
TOP VIEW
(Not to Scale)
8
NC
7
NC
6
VOUT
5
NC
NC = NO CONNECT
00163-002
Figure 1. 8-Lead SOIC (R-8)
Figure 2. 8-Lead TSSOP (RU-8)
GND
VOUT
3
2
1
VIN
TOP VIEW
(Not to Scale)
00163-003
ADR291
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Figure 3. 3-Lead TO-92 (T-3)
GENERAL DESCRIPTION
The ADR291 and ADR292 are low noise, micropower precision
voltage references that use an XFET® reference circuit. The new
XFET architecture offers significant performance improvements
over traditional band gap and buried Zener-based references.
Improvements include one quarter the voltage noise output of
band gap references operating at the same current, very low and
ultralinear temperature drift, low thermal hysteresis, and
excellent long-term stability.
The ADR291/ADR292 family is a series of voltage references
providing stable and accurate output voltages from supplies as
low as 2.8 V for the ADR291. Output voltage options are 2.5 V
and 4.096 V for the ADR291 and ADR292, respectively.
Quiescent current is only 12 μA, making these devices ideal for
battery-powered instrumentation. Three electrical grades are
available offering initial output accuracies of ±2 mV, ±3 mV,
and ±6 mV maximum for the ADR291, and ±3 mV, ±4 mV,
and ±6 mV maximum for the ADR292. Temperature
coefficients for the three grades are 8 ppm/°C, 15 ppm/°C, and
25 ppm/°C maximum, respectively. Line regulation and load
regulation are typically 30 ppm/V and 30 ppm/mA, maintaining
the reference’s overall high performance. For a device with 5.0 V
output, refer to the ADR293 data sheet.
The ADR291 and ADR292 references are specified over the
extended industrial temperature range of −40°C to +125°C.
Devices are available in the 8-lead SOIC, 8-lead TSSOP, and
3-lead TO-92 packages.
Table 1. ADR291/ADR292 Product
Part No.
ADR291
ADR292
Output
Voltage (V)
2.500
4.096
Initial
Accuracy (±%)
0.08, 0.12, 0.24
0.07, 0.10, 0.15
Temperature
Coefficient
(ppm/°C) Max
8, 15, 25
8, 15, 25
Rev. E
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.
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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.
ADR291/ADR292
TABLE OF CONTENTS
Features .............................................................................................. 1
Device Power Dissipation Considerations.............................. 13
Applications....................................................................................... 1
Basic Voltage Reference Connections ..................................... 13
Connection Diagrams...................................................................... 1
Noise Performance ..................................................................... 13
General Description ......................................................................... 1
Turn-On Time ............................................................................ 13
Revision History ............................................................................... 2
Applications Information .............................................................. 14
Specifications..................................................................................... 3
Negative Precision Reference Without Precision Resistors.. 14
ADR291 Electrical Specifications............................................... 3
Precision Current Source .......................................................... 14
ADR292 Electrical Specifications............................................... 4
High Voltage Floating Current Source .................................... 14
Absolute Maximum Ratings............................................................ 6
Kelvin Connections.................................................................... 15
ESD Caution.................................................................................. 6
Low Power, Low Voltage Reference for Data Converters ..... 15
Pin Configurations and Function Descriptions ........................... 7
Voltage Regulator for Portable Equipment ............................. 15
Typical Performance Characteristics ............................................. 8
Outline Dimensions ....................................................................... 16
Terminology .................................................................................... 12
Ordering Guide .......................................................................... 17
Theory of Operation ...................................................................... 13
REVISION HISTORY
12/07—Rev. D to Rev. E
Changes to Features.......................................................................... 1
Changes to Figure 34...................................................................... 14
9/03—Rev. B to Rev. C
Deleted ADR290.................................................................Universal
Changes to Specifications.................................................................2
Changes to Ordering Guide .............................................................4
Updated Outline Dimensions....................................................... 13
www.BDTIC.com/ADI
3/06—Rev. C to Rev. D
Updated Format..................................................................Universal
Change to Table 8 ............................................................................. 6
Updated Outline Dimensions ....................................................... 15
Changes to Ordering Guide .......................................................... 16
Rev. E | Page 2 of 20
ADR291/ADR292
SPECIFICATIONS
ADR291 ELECTRICAL SPECIFICATIONS
VS = 3.0 V to 15 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter
E GRADE
Output Voltage
Initial Accuracy
Symbol
Conditions
Min
Typ
Max
Unit
VOUT
VOERR
IOUT = 0 mA
2.498
–2
–0.08
2.500
2.502
+2
+0.08
V
mV
%
F GRADE
Output Voltage
Initial Accuracy
VOUT
VOERR
IOUT = 0 mA
2.497
–3
–0.12
2.500
2.503
+3
+0.12
V
mV
%
G GRADE
Output Voltage
Initial Accuracy
VOUT
VOERR
IOUT = 0 mA
2.494
–6
–0.24
2.500
2.506
+6
+0.24
V
mV
%
∆VOUT/∆VIN
IOUT = 0 mA
30
40
100
125
ppm/V
ppm/V
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
30
40
50
8
480
100
125
ppm/mA
ppm/mA
ppm
μV p-p
nV/√Hz
Typ
Max
Unit
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
LONG-TERM STABILITY
NOISE VOLTAGE
WIDEBAND NOISE DENSITY
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∆VOUT
eN
eN
After 1000 hours of operation @ 125°C
0.1 Hz to 10 Hz
@ 1 kHz
VS = 3.0 V to 15 V, TA = −25°C to +85°C, unless otherwise noted.
Table 3.
Parameter
TEMPERATURE COEFFICIENT
E Grade
F Grade
G Grade
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
Symbol
Conditions
TCVOUT
IOUT = 0 mA
3
5
10
8
15
25
ppm/°C
ppm/°C
ppm/°C
∆VOUT/∆VIN
IOUT = 0 mA
35
50
125
150
ppm/V
ppm/V
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
20
30
125
150
ppm/mA
ppm/mA
Rev. E | Page 3 of 20
Min
ADR291/ADR292
VS = 3.0 V to 15 V, TA = −40°C to+125°C, unless otherwise noted.
Table 4.
Parameter
TEMPERATURE COEFFICIENT
E Grade
F Grade
G Grade
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
SUPPLY CURRENT
Symbol
Conditions
TCVOUT
THERMAL HYSTERESIS
VOUT-HYS
Min
Typ
Max
Unit
IOUT = 0 mA
3
5
10
10
20
30
ppm/°C
ppm/°C
ppm/°C
∆VOUT/∆VIN
IOUT = 0 mA
40
70
200
250
ppm/V
ppm/V
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
IS
TA = 25°C
−40°C ≤ TA ≤ +125°C
8-lead SOIC, 8-lead TSSOP
20
30
9
12
50
200
300
12
15
ppm/mA
ppm/mA
μA
μA
ppm
Typ
Max
Unit
ADR292 ELECTRICAL SPECIFICATIONS
VS = 5 V to 15 V, TA = 25°C, unless otherwise noted.
Table 5.
Parameter
E GRADE
Output Voltage
Initial Accuracy
Symbol
Conditions
Min
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VOUT
VOERR
IOUT = 0 mA
4.093
−3
−0.07
4.096
4.099
+3
+0.07
V
mV
%
F GRADE
Output Voltage
Initial Accuracy
VOUT
VOERR
IOUT = 0 mA
4.092
−4
−0.10
4.096
4.1
+4
+0.10
V
mV
%
G GRADE
Output Voltage
Initial Accuracy
VOUT
VOERR
IOUT = 0 mA
4.090
−6
−0.15
4.096
4.102
+6
+0.15
V
mV
%
∆VOUT/∆VIN
VS = 4.5 V to 15 V, IOUT = 0 mA
30
40
100
125
ppm/V
ppm/V
30
40
50
100
125
ppm/mA
ppm/mA
ppm
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
LONG-TERM STABILITY
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
∆VOUT
NOISE VOLTAGE
WIDEBAND NOISE DENSITY
eN
eN
After 1000 hours of operation @
125°C
0.1 Hz to 10 Hz
@ 1 kHz
Rev. E | Page 4 of 20
12
640
μV p-p
nV/√Hz
ADR291/ADR292
VS = 5 V to 15 V, TA = −25°C to +85°C, unless otherwise noted.
Table 6.
Parameter
TEMPERATURE COEFFICIENT
E Grade
F Grade
G Grade
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
Symbol
Conditions
TCVOUT
Min
Typ
Max
Unit
IOUT = 0 mA
3
5
10
8
15
25
ppm/°C
ppm/°C
ppm/°C
∆VOUT/ΔVIN
VS = 4.5 V to 15 V, IOUT = 0 mA
35
50
125
150
ppm/V
ppm/V
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
20
30
125
150
ppm/mA
ppm/mA
Typ
Max
Unit
3
5
10
10
20
30
ppm/°C
ppm/°C
ppm/°C
VS = 5 V to 15 V, TA = −40°C to +125°C, unless otherwise noted.
Table 7.
Parameter
TEMPERATURE COEFFICIENT
E Grade
F Grade
G Grade
LINE REGULATION
E/F Grades
G Grade
LOAD REGULATION
E/F Grades
G Grade
SUPPLY CURRENT
Symbol
Conditions
TCVOUT
IOUT = 0 mA
THERMAL HYSTERESIS
VOUT-HYS
Min
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∆VOUT/∆VIN
VS = 4.5 V to 15 V, IOUT = 0 mA
40
70
200
250
ppm/V
ppm/V
∆VOUT/∆ILOAD
VS = 5.0 V, IOUT = 0 mA to 5 mA
IS
TA = 25°C
−40°C ≤ TA ≤ +125°C
8-lead SOIC, 8-lead TSSOP
20
30
10
12
50
200
300
15
18
ppm/mA
ppm/mA
μA
μA
ppm
Rev. E | Page 5 of 20
ADR291/ADR292
ABSOLUTE MAXIMUM RATINGS
Remove power before inserting or removing units from their
sockets.
Table 9. Package Types
Package Type
8-Lead SOIC (R)
8-Lead TSSOP (RU)
3-Lead TO-92 (T)
Table 8.
Parameter
Supply Voltage
Output Short-Circuit Duration to GND
Storage Temperature Range
T, R, RU Packages
Operating Temperature Range
ADR291/ADR292
Junction Temperature Range
T, R, RU Packages
Lead Temperature (Soldering, 60 sec)
Rating
18 V
Indefinite
1
−65°C to +150°C
−40°C to +125°C
−65°C to +125°C
300°C
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.
θJA1
158
240
160
θJC
43
43
–
Unit
°C/W
°C/W
°C/W
θJA is specified for worst-case conditions. For example, θJA is specified for a
device in socket testing. In practice, θJA is specified for a device soldered in
the circuit board.
Table 10. Other XFET Products
Part Number
ADR420
ADR421
ADR423
ADR425
Nominal Output
Voltage (V)
2.048
2.50
3.0
5.0
ESD CAUTION
www.BDTIC.com/ADI
Rev. E | Page 6 of 20
Package Type
8-Lead MSOP/SOIC
8-Lead MSOP/SOIC
8-Lead MSOP/SOIC
8-Lead MSOP/SOIC
ADR291/ADR292
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
NC
7
NC
6 VOUT
TOP VIEW
GND 4 (Not to Scale) 5 NC
NC = NO CONNECT
GND
NC
1
VIN
2
NC
3
GND
4
ADR291/
ADR292
TOP VIEW
(Not to Scale)
8
NC
7
NC
6
VOUT
5
NC
NC = NO CONNECT
Figure 4. 8-Lead SOIC (R-8)
VOUT
3
2
Pin No.
TSSOP
1, 3, 5, 7, 8
2
4
6
Figure 5. 8-Lead TSSOP (RU-8)
TO-92
N/A
1
2
3
Mnemonic
NC
VIN
GND
VOUT
TOP VIEW
(Not to Scale)
Figure 6. 3-Lead TO-92 (T-3)
Description
No Connect
Input Voltage
Ground
Output Voltage
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Rev. E | Page 7 of 20
VIN
ADR291
Table 11. Pin Function Descriptions
SOIC
1, 3, 5, 7, 8
2
4
6
1
00163-038
NC 3
8
00163-037
VIN 2
ADR291/
ADR292
00163-036
NC 1
ADR291/ADR292
TYPICAL PERFORMANCE CHARACTERISTICS
2.506
14
3 TYPICAL PARTS
VS = 5V
12
QUIESCENT CURRENT (μA)
2.500
2.498
2.496
0
–25
25
50
75
100
TA = –40°C
6
4
2
00163-004
2.494
–50
TA = +25°C
8
0
125
00163-007
2.502
TA = +125°C
10
0
2
4
6
8
10
INPUT VOLTAGE (V)
TEMPERATURE (°C)
VS = 5V
3 TYPICAL PARTS
VS = 5V
4.100
SUPPLY CURRENT (µA)
12
4.098
4.096
ADR291
ADR292
10
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4.094
8
00163-005
4.090
–50
–25
0
25
50
75
100
4
–50
125
00163-008
6
4.092
–25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
Figure 8. ADR292 VOUT vs. Temperature
Figure 11. ADR291/ADR292 Supply Current vs. Temperature
14
100
ADR291: VS = 3.0V TO 15V
ADR292: VS = 4.5V TO 15V
12
LINE REGULATION (ppm/V)
TA = +25°C
8
TA = –40°C
6
4
2
0
2
4
6
8
10
INPUT VOLTAGE (V)
12
IOUT = 0 mA
80
TA = +125°C
10
00163-006
OUTPUT VOLTAGE (V)
16
14
4.102
QUIESCENT CURRENT (μA)
14
Figure 10. ADR292 Quiescent Current vs. Input Voltage
Figure 7. ADR291 VOUT vs. Temperature
0
12
14
60
ADR292
40
20
00163-009
OUTPUT VOLTAGE (V)
2.504
ADR291
0
–50
16
–25
0
25
50
75
100
125
TEMPERATURE (°C)
Figure 9. ADR291 Quiescent Current vs. Input Voltage
Figure 12. ADR291/ADR292 Line Regulation vs. Temperature
Rev. E | Page 8 of 20
ADR291/ADR292
100
200
VS = 5V
IOUT = 0 mA
LOAD REGULATION (ppm/mA)
60
ADR291
40
20
ADR292
0
–50
00163-010
–25
0
25
50
75
100
160
IOUT = 1mA
120
IOUT = 5mA
80
40
0
–50
125
–25
0
TEMPERATURE (°C)
Figure 13. ADR291/ADR292 Line Regulation vs. Temperature
LOAD REGULATION (ppm/mA)
125
0.5
TA = +25°C
0.4
0.3
TA = –40°C
160
120
IOUT = 1mA
IOUT = 5mA
80
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0.2
00163-011
0
0.5
1.0
1.5
2.0
2.5
3.0 3.5
LOAD CURRENT (mA)
4.0
4.5
40
0
–50
5.0
–25
0
25
50
75
100
125
TEMPERATURE (°C)
Figure 17. ADR292 Load Regulation vs. Temperature
Figure 14. ADR291 Minimum Input-Output
Voltage Differential vs. Load Current
0
0.7
–250
0.6
ΔVOUT FROM NOMINAL (µV)
TA = +125°C
0.5
TA = +25°C
0.4
0.3
0.2
TA = –40°C
0
0.5
1.0
1.5
2.0
2.5
3.0 3.5
LOAD CURRENT (mA)
4.0
4.5
–750
TA = –40°C
–1000
TA = +125°C
–1250
–1500
–1750
00163-012
0.1
TA = +25°C
–500
–2000
0.1
5.0
Figure 15. ADR292 Minimum Input-Output
Voltage Differential vs. Load Current
00163-015
DIFFERENTIAL VOLTAGE (V)
100
VS = 5V
TA = +125°C
0.1
DIFFERENTIAL VOLTAGE (V)
75
200
0.6
0
50
Figure 16. ADR291 Load Regulation vs. Temperature
0.7
0
25
TEMPERATURE (°C)
00163-014
LINE REGULATION (ppm/V)
80
00163-013
ADR291: VS = 3.0V TO 15V
ADR292: VS = 4.5V TO 15V
1
SOURCING LOAD CURRENT (mA)
Figure 18. ADR291 ΔVOUT from Nominal vs. Load Current
Rev. E | Page 9 of 20
10
ADR291/ADR292
0
1s
100
–1000
–1550
90
TA = +25°C
TA = –40°C
TA = +125°C
2μV p-p
–2000
–2500
10
–3000
0%
–4000
0.1
00163-016
–3500
00163-019
ΔVOUT FROM NOMINAL (µV)
–500
1
SOURCING LOAD CURRENT (mA)
10
Figure 22. ADR291 0.1 Hz to 10 Hz Noise
Figure 19. ADR292 ΔVOUT from Nominal vs. Load Current
1000
VS = 5V
IL = 0 mA
VIN = 15V
TA = 25°C
800
OUTPUT IMPEDANCE (Ω)
40
700
ADR291
500
400
300
200
20
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10
100
0
10
30
100
FREQUENCY (Hz)
0
1000
00163-020
600
00163-017
VOLTAGE NOISE DENSITY (nV/√Hz)
900
50
ADR292
0
120
1k
10k
50
VS = 5V
IL = 0 mA
VS = 5V
100
OUTPUT IMPEDANCE (Ω)
40
80
60
40
30
20
100
FREQUENCY (Hz)
0
1000
00163-021
10
20
00163-018
RIPPLE REJECTION (dB)
100
FREQUENCY (Hz)
Figure 23. ADR291 Output Impedance vs. Frequency
Figure 20. Voltage Noise Density vs. Frequency
0
10
10
0
10
100
FREQUENCY (Hz)
1k
Figure 24. ADR292 Output Impedance vs. Frequency
Figure 21. ADR291/ADR292 Ripple Rejection vs. Frequency
Rev. E | Page 10 of 20
10k
ADR291/ADR292
IL = 5mA
500μ s
IL = 5mA
1ms
100
100
90
90
10
10
0%
0%
1V
00163-022
ON
1V
Figure 25. ADR291 Load Transient
IL = 5mA
CL = 1nF
OFF
00163-025
OFF
Figure 28. ADR291 Turn-On Time
IL = 0mA
1ms
100
100
90
90
10ms
10
10
0%
0%
00163-023
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1V
Figure 26. ADR291 Load Transient
1V
00163-026
ON
Figure 29. ADR291 Turn-Off Time
18
IL = 5mA
CL = 100nF
16
5ms
14
100
90
12
FREQUENCY
ON
10
8
6
10
2
00163-024
1V
00163-027
4
0%
0
–200
–180
–160
–140
–120
–100
–80
–60
–40
–20
0
20
40
60
80
100
120
140
160
180
200
MORE
OFF
TEMPERATURE
+25°C ≥ –40°C ≥
+85°C ≥ +25°C
VOUT DEVIATION (ppm)
Figure 30. Typical Hysteresis for the ADR291 Product
Figure 27. ADR291 Load Transient
Rev. E | Page 11 of 20
ADR291/ADR292
TERMINOLOGY
Line Regulation
Line regulation refers to the change in output voltage due to a
specified change in input voltage. It includes the effects of selfheating. Line regulation is expressed as percent-per-volt, partsper-million-per-volt, or microvolts-per-volt change in input
voltage.
Load Regulation
The change in output voltage is due to a specified change in
load current and includes the effects of self-heating. Load
regulation is expressed in microvolts-per-milliampere, partsper-million-per-milliampere, or ohms of dc output resistance.
Long-Term Stability
Long-term stability refers to the typical shift of output voltage at
25°C on a sample of parts subjected to a test of 1000 hours at
125°C.
TCVO [ppm/ ° C ] =
VOUT (t 0 ) − VOUT (t 1 )
VOUT (t 0 )
VO (25° C ) × (T2 − T1 )
× 10 6
where:
VOUT (25°C) = VOUT at 25°C.
VOUT (T1) = VOUT at Temperature 1.
VOUT (T2) = VOUT at Temperature 2.
NC = no connect.
There are internal connections at NC pins that are reserved for
manufacturing purposes. Users should not connect anything at
the NC pins.
Thermal Hysteresis
Thermal hysteresis is defined as the change of output voltage
after the device is cycled through temperatures from +25°C to
−40°C, then to +85°C, and back to +25°C. This is a typical value
from a sample of parts put through such a cycle.
ΔVOUT = VOUT (t 0 ) − VOUT (t 1 )
ΔVOUT [ppm ] =
VO (T2 ) − VO (T1 )
VOUT −HYS = VOUT (25° C) − VOUT_TC
× 10 6
VΟUT −HYS [ppm] =
where:
VOUT (t0) = VOUT at 25°C at Time 0.
VOUT (t1) = VOUT at 25°C after 1000 hours of operation at 125°C.
VOUT (25°C ) − VOUT_TC
VOUT (25° C)
where:
VOUT (25°C) = VOUT at 25°C.
VOUT_TC = VOUT at 25°C after temperature cycle from +25°C to
−40°C, then to +85°C, and back to +25°C.
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Temperature Coefficient
Temperature coefficient is the change of output voltage over
the operating temperature change, normalized by the output
voltage at 25°C, expressed in ppm/°C. The equation follows:
× 10 6
Rev. E | Page 12 of 20
ADR291/ADR292
THEORY OF OPERATION
The core of the XFET reference consists of two junction field
effect transistors, one having an extra channel implant to raise
its pinch-off voltage. By running the two JFETs at the same
drain current, the difference in pinch-off voltage can be amplified
and used to form a highly stable voltage reference. The intrinsic
reference voltage is around 0.5 V with a negative temperature
coefficient of about −120 ppm/K. This slope is essentially
locked to the dielectric constant of silicon and can be closely
compensated by adding a correction term generated in the same
fashion as the proportional-to-temperature (PTAT) term used
to compensate band gap references. Because most of the noise
of a band gap reference comes from the compensation circuitry,
the intrinsic temperature coefficient offers a significant advantage (being about 30 times lower), and therefore, requiring less
correction resulting in much lower noise.
The simplified schematic in Figure 31 shows the basic topology
of the ADR291/ADR292 series. The temperature correction
term is provided by a current source with a value designed to be
proportional to absolute temperature. The general equation is
DEVICE POWER DISSIPATION CONSIDERATIONS
The ADR291/ADR292 family of references is guaranteed to
deliver load currents to 5 mA with an input voltage that ranges
from 2.7 V to 15 V (minimum supply voltage depends on the
output voltage chosen). When these devices are used in
applications with large input voltages, care should be exercised
to avoid exceeding the published specifications for maximum
power dissipation or junction temperature that could result in
premature device failure. Use the following formula to calculate
maximum junction temperature or dissipation of a device:
PD =
TJ − TA
θ JA
where
TJ and TA are the junction and ambient temperatures,
respectively.
PD is the device power dissipation.
θJA is the device package thermal resistance.
BASIC VOLTAGE REFERENCE CONNECTIONS
References, in general, require a bypass capacitor connected
from the VOUT pin to the GND pin. The circuit in Figure 32
illustrates the basic configuration for the ADR291/ADR292
family of references. Note that the decoupling capacitors are not
required for circuit stability.
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⎛ R1 + R 2 + R3 ⎞
VOUT = ΔVP ⎜
⎟ + (I PTAT ) (R3)
R1
⎝
⎠
NC 1
where:
ΔVP is the difference in pinch-off voltage between the two FETs.
IPTAT is the positive temperature coefficient correction current.
2
+
The various versions of the ADR291/ADR292 family are created
by on-chip adjustment of R1 and R3 to achieve 2.500 V or
4.096 V at the reference output.
The process used for the XFET reference also features vertical
NPN and PNP transistors, the latter of which are used as output
devices to provide a very low dropout voltage.
VIN
I1
I1
1
VP
VOUT
R1
R2
IPTAT
R3
VOUT =
R1 + R2 + R3
× ΔVP = IPTAT × R3
R1
00163-028
GND
1 EXTRA CHANNEL IMPLANT
NC
10µF
ADR291/
ADR292
8
NC
7
NC
3
6
4
5
VOUT
0.1µF
0.1µF
NC
NC = NO CONNECT
00163-029
The ADR291/ADR292 series of references uses a reference
generation technique known as XFET (eXtra implanted junction FET). This technique yields a reference with low noise, low
supply current, and very low thermal hysteresis.
Figure 32. Basic Voltage Reference Configuration
NOISE PERFORMANCE
The noise generated by the ADR291/ADR292 family of references is typically less than 12 μV p-p over the 0.1 Hz to 10 Hz
band. The noise measurement is made with a band-pass filter
made of a 2-pole high-pass filter with a corner frequency at 0.1 Hz
and a 2-pole low-pass filter with a corner frequency at 10 Hz.
TURN-ON TIME
Upon application of power (cold start), the time required for
the output voltage to reach its final value within a specified
error band is defined as the turn-on settling time. Two components normally associated with this are the time it takes for
the active circuits to settle and for the thermal gradients on the
chip to stabilize. Figure 28 shows the turn-on settling time for
the ADR291.
Figure 31. ADR291/ADR292 Simplified Schematic
Rev. E | Page 13 of 20
ADR291/ADR292
APPLICATIONS INFORMATION
PRECISION CURRENT SOURCE
In many current-output CMOS DAC applications, where the
output signal voltage must be of the same polarity as the reference
voltage, it is often necessary to reconfigure a current-switching
DAC into a voltage-switching DAC through the use of a 1.25 V
reference, an op amp, and a pair of resistors. Directly using a
current-switching DAC requires an additional operational amplifier at the output to reinvert the signal. A negative voltage
reference is then desirable from the point that an additional
operational amplifier is not required for either reinversion
(current-switching mode) or amplification (voltage-switching
mode) of the DAC output voltage. In general, any positive voltage
reference can be converted into a negative voltage reference
through the use of an operational amplifier and a pair of matched
resistors in an inverting configuration. The disadvantage to that
approach is that the largest single source of error in the circuit is
the relative matching of the resistors used.
The circuit illustrated in Figure 33 avoids the need for tightly
matched resistors with the use of an active integrator circuit. In this
circuit, the output of the voltage reference provides the input drive
for the integrator. To maintain circuit equilibrium, the integrator
adjusts its output to establish the proper relationship between the
reference’s VOUT and GND. Thus, any negative output voltage
desired can be chosen by simply substituting for the appropriate
reference IC. There is one caveat with this approach: although railto-rail output amplifiers work best in the application, these
operational amplifiers require a finite amount (mV) of headroom
when required to provide any load current. The choice for the
circuit’s negative supply should take this issue into account.
In low power applications, there is often a need for a precision
current source that can operate on low supply voltages. As
shown in Figure 34, any one of the devices in the ADR291/
ADR292 family of references can be configured as a precision
current source. The circuit configuration illustrated is a floating
current source with a grounded load. The reference’s output
voltage is bootstrapped across RSET, which sets the output
current into the load. With this configuration, circuit precision
is maintained for load currents in the range from the reference’s
supply current, typically 12 μA to approximately 5 mA.
VIN
2
ADR291/
ADR292
VOUT 6
R1
GND
1µF
4
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VIN
P1
IOUT
RL
Figure 34. A Precision Current Source
HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit shown in Figure 35 can be used to generate a
floating current source with minimal self-heating. This
particular configuration operates on high supply voltages
determined by the breakdown voltage of the N-channel JFET.
+VS
2
E231
SILICONIX
1kΩ
VOUT 6
1µF
+5V
GND
100kΩ
1µF
A1
2
100Ω
VIN
ADR291/
ADR292
–VREF
2N3904
GND
–5V
4
00163-030
A1 = 1/2 OP291,
1/2 OP295
OP90
2.10kΩ
Figure 33. A Negative Precision Voltage Reference Uses No Precision Resistors
–VS
Figure 35. High Voltage Floating Current Source
Rev. E | Page 14 of 20
00163-032
ADR291/
ADR292
4
RSET
ISY
ADJUST
00163-031
NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
ADR291/ADR292
In many portable instrumentation applications, the PC board
area is directly related to cost; therefore, circuit interconnects
are reduced to a minimal width. These narrow lines can cause
large voltage drops if the voltage reference is required to provide
load currents to various functions. In fact, circuit interconnects
can exhibit a typical line resistance of 0.45 mΩ/square (1 oz. Cu,
for example). Force and sense connections, also referred to as
Kelvin connections, offer a convenient method of eliminating
the effects of voltage drops in circuit wires. Load currents flowing
through wiring resistance produce an error (VERROR = R × IL) at
the load. However, the Kelvin connection shown in Figure 36
overcomes the problem by including the wiring resistance
within the forcing loop of the op amp. Since the op amp senses
the load voltage, the op amp loop control forces the output to
compensate for the wiring error producing the correct voltage
at the load.
combined with the power dissipation of the ADR291 (60 μW),
the entire circuit still consumes about 25 mW.
+5V
ANALOG
SUPPLY
AVDD
RLW
ADR291/
ADR292
A1
VOUT 6
ADR291
MODE
DATA READY
DRDY
RANGES
SELECT
BP/UP
CS
READ (TRANSMIT)
SCLK
SERIAL CLOCK
SDATA
SERIAL CLOCK
CAL
CALIBRATE
CLKIN
ANALOG
INPUT
AIN
ANALOG
GROUND
AGND
CLKOUT
SC1
SC2
0.1µF
DGND
AVSS
0.1µF
0.1µF
DVSS
10µF
Figure 37. Low Power, Low Voltage Supply Reference for the AD7701
+VOUT
FORCE
VOLTAGE REGULATOR FOR PORTABLE
EQUIPMENT
100kΩ
The ADR291/ADR292 family of references is ideal for providing a stable, low cost, and low power reference voltage in
portable equipment power supplies. Figure 38 shows how the
ADR291 and ADR292 can be used in a voltage regulator that
not only has low output noise (as compared to switch mode
design) and low power, but also a very fast recovery after
current surges. Some precautions should be taken in the
selection of the output capacitors. Too high an ESR (effective
series resistance) could endanger the stability of the circuit. A
solid tantalum capacitor, 16 V or higher, and an aluminum
electrolytic capacitor, 10 V or higher, are recommended for C1
and C2, respectively. Also, the path from the ground side of C1
and C2 to the ground side of R1 should be kept as short as
possible.
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Figure 36. Advantage of Kelvin Connection
LOW POWER, LOW VOLTAGE REFERENCE FOR
DATA CONVERTERS
The ADR291/ADR292 family has a number of features that
makes it ideally suited for use with analog-to-digital and digitalto-analog converters. Because of its low supply voltage, the
ADR291 can be used with converters that run on 3 V supplies
without having to add a higher supply voltage for the reference.
The low quiescent current (12 μA maximum) and low noise,
tight temperature coefficient, combined with the high accuracy
of the ADR291/ADR292, make it ideal for low power applications such as handheld, battery-operated equipment.
One such ADC for which the ADR291 is well suited is the
AD7701. Figure 37 shows the ADR291 used as the reference
for this converter. The AD7701 is a 16-bit ADC 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. It contains a charge balancing
(Σ-Δ) ADC, calibration microcontroller with on-chip static
RAM, a clock oscillator, and a serial communications port.
CHARGER
INPUT
0.1µF
R3
510kΩ
2
VIN
ADR291/
ADR292
6V
LEAD-ACID +
BATTERY
This entire circuit runs on ±5 V supplies. The power dissipation
of the AD7701 is typically 25 mW and, when
VOUT 6
NC 3
GND
2
7
OP20
3
4
6
IRF9530
4
5V, 100mA
R1
402kΩ
1%
R2
402kΩ
1%
C1
68µF
TANT
+
+ C2
1000µF
ELECT
Figure 38. Voltage Regulator for Portable Equipment
Rev. E | Page 15 of 20
00163-035
A1 = 1/2 OP295
00163-033
4
0.1µF
SLEEP
AD7701
–5V
ANALOG
SUPPLY
RL
1µF
GND
RLW
DVDD
VREF
GND
+VOUT
SENSE
VIN
VIN
VOUT
0.1µF
VIN
2
10µF
0.1µF
00163-034
KELVIN CONNECTIONS
ADR291/ADR292
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
8
1
5
4
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
COPLANARITY
0.10
SEATING
PLANE
6.20 (0.2441)
5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
8
0.50 (0.0196)
0.25 (0.0099)
45°
1
8°
0°
0.25 (0.0098)
0.17 (0.0067)
4
0.65 BSC
0.15
0.05
1.20
MAX
COPLANARITY
0.10
0.30
0.19
SEATING 0.20
PLANE
0.09
0.75
0.60
0.45
Figure 40. 8-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-8)
Dimensions shown in millimeters
0.050 (1.27)
MAX
0.019 (0.482)
SQ
0.016 (0.407)
0.165 (4.19)
0.125 (3.18)
0.055 (1.40)
0.045 (1.15)
3
2
www.BDTIC.com/ADI
0.135 (3.43)
MIN
8°
0°
COMPLIANT TO JEDEC STANDARDS MO-153-AA
Figure 39. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
0.205 (5.21)
0.175 (4.45)
6.40 BSC
PIN 1
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-012-A A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
0.210 (5.33)
0.170 (4.32)
5
4.50
4.40
4.30
012407-A
4.00 (0.1574)
3.80 (0.1497)
3.10
3.00
2.90
0.105 (2.66)
0.095 (2.42)
1
0.115 (2.92)
0.080 (2.03)
0.500 (12.70) MIN
0.115 (2.92)
0.080 (2.03)
SEATING
PLANE
BOTTOM VIEW
COMPLIANT TO JEDEC STANDARDS TO-226-AA
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 41. 3-Lead Plastic Header-Style Package [TO-92]
(T-3)
Dimensions shown in inches and (millimeters)
Rev. E | Page 16 of 20
ADR291/ADR292
ORDERING GUIDE
Model
ADR291ER
ADR291ER-REEL7
ADR291ERZ 1
ADR291ERZ-REEL71
ADR291FR
ADR291FR-REEL
ADR291FR-REEL7
ADR291FRZ1
ADR291FRZ-REEL1
ADR291FRZ-REEL71
ADR291GR
ADR291GR-REEL
ADR291GR-REEL7
ADR291GRZ1
ADR291GRZ-REEL1
ADR291GRZ-REEL71
ADR291GRU
ADR291GRU-REEL7
ADR291GRUZ1
ADR291GRUZ-REEL1
ADR291GRUZ-REEL71
ADR291GT9
ADR291GT9-REEL
ADR291GT9Z1
ADR292ER
ADR292ER-REEL
ADR292ERZ1
ADR292ERZ-REEL1
ADR292FR
ADR292FR-REEL
ADR292FR-REEL7
ADR292FRZ1
ADR292FRZ-REEL1
ADR292FRZ-REEL71
ADR292GR
ADR292GR-REEL7
ADR292GRZ1
ADR292GRZ-REEL71
ADR292GRU
ADR292GRU-REEL7
ADR292GRUZ1
ADR292GRUZ-REEL71
1
Output
Voltage
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
2.50
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
4.096
Initial Accuracy
(±%)
0.08
0.08
0.08
0.08
0.12
0.12
0.12
0.12
0.12
0.12
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.24
0.07
0.07
0.07
0.07
0.10
0.10
0.10
0.10
0.10
0.10
0.15
0.15
0.15
0.15
0.24
0.15
0.24
0.15
Temperature
Coefficient Max
(ppm/°C)
8
8
8
8
15
15
15
15
15
15
25
25
25
25
25
25
25
25
25
25
25
25
25
25
8
8
8
8
15
15
15
15
15
15
25
25
25
25
25
25
25
25
Package
Description
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead TSSOP
8-Lead TSSOP
8-Lead TSSOP
8-Lead TSSOP
8-Lead TSSOP
3-Lead TO-92
3-Lead TO-92
3-Lead TO-92
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead SOIC_N
8-Lead TSSOP
8-Lead TSSOP
8-Lead TSSOP
8-Lead TSSOP
Package
Option
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
RU-8
RU-8
RU-8
RU-8
RU-8
T-3
T-3
T-3
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
R-8
RU-8
RU-8
RU-8
RU-8
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Z = RoHS Compliant Part.
Rev. E | Page 17 of 20
Ordering
Quantity
98
1,000
98
1,000
98
2,500
1,000
98
2,500
1,000
98
2,500
1,000
98
2,500
1,000
98
1,000
98
1,000
1,000
98
2,000
98
98
2,500
98
2,500
98
2,500
1,000
98
2,500
1,000
98
1,000
98
1,000
98
1,000
98
1,000
ADR291/ADR292
NOTES
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Rev. E | Page 18 of 20
ADR291/ADR292
NOTES
www.BDTIC.com/ADI
Rev. E | Page 19 of 20
ADR291/ADR292
NOTES
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©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D00163-0-12/07(E)
Rev. E | Page 20 of 20