Low Noise Micropower 2.5 V and
V
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4.096 V Precision Voltage References
FEATURES
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
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
ADR291/ADR292
CONNECTION DIAGRAMS
NC
1
ADR291/
V
2
IN
ADR292
NC
3
TOP VIEW
(Not to S cale)
4
GND
NC = NO CONNECT
Figure 1. 8-Lead SOIC (R-8)
1
NC
ADR291/
2
V
IN
ADR292
3
NC
GND
TOP VIEW
(Not to Scale)
4
NC = NO CONNECT
Figure 2. 8-Lead TSSOP (RU-8)
GND
OUT
321
ADR291
TOP VIEW
(Not to Scale)
Figure 3. 3-Lead TO-92 (T-3)
NC
8
NC
7
V
6
OUT
5
NC
00163-001
8
NC
7
NC
6
V
OUT
5
NC
00163-002
V
IN
00163-003
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
roviding stable and accurate output voltages from supplies as
p
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
b
attery-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
ext
ended 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
Temperature
Part No.
Output
V
oltage (V)
Initial
Accuracy (±%)
C
oefficient
(ppm/°C) Max
ADR291 2.500 0.08, 0.12, 0.24 8, 15, 25
ADR292 4.096 0.07, 0.10, 0.15 8, 15, 25
Rev. E
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
ADR291/ADR292
www.BDTIC.com/ADI
TABLE OF CONTENTS
Features.............................................................................................. 1
Applications....................................................................................... 1
Connection Diagrams...................................................................... 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
ADR291 Electrical Specifications............................................... 3
ADR292 Electrical Specifications............................................... 4
Absolute Maximum Ratings............................................................ 6
ESD Caution.................................................................................. 6
Pin Configurations and Function Descriptions ........................... 7
Typical Performance Characteristics ............................................. 8
Terminology .................................................................................... 12
Theory of Operation ...................................................................... 13
Device Power Dissipation Considerations.............................. 13
Basic Voltage Reference Connections ..................................... 13
Noise Performance..................................................................... 13
Turn-On Time ............................................................................ 13
Applications Information.............................................................. 14
Negative Precision Reference Without Precision Resistors.. 14
Precision Current Source.......................................................... 14
High Voltage Floating Current Source.................................... 14
Kelvin Connections.................................................................... 15
Low Power, Low Voltage Reference for Data Converters ..... 15
Voltage Regulator for Portable Equipment............................. 15
Outline Dimensions....................................................................... 16
Ordering Guide .......................................................................... 17
REVISION HISTORY
12/07—Rev. D to Rev. E
Changes to Features.......................................................................... 1
C
hanges to Figure 34...................................................................... 14
3/06—Rev. C to Rev. D
Updated Format..................................................................Universal
hange to Table 8 ............................................................................. 6
C
Updated Outline Dimensions....................................................... 15
Changes to Ordering Guide.......................................................... 16
9/03—Rev. B to Rev. C
Deleted ADR290................................................................. Universal
C
hanges to Specifications.................................................................2
Changes to Ordering Guide.............................................................4
Updated Outline Dimensions....................................................... 13
Rev. E | Page 2 of 20
ADR291/ADR292
www.BDTIC.com/ADI
SPECIFICATIONS
ADR291 ELECTRICAL SPECIFICATIONS
VS = 3.0 V to 15 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter Symbol Conditions Min Typ Max Unit
E GRADE
Output Voltage V
Initial Accuracy V
–0.08 +0.08 %
F GRADE
Output Voltage V
Initial Accuracy V
–0.12 +0.12 %
G GRADE
Output Voltage V
Initial Accuracy V
–0.24 +0.24 %
LINE REGULATION
E/F Grades ∆V
G Grade 40 125 ppm/V
LOAD REGULATION
E/F Grades ∆V
G Grade 40 125 ppm/mA
LONG-TERM STABILITY ∆V
NOISE VOLTAGE eN 0.1 Hz to 10 Hz 8 μV p-p
WIDEBAND NOISE DENSITY eN @ 1 kHz 480 nV/√Hz
V
= 3.0 V to 15 V, TA = −25°C to +85°C, unless otherwise noted.
S
I
OUT
–2 +2 mV
OERR
I
OUT
–3 +3 mV
OERR
I
OUT
–6 +6 mV
OERR
/∆VIN I
OUT
/∆I
OUT
LOAD
After 1000 hours of operation @ 125°C 50 ppm
OUT
= 0 mA 2.498 2.500 2.502 V
OUT
= 0 mA 2.497 2.500 2.503 V
OUT
= 0 mA 2.494 2.500 2.506 V
OUT
= 0 mA 30 100 ppm/V
OUT
VS = 5.0 V, I
= 0 mA to 5 mA 30 100 ppm/mA
OUT
Table 3.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCV
I
OUT
OUT
= 0 mA 3 8 ppm/°C
F Grade 5 15 ppm/°C
G Grade 10 25 ppm/°C
LINE REGULATION
E/F Grades ∆V
/∆VIN I
OUT
= 0 mA 35 125 ppm/V
OUT
G Grade 50 150 ppm/V
LOAD REGULATION
E/F Grades ∆V
OUT
/∆I
LOAD
VS = 5.0 V, I
= 0 mA to 5 mA 20 125 ppm/mA
OUT
G Grade 30 150 ppm/mA
Rev. E | Page 3 of 20
ADR291/ADR292
www.BDTIC.com/ADI
VS = 3.0 V to 15 V, TA = −40°C to+125°C, unless otherwise noted.
Table 4.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCV
F Grade 5 20 ppm/°C
G Grade 10 30 ppm/°C
LINE REGULATION
E/F Grades ∆V
G Grade 70 250 ppm/V
LOAD REGULATION
E/F Grades ∆V
G Grade 30 300 ppm/mA
SUPPLY CURRENT IS T
−40°C ≤ TA ≤ +125°C 12 15 μA
THERMAL HYSTERESIS V
ADR292 ELECTRICAL SPECIFICATIONS
VS = 5 V to 15 V, TA = 25°C, unless otherwise noted.
I
OUT
/∆VIN I
OUT
/∆I
OUT
OUT-HYS
VS = 5.0 V, I
LOAD
8-lead SOIC, 8-lead TSSOP 50 ppm
= 0 mA 3 10 ppm/°C
OUT
= 0 mA 40 200 ppm/V
OUT
= 0 mA to 5 mA 20 200 ppm/mA
OUT
= 25°C 9 12 μA
A
Table 5.
Parameter Symbol Conditions Min Typ Max Unit
E GRADE
Output Voltage V
Initial Accuracy V
I
OUT
−3 +3 mV
OERR
= 0 mA 4.093 4.096 4.099 V
OUT
−0.07 +0.07 %
F GRADE
Output Voltage V
Initial Accuracy V
I
OUT
−4 +4 mV
OERR
= 0 mA 4.092 4.096 4.1 V
OUT
−0.10 +0.10 %
G GRADE
Output Voltage V
Initial Accuracy V
I
OUT
−6 +6 mV
OERR
= 0 mA 4.090 4.096 4.102 V
OUT
−0.15 +0.15 %
LINE REGULATION
E/F Grades ∆V
/∆VIN V
OUT
= 4.5 V to 15 V, I
S
= 0 mA 30 100 ppm/V
OUT
G Grade 40 125 ppm/V
LOAD REGULATION
E/F Grades ∆V
OUT
/∆I
VS = 5.0 V, I
LOAD
= 0 mA to 5 mA 30 100 ppm/mA
OUT
G Grade 40 125 ppm/mA
LONG-TERM STABILITY ∆V
OUT
After 1000 hours of operation @
50 ppm
125°C
NOISE VOLTAGE eN 0.1 Hz to 10 Hz 12 μV p-p
WIDEBAND NOISE DENSITY eN @ 1 kHz 640 nV/√Hz
Rev. E | Page 4 of 20
ADR291/ADR292
www.BDTIC.com/ADI
VS = 5 V to 15 V, TA = −25°C to +85°C, unless otherwise noted.
Table 6.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCV
F Grade 5 15 ppm/°C
G Grade 10 25 ppm/°C
LINE REGULATION
E/F Grades ∆V
G Grade 50 150 ppm/V
LOAD REGULATION
E/F Grades ∆V
G Grade 30 150 ppm/mA
V
= 5 V to 15 V, TA = −40°C to +125°C, unless otherwise noted.
S
Table 7.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCV
F Grade 5 20 ppm/°C
G Grade 10 30 ppm/°C
LINE REGULATION
E/F Grades ∆V
G Grade 70 250 ppm/V
LOAD REGULATION
E/F Grades ∆V
G Grade 30 300 ppm/mA
SUPPLY CURRENT IS T
−40°C ≤ TA ≤ +125°C 12 18 μA
THERMAL HYSTERESIS V
I
OUT
/ΔVIN V
OUT
/∆I
OUT
OUT
OUT
OUT
OUT-HYS
VS = 5.0 V, I
LOAD
I
/∆VIN V
/∆I
V
LOAD
8-lead SOIC, 8-lead TSSOP 50 ppm
= 0 mA 3 8 ppm/°C
OUT
= 4.5 V to 15 V, I
S
OUT
= 0 mA 3 10 ppm/°C
OUT
= 4.5 V to 15 V, I
S
= 5.0 V, I
S
= 25°C 10 15 μA
A
OUT
= 0 mA 35 125 ppm/V
OUT
= 0 mA to 5 mA 20 125 ppm/mA
= 0 mA 40 200 ppm/V
OUT
= 0 mA to 5 mA 20 200 ppm/mA
Rev. E | Page 5 of 20
ADR291/ADR292
www.BDTIC.com/ADI
ABSOLUTE MAXIMUM RATINGS
Remove power before inserting or removing units from their
sockets.
Table 8.
Parameter Rating
Supply Voltage 18 V
Output Short-Circuit Duration to GND Indefinite
Storage Temperature Range
T, R, RU Packages −65°C to +150°C
Operating Temperature Range
ADR291/ADR292 −40°C to +125°C
Junction Temperature Range
T, R, RU Packages −65°C to +125°C
Lead Temperature (Soldering, 60 sec) 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.
Table 9. Package Types
Package Type θ
8-Lead SOIC (R) 158 43 °C/W
8-Lead TSSOP (RU) 240 43 °C/W
3-Lead TO-92 (T ) 160 – °C/W
1
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
Nominal Output
V
Part Number
ADR420 2.048 8-Lead MSOP/SOIC
ADR421 2.50 8-Lead MSOP/SOIC
ADR423 3.0 8-Lead MSOP/SOIC
ADR425 5.0 8-Lead MSOP/SOIC
oltage (V)
1
θJC Unit
JA
Package Type
ESD CAUTION
Rev. E | Page 6 of 20
ADR291/ADR292
V
www.BDTIC.com/ADI
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
OUT
(Not to Scale)
GND
321
ADR291
TOP VIEW
V
IN
00163-038
NC
1
2
V
IN
NC
3
(Not to S cale)
4
GND
NC = NO CONNECT
ADR291/
ADR292
TOP VIEW
NC
8
NC
7
6
V
OUT
5
NC
00163-036
1
NC
2
V
IN
3
NC
4
GND
NC = NO CONNECT
ADR291/
ADR292
TOP VIEW
(Not to Scale)
8
NC
7
NC
6
V
OUT
5
NC
00163-037
Figure 4. 8-Lead SOIC (R-8)
Figure 5. 8-Lead TSSOP (RU-8)
Figure 6. 3-Lead TO-92 (T-3)
Table 11. Pin Function Descriptions
Pin No.
SOIC TSSOP TO-92 Mnemonic Description
1, 3, 5, 7, 8 1, 3, 5, 7, 8 N/A NC No Connect
2 2 1 VIN Input Voltage
4 4 2 GND
6 6 3 V
Output Voltage
OUT
Ground
Rev. E | Page 7 of 20
ADR291/ADR292
www.BDTIC.com/ADI
TYPICAL PERFORMANCE CHARACTERISTICS
2.506
VS = 5V
2.504
2.502
2.500
2.498
OUTPUT VOLTAGE (V)
2.496
3 TYPICAL PARTS
14
12
10
8
6
4
QUIESCENT CURRENT (μA)
2
TA= +125°C
T
= +25°C
A
=–40°C
T
A
2.494
–50 125–25
Figure 7. ADR291 V
4.102
VS = 5V
4.100
4.098
4.096
4.094
OUTPUT VOLTAGE (V)
4.092
4.090
–50 125–25 0 25 50 75 100
Figure 8. ADR292 V
14
12
10
8
6
4
QUIESCENT CURRENT (μA)
2
0
0162
0 25 50 75 100
TEMPERATURE (°C)
vs. Temperature
OUT
TEMPERATURE (°C)
vs. Temperature
OUT
TA= +125°C
TA= +25°C
=–40°C
T
A
64 8 10 12 14
INPUT VOLTAGE (V)
Figure 9. ADR291 Quiescent Current vs. Input Voltage
3 TYPICAL PARTS
00163-004
00163-005
00163-006
0
012
64 8 10 12 14
INPUT VOLTAGE (V)
Figure 10. ADR292 Quiescent Current vs. Input Voltage
14
VS = 5V
12
10
8
SUPPLY CURRENT (µA)
6
4
–50 125–250 255075100
ADR292
TEMPERATURE (°C)
ADR291
Figure 11. ADR291/ADR292 Supply Current vs. Temperature
100
ADR291: VS = 3.0V TO 15V
ADR292: V
80
60
40
LINE REGULATION (ppm/V)
20
0
–50 125–25 0 25 50 75 100
= 4.5V TO 15V
S
TEMPERATURE (°
ADR292
C)
= 0 mA
I
OUT
ADR291
Figure 12. ADR291/ADR292 Line Regulation vs. Temperature
00163-007
6
00163-008
00163-009
Rev. E | Page 8 of 20
ADR291/ADR292
A
www.BDTIC.com/ADI
100
ADR291: VS = 3.0V TO 15V
ADR292: V
80
60
ADR291
40
= 4.5V TO 15V
S
I
OUT
= 0 mA
200
160
120
VS = 5V
I
= 1mA
OUT
= 5mA
I
80
OUT
LINE REGULATION (ppm/V)
20
0
–50 125–25 0 25 50 75 100
TEMPERATURE (°C)
ADR292
Figure 13. ADR291/ADR292 Line Regulation vs. Temperature
0.7
0.6
0.5
0.4
0.3
0.2
DIFFERENTIAL VOLTAGE (V)
0.1
0
TA= +125°C
T
= +25°C
A
=–40°C
T
A
0 5.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
LOAD CURRENT (mA)
Figure 14. ADR291 Minimum Input-Output
oltage Differential vs. Load Current
V
00163-010
00163-011
LOAD REGULATION (ppm/mA)
40
0
–50 125–25 0 25 50 75 100
TEMPERATURE (°C)
Figure 16. ADR291 Load Regulation vs. Temperature
200
VS = 5V
160
120
80
LOAD REGULATION (ppm/mA)
40
0
–50 125–25 0 25 50 75 100
I
OUT
= 1mA
TEMPERATURE (°C)
I
OUT
Figure 17. ADR292 Load Regulation vs. Temperature
00163-013
= 5mA
00163-014
0.7
0.6
0.5
0.4
0.3
0.2
DIFFERENTIAL VOLTAGE (V)
0.1
0
TA= +125°C
= +25°C
T
A
=–40°C
T
A
0 5.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
LOAD CURRENT (mA)
00163-012
Figure 15. ADR292 Minimum Input-Output
oltage Differential vs. Load Current
V
Rev. E | Page 9 of 20
0
–250
–500
L (µV)
–750
–1000
–1250
FROM NOMIN
OUT
–1500
ΔV
–1750
–2000
0.1 101
SOURCING LO AD CURRENT (mA)
Figure 18. ADR291 ΔV
T
= +25°C
A
T
= –40°C
A
from Nominal vs. Load Current
OUT
TA= +125°C
00163-015
ADR291/ADR292
A
2
www.BDTIC.com/ADI
0
–500
–1000
L (µV)
–1550
–2000
–2500
FROM NOMIN
OUT
–3000
ΔV
–3500
–4000
0.1 101
SOURCING LO AD CURRENT (mA)
T
A
= –40°C
T
= +25°C
A
TA= +125°C
100
90
μ
V p-p
10
0%
00163-016
1s
00163-019
Figure 19. ADR292 ΔV
1000
900
800
700
600
500
400
300
200
VOLTAGE NOISE DENSITY (nV/√Hz)
100
0
10 1000100
from Nominal vs. Load Current
OUT
ADR292
ADR291
FREQUENCY (Hz)
Figure 20. Voltage Noise Density vs. Frequency
120
100
80
60
40
RIPPLE REJECTION (dB)
20
VIN = 15V
T
VS = 5V
= 25°C
A
00163-017
Figure 22. ADR291 0.1 Hz to 10 Hz Noise
50
VS = 5V
I
= 0 mA
L
40
)
Ω
30
20
OUTPUT IMPEDANCE (
10
0
0 10k10
Figure 23. ADR291 Output I
50
V
= 5V
S
I
= 0 mA
L
40
)
Ω
30
20
OUTPUT IMPEDANCE (
10
100 1k
FREQUENCY (Hz)
mpedance vs. Frequency
00163-020
0
10 1000100
FREQUENCY (Hz)
00163-018
Figure 21. ADR291/ADR292 Ripple Rejection vs. Frequency
Rev. E | Page 10 of 20
0
0 10k10
Figure 24. ADR292 Output I
100 1k
FREQUENCY (Hz)
mpedance vs. Frequency
00163-021
ADR291/ADR292
O
O
O
www.BDTIC.com/ADI
ON
ON
FF
100
90
10
0%
Figure 25. ADR291 Load Transient
IL = 5mA
C
= 1nF
L
100
90
FF
10
0%
1msIL = 5mA
1V
1ms
1V
00163-022
00163-023
100
100
90
10
0%
Figure 28. ADR291 Turn-On Time
90
10
0%
500μsIL = 5mA
1V
00163-025
10msIL = 0mA
1V
00163-026
ON
Figure 26. ADR291 Load Transient
18
IL = 5mA
C
= 100nF
100
90
FF
10
0%
L
5ms
1V
00163-024
Figure 27. ADR291 Load Transient
16
14
12
10
8
FREQUENCY
6
4
2
0
Figure 30. Typical Hysteresis for the ADR291 Product
Figure 29. ADR291 Turn-Off Time
200
–
–180
–160
–140
–120
–100
–80
V
–60
–40
DEVIATION (ppm)
OUT
–20
0
204060
TEMPERATURE
+25
°C ≥ –40°C ≥
+85°C ≥ +25°C
80
100
120
140
160
180
200
MORE
00163-027
Rev. E | Page 11 of 20
ADR291/ADR292
(
)
(
)
tVt
(
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TERMINOLOGY
)()
−
TVTV
Line Regulation
Line regulation refers to the change in output voltage due to a
ecified change in input voltage. It includes the effects of self-
sp
heating. 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
lo
ad 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 o
n a sample of parts subjected to a test of 1000 hours at
125°C.
−=Δ
0
OUTOUT
OUT
=Δ
OUT
()
−
0
()
OUT
1
tV
OUT
0
()
tVtV
1
6
10ppm ×
V
[]
OUT
VV
where:
V
(t
V
OUT
(t1) = V
OUT
) = V
0
at 25°C at Time 0.
OUT
at 25°C after 1000 hours of operation at 125°C.
OUT
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:
2
[]
TCV
O
Cppm/ ×
O
=°
()
O
C25
where:
V
OUT
V
OUT
V
OUT
(25°C) = V
(T1) = V
(T2) = V
at 25°C.
OUT
at Temperature 1.
OUT
at Temperature 2.
OUT
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.
−°=
C)25(
−
=
−
HYSΟUT
[ppm]
V
VVV
V
OUT
where:
V
OUT
V
OUT_TC
(25°C) = V
= V
at 25°C.
OUT
at 25°C after temperature cycle from +25°C to
OUT
−40°C, then to +85°C, and back to +25°C.
1
O
()
−×°
OUT_TCOUTHYSOUT
−°
)25(
VCV
OUT_TCOUT
°
C)25(
6
10
TTV
12
6
×
10
Rev. E | Page 12 of 20
ADR291/ADR292
−
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THEORY OF OPERATION
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.
The core of the XFET reference consists of two junction field
fect transistors, one having an extra channel implant to raise
ef
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
o
f 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
321
RRR
++
⎛
VV
Δ=
⎜
R
⎝
⎞
()(
+
⎟
1
PTATPOUT
⎠
3
RI
)
where:
ΔVP is the difference in pinch-off voltage between the two FETs.
I
is the positive temperature coefficient correction current.
PTAT
The various versions of the ADR291/ADR292 family are created
y on-chip adjustment of R1 and R3 to achieve 2.500 V or
b
4.096 V at the reference output.
The process used for the XFET reference also features vertical
NPN an
d PNP transistors, the latter of which are used as output
devices to provide a very low dropout voltage.
V
IN
I
1I1
1
V
1
EXTRA CHANNEL IMPLANT
R1 + R2 + R3
V
= ×ΔVP = I
OUT
Figure 31. ADR291/ADR292 Simplified Schematic
R1
R1
P
R2
R3
× R3
PTAT
I
PTAT
GND
V
OUT
00163-028
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:
TT
J
A
P
=
D
θ
JA
where
T
and TA are the junction and ambient temperatures,
J
respectively.
P
is the device power dissipation.
D
θ
is the device package thermal resistance.
JA
BASIC VOLTAGE REFERENCE CONNECTIONS
References, in general, require a bypass capacitor connected
from the V
pin to the GND pin. The circuit in Figure 32
OUT
illustrates the basic configuration for the ADR291/ADR292
family of references. Note that the decoupling capacitors are not
required for circuit stability.
1
NC
ADR291/
2
ADR292
3
+
10µF
Figure 32. Basic Voltage Reference Configuration
0.1µF
NC
4
NC = NO CONNECT
8
NC
7
NC
V
OUT
6
5
NC
0.1µF
00163-029
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.
e ADR291.
th
Figure 28 shows the turn-on settling time for
Rev. E | Page 13 of 20
ADR291/ADR292
V
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APPLICATIONS INFORMATION
NEGATIVE PRECISION REFERENCE WITHOUT PRECISION RESISTORS
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
atched resistors with the use of an active integrator circuit. In this
m
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 V
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.
Figure 33. A Negative Precision Voltage Reference Uses No
and GND. Thus, any negative output voltage
OUT
IN
2
ADR291/
ADR292
V
OUT
GND
4
6
100kΩ
1kΩ
1µF
A1 = 1/2 OP291,
1/2 OP295
1µF
+5V
A1
–5V
100Ω
–V
Precision Resistors
REF
00163-030
PRECISION CURRENT SOURCE
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/
AD
R292 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 R
, which sets the output
SET
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.
IN
2
ADR291/
ADR292
V
6
OUT
R1
GND
4
Figure 34. A Precision Current Source
1µF
ADJUST
R
I
SY
R
SET
P1
I
OUT
L
00163-031
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.
+
S
E231
SILICONIX
2
V
IN
ADR291/
ADR292
GND
4
OP90
Figure 35. High Voltage Floating Current Source
2N3904
–V
S
2.10kΩ
00163-032
Rev. E | Page 14 of 20
ADR291/ADR292
V
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KELVIN CONNECTIONS
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 (V
= R × IL) at
ERROR
the load. However, the Kelvin connection shown in Figure 36
vercomes the problem by including the wiring resistance
o
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.
IN
R
LW
+V
2
ADR291/
ADR292
V
OUT
GND
4
6
1µF
100kΩ
V
IN
A1
A1 = 1/2 OP295
Figure 36. Advantage of Kelvin Connection
OUT
SENSE
R
LW
+V
OUT
FORCE
R
L
00163-033
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
or this converter. The AD7701 is a 16-bit ADC with on-chip
f
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.
This entire circuit runs on ±5 V supplies. The power dissipation
f the AD7701 is typically 25 mW and, when
o
combined with the power dissipation of the ADR291 (60 μW),
t
he entire circuit still consumes about 25 mW.
+5
ANALOG
SUPPLY
RANGES
SELECT
CALIBRATE
ANALOG
INPUT
ANALOG
GROUND
ANALOG
SUPPLY
0.1µF
–5V
0.1µF
10µF
V
V
ADR291
GND
0.1µF
OUT
AV
DD
DV
IN
V
REF
AD7701
BP/UP
CAL
A
IN
AGND
AV
SS
10µF0.1µF
SLEEP
MODE
DRDY
CS
SCLK
SDATA
CLKIN
CLKOUT
SC1
SC2
DGND
DV
DD
SS
0.1µF
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
0.1µF
Figure 37. Low Power, Low Voltage Supply Reference for the AD7701
VOLTAGE REGULATOR FOR PORTABLE EQUIPMENT
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
AD
R291 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.
CHARGER
INPUT
LEAD-ACID
BATTERY
0.1µF
2
V
IN
R3
510kΩ
ADR291/
ADR292
6V
+
V
GND
4
OUT
NC
402kΩ
6 2
3
R1
1%
7
6
OP20
3
4
R2
402kΩ
1%
68µF
TANT
IRF9530
C1
+
Figure 38. Voltage Regulator for Portable Equipment
5V, 100mA
C2
+
1000µF
ELECT
00163-034
0163-035
Rev. E | Page 15 of 20
ADR291/ADR292
Y
www.BDTIC.com/ADI
OUTLINE DIMENSIONS
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
0.25 (0.0098)
0.10 (0.0040)
COPLANARI TY
0.10
CONTROLLING DIMENSI ONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-O FF MI LLI METER EQ UIVALENTS FOR
REFERENCE O NLY AND ARE NOT APPROPRIATE FO R USE IN DE SIGN.
85
1
1.27 (0.0500 )
SEATING
PLANE
COMPLI ANT TO JEDEC S TANDARDS MS-012-A A
BSC
6.20 (0.2441)
5.80 (0.2284)
4
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0 201)
0.31 (0.0 122)
8°
0°
0.25 (0.0098)
0.17 (0.0067)
Figure 39. 8-Lead Standard Small Outline Package [SOIC_N]
Nar
row Body
(R-8)
Dimensions shown in millimeters and (inches)
0.50 (0.0 196)
0.25 (0.0 099)
1.27 (0.0 500)
0.40 (0.0 157)
45°
0.15
0.05
COPLANARIT
012407-A
0.10
Figure 40. 8-Lead Thin Shrink Small Outline Package [TSSOP]
3.10
3.00
2.90
8
5
4.50
6.40 BSC
4.40
4.30
41
PIN 1
0.65 BSC
1.20
MAX
0.30
SEATING
0.19
PLANE
COMPLIANT TO JEDEC STANDARDS MO-153-AA
0.20
0.09
8°
0°
(RU-8)
Dim
ensions shown in millimeters
0.75
0.60
0.45
0.210 (5.33)
0.170 (4.32)
0.205 (5.21)
0.175 (4.45)
0.135 (3.43)
0.050 (1.27)
MAX
0.019 (0.482)
0.016 (0.407)
MIN
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
0.500 (12.70) MIN
SEATING
PLANE
COMPLIANT TO JEDEC STANDARDS TO-226-AA
SQ
0.055 (1.40)
0.045 (1.15)
0.105 (2.66)
0.095 (2.42)
0.115 (2.92)
0.080 (2.03)
Figure 41. 3-Lead Plastic Header-Style Package [TO-92]
(T-3)
Dim
ensions shown in inches and (millimeters)
0.165 (4.19)
0.125 (3.18)
3
2
1
BOTTOM VIEW
0.115 (2.92)
0.080 (2.03)
Rev. E | Page 16 of 20
ADR291/ADR292
www.BDTIC.com/ADI
ORDERING GUIDE
Temperature
Output
Model
V
oltage
ADR291ER 2.50 0.08 8 8-Lead SOIC_N R-8 98
ADR291ER-REEL7 2.50 0.08 8 8-Lead SOIC_N R-8 1,000
ADR291ERZ
ADR291ERZ-REEL7
1
2.50 0.08 8 8-Lead SOIC_N R-8 98
1
2.50 0.08 8 8-Lead SOIC_N R-8 1,000
ADR291FR 2.50 0.12 15 8-Lead SOIC_N R-8 98
ADR291FR-REEL 2.50 0.12 15 8-Lead SOIC_N R-8 2,500
ADR291FR-REEL7 2.50 0.12 15 8-Lead SOIC_N R-8 1,000
ADR291FRZ
ADR291FRZ-REEL
ADR291FRZ-REEL7
1
2.50 0.12 15 8-Lead SOIC_N R-8 98
1
2.50 0.12 15 8-Lead SOIC_N R-8 2,500
1
2.50 0.12 15 8-Lead SOIC_N R-8 1,000
ADR291GR 2.50 0.24 25 8-Lead SOIC_N R-8 98
ADR291GR-REEL 2.50 0.24 25 8-Lead SOIC_N R-8 2,500
ADR291GR-REEL7 2.50 0.24 25 8-Lead SOIC_N R-8 1,000
ADR291GRZ
ADR291GRZ-REEL
ADR291GRZ-REEL7
1
2.50 0.24 25 8-Lead SOIC_N R-8 98
1
2.50 0.24 25 8-Lead SOIC_N R-8 2,500
1
2.50 0.24 25 8-Lead SOIC_N R-8 1,000
ADR291GRU 2.50 0.24 25 8-Lead TSSOP RU-8 98
ADR291GRU-REEL7 2.50 0.24 25 8-Lead TSSOP RU-8 1,000
ADR291GRUZ
1
2.50 0.24 25 8-Lead TSSOP RU-8 98
ADR291GRUZ-REEL12.50 0.24 25 8-Lead TSSOP RU-8 1,000
ADR291GRUZ-REEL712.50 0.24 25 8-Lead TSSOP RU-8 1,000
ADR291GT9 2.50 0.24 25 3-Lead TO-92 T-3 98
ADR291GT9-REEL 2.50 0.24 25 3-Lead TO-92 T-3 2,000
ADR291GT9Z
1
2.50 0.24 25 3-Lead TO-92 T-3 98
ADR292ER 4.096 0.07 8 8-Lead SOIC_N R-8 98
ADR292ER-REEL 4.096 0.07 8 8-Lead SOIC_N R-8 2,500
ADR292ERZ
ADR292ERZ-REEL
1
4.096 0.07 8 8-Lead SOIC_N R-8 98
1
4.096 0.07 8 8-Lead SOIC_N R-8 2,500
ADR292FR 4.096 0.10 15 8-Lead SOIC_N R-8 98
ADR292FR-REEL 4.096 0.10 15 8-Lead SOIC_N R-8 2,500
ADR292FR-REEL7 4.096 0.10 15 8-Lead SOIC_N R-8 1,000
ADR292FRZ
ADR292FRZ-REEL
ADR292FRZ-REEL7
1
4.096 0.10 15 8-Lead SOIC_N R-8 98
1
4.096 0.10 15 8-Lead SOIC_N R-8 2,500
1
4.096 0.10 15 8-Lead SOIC_N R-8 1,000
ADR292GR 4.096 0.15 25 8-Lead SOIC_N R-8 98
ADR292GR-REEL7 4.096 0.15 25 8-Lead SOIC_N R-8 1,000
ADR292GRZ
ADR292GRZ-REEL7
1
4.096 0.15 25 8-Lead SOIC_N R-8 98
1
4.096 0.15 25 8-Lead SOIC_N R-8 1,000
ADR292GRU 4.096 0.24 25 8-Lead TSSOP RU-8 98
ADR292GRU-REEL7 4.096 0.15 25 8-Lead TSSOP RU-8 1,000
ADR292GRUZ
1
4.096 0.24 25 8-Lead TSSOP RU-8 98
ADR292GRUZ-REEL714.096 0.15 25 8-Lead TSSOP RU-8 1,000
1
Z = RoHS Compliant Part.
Initial Accuracy
(±%)
C
oefficient Max
(ppm/°C)
Package
Description
Package
tion
Op
Ordering
Quantity
Rev. E | Page 17 of 20
ADR291/ADR292
www.BDTIC.com/ADI
NOTES
Rev. E | Page 18 of 20
ADR291/ADR292
www.BDTIC.com/ADI
NOTES
Rev. E | Page 19 of 20
ADR291/ADR292
www.BDTIC.com/ADI
NOTES
©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
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