Low Noise Micropower 2.5 V and
4.096 V Precision Voltage References
ADR291/ADR292
Rev. F
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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
CONNECTION DIAGRAMS
NC 1
VIN 2
NC 3
GND 4
NC8
NC7
VOUT
6
NC
5
NC = NO CONNECT
ADR291/
ADR292
TOP VIEW
(Not to Scale)
00163-001
Figure 1. 8-Lead SOIC (R-8)
1
2
3
4
V
IN
NC
GND
NC
8
7
6
5
NC
V
OUT
NC
NC
NC = NO CONNECT
00163-002
ADR291/
ADR292
TOP VIEW
(Not to Scale)
Figure 2. 8-Lead TSSOP (RU-8)
321
V
OUT
GND
V
IN
TOP VIEW
(Not to Scale)
ADR291
00163-003
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.
Output
Voltage (V)
Initial
Accuracy (±%)
Temperature
Coefficient
(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
ADR291/ADR292
Rev. F | Page 2 of 20
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
High Voltage Floating Current Source .................................... 14
Kelvin Connections .................................................................... 14
Low Power, Low Voltage Reference for Data Converters ..... 14
Voltage Regulator for Portable Equipment ............................. 15
Outline Dimensions ....................................................................... 16
Ordering Guide .......................................................................... 17
REVISION HISTORY
5/11—Rev. E to Rev. F
Deleted Negative Precision Reference Without Precision
Resistors Section ............................................................................. 14
Deleted Figure 33 and Figure 34, Renumbered Sequentially ... 14
Changes to Ordering Guide .......................................................... 17
12/07—Rev. D to Rev. E
Changes to Features .......................................................................... 1
Changes to Figure 34 ...................................................................... 14
3/06—Rev. C to Rev. D
Updated Format .................................................................. Universal
Change to Table 8 ............................................................................. 6
Updated Outline Dimensions ....................................................... 15
Changes to Ordering Guide .......................................................... 16
9/03—Rev. B to Rev. C
Deleted ADR290 ................................................................. Universal
Changes to Specifications ................................................................. 2
Changes to Ordering Guide ............................................................. 4
Updated Outline Dimensions ....................................................... 13
ADR291/ADR292
Rev. F | Page 3 of 20
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 VOUT I
OUT = 0 mA 2.498 2.500 2.502 V
Initial Accuracy VOERR –2 +2 mV
–0.08 +0.08 %
F GRADE
Output Voltage VOUT I
OUT = 0 mA 2.497 2.500 2.503 V
Initial Accuracy VOERR –3 +3 mV
–0.12 +0.12 %
G GRADE
Output Voltage VOUT I
OUT = 0 mA 2.494 2.500 2.506 V
Initial Accuracy VOERR –6 +6 mV
–0.24 +0.24 %
LINE REGULATION
E/F Grades ∆VOUT/∆VIN I
OUT = 0 mA 30 100 ppm/V
G Grade 40 125 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD V
S = 5.0 V, IOUT = 0 mA to 5 mA 30 100 ppm/mA
G Grade 40 125 ppm/mA
LONG-TERM STABILITY ∆VOUT After 1000 hours of operation @ 125°C 50 ppm
NOISE VOLTAGE eN 0.1 Hz to 10 Hz 8 μV p-p
WIDEBAND NOISE DENSITY eN @ 1 kHz 480 nV/√Hz
VS = 3.0 V to 15 V, TA = −25°C to +85°C, unless otherwise noted.
Table 3.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCVOUT I
OUT = 0 mA 3 8 ppm/°C
F Grade 5 15 ppm/°C
G Grade 10 25 ppm/°C
LINE REGULATION
E/F Grades ∆VOUT/∆VIN I
OUT = 0 mA 35 125 ppm/V
G Grade 50 150 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD V
S = 5.0 V, IOUT = 0 mA to 5 mA 20 125 ppm/mA
G Grade 30 150 ppm/mA
ADR291/ADR292
Rev. F | Page 4 of 20
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 TCVOUT I
OUT = 0 mA 3 10 ppm/°C
F Grade 5 20 ppm/°C
G Grade 10 30 ppm/°C
LINE REGULATION
E/F Grades ∆VOUT/∆VIN I
OUT = 0 mA 40 200 ppm/V
G Grade 70 250 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD V
S = 5.0 V, IOUT = 0 mA to 5 mA 20 200 ppm/mA
G Grade 30 300 ppm/mA
SUPPLY CURRENT IS T
A = 25°C 9 12 μA
−40°C ≤ TA ≤ +125°C 12 15 μA
THERMAL HYSTERESIS VOUT-HYS 8-lead SOIC, 8-lead TSSOP 50 ppm
ADR292 ELECTRICAL SPECIFICATIONS
VS = 5 V to 15 V, TA = 25°C, unless otherwise noted.
Table 5.
Parameter Symbol Conditions Min Typ Max Unit
E GRADE
Output Voltage VOUT I
OUT = 0 mA 4.093 4.096 4.099 V
Initial Accuracy VOERR −3 +3 mV
−0.07 +0.07 %
F GRADE
Output Voltage VOUT I
OUT = 0 mA 4.092 4.096 4.1 V
Initial Accuracy VOERR −4 +4 mV
−0.10 +0.10 %
G GRADE
Output Voltage VOUT I
OUT = 0 mA 4.090 4.096 4.102 V
Initial Accuracy VOERR −6 +6 mV
−0.15 +0.15 %
LINE REGULATION
E/F Grades ∆VOUT/∆VIN V
S = 4.5 V to 15 V, IOUT = 0 mA 30 100 ppm/V
G Grade 40 125 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD VS = 5.0 V, IOUT = 0 mA to 5 mA 30 100 ppm/mA
G Grade 40 125 ppm/mA
LONG-TERM STABILITY ∆VOUT After 1000 hours of operation @
125°C
50 ppm
NOISE VOLTAGE eN 0.1 Hz to 10 Hz 12 μV p-p
WIDEBAND NOISE DENSITY eN @ 1 kHz 640 nV/√Hz
ADR291/ADR292
Rev. F | Page 5 of 20
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 TCVOUT I
OUT = 0 mA 3 8 ppm/°C
F Grade 5 15 ppm/°C
G Grade 10 25 ppm/°C
LINE REGULATION
E/F Grades ∆VOUT/ΔVIN V
S = 4.5 V to 15 V, IOUT = 0 mA 35 125 ppm/V
G Grade 50 150 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD V
S = 5.0 V, IOUT = 0 mA to 5 mA 20 125 ppm/mA
G Grade 30 150 ppm/mA
VS = 5 V to 15 V, TA = −40°C to +125°C, unless otherwise noted.
Table 7.
Parameter Symbol Conditions Min Typ Max Unit
TEMPERATURE COEFFICIENT
E Grade TCVOUT I
OUT = 0 mA 3 10 ppm/°C
F Grade 5 20 ppm/°C
G Grade 10 30 ppm/°C
LINE REGULATION
E/F Grades ∆VOUT/∆VIN V
S = 4.5 V to 15 V, IOUT = 0 mA 40 200 ppm/V
G Grade 70 250 ppm/V
LOAD REGULATION
E/F Grades ∆VOUT/∆ILOAD V
S = 5.0 V, IOUT = 0 mA to 5 mA 20 200 ppm/mA
G Grade 30 300 ppm/mA
SUPPLY CURRENT IS T
A = 25°C 10 15 μA
−40°C ≤ TA ≤ +125°C 12 18 μA
THERMAL HYSTERESIS VOUT-HYS 8-lead SOIC, 8-lead TSSOP 50 ppm
ADR291/ADR292
Rev. F | Page 6 of 20
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 θJA1 θJC Unit
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
Part Number
Nominal Output
Voltage (V) Package Type
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
ESD CAUTION
ADR291/ADR292
Rev. F | Page 7 of 20
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
NC
1
V
IN 2
NC
3
GND
4
NC
8
NC
7
V
OUT
6
NC
5
NC = NO CONNECT
ADR291/
ADR292
TOP VIEW
(Not to Scale)
00163-036
Figure 4. 8-Lead SOIC (R-8)
1
2
3
4
V
IN
NC
GND
NC
8
7
6
5
NC
V
OUT
NC
NC
NC = NO CONNECT
00163-037
ADR291/
ADR292
TOP VIEW
(Not to Scale)
Figure 5. 8-Lead TSSOP (RU-8)
321
V
OUT
GND
V
IN
TOP VIEW
(Not to Scale)
ADR291
00163-038
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 Ground
6 6 3 VOUT Output Voltage
ADR291/ADR292
Rev. F | Page 8 of 20
TYPICAL PERFORMANCE CHARACTERISTICS
TEMPERATURE (°C)
2.506
2.494
–50 125–25
OUTPUT VOLTAGE (V)
0 255075100
2.504
2.502
2.500
2.498
2.496
V
S
= 5V 3 TYPICAL PARTS
00163-004
Figure 7. ADR291 VOUT vs. Temperature
4.102
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
4.100
4.098
4.096
4.094
4.092
3 TYPICAL PARTS
4.090
–50 125–25 0 25 50 75 100
00163-005
V
S
= 5V
Figure 8. ADR292 VOUT vs. Temperature
INPUT VOLTAGE (V)
14
00162
QUIESCENT CURRENT (μA)
64 8 10 12 14
12
8
6
4
2
10
T
A
= +125°C
T
A
= +25°C
T
A
=–40°C
00163-006
Figure 9. ADR291 Quiescent Current vs. Input Voltage
INPUT VOLTAGE (V)
14
0012
QUIESCENT CURRENT (μA)
64 8 10 12 14
12
8
6
4
2
10
00163-007
T
A
= +125°C
T
A
= +25°C
T
A
=–40°C
6
Figure 10. ADR292 Quiescent Current vs. Input Voltage
14
12
4
10
8
6
ADR291
ADR292
TEMPERATURE (°C)
–50 125–25 0 25 50 75 100
00163-008
VS = 5V
SUPPLY CURRENT (µA)
Figure 11. ADR291/ADR292 Supply Current vs. Temperature
100
80
0
60
40
20
TEMPERATURE (°C)
–50 125–25 0 25 50 75 100
00163-009
LINE REGULATION (ppm/V)
ADR291
ADR292
ADR291: V
S
= 3.0V TO 15V
ADR292: V
S
= 4.5V TO 15V I
OUT
= 0 mA
Figure 12. ADR291/ADR292 Line Regulation vs. Temperature
ADR291/ADR292
Rev. F | Page 9 of 20
100
80
0
60
40
20
TEMPERATURE (°C)
–50 125–25 0 25 50 75 100
00163-010
ADR292
ADR291
LINE REGULATION (ppm/V)
ADR291: V
S
= 3.0V TO 15V
ADR292: V
S
= 4.5V TO 15V I
OUT
= 0 mA
Figure 13. ADR291/ADR292 Line Regulation vs. Temperature
LOAD CURRENT (mA)
DIFFERENTIAL VOLTAGE (V)
0.7
0
0 5.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
0.6
0.5
0.4
0.3
0.2
0.1
TA= +125°C
TA= +25°C
TA=–40°C
00163-011
Figure 14. ADR291 Minimum Input-Output
Voltage Differential vs. Load Current
LOAD CURRENT (mA)
DIFFERENTIAL VOLTAGE (V)
0.7
0
0 5.00.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
0.6
0.5
0.4
0.3
0.2
0.1
00163-012
TA= +125°C
TA= +25°C
TA=–40°C
Figure 15. ADR292 Minimum Input-Output
Voltage Differential vs. Load Current
200
160
0
120
80
40
TEMPERATURE (°C)
–50 125–25 0 25 50 75 100
00163-013
LOAD REGULATION (ppm/mA)
VS = 5V
IOUT = 1mA
IOUT = 5mA
Figure 16. ADR291 Load Regulation vs. Temperature
200
160
0
120
80
40
TEMPERATURE (°C)
–50 125–25 0 25 50 75 100
00163-014
LOAD REGULATION (ppm/mA)
VS = 5V
IOUT = 1mA
IOUT = 5mA
Figure 17. ADR292 Load Regulation vs. Temperature
SOURCING LOAD CURRENT (mA)
0
–1250
–2000
0.1 101
∆V
OUT
FROM NOMIN
A
L (µV)
–1750
–1500
–500
–250
–1000
–750
T
A
= +125°C
T
A
= +25°C
T
A
= –40°C
00163-015
Figure 18. ADR291 ΔVOUT from Nominal vs. Load Current
ADR291/ADR292
Rev. F | Page 10 of 20
SOURCING LOAD CURRENT (mA)
0
–2500
–4000
0.1 101
∆V
OUT
FROM NOMIN
A
L (µV)
–3500
–3000
–1000
–500
–2000
–1550
00163-016
T
A
= +125°C
T
A
= +25°C
T
A
= –40°C
Figure 19. ADR292 ΔVOUT from Nominal vs. Load Current
FREQUENCY (Hz)
1000
500
010 1000100
VOLTAGE NOISE DENSITY (nV/√Hz)
100
200
800
900
300
400
600
700
00163-017
ADR291
ADR292 V
IN
= 15V
T
A
= 25°C
Figure 20. Voltage Noise Density vs. Frequency
FREQUENCY (Hz)
120
60
010 1000100
RIPPLE REJECTION (dB)
20
100
80
40
00163-018
VS = 5V
Figure 21. ADR291/ADR292 Ripple Rejection vs. Frequency
10
0%
100
90
1s
2
μ
V p-p
00163-019
Figure 22. ADR291 0.1 Hz to 10 Hz Noise
FREQUENCY (Hz)
50
40
00 10k10
OUTPUT IMPEDANCE (
Ω
)
100 1k
30
20
10
V
S
= 5V
I
L
= 0 mA
00163-020
Figure 23. ADR291 Output Impedance vs. Frequency
FREQUENCY (Hz)
50
40
00 10k10
OUTPUT IMPEDANCE (
Ω
)
100 1k
30
20
10
V
S
= 5V
I
L
= 0 mA
00163-021
Figure 24. ADR292 Output Impedance vs. Frequency
ADR291/ADR292
Rev. F | Page 11 of 20
10
0%
100
90
1msIL = 5mA
1V
O
FF
ON
00163-022
Figure 25. ADR291 Load Transient
10
0%
100
90
1ms
I
L
= 5mA
C
L
= 1nF
1V
O
FF
ON
00163-023
Figure 26. ADR291 Load Transient
10
0%
100
90
5ms
I
L
= 5mA
C
L
= 100nF
1V
O
FF
ON
00163-024
Figure 27. ADR291 Load Transient
10
0%
100
90
500
μ
sI
L
= 5mA
1V
00163-025
Figure 28. ADR291 Turn-On Time
10
0%
100
90
10msI
L
= 0mA
1V
00163-026
Figure 29. ADR291 Turn-Off Time
V
OUT
DEVIATION (ppm)
–
200
0
FREQUENCY
8
6
4
2
10
14
12
16
18
–180
–160
–140
–120
–100
–80
–60
–40
–20
0
20
40
60
80
100
120
140
160
180
200
MORE
TEMPERATURE
+25
°C ≥–40°C ≥
+85°C ≥+25°C
00163-027
Figure 30. Typical Hysteresis for the ADR291 Product
ADR291/ADR292
Rev. F | Page 12 of 20
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 self-
heating. Line regulation is expressed as percent-per-volt, parts-
per-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, parts-
per-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.
(
)
(
)
[]
()
()
()
6
10ppm ×
−
=Δ
−=Δ
0
OUT
1
OUT
0
OUT
OUT
1
OUT
0
OUTOUT
tV
tVtV
V
t
V
t
VV
where:
VOUT (t0) = VOUT at 25°C at Time 0.
VOUT (t1) = VOUT at 25°C after 1000 hours of operation at 125°C.
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:
[]
(
)()
()
()
6
10
C25
Cppm/ ×
−×°
−
=°
12
O
1
O
2
O
OTTV
TVTV
TCV
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.
6
10
C)25(
)25(
[ppm]
C)25(
×
°
−°
=
−°=
−
−
OUT
OUT_TCOUT
HYSΟUT
OUT_TCOUTHYSOUT
V
VCV
V
VVV
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.
ADR291/ADR292
Rev. F | Page 13 of 20
THEORY OF OPERATION
The ADR291/ADR292 series of references uses a reference
generation technique known as XFET (eXtra implanted junc-
tion 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
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 advan-
tage (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
()(
3
1321 RI
RRRR
VV PTATPOUT +
⎟
⎠
⎞
⎜
⎝
⎛++
Δ=
)
where:
ΔVP is the difference in pinch-off voltage between the two FETs.
IPTAT is the positive temperature coefficient correction current.
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.
V
OUT
V
IN
I
PTAT
GND
R1
R2
R3
I
1
I
1
1
1
EXTRA CHANNEL IMPLANT
V
OUT
= ×ΔV
P
= I
PTAT
× R3
R1 + R2 + R3
R1
V
P
00163-028
Figure 31. ADR291/ADR292 Simplified Schematic
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:
JA
A
J
D
TT
Pθ
−
=
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.
NC
NC
NC
NC
VOUT
NC
0.1µF
0.1µF
10µF
+
NC = NO CONNECT
1
2
3
4
8
7
6
5
00163-029
ADR291/
ADR292
Figure 32. Basic Voltage Reference Configuration
NOISE PERFORMANCE
The noise generated by the ADR291/ADR292 family of refer-
ences 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 com-
ponents 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.
ADR291/ADR292
Rev. F | Page 14 of 20
APPLICATIONS INFORMATION
HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit shown in Figure 33 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.
GND
2
4
+
V
S
ADR291/
ADR292
V
IN
E231
SILICONIX
2N3904
2.10kΩ
–V
S
OP90
00163-032
Figure 33. High Voltage Floating Current Source
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 (VERROR = R × IL) at
the load. However, the Kelvin connection shown in Figure 34
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.
A1
1µF 100kΩ
+VOUT
SENSE
A1 = 1/2 OP295
VIN
RLW
RL
RLW
+VOUT
FORCE
VOUT
GND
V
IN
2
6
4
00163-033
ADR291/
ADR292
Figure 34. 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 digital-
to-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 applica-
tions such as handheld, battery-operated equipment.
One such ADC for which the ADR291 is well suited is the
AD7701. Figure 35 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.
This entire circuit runs on ±5 V supplies. The power dissipation
of the AD7701 is typically 25 mW and, when
combined with the power dissipation of the ADR291 (60 μW),
the entire circuit still consumes about 25 mW.
BP/UP
CAL
V
REF
A
IN
AGND
AV
SS
AV
DD
DV
DD
SLEEP
MODE
DRDY
SCLK
CS
SDATA
CLKIN
CLKOUT
SC1
SC2
DGND
DV
SS
0.1µF
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
0.1µF
10µF0.1µF
–5V
ANALOG
SUPPLY
+5
V
ANALOG
SUPPLY
ANALOG
GROUND
ANALOG
INPUT
CALIBRATE
RANGES
SELECT
0.1µF
ADR291
0.1µF
GND
V
IN
V
OUT
10µF
0.1µF
AD7701
00163-034
Figure 35. Low Power, Low Voltage Supply Reference for the AD7701
ADR291/ADR292
Rev. F | Page 15 of 20
VOLTAGE REGULATOR FOR PORTABLE
EQUIPMENT
The ADR291/ADR292 family of references is ideal for provid-
ing a stable, low cost, and low power reference voltage in
portable equipment power supplies. Figure 36 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.
V
OUT
NC
GND
V
IN
0.1µF
LEAD-ACID
BATTERY
+
6V
CHARGER
INPUT
R1
402kΩ
1%
R2
402kΩ
1%
+C2
1000µF
ELECT
C1
68µF
TANT
+
5V, 100mA
IRF9530
OP20
2
6 2 7
6
4
3
3
4
0
0163-035
ADR291/
ADR292
R3
510kΩ
Figure 36. Voltage Regulator for Portable Equipment
ADR291/ADR292
Rev. F | Page 16 of 20
OUTLINE DIMENSIONS
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.
COMPLIANT TO JEDEC STANDARDS MS-012-A A
012407-A
0.25 (0.0098)
0.17 (0.0067)
1.27 (0.0500)
0.40 (0.0157)
0.50 (0.0196)
0.25 (0.0099) 45°
8°
0°
1.75 (0.0688)
1.35 (0.0532)
SEATING
PLANE
0.25 (0.0098)
0.10 (0.0040)
4
1
85
5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
1.27 (0.0500)
BSC
6.20 (0.2441)
5.80 (0.2284)
0.51 (0.0201)
0.31 (0.0122)
COPLANARITY
0.10
Figure 37. 8-Lead Standard Small Outline Package [SOIC_N]
Narrow Body
(R-8)
Dimensions shown in millimeters and (inches)
85
41
PIN 1
0.65 BSC
SEATING
PLANE
0.15
0.05
0.30
0.19
1.20
MAX
0.20
0.09
8°
0°
6.40 BSC
4.50
4.40
4.30
3.10
3.00
2.90
COPLANARIT
Y
0.10
0.75
0.60
0.45
COMPLIANT TO JEDEC STANDARDS MO-153-AA
Figure 38. 8-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-8)
Dimensions shown in millimeters
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
COMPLIANT TO JEDEC STANDARDS TO-226-AA
0.115 (2.92)
0.080 (2.03)
0.115 (2.92)
0.080 (2.03)
0.165 (4.19)
0.125 (3.18)
1
2
3
BOTTOM VIEW
SQ
0.019 (0.482)
0.016 (0.407)
0.105 (2.66)
0.095 (2.42)
0.055 (1.40)
0.045 (1.15)
SEATING
PLANE
0.500 (12.70) MIN
0.205 (5.21)
0.175 (4.45)
0.210 (5.33)
0.170 (4.32)
0.135 (3.43)
MIN
0.050 (1.27)
MAX
Figure 39. 3-Lead Plastic Header-Style Package [TO-92]
(T-3)
Dimensions shown in inches and (millimeters)
ADR291/ADR292
Rev. F | Page 17 of 20
ORDERING GUIDE
Model1
Output
Voltage
Initial Accuracy
(±%)
Temperature
Coefficient Max
(ppm/°C)
Package
Description
Package
Option
Ordering
Quantity
ADR291ERZ 2.50 0.08 8 8-Lead SOIC_N R-8 98
ADR291ERZ-REEL7 2.50 0.08 8 8-Lead SOIC_N R-8 1,000
ADR291FRZ 2.50 0.12 15 8-Lead SOIC_N R-8 98
ADR291FRZ-REEL 2.50 0.12 15 8-Lead SOIC_N R-8 2,500
ADR291FRZ-REEL7 2.50 0.12 15 8-Lead SOIC_N R-8 1,000
ADR291GRZ 2.50 0.24 25 8-Lead SOIC_N R-8 98
ADR291GRZ-REEL 2.50 0.24 25 8-Lead SOIC_N R-8 2,500
ADR291GRZ-REEL7 2.50 0.24 25 8-Lead SOIC_N R-8 1,000
ADR291GRUZ 2.50 0.24 25 8-Lead TSSOP RU-8 98
ADR291GRUZ-REEL 2.50 0.24 25 8-Lead TSSOP RU-8 1,000
ADR291GRUZ-REEL7 2.50 0.24 25 8-Lead TSSOP RU-8 1,000
ADR291GT9Z 2.50 0.24 25 3-Lead TO-92 T-3 98
ADR292ERZ 4.096 0.07 8 8-Lead SOIC_N R-8 98
ADR292ERZ-REEL 4.096 0.07 8 8-Lead SOIC_N R-8 2,500
ADR292FRZ 4.096 0.10 15 8-Lead SOIC_N R-8 98
ADR292FRZ-REEL 4.096 0.10 15 8-Lead SOIC_N R-8 2,500
ADR292FRZ-REEL7 4.096 0.10 15 8-Lead SOIC_N R-8 1,000
ADR292GRZ 4.096 0.15 25 8-Lead SOIC_N R-8 98
ADR292GRZ-REEL7 4.096 0.15 25 8-Lead SOIC_N R-8 1,000
ADR292GRUZ 4.096 0.24 25 8-Lead TSSOP RU-8 98
ADR292GRUZ-REEL7 4.096 0.15 25 8-Lead TSSOP RU-8 1,000
1 Z = RoHS Compliant Part.
ADR291/ADR292
Rev. F | Page 18 of 20
NOTES
ADR291/ADR292
Rev. F | Page 19 of 20
NOTES
ADR291/ADR292
Rev. F | Page 20 of 20
NOTES
©2007–2011 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D00163-0-5/11(F)
