Document Outline
- Specifications
- Pinout
- Package drawings
- Ordering Guide
- Features
- Applications
- Product Description
- Absolute Maximum Ratings
- Circuit Description
- OTHER XFET PRODUCTS
- PARAMETER DEFINITION
- APPLICATIONS SECTION
- Diagrams
- ADR290/ADR291/ADR292 Simplified Schematic
- Basic Voltage Reference Configuration
- Negative Precision Voltage Reference Uses No Precision Resistors
- A Precision Current Source
- High Voltage Floating Current Source
- Advantage of Kelvin Connection
- Low Power, Low Voltage Supply Reference for the AD7701
- Voltage Regulator for Portable Equipment
PIN CONFIGURATIONS
8-Lead Narrow Body SO (SO Suffix)
1
2
3
4
8
7
6
5
V
OUT
V
IN
GND
NC
NC
NC
NC
NC
ADR29x
TOP VIEW
(Not to Scale)
NC = NO CONNECT
8-Lead TSSOP (RU Suffix)
1
2
3
4
8
7
6
5
V
OUT
V
IN
GND
NC
NC
NC
NC
NC
ADR29x
TOP VIEW
(Not to Scale)
NC = NO CONNECT
REV. B
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
Low Noise Micropower
2.048 V, 2.5 V, and 4.096 V
Precision Voltage References
ADR290/ADR291/ADR292
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 2001
FEATURES
Supply Range
2.35 V to 15 V, ADR290
2.8 V to 15 V, ADR291
4.4 V to 15 V, ADR292
Supply Current 12 A Max
Low-Noise 6 V, 8 V, 12 V p-p (0.1 Hz10 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
A/D and D/A Converter Reference
Solar-Powered Applications
Loop-Current-Powered Instruments
GENERAL DESCRIPTION
The ADR290, ADR291 and ADR292 are low noise, micro-
power precision voltage references that use an XFET
reference
circuit. The new XFET
architecture offers significant perfor-
mance improvements over traditional bandgap and Buried
Zener-based references. Improvements include: one quarter the
voltage noise output of bandgap references operating at the
same current, very low and ultralinear temperature drift, low
thermal hysteresis and excellent long-term stability.
The ADR29x family are series voltage references providing stable
and accurate output voltages from supplies as low as 2.35 V for the
ADR290. Output voltage options are 2.048 V, 2.5 V, and 4.096 V
for the ADR290, ADR291, and ADR292 respectively. Quiescent
XFET is a registered trademark of Analog Devices, Inc.
current is only 12
A, 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
max for the ADR290 and ADR291, and
3 mV, 4 mV and
6 mV max for the ADR292. Temperature coefficients for the
three grades are 8 ppm/
C, 15 ppm/C, and 25 ppm/C max,
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 ADR290, 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 and 8-lead
TSSOP packages.
ADR29x Product
Output Voltage
Initial Accuracy
Temperature Coefficient
Part Number
(V)
(%)
(ppm/ C) Max
ADR290
2.048
0.10, 0.15, 0.29
8, 15, 25
ADR291
2.500
0.08, 0.12, 0.24
8, 15, 25
ADR292
4.096
0.07, 0.10, 0.15
8, 15, 25
ADR293
5.000
(See ADR293 Data Sheet)
REV. B
ADR290/ADR291/ADR292
2
ADR290SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
E GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.046
2.048 2.050
V
Initial Accuracy
V
OERR
2
+2
mV
0.10
+0.10
%
F GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.045
2.048 2.051
V
Initial Accuracy
V
OERR
3
+3
mV
0.15
+0.15
%
G GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.042
2.048 2.054
V
Initial Accuracy
V
OERR
6
+6
mV
0.29
+0.29
%
LINE REGULATION
"E/F" Grades
V
O
/
V
IN
2.7 V to 15 V, I
OUT
= 0 mA
30
100
ppm/V
"G" Grade
40
125
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
30
100
ppm/mA
"G" Grade
40
125
ppm/mA
LONG-TERM STABILITY
V
O
After 1000 hrs of Operation @ 125
C
50
ppm
NOISE VOLTAGE
e
N
0.1 Hz to 10 Hz
6
V p-p
WIDEBAND NOISE DENSITY
e
N
@ 1 kHz
420
nV/
Hz
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
I
OUT
= 0 mA
3
8
ppm/
C
"F" Grade
6
15
ppm/
C
"G" Grade
10
25
ppm/
C
LINE REGULATION
"E/F" Grades
V
O
/
V
IN
2.7 V to 15 V, I
OUT
= 0 mA
35
125
ppm/V
"G" Grade
50
150
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
125
ppm/mA
"G" Grade
30
150
ppm/mA
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
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
V
O
/
V
IN
2.7 V to 15 V, I
OUT
= 0 mA
40
200
ppm/V
"G" Grade
70
250
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
200
ppm/mA
"G" Grade
30
300
ppm/mA
SUPPLY CURRENT
I
S
T
A
= +25
C
8
12
A
40
C T
A
+125C
12
15
A
THERMAL HYSTERESIS
V
OHYS
SO-8, TSSOP-8
50
ppm
Specifications subject to change without notice.
(V
S
= 2.7 V, T
A
= +25 C unless otherwise noted)
(V
S
= 2.7 V, T
A
= 40 C
T
A
+125 C unless otherwise noted)
(V
S
= 2.7 V, T
A
= 25 C
T
A
+85 C unless otherwise noted)
ADR291SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
E GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.498
2.500 2.502
V
Initial Accuracy
V
OERR
2
+2
mV
0.08
+0.08
%
F GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.497
2.500 2.503
V
Initial Accuracy
V
OERR
3
+3
mV
0.12
+0.12
%
G GRADE
Output Voltage
V
O
I
OUT
= 0 mA
2.494
2.500 2.506
V
Initial Accuracy
V
OERR
6
+6
mV
0.24
+0.24
%
LINE REGULATION
"E/F" Grades
V
O
/
V
IN
3.0 V to 15 V, I
OUT
= 0 mA
30
100
ppm/V
"G" Grade
40
125
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
30
100
ppm/mA
"G" Grade
40
125
ppm/mA
LONG-TERM STABILITY
V
O
After 1000 hrs of Operation @ 125
C
50
ppm
NOISE VOLTAGE
e
N
0.1 Hz to 10 Hz
8
V p-p
WIDEBAND NOISE DENSITY
e
N
@ 1 kHz
480
nV/
Hz
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
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
V
O
/
V
IN
3.0 V to 15 V, I
OUT
= 0 mA
35
125
ppm/V
"G" Grade
50
150
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
125
ppm/mA
"G" Grade
30
150
ppm/mA
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
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
V
O
/
V
IN
3.0 V to 15 V, I
OUT
= 0 mA
40
200
ppm/V
"G" Grade
70
250
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
200
ppm/mA
"G" Grade
30
300
ppm/mA
SUPPLY CURRENT
I
S
T
A
= +25
C
9
12
A
40
C T
A
+125C
12
15
A
THERMAL HYSTERESIS
V
OHYS
SO-8, TSSOP-8
50
ppm
Specifications subject to change without notice.
ADR290/ADR291/ADR292
REV. B
3
(V
S
= 3.0 V, T
A
= +25 C unless otherwise noted)
(V
S
= 3.0 V, T
A
= 40 C
T
A
+125 C unless otherwise noted)
(V
S
= 3.0 V, T
A
= 25 C
T
A
+85 C unless otherwise noted)
REV. B
ADR290/ADR291/ADR292
4
ADR292SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
E GRADE
Output Voltage
V
O
I
OUT
= 0 mA
4.093
4.096 4.099
V
Initial Accuracy
V
OERR
3
+3
mV
0.07
+0.07
%
F GRADE
Output Voltage
V
O
I
OUT
= 0 mA
4.092
4.096 4.1
V
Initial Accuracy
V
OERR
4
+4
mV
0.10
+0.10
%
G GRADE
Output Voltage
V
O
I
OUT
= 0 mA
4.090
4.096 4.102
V
Initial Accuracy
V
OERR
6
+6
mV
0.15
+0.15
%
LINE REGULATION
"E/F" Grades
V
O
/
V
IN
4.5 V to 15 V, I
OUT
= 0 mA
30
100
ppm/V
"G" Grade
40
125
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
30
100
ppm/mA
"G" Grade
40
125
ppm/mA
LONG-TERM STABILITY
V
O
After 1000 hrs of Operation @ 125
C
50
ppm
NOISE VOLTAGE
e
N
0.1 Hz to 10 Hz
12
V p-p
WIDEBAND NOISE DENSITY
e
N
@ 1 kHz
640
nV/
Hz
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
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
V
O
/
V
IN
4.5 V to 15 V, I
OUT
= 0 mA
35
125
ppm/V
"G" Grade
50
150
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
125
ppm/mA
"G" Grade
30
150
ppm/mA
ELECTRICAL SPECIFICATIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TEMPERATURE COEFFICIENT
"E" Grade
TCV
O
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
V
O
/
V
IN
4.5 V to 15 V, I
OUT
= 0 mA
40
200
ppm/V
"G" Grade
70
250
ppm/V
LOAD REGULATION
"E/F" Grades
V
O
/
I
LOAD
V
S
= 5.0 V, 0 mA to 5 mA
20
200
ppm/mA
"G" Grade
30
300
ppm/mA
SUPPLY CURRENT
I
S
T
A
= +25
C
10
15
A
40
C T
A
+125C
12
18
A
THERMAL HYSTERESIS
V
OHYS
SO-8, TSSOP-8
50
ppm
Specifications subject to change without notice.
(V
S
= 5 V, T
A
= +25 C unless otherwise noted)
(V
S
= 5 V, T
A
= 40 C
T
A
+125 C unless otherwise noted)
(V
S
= 5 V, T
A
= 25 C
T
A
+85 C unless otherwise noted)
ADR290/ADR291/ADR292
REV. B
5
ABSOLUTE MAXIMUM RATINGS
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
Output Short-Circuit Duration to GND . . . . . . . . . . Indefinite
Storage Temperature Range
SO, RU Package . . . . . . . . . . . . . . . . . . .
65
C to 150C
Operating Temperature Range
ADR290/ADR291/ADR292 . . . . . . . . . . .
40
C to 125C
Junction Temperature Range
SO, RU Package . . . . . . . . . . . . . . . . . . .
65
C to 125C
Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . . 300
C
NOTES
1. Stresses above those listed under Absolute Maximum Ratings may
cause permanent damage to the device. This is a stress rating only; functional
operation at or above this specification is not implied. Exposure to the
above maximum rating conditions for extended periods may affect device
reliability.
2. Remove power before inserting or removing units from their sockets.
Package Type
JA
*
JC
Unit
8-Lead SOIC (SO)
158
43
C/W
8-Lead TSSOP (RU)
240
43
C/W
*
JA
is specified for worst-case conditions, i.e.,
JA
is specified for device in socket
testing. In practice,
JA
is specified for a device soldered in the circuit board.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADR290/ADR291/ADR292 features proprietary ESD protection circuitry, perma-
nent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore,
proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
ORDERING GUIDE
Temperature
Number of
Output
Initial
Coefficient
Package
Package
Parts per
Model
Voltage
Accuracy (%)
Max (ppm/ C)
Description
Option
Package
ADR290
ER, ER-REEL7, ER-REEL
2.048
0.10
8
SOIC
SO-8
98, 1000, 2500
FR, FR-REEL7, FR-REEL
2.048
0.15
15
SOIC
SO-8
98, 1000, 2500
GR, GR-REEL7, GR-REEL
2.048
0.29
25
SOIC
SO-8
98, 1000, 2500
GRU-REEL7, GRU-REEL
2.048
0.29
25
TSSOP
RU-8
1000, 2500
ADR291
ER, ER-REEL7, ER-REEL
2.50
0.08
8
SOIC
SO-8
98, 1000, 2500
FR, FR-REEL7, FR-REEL
2.50
0.12
15
SOIC
SO-8
98, 1000, 2500
GR, GR-REEL7, GR-REEL
2.50
0.24
25
SOIC
SO-8
98, 1000, 2500
GRU-REEL7, GRU-REEL
2.50
0.24
25
TSSOP
RU-8
1000, 2500
ADR292
ER, ER-REEL7, ER-REEL
4.096
0.07
8
SOIC
SO-8
98, 1000, 2500
FR, FR-REEL7, FR-REEL
4.096
0.10
15
SOIC
SO-8
98, 1000, 2500
GR, GR-REEL7, GR-REEL
4.096
0.15
25
SOIC
SO-8
98, 1000, 2500
GRU-REEL7, GRU-REEL
4.096
0.15
25
TSSOP
RU-8
1000, 2500
See ADR293 data sheet for ordering guide.
OTHER XFET PRODUCTS
Part
Nominal Output
Package
Number
Voltage (V)
Type
ADR420
2.048
8-Lead_
SOIC/SOIC
ADR421
2.50
8-Lead_
SOIC/SOIC
REV. B
ADR290/ADR291/ADR292
6
PARAMETER DEFINITION
Line Regulation
The change in output voltage due to a specified change in input
voltage. It includes the effects of self-heating. Line regulation is
expressed in either percent-per-volt, parts-per-million-per-
volt, or microvolts-per-volt change in input voltage.
Load Regulation
The change in output voltage due to a specified change in load
current. It includes the effects of self-heating. Load regulation
is expressed in either microvolts-per-milliampere, parts-per-
million-per-milliampere, or ohms of dc output resistance.
Long-Term Stability
Typical shift of output voltage at 25
C on a sample of parts
subjected to high-temperature operating life test of 1000
hours at 125
C.
V
V
t
V
t
V
ppm
V
t
V
t
V
t
O
O
O
O
O
O
=
( )
( )
=
( )
( )
( )
0
O
1
0
1
0
[
]
10
6
Where
V
O
(t
0
) = V
O
at 25
C at time 0
V
O
(t
1
) = V
O
at 25
C after 1000 hours operation at 125C
Temperature Coefficient
The change of output voltage over the operating temperature
change and normalized by the output voltage at 25
C, expressed
in ppm/
C. The equation follows:
TCV
ppm C
V T
V T
V
C
T
T
O
O
O
O
[
/
]
(
)
( )
(
) (
)
=
2
1
2
1
6
25
10
Where
V
O
(25
C) = V
O
at 25
C
V
O
(T
1
) = V
O
at Temperature 1
V
O
(T
2
) = V
O
at Temperature 2
NC = No Connect
(There are in fact internal connections at NC pins which are
reserved for manufacturing purposes. Users should not connect
anything at NC pins.)
Thermal Hysteresis
Thermal hysteresis is defined as the change of output voltage af-
ter the device is cycled through temperature from +25
C to
40
C to +85C and back to +25C. This is a typical value from
a sample of parts put through such a cycle.
V
V
C
V
V
ppm
V
C
V
V
C
O HYS
O
O TC
O HYS
O
O TC
O
_
_
(
)
[
]
(
)
(
)
=
=
25
25
25
10
6
Where
V
O
(25
C) = V
O
at 25
C
V
OTC
= V
O
at 25
C after temperature cycle at +25C to
40
C to +85C and back to +25C
TEMPERATURE C
2.054
2.042
50
125
25
OUTPUT VOLTAGE V
0
25
50
75
100
2.052
2.050
2.048
2.046
2.044
V
S
= 5V
3 TYPICAL PARTS
TPC 1. ADR290 V
OUT
vs. Temperature
TEMPERATURE C
2.506
2.494
50
125
25
OUTPUT VOLTAGE
V
0
25
50
75
100
2.504
2.502
2.500
2.498
2.496
V
S
= 5V
3 TYPICAL PARTS
TPC 2. ADR291 V
OUT
vs. Temperature
TEMPERATURE C
4.102
4.090
50
125
25
OUTPUT VOLTAGE
V
0
25
50
75
100
4.100
4.098
4.096
4.094
4.092
V
S
= 5V
3 TYPICAL PARTS
TPC 3. ADR292 V
OUT
vs. Temperature
INPUT VOLTAGE V
14
0
0
16
2
QUIESCENT CURRENT
A
4
6
8
10
12
14
12
8
6
4
2
10
T
A
= +125 C
T
A
= +25 C
T
A
= 40 C
TPC 4. ADR290 Quiescent Current vs. Input Voltage
INPUT VOLTAGE V
14
0
0
16
2
QUIESCENT CURRENT
A
4
6
8
10
12
14
12
8
6
4
2
10
T
A
= +125 C
T
A
= +25 C
T
A
= 40 C
TPC 5. ADR291 Quiescent Current vs. Input Voltage
INPUT VOLTAGE V
16
0
0
16
2
QUIESCENT CURRENT
A
4
6
8
10
12
14
12
8
6
4
2
10
T
A
= +125 C
T
A
= +25 C
T
A
= 40 C
14
TPC 6. ADR292 Quiescent Current vs. Input Voltage
Typical Performance CharacteristicADR290/ADR291/ADR292
REV. B
7
REV. B
ADR290/ADR291/ADR292
8
TEMPERATURE C
14
12
4
50
125
25
SUPPLY CURRENT
A
0
25
50
75
100
10
8
6
V
S
= 5V
ADR290
ADR291
ADR292
TPC 7. ADR290/ADR291/ADR292 Supply Current vs.
Temperature
TEMPERATURE C
100
80
0
50
125
25
LINE REGULATION
ppm/V
0
25
50
75
100
60
40
20
ADR290: V
S
= 2.7V TO 15V
ADR291: V
S
= 3.0V TO 15V
ADR292: V
S
= 4.5V TO 15V
ADR290
ADR292
ADR291
I
OUT
= 0mA
TPC 8. ADR290/ADR291/ADR292 Line Regulation vs.
Temperature
TEMPERATURE C
100
80
0
50
125
25
LINE REGULATION
ppm/V
0
25
50
75
100
60
40
20
ADR290: V
S
= 2.7V TO 7.0V
ADR291: V
S
= 3.0V TO 7.0V
ADR292: V
S
= 4.5V TO 9.0V
ADR292
ADR290
I
OUT
= 0mA
ADR291
TPC 9. ADR290/ADR291/ADR292 Line Regulation vs.
Temperature
LOAD CURRENT mA
0.7
0
0
5.0
0.5
DIFFERENTIAL VOLTAGE
V
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
T
A
= +25 C
T
A
= 40 C
T
A
= +125 C
TPC 10. ADR290 Minimum Input-Output Voltage
Differential vs. Load Current
LOAD CURRENT mA
DIFFERENTIAL VOLTAGE
V
0.7
0
0
5.0
0.5
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
T
A
= +25 C
T
A
= 40 C
T
A
= +125 C
TPC 11. ADR291 Minimum Input-Output Voltage
Differential vs. Load Current
LOAD CURRENT mA
0.7
0
0
5.0
0.5
DIFFERENTIAL VOLTAGE
V
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
T
A
= +25 C
T
A
= 40 C
T
A
= +125 C
TPC 12. ADR292 Minimum Input-Output Voltage
Differential vs. Load Current
ADR290/ADR291/ADR292
REV. B
9
TEMPERATURE C
200
160
0
50
125
25
LINE REGULATION
ppm/mA
0
25
50
75
100
120
80
40
I
OUT
= 1mA
I
OUT
= 5mA
V
S
= 5V
TPC 13. ADR290 Line Regulation vs. Temperature
TEMPERATURE C
200
160
0
50
125
25
LOAD REGULATION
ppm/mA
0
25
50
75
100
120
80
40
V
S
= 5V
I
OUT
= 1mA
I
OUT
= 5mA
TPC 14. ADR291 Load Regulation vs. Temperature
TEMPERATURE C
200
160
0
50
125
25
LOAD REGULATION
ppm/mA
0
25
50
75
100
120
80
40
V
S
= 5V
I
OUT
= 1mA
I
OUT
= 5mA
TPC 15. ADR292 Load Regulation vs. Temperature
SOURCING LOAD CURRENT mA
500
250
1000
0.1
10
1
V
OUT
FROM NOMINAL
V
750
500
0
250
T
A
= +25 C
T
A
= +125 C
T
A
= 40 C
TPC 16. ADR290
V
OUT
from Nominal vs. Load Current
SOURCING LOAD CURRENT mA
0
1250
2000
0.1
10
1
V
OUT
FROM NOMINAL
V
1750
1500
500
250
T
A
= +25 C
T
A
= +125 C
T
A
= 40 C
1000
750
TPC 17. ADR291
V
OUT
from Nominal vs. Load Current
SOURCING LOAD CURRENT mA
0
2500
4000
0.1
10
1
V
OUT
FROM NOMINAL
V
3500
3000
1000
500
T
A
= +25 C
T
A
= +125 C
T
A
= 40 C
2000
1500
TPC 18. ADR292
V
OUT
from Nominal vs. Load Current
REV. B
ADR290/ADR291/ADR292
10
FREQUENCY Hz
1000
500
0
10
1000
100
VOLTAGE NOISE DENSITY
nV/
Hz
100
200
800
900
300
400
600
700
ADR290
ADR292
V
IN
= 15V
T
A
= 25 C
ADR291
TPC 19. Voltage Noise Density vs. Frequency
FREQUENCY Hz
120
60
0
10
1000
100
RIPPLE REJECTION
dB
20
100
80
V
S
= 5V
40
TPC 20. ADR290/ADR291/ADR292 Ripple Rejection vs.
Frequency
10
0%
100
90
1s
2 V p-p
TPC 21. ADR290 0.1 Hz to 10 Hz Noise
FREQUENCY Hz
50
40
0
0
10k
10
OUTPUT IMPEDANCE
100
1k
30
20
10
V
S
= 5V
I
L
= 0 mA
TPC 22. ADR290 Output Impedance vs. Frequency
FREQUENCY Hz
50
40
0
0
10k
10
OUTPUT IMPEDANCE
100
1k
30
20
10
V
S
= 5V
I
L
= 0 mA
TPC 23. ADR291 Output Impedance vs. Frequency
FREQUENCY Hz
50
40
0
0
10k
10
OUTPUT IMPEDANCE
100
1k
30
20
10
V
S
= 5V
I
L
= 0 mA
TPC 24. ADR292 Output Impedance vs. Frequency
ADR290/ADR291/ADR292
REV. B
11
10
0%
100
90
1ms
I
L
= 5mA
1V
OFF
ON
TPC 25. ADR291 Load Transient
10
0%
100
90
1ms
I
L
= 5mA
C
L
= 1nF
1V
OFF
ON
TPC 26. ADR291 Load Transient
10
0%
100
90
5ms
I
L
= 5mA
C
L
= 100nF
1V
OFF
ON
TPC 27. ADR291 Load Transient
10
0%
100
90
500 s
I
L
= 5mA
1V
TPC 28. ADR291 Turn-On Time
10
0%
100
90
10ms
I
L
= 0mA
1V
TPC 29. ADR291 Turn-Off Time
V
OUT
DEVIATION ppm
200
0
FREQ
UENCY
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
TPC 30. Typical Hysteresis for the ADR291 Product
REV. B
ADR290/ADR291/ADR292
12
Device Power Dissipation Considerations
The ADR29x 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 output voltage
option). 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 junc-
tion temperature that could result in premature device failure.
The following formula should be used to calculate a device's maxi-
mum junction temperature or dissipation:
P
T
T
D
A
A
=
J
J
In this equation, T
J
and T
A
are the junction and ambient tem-
peratures, respectively, P
D
is the device power dissipation, and
JA
is the device package thermal resistance.
Basic Voltage Reference Connections
References, in general, require a bypass capacitor connected
from the V
OUT
pin to the GND pin. The circuit in Figure 2
illustrates the basic configuration for the ADR29x family of ref-
erences. Note that the decoupling capacitors are not required for
circuit stability.
ADR29x
1
2
3
4
8
7
6
5
NC
NC
NC
NC
OUTPUT
NC
0.1 F
0.1 F
10 F
+
NC = NO CONNECT
Figure 2. Basic Voltage Reference Configuration
Noise Performance
The noise generated by the ADR29x family of references is typi-
cally less than 12
V p-p over the 0.1 Hz to 10 Hz band. TPC
21 shows the 0.1 Hz to 10 Hz noise of the ADR290 which is only
6
V p-p. The noise measurement is made with a bandpass 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 nor-
mally associated with this are the time for the active circuits to
settle, and the time for the thermal gradients on the chip to sta-
bilize. TPC 28 shows the turn-on settling time for the ADR291.
THEORY OF OPERATION
The ADR29x series of references uses a new 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-
effect transistors, one of which has 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 bandgap references. The big advantage
over a bandgap reference is that the intrinsic temperature coeffi-
cient is some thirty times lower (therefore less correction is
needed) and this results in much lower noise since most of the
noise of a bandgap reference comes from the temperature com-
pensation circuitry.
The simplified schematic below shows the basic topology of the
ADR29x series. The temperature correction term is provided by
a current source with value designed to be proportional to abso-
lute temperature. The general equation is:
V
V
R
R
R
R
I
R
OUT
P
PTAT
=
+
+
+
( )( )
1
2
3
1
3
where
V
P
is the difference in pinch-off voltage between the two
FETs, and I
PTAT
is the positive temperature coefficient correc-
tion current. The various versions of the ADR29x family are
created by on-chip adjustment of R1 and R3 to achieve 2.048 V,
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 drop-out voltage.
V
OUT
V
IN
I
PTAT
GND
R1
R2
R3
I
1
I
1
*
*
EXTRA
CHANNEL
IMPLANT
V
OUT
=
R1
+
R2
+
R3
R1
V
P
+ I
PTAT
R3
V
P
Figure 1. ADR290/ADR291/ADR292 Simplified Schematic
ADR290/ADR291/ADR292
REV. B
13
APPLICATIONS SECTION
A 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 required 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. Using a current-
switching DAC directly requires the need for 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 volt-
age reference through the use of an operational amplifier and a
pair of matched resistors in an inverting configuration. The dis-
advantage 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 3 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. The integrator, to maintain circuit
equilibrium adjusts its output to establish the proper relationship
between the reference's V
OUT
and GND. Thus, any negative
output voltage desired can be chosen by simply substituting for
the appropriate reference IC. One caveat with this approach
should be mentioned: although rail-to-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.
A1
100
+5V
5V
1k
1 F
100k
V
OUT
GND
V
IN
ADR29x
V
REF
A1 = 1/2 OP291,
1/2 OP295
1 F
Figure 3. A Negative Precision Voltage Reference Uses No
Precision Resistors
A Precision Current Source
Many times in low power applications, the need arises for a pre-
cision current source that can operate on low supply voltages.
As shown in Figure 4, any one of the devices in the ADR29x
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
SET,
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
A to approximately 5 mA.
1 F
V
OUT
GND
V
IN
ADR29x
I
OUT
R
L
I
SY
ADJUST
R1
P1
R
SET
Figure 4. A Precision Current Source
High Voltage Floating Current Source
The circuit of Figure 5 can be used to generate a floating
current source with minimal self heating. This particular con-
figuration can operate on high supply voltages determined by
the breakdown voltage of the N-channel JFET.
+V
S
OP90
ADR29
X
V
IN
GND
E231
SILICONIX
2N3904
2.10k
V
S
Figure 5. High Voltage Floating Current Source
Kelvin Connections
In many portable instrumentation applications, where PC board
cost and area go hand-in-hand, circuit interconnects are very often
of dimensionally minimum width. These narrow lines can cause
large voltage drops if the voltage reference is required to provide
load currents to various functions. In fact, a circuit's interconnects
can exhibit a typical line resistance of 0.45 m
/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
ERROR
= R I
L
) at
the load. However, the Kelvin connection of Figure 6, overcomes
the problem by including the wiring resistance within the forcing
loop of the op amp. Since the op amp senses the load voltage, op
amp loop control forces the output to compensate for the wiring
error and to produce the correct voltage at the load.
REV. B
ADR290/ADR291/ADR292
14
A1
1 F
100k
V
OUT
GND
V
IN
ADR29x
+V
OUT
SENSE
A1 = 1/2 OP295
V
IN
R
LW
R
L
R
LW
+V
OUT
FORCE
Figure 6. Advantage of Kelvin Connection
Low Power, Low Voltage Reference For Data Converters
The ADR29x family has a number of features that makes it
ideally suited for use with A/D and D/A converters. The low
supply voltage required makes it possible to use the ADR290
and ADR291 with today's converters that run on 3 V supplies
without having to add a higher supply voltage for the reference.
The low quiescent current (12
A max) and low noise, tight
temperature coefficient, combined with the high accuracy of
the ADR29x makes it ideal for low power applications such
as hand-held, battery operated equipment.
One such ADC for which the ADR291 is well suited is the
AD7701. Figure 7 shows the ADR291 used as the reference for
this converter. The AD7701 is a 16-bit A/D converter 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 (sigma-delta) ADC, calibration microcontroller with
on-chip static RAM, a clock oscillator and a serial communica-
tions 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
W), 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
0.1 F
DATA
READY
READ
(TRANSMIT)
SERIAL
CLOCK
SERIAL
CLOCK
0.1 F
10 F
0.1 F
5V
ANALOG
SUPPLY
ANALOG
GROUND
ANALOG
INPUT
CALIBRATE
RANGES
SELECT
0.1 F
ADR291
0.1 F
GND
V
IN
V
OUT
+5V
ANALOG
SUPPLY
10 F
0.1 F
AD7701
Figure 7. Low Power, Low Voltage Supply Reference for
the AD7701
Voltage Regulator For Portable Equipment
The ADR29x family of references is ideal for providing a stable,
low cost and low power reference voltage in portable equipment
power supplies. Figure 8 shows how the ADR290/ADR291/
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 out-
put 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.
ADR29x
V
OUT
GND
V
IN
0.1 F
LEAD-ACID
BATTERY
+
6V
CHARGER
INPUT
R1
402k
1%
R2
402k
1%
+ C2
1000 F
ELECT
C1
68 F
TANT
+
5V, 100mA
IRF9530
R3
510k
OP20
TEMP
Figure 8. Voltage Regulator for Portable Equipment
ADR290/ADR291/ADR292
REV. B
15
8-Lead Narrow Body SO (SO Suffix)
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
0
0.0196 (0.50)
0.0099 (0.25)
45
8
5
4
1
0.1968 (5.00)
0.1890 (4.80)
0.2440 (6.20)
0.2284 (5.80)
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.0500 (1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
SEATING
PLANE
0.0098 (0.25)
0.0040 (0.10)
0.0192 (0.49)
0.0138 (0.35)
8-Lead TSSOP (RU Suffix)
8
5
4
1
0.256 (6.50)
0.246 (6.25)
0.177 (4.50)
0.169 (4.30)
PIN 1
0.0256 (0.65)
BSC
0.122 (3.10)
0.114 (2.90)
SEATING
PLANE
0.006 (0.15)
0.002 (0.05)
0.0118 (0.30)
0.0075 (0.19)
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
0.028 (0.70)
0.020 (0.50)
8
0
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
C0016303/01 (B)
PRINTED IN U.S.A.
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