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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 Hz-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 A/D and D/A Converter Reference Solar-Powered Applications Loop-Current-Powered Instruments
Low Noise Micropower 2.048 V, 2.5 V, and 4.096 V Precision Voltage References ADR290/ADR291/ADR292
PIN CONFIGURATIONS 8-Lead Narrow Body SO (SO Suffix)
NC 1 VIN 2 8 NC 7 NC TOP VIEW NC 3 (Not to Scale) 6 VOUT 5 NC
ADR29x
GND 4
NC = NO CONNECT
8-Lead TSSOP (RU Suffix)
NC 1 VIN 2 8 NC
7 NC TOP VIEW NC 3 (Not to Scale) 6 VOUT 5 NC
ADR29x
GND 4
NC = NO CONNECT
GENERAL DESCRIPTION
The ADR290, ADR291 and ADR292 are low noise, micropower precision voltage references that use an XFET(R) reference circuit. The new XFET architecture offers significant performance 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
current is only 12 A, making these devices ideal for batterypowered 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 -40C to +125C. Devices are available in the 8-lead SOIC and 8-lead TSSOP packages.
ADR29x Product
Part Number ADR290 ADR291 ADR292 ADR293
Output Voltage (V) 2.048 2.500 4.096 5.000
Initial Accuracy (%)
Temperature Coefficient (ppm/ C) Max
0.10, 0.15, 0.29 8, 15, 25 0.08, 0.12, 0.24 8, 15, 25 0.07, 0.10, 0.15 8, 15, 25 (See ADR293 Data Sheet)
XFET is a registered trademark of Analog Devices, Inc.
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. 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 (c) Analog Devices, Inc., 2001
ADR290/ADR291/ADR292
ADR290-SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Parameter E GRADE Output Voltage Initial Accuracy F GRADE Output Voltage Initial Accuracy G GRADE Output Voltage Initial Accuracy LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG-TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY
(VS = 2.7 V, TA = +25 C unless otherwise noted)
Conditions IOUT = 0 mA Min 2.046 -2 -0.10 2.045 -3 -0.15 2.042 -6 -0.29 Typ Max Unit V mV % V mV % V mV % ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz
Symbol VO VOERR
2.048 2.050 +2 +0.10 2.048 2.051 +3 +0.15 2.048 2.054 +6 +0.29 30 40 30 40 50 6 420 100 125 100 125
VO VOERR
IOUT = 0 mA
VO VOERR VO/VIN VO/ILOAD VO eN eN
IOUT = 0 mA
2.7 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA After 1000 hrs of Operation @ 125C 0.1 Hz to 10 Hz @ 1 kHz
ELECTRICAL SPECIFICATIONS (V = 2.7 V, T = -25 C T +85 C unless otherwise noted)
S
A
A
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade
Symbol TCVO
Conditions IOUT = 0 mA
Min
Typ 3 6 10 35 50 20 30
Max 8 15 25 125 150 125 150
Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA
VO/VIN VO/ILOAD
2.7 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA
ELECTRICAL SPECIFICATIONS (V = 2.7 V, T =
S
A
40 C TA +125 C unless otherwise noted)
Min Typ 3 5 10 40 70 20 30 8 12 50 Max 10 20 30 200 250 200 300 12 15 Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm REV. B
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS
Specifications subject to change without notice.
Symbol TCVO
Conditions IOUT = 0 mA
VO/VIN VO/ILOAD IS VO-HYS
2.7 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA TA = +25C -40C TA +125C SO-8, TSSOP-8 -2-
ADR291-SPECIFICATIONS
ELECTRICAL SPECIFICATIONS (V = 3.0 V, T = +25 C unless otherwise noted)
S
ADR290/ADR291/ADR292
A
Parameter E GRADE Output Voltage Initial Accuracy F GRADE Output Voltage Initial Accuracy G GRADE Output Voltage Initial Accuracy LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG-TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY
Symbol VO VOERR
Conditions IOUT = 0 mA
Min 2.498 -2 -0.08 2.497 -3 -0.12 2.494 -6 -0.24
Typ
Max
Unit V mV % V mV % V mV % ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz
2.500 2.502 +2 +0.08 2.500 2.503 +3 +0.12 2.500 2.506 +6 +0.24 30 40 30 40 50 8 480 100 125 100 125
VO VOERR
IOUT = 0 mA
VO VOERR VO/VIN VO/ILOAD VO eN eN
IOUT = 0 mA
3.0 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA After 1000 hrs of Operation @ 125C 0.1 Hz to 10 Hz @ 1 kHz
ELECTRICAL SPECIFICATIONS
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade
(VS = 3.0 V, TA = -25 C TA +85 C unless otherwise noted)
Conditions IOUT = 0 mA Min Typ 3 5 10 35 50 20 30 Max 8 15 25 125 150 125 150 Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA
Symbol TCVO
VO/VIN VO/ILOAD
3.0 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA
ELECTRICAL SPECIFICATIONS (V = 3.0 V, T = -40 C T +125 C unless otherwise noted)
S
A
A
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS
Specifications subject to change without notice.
Symbol TCVO
Conditions IOUT = 0 mA
Min
Typ 3 5 10 40 70 20 30 9 12 50
Max 10 20 30 200 250 200 300 12 15
Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm
VO/VIN VO/ILOAD IS VO-HYS
3.0 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA TA = +25C -40C TA +125C SO-8, TSSOP-8
REV. B
-3-
ADR290/ADR291/ADR292
ADR292-SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
Parameter E GRADE Output Voltage Initial Accuracy F GRADE Output Voltage Initial Accuracy G GRADE Output Voltage Initial Accuracy LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade LONG-TERM STABILITY NOISE VOLTAGE WIDEBAND NOISE DENSITY
(VS = 5 V, TA = +25 C unless otherwise noted)
Conditions IOUT = 0 mA Min 4.093 -3 -0.07 4.092 -4 -0.10 4.090 -6 -0.15 Typ Max Unit V mV % V mV % V mV % ppm/V ppm/V ppm/mA ppm/mA ppm V p-p nV/Hz
Symbol VO VOERR
4.096 4.099 +3 +0.07 4.096 4.1 +4 +0.10 4.096 4.102 +6 +0.15 30 40 30 40 50 12 640 100 125 100 125
VO VOERR
IOUT = 0 mA
VO VOERR VO/VIN VO/ILOAD VO eN eN
IOUT = 0 mA
4.5 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA After 1000 hrs of Operation @ 125C 0.1 Hz to 10 Hz @ 1 kHz
ELECTRICAL SPECIFICATIONS (V = 5 V, T = -25 C T +85 C unless otherwise noted)
S
A
A
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade
Symbol TCVO
Conditions IOUT = 0 mA
Min
Typ 3 5 10 35 50 20 30
Max 8 15 25 125 150 125 150
Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA
VO/VIN VO/ILOAD
4.5 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA
ELECTRICAL SPECIFICATIONS (V = 5 V, T = -40 C T +125 C unless otherwise noted)
S
A
A
Parameter TEMPERATURE COEFFICIENT "E" Grade "F" Grade "G" Grade LINE REGULATION "E/F" Grades "G" Grade LOAD REGULATION "E/F" Grades "G" Grade SUPPLY CURRENT THERMAL HYSTERESIS
Specifications subject to change without notice.
Symbol TCVO
Conditions IOUT = 0 mA
Min
Typ 3 5 10 40 70 20 30 10 12 50
Max 10 20 30 200 250 200 300 15 18
Unit ppm/C ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA A A ppm REV. B
VO/VIN VO/ILOAD IS VO-HYS
4.5 V to 15 V, IOUT = 0 mA
VS = 5.0 V, 0 mA to 5 mA TA = +25C -40C TA +125C SO-8, TSSOP-8 -4-
ADR290/ADR291/ADR292
ABSOLUTE MAXIMUM RATINGS
Package Type 8-Lead SOIC (SO) 8-Lead TSSOP (RU)
Supply Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V Output Short-Circuit Duration to GND . . . . . . . . . . Indefinite Storage Temperature Range SO, RU Package . . . . . . . . . . . . . . . . . . . 65C to 150C Operating Temperature Range ADR290/ADR291/ADR292 . . . . . . . . . . . 40C to 125C Junction Temperature Range SO, RU Package . . . . . . . . . . . . . . . . . . . 65C to 125C Lead Temperature (Soldering, 60 sec) . . . . . . . . . . . . . 300C
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.
JA*
JC
Unit C/W C/W
158 240
43 43
*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, permanent 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
Model ADR290 ER, ER-REEL7, ER-REEL FR, FR-REEL7, FR-REEL GR, GR-REEL7, GR-REEL GRU-REEL7, GRU-REEL ADR291 ER, ER-REEL7, ER-REEL FR, FR-REEL7, FR-REEL GR, GR-REEL7, GR-REEL GRU-REEL7, GRU-REEL ADR292 ER, ER-REEL7, ER-REEL FR, FR-REEL7, FR-REEL GR, GR-REEL7, GR-REEL GRU-REEL7, GRU-REEL
Output Voltage 2.048 2.048 2.048 2.048 2.50 2.50 2.50 2.50 4.096 4.096 4.096 4.096
Initial Accuracy (%) 0.10 0.15 0.29 0.29 0.08 0.12 0.24 0.24 0.07 0.10 0.15 0.15
Temperature Coefficient Max (ppm/ C) 8 15 25 25 8 15 25 25 8 15 25 25
Package Description SOIC SOIC SOIC TSSOP SOIC SOIC SOIC TSSOP SOIC SOIC SOIC TSSOP
Package Option SO-8 SO-8 SO-8 RU-8 SO-8 SO-8 SO-8 RU-8 SO-8 SO-8 SO-8 RU-8
Number of Parts per Package 98, 1000, 2500 98, 1000, 2500 98, 1000, 2500 1000, 2500 98, 1000, 2500 98, 1000, 2500 98, 1000, 2500 1000, 2500 98, 1000, 2500 98, 1000, 2500 98, 1000, 2500 1000, 2500
See ADR293 data sheet for ordering guide.
OTHER XFET PRODUCTS
Part Number ADR420 ADR421
Nominal Output Voltage (V) 2.048 2.50
Package Type 8-Lead_SOIC/SOIC 8-Lead_SOIC/SOIC
REV. B
-5-
ADR290/ADR291/ADR292
PARAMETER DEFINITION Line Regulation Thermal Hysteresis
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-pervolt, or microvolts-per-volt change in input voltage.
Load Regulation
Thermal hysteresis is defined as the change of output voltage after the device is cycled through temperature from +25C to -40C to +85C and back to +25C. This is a typical value from a sample of parts put through such a cycle.
VO - HYS = VO (25C ) - VO _ TC VO - HYS [ ppm] = VO (25C ) - VO _ TC x 106 VO (25C )
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-permillion-per-milliampere, or ohms of dc output resistance.
Long-Term Stability
Where VO (25C) = VO at 25C VO-TC = VO at 25C after temperature cycle at +25C to -40C to +85C and back to +25C
Typical shift of output voltage at 25C on a sample of parts subjected to high-temperature operating life test of 1000 hours at 125C.
VO = VO (t0 ) - VO (t1 ) V (t ) - VO (t1 ) VO [ ppm] = O 0 x 106 VO (t0 )
Where VO (t0 ) = VO at 25C at time 0 VO (t1 ) = VO at 25C 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 25C, expressed in ppm/C. The equation follows:
TCVO [ ppm / C ] =
Where VO (25C) = VO at 25C
VO (T2 ) - VO (T1 ) x 106 VO (25C ) x (T2 - T1 )
VO(T1 ) = VO at Temperature 1 VO(T2 ) = VO 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.)
-6-
REV. B
Typical Performance Characteristic-ADR290/ADR291/ADR292
2.054 VS = 5V 2.052 3 TYPICAL PARTS
12 14
A
OUTPUT VOLTAGE - V
10
TA = +125 C
2.050
QUIESCENT CURRENT -
8 6 4
TA = +25 C TA = -40 C
2.048
2.046
2.044
2 0
2.042 -50
-25
0
25
50
75
100
125
0
2
4
TEMPERATURE - C
6 8 10 INPUT VOLTAGE - V
12
14
16
TPC 1. ADR290 VOUT vs. Temperature
TPC 4. ADR290 Quiescent Current vs. Input Voltage
2.506 VS = 5V 2.504 3 TYPICAL PARTS
14 12
A
TA = +125 C 10
OUTPUT VOLTAGE - V
2.502
QUIESCENT CURRENT -
8 6 4
TA = +25 C TA = -40 C
2.500
2.498
2.496
2 0
2.494 -50
-25
0
25
50
75
100
125
0
2
4
TEMPERATURE - C
6 8 10 INPUT VOLTAGE - V
12
14
16
TPC 2. ADR291 VOUT vs. Temperature
TPC 5. ADR291 Quiescent Current vs. Input Voltage
4.102 VS = 5V 4.100 3 TYPICAL PARTS
16 14 12 10 8 6 4 2 0
OUTPUT VOLTAGE - V
4.098
QUIESCENT CURRENT -
A
TA = +125 C TA = +25 C TA = -40 C
4.096
4.094
4.092
4.090 -50
-25
0
25
50
75
100
125
0
2
4
TEMPERATURE - C
6 8 10 INPUT VOLTAGE - V
12
14
16
TPC 3. ADR292 VOUT vs. Temperature
TPC 6. ADR292 Quiescent Current vs. Input Voltage
REV. B
-7-
ADR290/ADR291/ADR292
14 VS = 5V
0.6 0.7
DIFFERENTIAL VOLTAGE - V
12
ADR292
ADR291
0.5 TA = +125 C 0.4 0.3 0.2
SUPPLY CURRENT -
A
TA = -40 C
10
8 ADR290
TA = +25 C
6
0.1
4 -50
-25
0
25
50
75
100
125
0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0
TEMPERATURE - C
TPC 7. ADR290/ADR291/ADR292 Supply Current vs. Temperature
TPC 10. ADR290 Minimum Input-Output Voltage Differential vs. Load Current
100 ADR290: VS = 2.7V TO 15V ADR291: VS = 3.0V TO 15V ADR292: VS = 4.5V TO 15V IOUT = 0mA
0.7 0.6
DIFFERENTIAL VOLTAGE - V
LINE REGULATION - ppm/V
80
TA = +125 C 0.5 TA = +25 C 0.4 0.3 TA = -40 C 0.2
60 ADR292
40
20 ADR290 ADR291 0 -50 -25 0 25 50 75 100 125
0.1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0
TEMPERATURE - C
TPC 8. ADR290/ADR291/ADR292 Line Regulation vs. Temperature
TPC 11. ADR291 Minimum Input-Output Voltage Differential vs. Load Current
100 ADR290: VS = 2.7V TO 7.0V ADR291: VS = 3.0V TO 7.0V ADR292: VS = 4.5V TO 9.0V IOUT = 0mA
0.7 0.6
DIFFERENTIAL VOLTAGE - V
LINE REGULATION - ppm/V
80
TA = +125 C 0.5 TA = +25 C 0.4 0.3 0.2
60 ADR291 40 ADR290
TA = -40 C
20
ADR292
0.1
0 -50
-25
0
25
50
75
100
125
0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 LOAD CURRENT - mA 4.0 4.5 5.0
TEMPERATURE - C
TPC 9. ADR290/ADR291/ADR292 Line Regulation vs. Temperature
TPC 12. ADR292 Minimum Input-Output Voltage Differential vs. Load Current
-8-
REV. B
ADR290/ADR291/ADR292
200 VS = 5V 500 250
LINE REGULATION - ppm/mA
VOUT FROM NOMINAL -
V
0
160
120 IOUT = 1mA
TA = +25 C
-250 TA = +125 C -500 TA = -40 C
80
40 IOUT = 5mA 0 -50
-750
-25
0
25
50
75
100
125
-1000 0.1
TEMPERATURE - C
1 SOURCING LOAD CURRENT - mA
10
TPC 13. ADR290 Line Regulation vs. Temperature
TPC 16. ADR290 VOUT from Nominal vs. Load Current
200 VS = 5V
0 -250
V
LOAD REGULATION - ppm/mA
160 IOUT = 1mA 120 IOUT = 5mA 80
TA = +25 C -500 -750 TA = -40 C -1000 -1250 -1500 -1750 TA = +125 C
40
0 -50
VOUT FROM NOMINAL -
-25
0
25
50
75
100
125
-2000 0.1
TEMPERATURE - C
1 SOURCING LOAD CURRENT - mA
10
TPC 14. ADR291 Load Regulation vs. Temperature
TPC 17. ADR291 VOUT from Nominal vs. Load Current
200 VS = 5V
0 -500
V
LOAD REGULATION - ppm/mA
160
-1000
VOUT FROM NOMINAL -
120 IOUT = 1mA IOUT = 5mA 80
-1500 -2000 -2500 -3000 -3500
TA = -40 C
TA = +25 C TA = +125 C
40
0 -50
-25
0
25
50
75
100
125
-4000 0.1
TEMPERATURE - C
1 SOURCING LOAD CURRENT - mA
10
TPC 15. ADR292 Load Regulation vs. Temperature
TPC 18. ADR292 VOUT from Nominal vs. Load Current
REV. B
-9-
ADR290/ADR291/ADR292
1000 900 ADR292 VIN = 15V TA = 25 C
50 VS = 5V IL = 0 mA 40
OUTPUT IMPEDANCE -
1000
VOLTAGE NOISE DENSITY - nV/ Hz
800 700 ADR291 600 500 400 300 200 100 0 10 100 FREQUENCY - Hz ADR290
30
20
10
0
0
10
100 FREQUENCY - Hz
1k
10k
TPC 19. Voltage Noise Density vs. Frequency
TPC 22. ADR290 Output Impedance vs. Frequency
120 VS = 5V 100
50 VS = 5V IL = 0 mA 40
OUTPUT IMPEDANCE -
RIPPLE REJECTION - dB
80
30
60
20
40
20
10
0 10
100 FREQUENCY - Hz
1000
0
0
10
100 FREQUENCY - Hz
1k
10k
TPC 20. ADR290/ADR291/ADR292 Ripple Rejection vs. Frequency
TPC 23. ADR291 Output Impedance vs. Frequency
50
1s
100 90
VS = 5V IL = 0 mA 40
OUTPUT IMPEDANCE -
30
2 V p-p
20
10 0%
10
0
0
10
100 FREQUENCY - Hz
1k
10k
TPC 21. ADR290 0.1 Hz to 10 Hz Noise
TPC 24. ADR292 Output Impedance vs. Frequency
-10-
REV. B
ADR290/ADR291/ADR292
IL = 5mA OFF
100 100 90
1ms
IL = 5mA
500 s
ON
90
10 0%
10 0%
1V
1V
TPC 25. ADR291 Load Transient
TPC 28. ADR291 Turn-On Time
IL = 5mA CL = 1nF
100
1ms
100 90
IL = 0mA
10ms
OFF ON
90
10 0%
10 0%
1V
1V
TPC 26. ADR291 Load Transient
TPC 29. ADR291 Turn-Off Time
18
IL = 5mA CL = 100nF
100
5ms
16 14 12
TEMPERATURE +25 C -40 C 85 C +25 C
OFF ON
90
FREQUENCY
10 0%
10 8 6 4
1V
2 0
TPC 27. ADR291 Load Transient
TPC 30. Typical Hysteresis for the ADR291 Product
REV. B
-11-
-200 -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140 160 180 200 MORE
VOUT DEVIATION - ppm
ADR290/ADR291/ADR292
THEORY OF OPERATION Device Power Dissipation Considerations
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 fieldeffect 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 coefficient 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 compensation 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 absolute temperature. The general equation is:
VOUT R1 + R2 + R3 = VP + I PTAT R3 R1
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 junction temperature that could result in premature device failure. The following formula should be used to calculate a device's maximum junction temperature or dissipation:
PD = TJ - T A JA
In this equation, TJ and TA are the junction and ambient temperatures, respectively, PD 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 VOUT pin to the GND pin. The circuit in Figure 2 illustrates the basic configuration for the ADR29x family of references. Note that the decoupling capacitors are not required for circuit stability.
NC 1 2 8 NC
ADR29x
7 NC 6 OUTPUT 0.1 F
(
)( )
+ 10 F
NC 3 0.1 F 4
5 NC
where VP is the difference in pinch-off voltage between the two FETs, and IPTAT is the positive temperature coefficient correction 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.
VIN I1 I1
NC = NO CONNECT
Figure 2. Basic Voltage Reference Configuration
Noise Performance
The noise generated by the ADR29x family of references is typically 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
* VP R1
VOUT IPTAT R2 R3 GND
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 for the active circuits to settle, and the time for the thermal gradients on the chip to stabilize. TPC 28 shows the turn-on settling time for the ADR291.
* EXTRA CHANNEL IMPLANT R1 + R2 + R3 VOUT = VP + IPTAT R1
R3
Figure 1. ADR290/ADR291/ADR292 Simplified Schematic
-12-
REV. B
ADR290/ADR291/ADR292
APPLICATIONS SECTION A Negative Precision Reference without Precision Resistors
VIN
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 currentswitching 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 (voltageswitching 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 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 VOUT 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.
VIN
ADR29x
VOUT R1 GND 1F ISY ADJUST P1 IOUT RL
RSET
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 configuration can operate on high supply voltages determined by the breakdown voltage of the N-channel JFET.
+VS E231 SILICONIX
VIN
ADR29X
GND
OP90
2N3904
2.10k
ADR29x
VOUT 1k 1F +5V GND 100 A1
-VS
Figure 5. High Voltage Floating Current Source
Kelvin Connections
100k
1F
-VREF
-5V A1 = 1/2 OP291, 1/2 OP295
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 precision 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 RSET, which sets the output current into the load. With this configuration, circuit precision is maintained for load currents in the range from the reference's supply current, typically 12 A to approximately 5 mA.
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 (VERROR = R IL ) 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
-13-
ADR290/ADR291/ADR292
VIN RLW VIN +VOUT SENSE RLW A1 VOUT 1F GND A1 = 1/2 OP295 100k
Voltage Regulator For Portable Equipment
ADR29x
+VOUT FORCE RL
Figure 6. Advantage of Kelvin Connection
Low Power, Low Voltage Reference For Data Converters
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 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
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 onchip 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 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 W), the entire circuit still consumes about 25 mW.
+5V ANALOG SUPPLY
0.1 F R3 510k
VIN
ADR29x
6V LEAD-ACID BATTERY + VOUT TEMP GND OP20 IRF9530
5V, 100mA R1 402k 1% R2 402k 1% C1 68 F TANT + + C2 1000 F ELECT
Figure 8. Voltage Regulator for Portable Equipment
0.1 F
10 F AVDD VIN VOUT DVDD VREF SLEEP MODE DRDY DATA READY READ (TRANSMIT) SERIAL CLOCK SERIAL CLOCK 0.1 F
0.1 F
ADR291
GND
AD7701
RANGES SELECT CALIBRATE ANALOG INPUT ANALOG GROUND 0.1 F AVSS -5V ANALOG SUPPLY BP/UP CAL
CS SCLK SDATA
CLKIN AIN AGND CLKOUT SC1 SC2 DGND 0.1 F DVSS
0.1 F
10 F
Figure 7. Low Power, Low Voltage Supply Reference for the AD7701
-14-
REV. B
ADR290/ADR291/ADR292
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Narrow Body SO (SO Suffix)
0.1968 (5.00) 0.1890 (4.80)
8 5 4
0.1574 (4.00) 0.1497 (3.80) PIN 1
1
0.2440 (6.20) 0.2284 (5.80)
0.0500 (1.27) BSC 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 0.0688 (1.75) 0.0532 (1.35) 0.0192 (0.49) 0.0138 (0.35) 8 0.0098 (0.25) 0 0.0075 (0.19)
0.0196 (0.50) 0.0099 (0.25)
45
0.0500 (1.27) 0.0160 (0.41)
8-Lead TSSOP (RU Suffix)
0.122 (3.10) 0.114 (2.90)
8
5
0.177 (4.50) 0.169 (4.30) 0.256 (6.50) 0.246 (6.25)
1 4
PIN 1 0.0256 (0.65) BSC 0.006 (0.15) 0.002 (0.05) SEATING PLANE 0.0118 (0.30) 0.0075 (0.19)
0.0433 (1.10) MAX 0.0079 (0.20) 0.0035 (0.090)
8 0
0.028 (0.70) 0.020 (0.50)
REV. B
-15-
PRINTED IN U.S.A.
C00163-0-3/01 (B)

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