Precision Low Power 2.048 V
SOT-23 Voltage Reference
ADR370
FEATURES
APPLICATIONS
PIN CONFIGURATION
VIN 1
ADR370
VOUT
3
GND
03432-001
Initial accuracy: ±4 mV maximum
Initial accuracy error: ±0.2%
Low TCVO
±50 ppm/°C maximum from −40°C to +125°C
30 ppm/°C maximum from +25°C to +70°C
Load regulation: 400 μV/mA, 100 ppm/mA
Line regulation: 25 μV/V, 20 ppm/V
Wide operating range: VIN = 2.3 V to 15 V
Low power: 72 μA maximum
High output sink/source current: ±5 mA minimum
Wide temperature range: −40°C to +125°C
Tiny 3-lead SOT-23 package with standard pin configuration
2
Figure 1. 3-Lead SOT-23
Table 1. ADR370 Products
Products
ADR370BRT-REEL7
ADR370ART-REEL7
Output
Voltage (V)
2.048
2.048
Initial
Accuracy ±
(mV) (%)
4
0.2
10
0.5
Temperature
Coefficient
(ppm/°C)
50
100
Battery-powered instrumentation
Portable medical instruments
Data acquisition systems
Industrial process control systems
Automotive
GENERAL DESCRIPTION
The ADR3701 is a low cost, 3-terminal (series) band gap voltage
reference featuring high accuracy, high stability, and low power
consumption packaged in a tiny 3-lead SOT-23 package. Precise
matching and thermal tracking of on-chip components, as well
as patented temperature drift curvature correction design
techniques, have been employed to ensure that the ADR370
provides an accurate 2.048 V output.
1
This micropowered, low dropout voltage device sources or sinks
up to 5 mA of load current while providing a stable 2.048 V
output. The compact footprint, high accuracy, and operating
range of 2.3 V to 15 V make the ADR370 ideal for use in 3 V
and 5 V systems where there can be wide variations in supply
voltage and a need to minimize power dissipation.
The ADR370 is offered in A and B grades; all devices are
specified over the extended industrial range of −40°C to +125°C.
Protected by U.S. Patent No. 5,969,657; other patents pending.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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 ©2003–2007 Analog Devices, Inc. All rights reserved.
ADR370
TABLE OF CONTENTS
Features .............................................................................................. 1
Theory of Operation .........................................................................8
Applications ....................................................................................... 1
Applying the ADR370...................................................................8
Pin Configuration ............................................................................. 1
Applications Information .................................................................9
General Description ......................................................................... 1
Low Cost Negative Reference ......................................................9
Revision History ............................................................................... 2
Precision Negative Reference .......................................................9
Specifications..................................................................................... 3
Low Cost Current Source .............................................................9
Electrical Characteristics ............................................................. 3
Precision Current Source with Adjustable Output ...................9
Absolute Maximum Ratings............................................................ 4
12-Bit Precision Programmable Current Source ................... 10
Thermal Resistance ...................................................................... 4
Precision Boosted Output Regulator ....................................... 10
ESD Caution .................................................................................. 4
Outline Dimensions ....................................................................... 11
Typical Performance Characteristics ............................................. 5
Ordering Guide .......................................................................... 11
Terminology ...................................................................................... 7
REVISION HISTORY
12/07—Rev. B to Rev. C
Changes to Line Regulation Specification..................................... 3
9/07—Rev. A to Rev. B
Updated Format .................................................................. Universal
Changes to Table 2 ............................................................................ 3
Changes to Ordering Guide .......................................................... 11
Updated Outline Dimensions ....................................................... 11
7/03—Rev. 0 to Rev. A
Changes to Features.......................................................................... 1
Changes to Table I ............................................................................ 1
Changes to Electrical Characteristics ............................................ 2
Changes to Absolute Maximum Ratings ....................................... 3
Changes to Ordering Guide ............................................................ 3
Changes to Parameter Definitions ................................................. 6
Updated Outline Dimensions ......................................................... 9
Rev. C | Page 2 of 12
ADR370
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
TA = TMIN to TMAX, VIN = 5 V, unless otherwise noted.
Table 2.
Parameter
OUTPUT VOLTAGE (@ 25°C)
INITIAL ACCURACY ERROR
A Grade
Symbol
VO
VOERR
Conditions
Typ
2.048
−10
−0.5
−4
−0.2
B Grade
OUTPUT VOLTAGE TEMPERATURE DRIFT 1
A Grade
B Grade
TCVO
SUPPLY HEADROOM
LOAD REGULATION
VIN − VOUT
TA = −40°C to +125°C
TA = −40°C to +125°C
TA = 25°C to 70°C
LINE REGULATION
RIPPLE REJECTION
QUIESCENT CURRENT
SHORT-CIRCUIT CURRENT TO GROUND
NOISE VOLTAGE (@ 25°C)
ΔVOUT/ΔVIN
TURN-ON SETTLING TIME
LONG-TERM STABILITY
OUTPUT VOLTAGE HYSTERESIS
TEMPERATURE RANGE
CL = 0.2 μF
1
Min
2.044
Max
2.052
Unit
V
+10
+0.5
+4
+0.2
mV
%
mV
%
100
50
30
ppm/°C
ppm/°C
ppm/°C
mV
mV/mA
mV/mA
mV/mA
ppm/V
200
0 mA < IOUT < 5 mA @ 25°C
−3 mA < IOUT < 0 mA @ 25°C
−0.1 mA < IOUT < +0.1 mA
VOUT + 200 mV < VIN < 15 V
IOUT = 0 mA
VIN = 5 V ± 100 mV (f = 120 Hz)
+0.400
+0.600
+4.75
20
80
72
15
0.1 Hz to 10 Hz
10 Hz to 10 kHz
70
50
100
1000 hours @ 25°C
100
115
−40
Guaranteed by characterization.
Rev. C | Page 3 of 12
+125
dB
μA
mA
μV p-p
μV rms
μs
ppm/1000 hrs
ppm
°C
ADR370
ABSOLUTE MAXIMUM RATINGS
Ratings at 25°C, unless otherwise noted.
THERMAL RESISTANCE
Table 3.
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Parameter
Supply Voltage
Storage Temperature Range
Operating Temperature Range
Lead Temperature
Soldering, 60 sec
Infrared, 15 sec
Rating
18 V
−65°C to +125°C
−40°C to +125°C
Table 4.
Package Type
3-Lead SOT-23 (RT)
215°C
220°C
ESD CAUTION
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.
Rev. C | Page 4 of 12
θJA
220
θJC
102
Unit
°C/W
ADR370
TYPICAL PERFORMANCE CHARACTERISTICS
12
6
10
4
LINE REGULATION (ppm/V)
VIN = 5V TO 15V
8
–40°C
4
+125°C
2
0
+25°C
–4
–4
–3
–2
–1
0
1
2
3
4
–2
–4
–6
–8
03432-002
–2
0
–10
–40
5
LOAD (mA)
03432-005
ΔVO (mV)
6
2
45
125
TEMPERATURE (°C)
Figure 2. Load Regulation vs. Load Current
Figure 5. Line Regulation vs. Temperature
2.048
2.046
VOLTAGE (10µV/DIV)
OUTPUT VOLTAGE (V)
VIN = 5V
2.044
2.042
VIN = 15V
2.040
03432-003
2.036
–40
03432-006
2.038
125
45
TIME (0.1s/DIV)
TEMPERATURE (°C)
Figure 6. Voltage Noise 0.1 Hz to 10 Hz
Figure 3. Output Voltage vs. Temperature
80
VOLTAGE (200µV/DIV)
VIN = 15V
60
VIN = 5V
50
40
20
–40
03432-007
30
03432-004
SUPPLY CURRENT (µA)
70
45
125
TIME (0.1s/DIV)
TEMPERATURE (°C)
Figure 7. Voltage Noise 10 Hz to 100 kHz
Figure 4. Supply Current vs. Temperature
Rev. C | Page 5 of 12
ADR370
CL = 0.1µF
CBY = 0.1µF
CL = 0.22µF
VOUT = 1V/DIV
VOLTAGE (V)
VOLTAGE (V)
VIN = 1V/DIV
03432-010
VOUT = 1V/DIV
03432-008
VIN = 5V/DIV
TIME (100µs/DIV)
TIME (100µs/DIV)
Figure 8. Turn-On Response
Figure 10. Line Transient Response
CBY = 0.1µF
CL = 0.1µF
RLOAD = 1kΩ
VOLTAGE (V)
VOLTAGE (V)
VOUT = 20mV/DIV
VOUT = 1V/DIV
VIN = 2V/DIV
03432-009
03432-011
VIN = 5V/DIV
TIME (100ms/DIV)
TIME (100µs/DIV)
Figure 11. Load Transient Response
Figure 9. Turn-Off Response
Rev. C | Page 6 of 12
ADR370
TERMINOLOGY
Temperature Coefficient
Temperature coefficient is the change of output voltage with
respect to operating temperature changes, normalized by the
output voltage at 25°C. This parameter is expressed in ppm/°C
and can be determined by the following equation:
VO (T2 ) − VO (T1 )
ppm ⎤
=
× 10 6
TCVO ⎡⎢
⎥
⎣ ° C ⎦ VO (25° C ) × (T2 − T1 )
Long-Term Stability
Long-term stability is the typical shift of output voltage at 25°C
on a sample of parts subjected to a test of 1000 hours at 25°C.
ΔVO = VO (t 1 ) − VO (t 2 )
ΔVO [ppm ] =
(1)
VO (t 1 ) − VO (t 2 )
× 10 6
VO (t 1 )
(2)
where:
VO(t1) = VO at 25°C at Time 0.
VO(t2) = VO at 25°C after 1000 hours operation at 25°C.
where:
VO(25°C) = VO at 25°C.
VO(T1) = VO at Temperature 1.
VO(T2) = VO at Temperature 2.
Line Regulation
Line regulation is the change in output voltage due to a
specified change in input voltage. This parameter accounts for
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
Load regulation is the change in output voltage due to a
specified change in load current. This parameter accounts for
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.
Thermal Hysteresis
Thermal hysteresis is defined as the change of output voltage
after the device is cycled through temperature from +25°C to
−40°C to +125°C and back to +25°C. This is a typical value
from a sample of parts put through such a cycle.
VO _ HYS = VO (25° C ) − VO _ TC
VO _ HYS [ppm ] =
VO (25° C ) − VO _ TC
VO (25° C )
× 10 6
(3)
where:
VO(25°C) = VO at 25°C.
VO_TC = VO at 25°C after temperature cycle of +25°C to −40°C to
+125°C and back to +25°C.
Rev. C | Page 7 of 12
ADR370
THEORY OF OPERATION
APPLYING THE ADR370
To achieve the specified performance, two external components
should be used in conjunction with the ADR370: a 4.7 μF capacitor and a 1 μF capacitor. The 4.7 μF capacitor should be applied
to the input, and the 1 μF capacitor should be applied to the
output. Figure 13 shows the ADR370 with both the input and
output capacitors attached.
For further transient response optimization, an additional 0.1 μF
capacitor in parallel with the 4.7 μF input capacitor can be used.
A 1 μF output capacitor provides stable performance for all
loading conditions. The ADR370 can, however, operate under
low (−100 μA < IOUT < +100 μA) current conditions with just
a 0.2 μF output capacitor and a 1 μF input capacitor.
CIN
4.7µF
COUT
1µF
VIN
R4
ADR370
GND
VOUT
Figure 13. Typical Connection Diagram
R3
VOUT
R5
VDS
R2
V1
GND
03432-012
R6
R1
VIN
03432-013
The ADR370 uses the band gap concept to produce a stable,
low temperature coefficient voltage reference suitable for high
accuracy data acquisition components and systems. This device
makes use of the underlying temperature characteristics of a
silicon transistor’s base-emitter voltage (VBE) in the forwardbiased operating region. Under this condition, all such transistors
have a −2 mV/°C temperature coefficient (TC) and a VBE that,
when extrapolated to absolute zero, 0 K, (with collector current
proportional to absolute temperature), approximate the silicon
band gap voltage. By summing a voltage that has an equal and
opposite temperature coefficient of 2 mV/°C with a VBE of a
forward-biased transistor, an almost zero TC reference can be
developed. The simplified circuit diagram in Figure 12 shows
how a compensating voltage, V1, is achieved by driving two
transistors at different current densities and amplifying the
resulting VBE difference (ΔVBE, which has a positive TC). The
sum (VBG) of VBE and V1 is then buffered and amplified to
produce a stable reference voltage of 2.048 V at the output.
Figure 12. Simplified Schematic
Rev. C | Page 8 of 12
ADR370
APPLICATIONS INFORMATION
VL + 2.5V < VDD < VL + 12V
LOW COST NEGATIVE REFERENCE
ADR370
A low cost negative reference can be obtained by leveraging the
current sinking capability of the ADR370. By simply tying the
VOUT terminal to ground and adding a bias resistor (RSET) to
the GND pin of the device, a negative voltage reference can be
obtained as shown in Figure 14. RSET should be chosen such that
ISET remains between 1 mA and 5 mA.
VIN
VOUT
RSET
GND
ISET =
2.048V
RSET
VL
Iq = 65µA
RL
IL
03432-016
VDD
ADR370
Figure 16. Low Cost Current Source
VOUT
VIN
PRECISION CURRENT SOURCE WITH ADJUSTABLE
OUTPUT
GND
–VREF
A precision current source can be implemented with the circuit
shown in Figure 17. By adding a mechanical or digital potentiometer, this circuit becomes an adjustable current source. If a
digital potentiometer such as the AD5201 is used, the load
current is simply the voltage across Terminal B-to-Terminal W
of the digital potentiometer divided by RSET.
ISET
03432-014
RSET
VSS
Figure 14. Low Cost Negative Reference
PRECISION NEGATIVE REFERENCE
Without using any matching resistors, a precision negative
reference can be obtained using the configuration shown in
Figure 15. The voltage difference between VOUT and GND of
the ADR370 is 2.048 V. Because VOUT is at virtual ground, U2
closes the loop by forcing the GND pin to be the negative
reference node. U2 should be a low offset voltage precision
op amp, such as the OP1177.
IL =
VREF × D
RSET × 256
(5)
where D is the decimal equivalent of the digital potentiometer
input code.
12V
ADR370
0V TO (2.048V + VL)
U1
VIN
VOUT
2.3V TO 12V
B
ADR370
VIN
GND
AD5201
W
A
VOUT
RSET
+15V
GND
+12V
U2
–VREF
OP1177
VL
–12V
RL
IL
03432-017
–15V
–2.048V TO VL
03432-015
OP1177
Figure 15. Precision Negative Reference
LOW COST CURRENT SOURCE
Figure 17. Programmable 0 mA to 5 mA Current Source
Figure 16 illustrates how a simple, low cost current source can
be configured using the ADR370. The load current, IL, is simply
the sum of ISET and the quiescent current, Iq. ISET is simply the
reference voltage generated by the ADR370 divided by RSET.
I SET =
2.048 V
RSET
To optimize the resolution of this circuit, dual-supply op amps
should be used because the ground potential of the ADR370
can swing from −2.048 V at zero scale to VL at full scale of the
potentiometer setting.
(4)
The quiescent current, Iq, varies slightly with load. The variation
in Iq limits the use of this circuit to general-purpose applications.
Rev. C | Page 9 of 12
ADR370
12-BIT PRECISION PROGRAMMABLE CURRENT
SOURCE
PRECISION BOOSTED OUTPUT REGULATOR
A precision voltage output with boosted current can be realized
with the circuit shown in Figure 19. In this circuit, VOUT is
maintained by the ADR370 at 2.048 V.
By replacing the potentiometer in Figure 17 with a 12-bit
precision DAC, such as the AD5322, a higher precision
programmable current source can be achieved. Figure 18
illustrates the implementation of this circuit. The load current
can be determined with the following equation:
IL =
VREF (1 − D )
R SET × 4096
The ADR370 sources a maximum of 5 mA if the load current (IL)
is more than 5 mA and if the current is furnished by the
transistor (Q1) and the input voltage supply (VDD).
4V TO 12V
VDD
(6)
R1
10kΩ
The compliance voltage should be kept low so that the supply
voltage to U2, between VDD and GND, does not fall below 2.5 V.
2N3906
Q1
U1
+5V
ADR370
ADR370
VIN
VOUT
VREF (1 – D2/N)
U2
GND
GND
VREF
+5V
VOUT
AD5322
VOUT
VDD
RL
IL
03432-019
VIN
RSET
+5V
GND
2
U3
1
OP1177
TOL ±0.05%
V+
V–
3
VL
11
RL
IL
03432-018
–5V
Figure 18. 12-Bit Programmable Current Source
Figure 19. Precision Boosted Output Regulator
Q1 is turned on to regulate current as needed. R1 is required to
bias the base of Q1 and must be large enough to comply with
the supply current requirements of the ADR370. The supply
voltage can be as low as 4 V.
The maximum current output of this circuit is limited by the
power dissipation of the bipolar transistor, Q1.
PDISS = (VDD − 2.048) × IL
(7)
When using the 2N3906 PNP transistor shown in Figure 19,
a 4 V power supply (RL) should be chosen so that a maximum
of 100 mA is drawn from the circuit, which limits the power
dissipation of Q1 to ~200 mW.
Rev. C | Page 10 of 12
ADR370
OUTLINE DIMENSIONS
1.55
1.50
1.45
1.10
1.00
0.90
2.05
2.00
1.95
8.30
8.00
7.70
1.00 MIN
0.35
0.30
0.25
14.40 MIN
1.50 MIN
2.80
2.70
2.60
3.55
3.50
3.45
3.20
3.10
2.90
7” REEL 100.00
OR
13” REEL 330.00
1.10
1.00
0.90
7” REEL 50.00 MIN
OR
13” REEL 100.00 MIN
13.20
13.00
12.80
20.20
MIN
0.75 MIN
9.90
8.40
6.90
DIRECTION OF UNREELING
053006-0
4.10
4.00
3.90
Figure 20. SOT-23-3 Tape and Reel Outline Dimensions
Dimensions shown in millimeters
3.04
2.80
1.40
1.20
2.64
2.10
3
1
2
0.60
0.45
1.03
0.89
2.05
1.78
1.12
0.89
0.100
0.013
0.180
0.085
0.51
0.37
0.55
REF
COMPLIANT TO JEDEC STANDARDS TO-236-AB
092707-A
SEATING
PLANE
Figure 21. 3-Lead Small Outline Transistor Package [SOT-23-3]
(RT-3)
Dimensions shown in millimeters
ORDERING GUIDE
Model
ADR370ART-R2
ADR370ART-REEL7
ADR370ARTZ-REEL7 1
ADR370BRT-R2
ADR370BRT-REEL7
ADR370BRTZ-R21
ADR370BRTZ-REEL71
1
Output
Voltage
(V)
2.048
2.048
2.048
2.048
2.048
2.048
2.048
Initial
Accuracy ±
(mV) (%)
10
0.5
10
0.5
10
0.5
4
0.5
4
0.2
4
0.5
4
0.2
Temperature
Coefficient
(ppm/°C)
100
100
100
50
50
50
50
Temperature
Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Z = RoHS Compliant Part.
Rev. C | Page 11 of 12
Package
Description
3-Lead SOT-23-3
3-Lead SOT-23-3
3-Lead SOT-23-3
3-Lead SOT-23-3
3-Lead SOT-23-3
3-Lead SOT-23-3
3-Lead SOT-23-3
Package
Option
RT-3
RT-3
RT-3
RT-3
RT-3
RT-3
RT-3
Ordering
Quantity
250
3,000
3,000
250
3,000
250
3,000
Branding
RPA
RPA
L26
RPB
RPB
L27
L27
ADR370
NOTES
©2003–2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D03432-0-12/07(C)
Rev. C | Page 12 of 12
