Precision Low Power 2.048 V
SOT-23 Voltage Reference
ADR370
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.
FEATURES
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
APPLICATIONS
Battery-powered instrumentation
Portable medical instruments
Data acquisition systems
Industrial process control systems
Automotive
PIN CONFIGURATION
03432-001
3
ADR370
GND
1
2
V
IN
V
OUT
Figure 1. 3-Lead SOT-23
Table 1. ADR370 Products
Products
Output
Voltage (V)
Initial
Accuracy ±
Temperature
Coefficient
(ppm/°C)
(mV) (%)
ADR370BRT-REEL7 2.048 4 0.2 50
ADR370ART-REEL7 2.048 10 0.5 100
GENERAL DESCRIPTION
The ADR370 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.
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.
ADR370
Rev. C | Page 2 of 12
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Pin Configuration ............................................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Electrical Characteristics ............................................................. 3
Absolute Maximum Ratings ............................................................ 4
Thermal Resistance ...................................................................... 4
ESD Caution .................................................................................. 4
Typical Performance Characteristics ............................................. 5
Terminology ...................................................................................... 7
Theory of Operation .........................................................................8
Applying the ADR370 ...................................................................8
Applications Information .................................................................9
Low Cost Negative Reference ......................................................9
Precision Negative Reference .......................................................9
Low Cost Current Source .............................................................9
Precision Current Source with Adjustable Output ...................9
12-Bit Precision Programmable Current Source ................... 10
Precision Boosted Output Regulator ....................................... 10
Outline Dimensions ....................................................................... 11
Ordering Guide .......................................................................... 11
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
ADR370
Rev. C | Page 3 of 12
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
TA = TMIN to TMAX, VIN = 5 V, unless otherwise noted.
Table 2.
Parameter Symbol Conditions Min Typ Max Unit
OUTPUT VOLTAGE (@ 25°C) VO 2.044 2.048 2.052 V
INITIAL ACCURACY ERROR VOERR
A Grade −10 +10 mV
−0.5 +0.5 %
B Grade −4 +4 mV
−0.2 +0.2 %
OUTPUT VOLTAGE TEMPERATURE DRIFT1 TCVO
A Grade TA = −40°C to +125°C 100 ppm/°C
B Grade TA = −40°C to +125°C 50 ppm/°C
T
A = 25°C to 70°C 30 ppm/°C
SUPPLY HEADROOM VIN − VOUT 200 mV
LOAD REGULATION 0 mA < IOUT < 5 mA @ 25°C +0.400 mV/mA
−3 mA < IOUT < 0 mA @ 25°C +0.600 mV/mA
−0.1 mA < IOUT < +0.1 mA +4.75 mV/mA
LINE REGULATION VOUT + 200 mV < VIN < 15 V 20 ppm/V
I
OUT = 0 mA
RIPPLE REJECTION ΔVOUT/ΔVIN VIN = 5 V ± 100 mV (f = 120 Hz) 80 dB
QUIESCENT CURRENT 72 μA
SHORT-CIRCUIT CURRENT TO GROUND 15 mA
NOISE VOLTAGE (@ 25°C) 0.1 Hz to 10 Hz 70 μV p-p
10 Hz to 10 kHz 50 μV rms
TURN-ON SETTLING TIME CL = 0.2 μF 100 μs
LONG-TERM STABILITY 1000 hours @ 25°C 100 ppm/1000 hrs
OUTPUT VOLTAGE HYSTERESIS 115 ppm
TEMPERATURE RANGE −40 +125 °C
1 Guaranteed by characterization.
ADR370
Rev. C | Page 4 of 12
ABSOLUTE MAXIMUM RATINGS
Ratings at 25°C, unless otherwise noted.
Table 3.
Parameter Rating
Supply Voltage 18 V
Storage Temperature Range −65°C to +125°C
Operating Temperature Range −40°C to +125°C
Lead Temperature
Soldering, 60 sec 215°C
Infrared, 15 sec 220°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.
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 4.
Package Type θJA θ
JC Unit
3-Lead SOT-23 (RT) 220 102 °C/W
ESD CAUTION
ADR370
Rev. C | Page 5 of 12
TYPICAL PERFORMANCE CHARACTERISTICS
03432-002
12
–4
–4 5
LOAD (mA)
ΔV
O
(mV)
10
8
6
4
2
0
–2
–3 –2 –1 0 1 2 3 4
–40°C
+25°C
+125°C
Figure 2. Load Regulation vs. Load Current
03432-003
2.048
2.036
–40 125
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
2.046
2.044
2.042
2.040
2.038
45
V
IN
= 5V
V
IN
= 15V
Figure 3. Output Voltage vs. Temperature
03432-004
80
20
–40 125
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
70
60
50
40
30
45
V
IN
= 5V
V
IN
= 15V
Figure 4. Supply Current vs. Temperature
03432-005
6
–10
–40 125
TEMPERATURE (°C)
LINE REGULATION (ppm/V)
2
–2
4
0
–4
–6
–8
45
V
IN
= 5V TO 15V
Figure 5. Line Regulation vs. Temperature
03432-006
TIME (0.1s/DIV)
VOLTAGE (10µV/DIV)
Figure 6. Voltage Noise 0.1 Hz to 10 Hz
03432-007
TIME (0.1s/DIV)
VOLTAGE (200µV/DIV)
Figure 7. Voltage Noise 10 Hz to 100 kHz
ADR370
Rev. C | Page 6 of 12
03432-008
TIME (100µs/DIV)
VOLTAGE (V)
C
BY
= 0.1µF
C
L
= 0.22µF
V
OUT
= 1V/DIV
V
IN
= 5V/DIV
Figure 8. Turn-On Response
03432-009
TIME (100µs/DIV)
VOLTAGE (V)
R
LOAD
= 1kΩ
V
OUT
= 1V/DIV
V
IN
= 5V/DIV
Figure 9. Turn-Off Response
03432-010
TIME (100µs/DIV)
VOLTAGE (V)
C
L
= 0.1µF
V
OUT
= 1V/DIV
V
IN
= 1V/DIV
Figure 10. Line Transient Response
03432-011
TIME (100ms/DIV)
VOLTAGE (V)
C
BY
= 0.1µF
C
L
= 0.1µF
V
OUT
= 20mV/DIV
V
IN
= 2V/DIV
Figure 11. Load Transient Response
ADR370
Rev. C | Page 7 of 12
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:
() ()
()
()
6
10
C25C
ppm ×
−×°
−
=
⎥
⎦
⎤
⎢
⎣
⎡
°12
O
1
O
2
O
OTTV
TVTV
TCV (1)
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.
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.
(
)
(
)
[]
() ()
()
6
10ppm ×
−
=Δ
−
=
Δ
1
O
2
O
1
O
O
2
O
1
OO
tV
tVtV
V
tVtVV
(2)
where:
VO(t1) = VO at 25°C at Time 0.
VO(t2) = VO at 25°C after 1000 hours operation at 25°C.
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.
(
)
[]
()
()
6
_
_
_
_
10
C25
C25
ppm
C25
×
°
−°
=
−°
=
O
TCO
O
HYSO
TCO
OHYSO
V
VV
V
VVV
(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.
ADR370
Rev. C | Page 8 of 12
THEORY OF OPERATION
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 forward-
biased 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.
03432-012
R3
R4
V
IN
V
OUT
R5
V
DS
R6
GND
R2
R1 V1
Figure 12. Simplified Schematic
APPLYING THE ADR370
To achieve the specified performance, two external components
should be used in conjunction with the ADR370: a 4.7 μF capa-
citor 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.
03432-013
C
IN
4.7µF
V
IN
V
OUT
C
OUT
1µF
ADR370
GND
Figure 13. Typical Connection Diagram
ADR370
Rev. C | Page 9 of 12
APPLICATIONS INFORMATION
LOW COST NEGATIVE REFERENCE
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.
03432-014
V
DD
V
SS
R
SET
I
SET
–VREF
V
IN
V
OUT
ADR370
GND
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.
03432-015
U1
+15V
–15V
U2
OP1177
–VREF
2.3V TO 12
V
V
IN
V
OUT
ADR370
GND
Figure 15. Precision Negative Reference
LOW COST 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.
SET
SET R
IV048.2
= (4)
The quiescent current, Iq, varies slightly with load. The variation
in Iq limits the use of this circuit to general-purpose applications.
0
3432-016
R
SET
I
SET
=
R
L
I
L
V
L
I
q
= 65µA
V
L
+ 2.5V < V
DD
< V
L
+ 12V
V
IN
V
OUT
ADR370
GND
2.048V
R
SET
Figure 16. Low Cost Current Source
PRECISION CURRENT SOURCE WITH ADJUSTABLE
OUTPUT
A precision current source can be implemented with the circuit
shown in Figure 17. By adding a mechanical or digital potenti-
ometer, 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.
256×
×
=
SET
REF
LR
DV
I (5)
where D is the decimal equivalent of the digital potentiometer
input code.
03432-017
+12V
–12V
OP1177
12
V
VIN VOUT
ADR370
AD5201
GND
RSET
RLIL
VL
0V TO (2.048V + VL)
–2.048V TO VL
B
A
W
Figure 17. Programmable 0 mA to 5 mA Current Source
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.
ADR370
Rev. C | Page 10 of 12
12-BIT PRECISION PROGRAMMABLE CURRENT
SOURCE
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:
()
4096
1
×
−
=
SET
REF
LR
DV
I (6)
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.
03432-018
+5V
–5V
OP1177
+5
V
+5V
U1
V
IN
V
OUT
ADR370
GND
R
SET
R
L
I
L
V
L
VREF (1 – D2/N)
1
2
3
11
V+
V–
U2
U3 TOL ±0.05%
V
REF
V
DD
V
OUT
GND
AD5322
Figure 18. 12-Bit 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.
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).
03432-019
V
IN
V
DD
V
OUT
ADR370
GND R
L
I
L
4V TO 12
V
R1
10kΩ
2N3906
Q1
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.
ADR370
Rev. C | Page 11 of 12
OUTLINE DIMENSIONS
053006-0
20.20
MIN
1.00 MIN 0.75 MIN
1.10
1.00
0.90
1.50 MIN
7” REEL 100.00
OR
13” REEL 330.00
7” REEL 50.00 MIN
OR
13” REEL 100.00 MIN
DIRECTION OF UNREELING
0.35
0.30
0.25
2.80
2.70
2.60
1.55
1.50
1.45
4.10
4.00
3.90 1.10
1.00
0.90
2.05
2.00
1.95
8.30
8.00
7.70
3.20
3.10
2.90
3.55
3.50
3.45
13.20
13.00
12.80
14.40 MIN
9.90
8.40
6.90
Figure 20. SOT-23-3 Tape and Reel Outline Dimensions
Dimensions shown in millimeters
COMPLIANT TO JEDEC STANDARDS TO-236-AB
092707-A
12
3
SEATING
PLANE
2.64
2.10
3.04
2.80
1.40
1.20
2.05
1.78
0.100
0.013
1.03
0.89
0.60
0.45
0.51
0.37
1.12
0.89
0.180
0.085
0.55
REF
Figure 21. 3-Lead Small Outline Transistor Package [SOT-23-3]
(RT-3)
Dimensions shown in millimeters
ORDERING GUIDE
Model
Output
Voltage
(V)
Initial
Accuracy ± Temperature
Coefficient
(ppm/°C)
Temperature
Range
Package
Description
Package
Option
Ordering
Quantity Branding (mV) (%)
ADR370ART-R2 2.048 10 0.5 100 −40°C to +125°C 3-Lead SOT-23-3 RT-3 250 RPA
ADR370ART-REEL7 2.048 10 0.5 100 −40°C to +125°C 3-Lead SOT-23-3 RT-3 3,000 RPA
ADR370ARTZ-REEL71
2.048 10 0.5 100 −40°C to +125°C 3-Lead SOT-23-3 RT-3 3,000 L26
ADR370BRT-R2 2.048 4 0.5 50 −40°C to +125°C 3-Lead SOT-23-3 RT-3 250 RPB
ADR370BRT-REEL7 2.048 4 0.2 50 −40°C to +125°C 3-Lead SOT-23-3 RT-3 3,000 RPB
ADR370BRTZ-R21
2.048 4 0.5 50 −40°C to +125°C 3-Lead SOT-23-3 RT-3 250 L27
ADR370BRTZ-REEL71
2.048 4 0.2 50 −40°C to +125°C 3-Lead SOT-23-3 RT-3 3,000 L27
1 Z = RoHS Compliant Part.
ADR370
Rev. C | Page 12 of 12
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)
