Precision, Micropower LDO Voltage
References in TSOT
ADR121/ADR125/ADR127
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 that may result from its use. Specifications subject to change without notice. No
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Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2006–2008 Analog Devices, Inc. All rights reserved.
FEATURES
Initial accuracy
A grade: ±0.24%
B grade: ±0.12%
Maximum temperature coefficient
A grade: 25 ppm/°C
B grade: 9 ppm/°C
Low dropout: 300 mV for ADR121/ADR125
High output current: +5 mA/−2 mA
Low typical operating current: 85 μA
Input range: 2.7 V to 18 V for ADR127
Temperature range: −40°C to +125°C
Tiny TSOT (UJ-6) package
APPLICATIONS
Battery-powered instrumentation
Portable medical equipment
Data acquisition systems
Automotive
PIN CONFIGURATION
NC11
GND 2
VIN 3
NC1
6
VOUT
4
NC1
1MUST BE LEFT FLOATING
5
NC = NO CONNECT
ADR12x
TOP VIEW
(Not to Scale)
05725-001
Figure 1.
GENERAL DESCRIPTION
The ADR121/ADR125/ADR127 are a family of micropower,
high precision, series mode, band gap references with sink and
source capability. The parts feature high accuracy and low
power consumption in a tiny package. The ADR12x design
includes a patented temperature-drift curvature correction
technique that minimizes the nonlinearities in the output
voltage vs. temperature characteristics.
The ADR12x is a low dropout voltage reference, requiring only
300 mV for the ADR121/ADR125 and 1.45 V for the ADR127
above the nominal output voltage on the input to provide a
stable output voltage. This low dropout performance, coupled
with the low 85 μA operating current, makes the ADR12x ideal
for battery-powered applications.
Available in an extended industrial temperature range of −40°C
to +125°C, the ADR121/ADR125/ADR127 are housed in the
tiny TSOT (UJ-6) package.
ADR121/ADR125/ADR127
Rev. B | Page 2 of 20
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Pin Configuration ............................................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
ADR121 Electrical Characteristics ............................................. 3
ADR125 Electrical Characteristics ............................................. 4
ADR127 Electrical Characteristics ............................................. 5
Absolute Maximum Ratings ............................................................ 6
Thermal Resistance ...................................................................... 6
ESD Caution .................................................................................. 6
Typical Performance Characteristics ............................................. 7
Terminology .................................................................................... 15
Theory of Operation ...................................................................... 16
Power Dissipation Considerations ........................................... 16
Input Capacitor ........................................................................... 16
Output Capacitor ........................................................................ 16
Applications Information .............................................................. 17
Basic Voltage Reference Connection ....................................... 17
Stacking Reference ICs for Arbitrary Outputs ....................... 17
Negative Precision Reference Without Precision Resistors .. 17
General-Purpose Current Source ............................................ 17
Outline Dimensions ....................................................................... 18
Ordering Guide .......................................................................... 18
REVISION HISTORY
1/08—Rev. A to Rev. B
Changes to Table 1 ............................................................................ 3
Changes to Table 2 ............................................................................ 4
Changes to Table 3 .............................................................................5
Changes to Figure 52 ...................................................................... 17
Changes to Ordering Guide ......................................................... 18
5/07—Rev. 0 to Rev. A
Changes to Table 1 ............................................................................ 3
Changes to Table 2 ............................................................................ 4
Changes to Table 3 ............................................................................ 5
Added Thermal Hysteresis Equation ............................................. 7
Changes to Ordering Guide .......................................................... 18
6/06—Revision 0: Initial Version
ADR121/ADR125/ADR127
Rev. B | Page 3 of 20
SPECIFICATIONS
ADR121 ELECTRICAL CHARACTERISTICS
TA = 25°C, VIN = 2.8 V to 18 V, IOUT = 0 mA, unless otherwise noted.
Table 1.
Parameter Symbol Conditions/Comments Min Typ Max Unit
OUTPUT VOLTAGE VOUT
B Grade 2.497 2.5 2.503 V
A Grade 2.494 2.5 2.506 V
INITIAL ACCURACY ERROR VOERR
B Grade −0.12 +0.12 %
A Grade −0.24 +0.24 %
TEMPERATURE COEFFICIENT TCVOUT −40°C < TA < +125°C
B Grade 3 9 ppm/°C
A Grade 15 25 ppm/°C
DROPOUT (VOUT − VIN) VDO I
OUT = 0 mA 300 mV
LOAD REGULATION −40°C < TA < +125°C; VIN = 5.0 V,
0 mA < IOUT < 5 mA
80 300 ppm/mA
−40°C < TA < +125°C; VIN = 5.0 V,
−2 mA < IOUT < 0 mA
50 300 ppm/mA
LINE REGULATION 2.8 V to 18 V, IOUT = 0 mA −50 +3 +50 ppm/V
PSRR f = 60 Hz −90 dB
QUIESCENT CURRENT IQ −40°C < TA < +125°C, no load
V
IN = 18 V 95 125 μA
V
IN = 2.8 V 80 95 μA
SHORT-CIRCUIT CURRENT TO GROUND VIN = 2.8 V 18 mA
V
IN = 18 V 40 mA
VOLTAGE NOISE f = 10 kHz 500 nV/√Hz
f = 0.1 Hz to 10 Hz 18 μV p-p
TURN-ON SETTLING TIME To 0.1%, CL = 0.2 μF 100 μs
LONG-TERM STABILITY 1000 hours @ 25°C 150 ppm/1000 hrs
OUTPUT VOLTAGE HYSTERESIS See the Terminology section 300 ppm
ADR121/ADR125/ADR127
Rev. B | Page 4 of 20
ADR125 ELECTRICAL CHARACTERISTICS
TA = 25°C, VIN = 5.3 V to 18 V, IOUT = 0 mA, unless otherwise noted.
Table 2.
Parameter Symbol Conditions/Comments Min Typ Max Unit
OUTPUT VOLTAGE VOUT
B Grade 4.994 5.0 5.006 V
A Grade 4.988 5.0 5.012 V
INITIAL ACCURACY ERROR VOERR
B Grade −0.12 +0.12 %
A Grade −0.24 +0.24 %
TEMPERATURE COEFFICIENT TCVOUT −40°C < TA < +125°C
B Grade 3 9 ppm/°C
A Grade 15 25 ppm/°C
DROPOUT (VOUT − VIN) VDO I
OUT = 5 mA 300 mV
LOAD REGULATION −40°C < TA < +125°C; VIN = 6.0 V,
0 mA < IOUT < 5 mA
35 200 ppm/mA
−40°C < TA < +125°C; VIN = 6.0 V,
−2 mA < IOUT < 0 mA
35 200 ppm/mA
LINE REGULATION 5.3 V to 18 V, IOUT = 0 mA 30 ppm/V
PSRR f = 60 Hz −90 dB
QUIESCENT CURRENT IQ −40°C < TA < +125°C, no load
V
IN = 18 V 95 125 μA
V
IN = 5.3 V 80 95 μA
SHORT-CIRCUIT CURRENT TO GROUND VIN = 5.3 V 25 mA
V
IN = 18 V 40 mA
VOLTAGE NOISE f = 10 kHz 900 nV/√Hz
f = 0.1 Hz to 10 Hz 36 μV p-p
TURN-ON SETTLING TIME To 0.1%, CL = 0.2 μF 100 μs
LONG-TERM STABILITY 1000 hours @ 25°C 150 ppm/1000 hrs
OUTPUT VOLTAGE HYSTERESIS See the Terminology section 300 ppm
ADR121/ADR125/ADR127
Rev. B | Page 5 of 20
ADR127 ELECTRICAL CHARACTERISTICS
TA = 25°C, VIN = 2.7 V to 18 V, IOUT = 0 mA, unless otherwise noted.
Table 3.
Parameter Symbol Conditions/Comments Min Typ Max Unit
OUTPUT VOLTAGE VOUT
B Grade 1.2485 1.25 1.2515 V
A Grade 1.2470 1.25 1.2530 V
INITIAL ACCURACY ERROR VOERR
B Grade −0.12 +0.12 %
A Grade −0.24 +0.24 %
TEMPERATURE COEFFICIENT TCVOUT −40°C < TA < +125°C
B Grade 3 9 ppm/°C
A Grade 15 25 ppm/°C
DROPOUT (VOUT − VIN) VDO I
OUT = 0 mA 1.45 V
LOAD REGULATION −40°C < TA < +125°C; VIN = 3.0 V,
0 mA < IOUT < 5 mA
85 400 ppm/mA
−40°C < TA < +125°C; VIN = 3.0 V,
−2 mA < IOUT < 0 mA
65 400 ppm/mA
LINE REGULATION 2.7 V to 18 V, IOUT = 0 mA 30 90 ppm/V
PSRR f = 60 Hz −90 dB
QUIESCENT CURRENT IQ −40°C < TA < +125°C, no load
V
IN = 18 V 95 125 μA
V
IN = 2.7 V 80 95 μA
SHORT-CIRCUIT CURRENT TO GROUND VIN = 2.7 V 15 mA
V
IN = 18 V 30 mA
VOLTAGE NOISE f = 10 kHz 300 nV/√Hz
f = 0.1 Hz to 10 Hz 9 μV p-p
TURN-ON SETTLING TIME To 0.1%, CL = 0.2 μF 80 μs
LONG-TERM STABILITY 1000 hours @ 25°C 150 ppm/1000 hrs
OUTPUT VOLTAGE HYSTERESIS See the Terminology section 300 ppm
ADR121/ADR125/ADR127
Rev. B | Page 6 of 20
ABSOLUTE MAXIMUM RATINGS
Table 4.
Parameter Rating
VIN to GND 20 V
Internal Power Dissipation
TSOT (UJ-6) 40 mW
Storage Temperature Range −65°C to +150°C
Operating Temperature Range −40°C to +125°C
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C
Infrared (15 sec) 220°C
THERMAL RESISTANCE
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 5.
Package Type θJA θ
JC Unit
6-Lead TSOT (UJ-6) 230 146 °C/W
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.
ADR121/ADR125/ADR127
Rev. B | Page 7 of 20
TYPICAL PERFORMANCE CHARACTERISTICS
1.256
1.244
–40 125
TEMPERATURE (°C)
V
OUT
(V)
05725-006
1.246
1.248
1.250
1.252
1.254
–25 –10 5 20 35 50 65 80 95 110
Figure 2. ADR127 VOUT vs. Temperature
2.510
2.490
–40 125
TEMPERATURE (°C)
V
OUT
(V)
05725-007
2.492
2.494
2.496
2.498
2.500
2.502
2.504
2.506
2.508
–25–105 203550658095110
Figure 3. ADR121 VOUT vs. Temperature
5.020
4.980
–40 125
TEMPERATURE (°C)
V
OUT
(V)
05725-008
–25–105 203550658095110
4.985
4.990
4.995
5.000
5.005
5.010
5.015
Figure 4. ADR125 VOUT vs. Temperature
5
0
–50 50
TEMPERATURE COEFFICIENT (ppm/°C)
NUMBER OF PARTS
05725-009
1
2
3
4
–40–30–20–100 10203040
Figure 5. ADR127 Temperature Coefficient
5
0
–50 50
TEMPERATURE COEFFICIENT (ppm/°C)
NUMBER OF PARTS
05725-011
1
2
3
4
–40–30–20–100 10203040
Figure 6. ADR121 Temperature Coefficient
5
0
–50 50
TEMPERATURE COEFFICIENT (ppm/°C)
NUMBER OF PARTS
05725-010
1
2
3
4
–40–30–20–100 10203040
Figure 7. ADR125 Temperature Coefficient
ADR121/ADR125/ADR127
Rev. B | Page 8 of 20
3.0
2.0
–2–1012345
LOAD CURRENT (mA)
VIN_MIN (V)
0
5725-012
2.2
2.4
2.6
2.8
+125°C
–40°C
+25°C
Figure 8. ADR127 Minimum Input Voltage vs. Load Current
3.5
2.5
–2–1012345
LOAD CURRENT (mA)
V
IN
_MIN (V)
05725-013
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
–40°C
+25°C
+125°C
Figure 9. ADR121 Minimum Input Voltage vs. Load Current
6.2
5.0
–2–1012345
LOAD CURRENT (mA)
V
IN
_MIN (V)
05725-014
+25°C
+125°C
5.2
5.4
5.6
5.8
6.0
–40°C
Figure 10. ADR125 Minimum Input Voltage vs. Load Current
120
0
21
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
8
0
5725-015
20
40
60
80
100
3 4 5 6 7 8 9 1011121314151617
+25°C
–40°C
+125°C
Figure 11. ADR127 Supply Current vs. Input Voltage
120
0
21
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
8
05725-016
20
40
60
80
100
3 4 5 6 7 8 9 1011121314151617
+25°C
–40°C
+125°C
Figure 12. ADR121 Supply Current vs. Input Voltage
120
0
51
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
8
0
5725-017
20
40
60
80
100
6 7 8 9 1011121314151617
+25°C
–40°C
+125°C
Figure 13. ADR125 Supply Current vs. Input Voltage
ADR121/ADR125/ADR127
Rev. B | Page 9 of 20
6
0
–2 5
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
05725-018
5
4
3
2
1
–101234
— +125°C
— +25°C
— –40°C
Figure 14. ADR127 Supply Current vs. Load Current
6
0
–2 5
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
05725-019
5
4
3
2
1
–101234
— +125°C
— +25°C
— –40°C
Figure 15. ADR121 Supply Current vs. Load Current
6
0
–2 5
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
05725-020
5
4
3
2
1
–101234
— +125°C
— +25°C
— –40°C
Figure 16. ADR125 Supply Current vs. Load Current
0
–50
–40 125
TEMPERATURE (°C)
LINE REGULATION (ppm/V)
05725-021
–40
–30
–20
–10
–25 –10 5 20 35 50 65 80 95 110
V
IN
= 2.7V TO 18V
Figure 17. ADR127 Line Regulation vs. Temperature
3
–3
–40 125
TEMPERATURE (°C)
LINE REGULATION (ppm/V)
05725-022
–2
–1
0
2
–25 –10 5 20 35 50 65 80 95 110
1
V
IN
= 2.8V TO 18V
Figure 18. ADR121 Line Regulation vs. Temperature
6
–6
–40 125
TEMPERATURE (°C)
LINE REGULATION (ppm/V)
05725-023
–4
–2
0
4
–25 –10 5 20 35 50 65 80 95 110
2V
IN
= 5.3V TO 18V
Figure 19. ADR125 Line Regulation vs. Temperature
ADR121/ADR125/ADR127
Rev. B | Page 10 of 20
200
–200
–40 125
TEMPERATURE (°C)
LOAD REGULATION (ppm/mA)
05725-024
–25 –10 5 20 35 50 65 80 95 110
150
100
50
0
–50
–100
–150
2mA SINKING, V
IN
= 3V
5mA SOURCING, V
IN
= 3V
Figure 20. ADR127 Load Regulation vs. Temperature
100
–100
–40 125
TEMPERATURE (°C)
LOAD REGULATION (ppm/mA)
05725-025
–25 –10 5 20 35 50 65 80 95 110
5mA SOURCING, V
IN
= 5V
80
60
40
20
0
–20
–40
–60
–80
2mA SINKING, V
IN
= 5V
Figure 21. ADR121 Load Regulation vs. Temperature
50
–50
–40 125
TEMPERATURE (°C)
LOAD REGULATION (ppm/mA)
05725-026
–25 –10 5 20 35 50 65 80 95 110
40
30
20
10
0
–10
–20
–30
–40
2mA SINKING, V
IN
= 6V
5mA SOURCING, V
IN
= 6V
Figure 22. ADR125 Load Regulation vs. Temperature
05725-027
1
C
IN
= C
OUT
= 0.1µF
2µV/DIV TIME (1s/DIV)
CH1 p-p
5.76µV
CH1 rms
0.862µV
Figure 23. ADR127 0.1 Hz to 10 Hz Noise
05725-028
1
C
IN
= C
OUT
= 0.1µF
5µV/DIV TIME (1s/DIV)
CH1 p-p
10.8µV
CH1 rms
1.75µV
Figure 24. ADR121 0.1 Hz to 10 Hz Noise
05725-029
1
C
IN
= C
OUT
= 0.1µF
10µV/DIV TIME (1s/DIV)
CH1 p-p
20.6µV
CH1 rms
3.34µV
Figure 25. ADR125 0.1 Hz to 10 Hz Noise
ADR121/ADR125/ADR127
Rev. B | Page 11 of 20
05725-030
1
C
IN
= C
OUT
= 0.1µF
50µV/DIV TIME (1s/DIV)
CH1 p-p
287µV
CH1 rms
38.8µV
Figure 26. ADR127 10 Hz to 10 kHz Noise
05725-031
1
C
IN
= C
OUT
= 0.1µF
100µV/DIV TIME (1s/DIV)
CH1 p-p
450µV
CH1 rms
58.1µV
Figure 27. ADR121 10 Hz to 10 kHz Noise
05725-032
1
C
IN
= C
OUT
= 0.1µF
200µV/DIV TIME (1s/DIV)
CH1 p-p
788µV
CH1 rms
115µV
Figure 28. ADR125 10 Hz to 10 kHz Noise
05725-033
1
2
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
V
OUT
500mV/DIV
TIME (200µs/DIV)
Figure 29. ADR127 Turn-On Response
05725-034
1
2
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
V
OUT
500mV/DIV
TIME (40µs/DIV)
Figure 30. ADR127 Turn-On Response
05725-035
1
2
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
V
OUT
500mV/DIV TIME (100µs/DIV)
Figure 31. ADR127 Turn-Off Response
ADR121/ADR125/ADR127
Rev. B | Page 12 of 20
05725-036
1
2
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
V
OUT
1V/DIV
TIME (100µs/DIV)
Figure 32. ADR121 Turn-On Response
05725-037
1
2
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
V
OUT
1V/DIV TIME (40µs/DIV)
Figure 33. ADR121 Turn-On Response
05725-038
1
2
V
OUT
1V/DIV
TIME (200µs/DIV)
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
Figure 34. ADR121 Turn-Off Response
05725-039
1
2
V
IN
2V/DIV
V
OUT
2V/DIV
TIME (100µs/DIV)
C
IN
= C
OUT
= 0.1µF
Figure 35. ADR125 Turn-On Response
05725-040
1
2
V
IN
2V/DIV
V
OUT
2V/DIV TIME (20µs/DIV)
C
IN
= C
OUT
= 0.1µF
Figure 36. ADR125 Turn-On Response
05725-041
1
2
V
IN
2V/DIV
V
OUT
2V/DIV
TIME (20µs/DIV)
C
IN
= C
OUT
= 0.1µF
Figure 37. ADR125 Turn-Off Response
ADR121/ADR125/ADR127
Rev. B | Page 13 of 20
05725-042
1
2
VIN 1V/DIV
LINE INTERRUPTION
VOUT
500mV/DIV TIME (200µs/DIV)
CIN = COUT = 0.1µF
Figure 38. ADR127 Line Transient Response
05725-043
1
2
V
OUT
500mV/DIV
TIME (400µs/DIV)
C
IN
= C
OUT
= 0.1µF
V
IN
1V/DIV
LINE INTERRUPTION
Figure 39. ADR121 Line Transient Response
05725-044
1
2
V
OUT
500mV/DIV TIME (400µs/DIV)
C
IN
= C
OUT
= 0.1µF
V
IN
1V/DIV
LINE INTERRUPTION
Figure 40. ADR125 Line Transient Response
05725-045
2
1
V
OUT
20mV/DIV TIME (40µs/DIV)
2.50V
1.25V
V
IN
500mV/DIV
C
IN
= C
OUT
= 0.1µF
625ΩLOAD
2mA SINKING
Figure 41. ADR127 Load Transient Response (Sinking)
05725-046
1
2
V
OUT
100mV/DIV TIME (40µs/DIV)
1.25
V
0V
V
IN
500mV/DIV
C
IN
= C
OUT
= 0.1µF
250ΩLOAD
5mA SOURCING
Figure 42. ADR127 Load Transient Response (Sourcing)
05725-047
1
2
V
OUT
10mV/DIV TIME (40µs/DIV)
5V
2.5V
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
1250ΩLOAD
2mA SINKING
Figure 43. ADR121 Load Transient Response (Sinking)
ADR121/ADR125/ADR127
Rev. B | Page 14 of 20
05725-048
1
2
V
OUT
100mV/DIV TIME (40µs/DIV)
2.5V
0V
V
IN
1V/DIV
C
IN
= C
OUT
= 0.1µF
500ΩLOAD
5mA SOURCING
Figure 44. ADR121 Load Transient Response (Sourcing)
05725-049
1
2
V
OUT
20mV/DIV TIME (40µs/DIV)
10V
5V
V
IN
2V/DIV
C
IN
= C
OUT
= 0.1µF
2.5kΩLOAD
2mA SINKING
Figure 45. ADR125 Load Transient Response (Sinking)
05725-050
1
2
V
OUT
100mV/DIV TIME (40µs/DIV)
5V
0V
V
IN
2V/DIV
C
IN
= C
OUT
= 0.1µF
1kΩLOAD
5mA SOURCING
Figure 46. ADR125 Load Transient Response (Sourcing)
0
–20
–40
–60
–80
–100
–120
–140
–160
–180
–200
10 100M
(dB)
05725-051
100 1k 10k 100k 1M 10M
1
Figure 47. ADR121/ADR125/ADR127 PSRR
10
OUTPUT IMPEDANCE (Ω)
0
5725-054
100
FREQUENCY (Hz)
1k 10k 100k
1
ADR121
ADR125
ADR127
50
45
40
35
30
25
20
15
10
5
0
Figure 48. ADR121/ADR125/ADR127 Output Impedance vs. Frequency
ADR121/ADR125/ADR127
Rev. B | Page 15 of 20
TERMINOLOGY
Temperature Coefficient
The change in output voltage with respect to operating
temperature change normalized by the output voltage at 25°C.
This parameter is expressed in ppm/°C and can be determined
as follows:
[]
() ()
()( )
6
10
C25
Cppm/ ×
−×°
−
=°
12OUT
1OUT2
UT
O
OUT TTV
TVTV
TCV (1)
where:
VOUT(25°C) = VOUT at 25°C.
VOUT(T1) = VOUT at Temperature 1.
VOUT(T2) = VOUT at Temperature 2.
Line Regulation
The change in the output voltage due to a specified change
in input voltage. This parameter accounts for the effects of
self-heating. Line regulation is expressed in percent per volt,
parts-per-million per volt, or microvolts per voltage change in
input voltage.
Load Regulation
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 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 a test of 1000 hours at 25°C.
(
)()
[]
() ()
()
6
10ppm ×
−
=Δ
−
Δ
0OUT
1OUT0OUT
OUT
1
UT
O0OUT
UT
O
tV tVtV
V
tVtVV (2)
where:
VOUT(t0) = VOUT at 25°C at Time 0.
VOUT(t1) = VOUT at 25°C after 1000 hours operating at 25°C.
Thermal Hysteresis
The change in output voltage after the device is cycled through
temperatures 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.
(
)
TCOUTOUTHYSOUT VVV __ C25 −°
=
(3)
[]
()
()
6
_
_10
C25
C25
ppm ×
°
−°
=
OU
T
TCOUT
UT
O
HYSOUT V
VV
V
where:
VOUT(25°C) = VOUT at 25°C.
VOUT_TC = VOUT at 25°C after temperature cycle at +25°C to
−40°C to +125°C and back to +25°C.
ADR121/ADR125/ADR127
Rev. B | Page 16 of 20
THEORY OF OPERATION
The ADR12x band gap references are the high performance
solution for low supply voltage and low power applications.
The uniqueness of these products lies in their architecture.
POWER DISSIPATION CONSIDERATIONS
The ADR12x family is capable of delivering load currents up to
5 mA with an input range from 3.0 V to 18 V. When this device
is used in applications with large input voltages, care must be
taken to avoid exceeding the specified maximum power
dissipation or junction temperature because this could result
in premature device failure.
Use the following formula to calculate a device’s maximum
junction temperature or dissipation:
JA
A
J
Dθ
TT
P−
= (4)
where:
TJ is the junction temperature.
TA is the ambient temperature.
PD is the device power dissipation.
θJA is the device package thermal resistance.
INPUT CAPACITOR
Input capacitors are not required on the ADR12x. There is no
limit for the value of the capacitor used on the input, but a 1 μF
to 10 μF capacitor on the input may improve transient response
in applications where there is a sudden supply change. An
additional 0.1 μF capacitor in parallel also helps reduce noise
from the supply.
OUTPUT CAPACITOR
The ADR12x requires a small 0.1 μF capacitor for stability.
Additional 0.1 μF to 10 μF capacitance in parallel can improve
load transient response. This acts as a source of stored energy
for a sudden increase in load current. The only parameter
affected with the additional capacitance is turn-on time.
ADR121/ADR125/ADR127
Rev. B | Page 17 of 20
APPLICATIONS INFORMATION
BASIC VOLTAGE REFERENCE CONNECTION
The circuit in Figure 49 illustrates the basic configuration for
the ADR12x family voltage reference.
NC
V
OUT
NC
ADR12x
1
2
3
6
5
4
NC
GND
V
IN
0.1µF 0.1µF
OUTPUTINPUT
+ +
05725-002
Figure 49. Basic Configuration for the ADR12x Family
STACKING REFERENCE ICs FOR ARBITRARY
OUTPUTS
Some applications may require two reference voltage sources
that are a combined sum of the standard outputs. Figure 50
shows how this stacked output reference can be implemented.
NC
V
OUT
NC
ADR12x
1
2
3
6
5
4
NC
GND
V
IN
NC
V
OUT
NC
ADR12x
1
2
3
6
5
4
NC
GND
V
IN
V
OUT2
V
OUT1
V
IN
0.1µF0.1µF
0.1µF0.1µF
U2
U1
05725-003
Figure 50. Stacking References with the ADR12x
Two reference ICs are used and fed from an unregulated input,
VIN. The outputs of the individual ICs are connected in series,
which provides two output voltages, VOUT1 and VOUT2. VOUT1 is
the terminal voltage of U1, whereas VOUT2 is the sum of this
voltage and the terminal of U2. U1 and U2 are chosen for the
two voltages that supply the required outputs (see Table 6). For
example, if U1 and U2 are ADR127s and VIN ≥ 3.95 V, VOUT1 is
1.25 V and VOUT2 is 2.5 V.
Table 6. Required Outputs
U1/U2 VOUT2 V
OUT1
ADR127/ADR121 1.25 V 3.75 V
ADR127/ADR125 1.25 V 6.25 V
ADR121/ADR125 2.5 V 7.5 V
NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
A negative reference is easily generated by adding an op
amp, for example, the AD8603, and is configured as shown in
Figure 51. VOUT is at virtual ground and, therefore, the negative
reference can be taken directly from the output of the op amp.
The op amp must be dual-supply, low offset, and rail-to-rail if
the negative supply voltage is close to the reference output.
NC
V
OUT
NC
ADR127
AD8603
1
2
3
6
5
4
NC
GND
–
V+
V– 3
2
+
V
IN
05725-055
0.1µF
+V
DD
–V
REF
1kΩ
–V
DD
Figure 51. Negative Reference
GENERAL-PURPOSE CURRENT SOURCE
In low power applications, the need can arise for a precision
current source that can operate on low supply voltages. The
ADR12x can be configured as a precision current source (see
Figure 52). The circuit configuration shown 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 ranging from the reference’s supply current, typi-
cally 85 μA, to approximately 5 mA.
NC
VOUT
NC
RL
ADR12x
1
2
3
6
5
4
NC
GND
VIN
ISY
+
DD
RSET
P1
ISET
05725-005
Figure 52. ADR12x Trim Configuration
ADR121/ADR125/ADR127
Rev. B | Page 18 of 20
OUTLINE DIMENSIONS
13
45
2
6
2.90 BSC
1.60 BSC 2.80 BSC
1.90
BSC
0.95 BSC
0.20
0.08
8°
4°
0°
0.50
0.30
0.10 MAX
*0.90
0.87
0.84
SEATING
PLANE
*1.00 MAX
0.60
0.45
0.30
PIN 1
INDICATO
R
*COMPLIANT TO JEDEC STANDARDS MO-193-AA WITH
THE EXCEPTION OF PACKAGE HEIGHT AND THICKNESS.
Figure 53. 6-Lead Thin Small Outline Transistor Package [TSOT]
(UJ-6)
Dimensions shown in millimeters
ORDERING GUIDE
Model
Output
Voltage
(VOUT)
Initial
Accuracy Temperature
Coefficient
(ppm/°C)
Temperature
Range
Package
Description
Package
Option
Ordering
Quantity Branding
mV ±%
ADR121AUJZ-REEL71
2.5 2.5 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0N
ADR121AUJZ-R21
2.5 2.5 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 250 R0N
ADR121BUJZ-REEL71
2.5 2.5 0.12 9 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0P
ADR125AUJZ-REEL71
5.0 5.0 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0Q
ADR125AUJZ-R21
5.0 5.0 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 250 R0Q
ADR125BUJZ-REEL71
5.0 5.0 0.12 9 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0R
ADR127AUJZ-REEL71
1.25 3 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0S
ADR127AUJZ-R21
1.25 3 0.24 25 −40°C to +125°C 6-Lead TSOT UJ-6 250 R0S
ADR127BUJZ-REEL71
1.25 1.5 0.12 9 −40°C to +125°C 6-Lead TSOT UJ-6 3,000 R0T
1 Z = RoHS Compliant Part.
ADR121/ADR125/ADR127
Rev. B | Page 19 of 20
NOTES
ADR121/ADR125/ADR127
Rev. B | Page 20 of 20
NOTES
©2006–2008 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05725-0-1/08(B)