AD ADR380ART-R2

Precision Low-Drift 2.048 V/2.500 V
SOT-23 Voltage Reference
ADR380/ADR381
FEATURES
Initial Accuracy: ⴞ5 mV/ⴞ6 mV max
Initial Accuracy Error: ⴞ0.24%/ⴞ0.24%
Low TCV O: 25 ppm/ⴗC max
Load Regulation: 70 ppm/mA
Line Regulation: 25 ppm/V
Wide Operating Range:
2.4 V to 18 V for ADR380
2.8 V to 18 V for ADR381
Low Power: 120 ␮A max
High Output Current: 5 mA
Wide Temperature Range: –40ⴗC to +85ⴗC
Tiny 3-Lead SOT-23 Package with Standard Pinout
APPLICATIONS
Battery-Powered Instrumentation
Portable Medical Instruments
Data Acquisition Systems
Industrial Process Control Systems
Hard Disk Drives
Automotive
PIN CONFIGURATION
3-Lead SOT-23
(RT Suffix)
VIN 1
ADR380/
ADR381
(Not to Scale)
3
GND
VOUT 2
Table I. ADR38x Products
Part Number
Nominal Output Voltage (V)
ADR380
ADR381
2.048
2.500
GENERAL DESCRIPTION
The ADR380 and ADR381 are precision 2.048 V and 2.500 V
band gap voltage references featuring high accuracy, high stability, and low-power consumption in a tiny footprint. Patented
temperature drift curvature correction techniques minimize
nonlinearity of the voltage change with temperature. The wide
operating range and low power consumption make them ideal
for 3 V to 5 V battery-powered applications.
The ADR380 and ADR381 are micropower, low dropout
voltage (LDV) devices that provide a stable output voltage from
supplies as low as 300 mV above the output voltage. They are
specified over the industrial (–40°C to +85°C) temperature
range. ADR380/ADR381 is available in the tiny 3-lead SOT-23
package.
REV. A
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. 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: 781/326-8703
© 2004 Analog Devices, Inc. All rights reserved.
ADR380/ADR381–SPECIFICATIONS
ADR380 ELECTRICAL CHARACTERISTICS (@ V
Parameter
Symbol
Output Voltage
Initial Accuracy Error
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
⌬VO/DVIN
Load Regulation
⌬VO/DILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
eN
tR
⌬VO
VO_HYS
RRR
ISC
IN
= 5.0 V, TA = 25ⴗC unless otherwise noted.)
Conditions
Min
–40°C < TA < +85°C
0°C < TA< 70°C
IL ≤ 3 mA
VIN = 2.5 V to 15 V
–40°C < TA < +85°C
VIN = 3 V, ILOAD = 0 mA to 5 mA
–40°C < TA < +85°C
No Load
–40°C < TA < +85°C
0.1 Hz to 10 Hz
Typ
Max
Unit
2.053
+5
+0.24
25
21
25
V
mV
%
ppm/°C
ppm/°C
mV
ppm/V
70
ppm/mA
120
140
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
Max
Unit
2.053
+5
+0.24
25
21
V
mV
%
ppm/°C
ppm/°C
mV
10
25
ppm/V
100
70
120
140
ppm/mA
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
2.043 2.048
–5
–0.24
5
3
300
10
100
5
20
50
40
85
25
1,000 Hrs
fIN = 60 Hz
Specifications subject to change without notice.
ADR380 ELECTRICAL CHARACTERISTICS (@ V
Parameter
Symbol
Output Voltage
Initial Accuracy Error
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
⌬VO/DVIN
Load Regulation
⌬VO/DILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
eN
tR
⌬VO
VO_HYS
RRR
ISC
IN
= 15.0 V, TA = 25ⴗC unless otherwise noted.)
Conditions
–40°C < TA < +85°C
0°C < TA < 70°C
IL ≤ 3 mA
VIN = 2.5 V to 15 V
–40°C < TA < +85°C
VIN = 3 V, ILOAD = 0 mA to 5 mA
–40°C < TA < +85°C
No Load
–40°C < TA < +85°C
0.1 Hz to 10 Hz
1,000 Hrs
fIN = 60 Hz
Min
Typ
2.043 2.048
–5
–0.24
5
3
300
5
20
50
40
85
25
Specifications subject to change without notice.
–2–
REV. A
ADR380/ADR381
SPECIFICATIONS (continued)
ADR381 ELECTRICAL CHARACTERISTICS (@ V
Parameter
Symbol
Output Voltage
Initial Accuracy Error
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
⌬VO/DVIN
Load Regulation
⌬VO/DILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
eN
tR
⌬VO
VO_HYS
RRR
ISC
IN
= 5.0 V, TA = 25ⴗC unless otherwise noted.)
Conditions
Min
–40°C < TA < +85°C
0°C < TA < 70°C
IL ≤ 2 mA
VIN = 2.8 V to 15 V
–40°C < TA < +85°C
VIN = 3.5 V, ILOAD = 0 mA to 5 mA
–40°C < TA < +85°C
No Load
–40°C < TA < +85°C
0.1 Hz to 10 Hz
Typ
2.494 2.5
–6
–0.24
5
3
300
10
100
Max
Unit
2.506
+6
+0.24
25
21
25
V
mV
%
ppm/°C
ppm/°C
mV
ppm/V
70
ppm/mA
120
140
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
Max
Unit
2.506
+6
+0.24
25
21
25
V
mV
%
ppm/°C
ppm/°C
mV
ppm/V
70
ppm/mA
120
140
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
5
20
50
75
85
25
1,000 Hrs
fIN = 60 Hz
Specifications subject to change without notice.
ADR381 ELECTRICAL CHARACTERISTICS (@ V
Parameter
Symbol
Output Voltage
Initial Accuracy Error
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
⌬VO/DVIN
Load Regulation
⌬VO/DILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
eN
tR
⌬VO
VO_HYS
RRR
ISC
IN
= 15.0 V, TA = 25ⴗC unless otherwise noted.)
Conditions
–40°C < TA < +85°C
0°C < TA< 70°C
IL ≤ 2 mA
VIN = 2.8 V to 15 V
–40°C < TA < +85°C
VIN = 3.5 V, ILOAD = 0 mA to 5 mA
–40°C < TA < +85°C
No Load
–40°C < TA < +85°C
0.1 Hz to 10 Hz
1,000 Hrs
fIN = 60 Hz
Specifications subject to change without notice.
REV. A
–3–
Min
Typ
2.494 2.5
–6
–0.24
5
3
300
10
100
5
20
50
75
85
25
ADR380/ADR381
ABSOLUTE MAXIMUM RATINGS 1
PIN CONFIGURATION
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
Output Short-Circuit Duration to GND
VIN > 15 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 sec
VIN ≤ 15 V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indefinite
Storage Temperature Range
RT Package . . . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Operating Temperature Range
ADR380/ADR381 . . . . . . . . . . . . . . . . . . . . –40°C to +85°C
Junction Temperature Range
RT Package . . . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering, 60 Sec) . . . . . . . . 300°C
Package Type
␪JA2
␪JC
Unit
3-Lead SOT-23 (RT)
333
—
°C/W
3-Lead SOT-23
(RT Suffix)
ADR380/
ADR381
VIN 1
(Not to Scale)
3
GND
VOUT 2
NOTES
1
Absolute maximum ratings apply at 25°C, unless otherwise noted.
2
θJA is specified for the worst-case conditions, i.e., θJA is specified for device
soldered in circuit board for surface-mount packages.
ORDERING GUIDE
Model
Temperature
Range
Package
Description
Package
Option
Branding
Output
Voltage
Number of
Parts per Reel
ADR380ART-R2
ADR380ART-REEL7
ADR380ARTZ-REEL7*
ADR381ART-R2
ADR381ART-REEL7
ADR381ARTZ-REEL7*
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
SOT-23
RT-3
RT-3
RT-3
RT-3
RT-3
RT-3
R2A
R2A
R2A
R3A
R3A
R3A
2.048
2.048
2.048
2.500
2.500
2.500
250
3,000
3,000
250
3,000
3,000
*Z = Pb-free part
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4,000 V readily
accumulate on the human body and test equipment and can discharge without detection. Although the
ADR380/ADR381 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.
–4–
REV. A
ADR380/ADR381
PARAMETER DEFINITIONS
Long-Term Stability
Temperature Coefficient
A typical shift in output voltage over 1,000 hours at a controlled
temperature. The graphs TPC 24 and TPC 25 show a sample
of parts measured at different intervals in a controlled environment of 50°C for 1,000 hours.
The change of output voltage over the operating temperature
change and normalized by the output voltage at 25°C, expressed
in ppm/°C. The equation follows:
TCVO [ ppm / °C ] =
VO (T2 ) – VO (T1 )
VO (25°C ) × (T2 – T1 )
∆VO = VO (t0 ) –VO (t1 )
× 106
∆VO [ ppm ] =
where:
VO (t0 ) –VO (t1 )
VO (t0 )
× 106
where:
VO (25°C) = VO at 25°C.
VO (T1) = VO at Temperature 1.
VO (t0) = VO at Time 0.
VO (T2) = VO at Temperature 2.
VO (t1) = VO after 1,000 hours’ operation at a controlled
temperature.
Line Regulation
Note that 50°C was chosen since most applications we have
experienced run at a higher temperature than 25°C.
The change in output voltage due to a specified change in input
voltage. It includes the effects of self-heating. Line regulation is
expressed in either percent per volt, parts-per-million per volt,
or microvolts per volt change in input voltage.
Thermal Hysteresis
The change of output voltage after the device is cycled through
temperature from +25°C to –40°C to +85°C and back to +25°C.
This is a typical value from a sample of parts put through
such a cycle.
Load Regulation
The change in output voltage due to a specified change in load
current. It includes the effects of self-heating. Load regulation is
expressed in either microvolts per milliampere, parts-permillion per milliampere, or ohms of dc output resistance.
VO_HYS = VO (25°C ) – VO_TC
VO_HYS [ ppm ] =
VO (25°C ) – VO_TC
VO (25°C )
× 106
where:
VO (25°C) = VO at 25°C.
VO_TC = VO at 25°C after temperature cycle at +25°C to –40°C
to +85°C and back to +25°C.
Typical Performance Characteristics
2.054
2.506
2.052
2.504
SAMPLE 1
2.050
2.502
VOUT (V)
VOUT (V)
SAMPLE 2
2.048
SAMPLE 3
2.046
2.042
–40
SAMPLE 2
SAMPLE 3
2.496
–15
10
35
TEMPERATURE (ⴗC)
60
2.494
–40
85
TPC 1. ADR380 Output Voltage vs. Temperature
REV. A
2.500
2.498
2.044
SAMPLE 1
–15
10
35
TEMPERATURE(ⴗC)
60
85
TPC 2. ADR381 Output Voltage vs. Temperature
–5–
ADR380/ADR381
140
30
TEMPERATURE +25ⴗC
–40ⴗC
+85ⴗC
+25ⴗC
120
SUPPLY CURRENT (␮A)
25
FREQUENCY
20
TOTAL NUMBER
OF DEVICES = 130
15
10
5
100
80
–40ⴗC
60
40
20
0
–11 –9 –7 –5 –3 –1
1
3 5 7
PPM (ⴗC)
9
0
2.5
11 13 15 17 19
TPC 3. ADR380 Output Voltage Temperature Coefficient
5.0
7.5
10.0
INPUT VOLTAGE (V)
12.5
15.0
TPC 6. ADR381 Supply Current vs. Input Voltage
60
70
TEMPERATURE +25ⴗC
–40ⴗC
+85ⴗC
+25ⴗC
IL = 0mA TO 5mA
60
40
LOAD REGULATION (ppm/mA)
50
FREQUENCY
+25ⴗC
+85ⴗC
TOTAL NUMBER
OF DEVICES IN
SAMPLE = 450
30
20
10
50
VIN = 3V
40
30
VIN = 5V
20
10
0
–15 –13 –11 –9 –7 –5 –3 –1 1 3
PPM (ⴗC)
5
7
9
0
–40
11 13 15
TPC 4. ADR381 Output Voltage Temperature Coefficient
–15
10
35
TEMPERATURE (ⴗC)
60
85
TPC 7. ADR380 Load Regulation vs. Temperature
70
140
IL = 5mA
+85ⴗC
+25ⴗC
60
LOAD REGULATION (ppm/mA)
SUPPLY CURRENT (␮A)
120
100
80
–40ⴗC
60
40
20
0
2.5
VIN = 3.5V
50
40
VIN = 5V
30
20
10
5.0
7.5
10.0
INPUT VOLTAGE (V)
12.5
0
–40
15.0
TPC 5. ADR380 Supply Current vs. Input Voltage
–15
10
35
TEMPERATURE (ⴗC)
60
85
TPC 8. ADR381 Load Regulation vs. Temperature
–6–
REV. A
ADR380/ADR381
0.8
5
VIN = 2.5V TO 15V
DIFFERENTIAL VOLTAGE (V)
LINE REGULATION (ppm/V)
4
3
2
1
0.6
+85ⴗC
0.4
+25ⴗC
0.2
–40ⴗC
0
–40
–15
10
35
TEMPERATURE (ⴗC)
60
0
85
TPC 9. ADR380 Line Regulation vs. Temperature
0
1
2
3
LOAD CURRENT (mA)
4
5
TPC 12. ADR381 Minimum Input/Output Voltage
Differential vs. Load Current
60
5
TEMPERATURE +25ⴗC
–40ⴗC
85ⴗC
+25ⴗC
VIN = 2.8V TO 15V
50
LINE REGULATION (ppm/V)
4
FREQUENCY
40
3
2
30
20
1
10
0
–40
–15
10
35
TEMPERATURE (ⴗC)
60
0
–260 –200 –140 –80 –20 40 100 160 220 280 340 400
VOUT DEVIATION (ppm)
85
TPC 10. ADR381 Line Regulation vs. Temperature
TPC 13. ADR381 VOUT Hysteresis
DIFFERENTIAL VOLTAGE (V)
0.8
0.6
2␮V/DIV
+85ⴗC
–40ⴗC
0.4
+25ⴗC
0.2
0
0
1
2
3
LOAD CURRENT (mA)
4
5
TIME (1s/DIV)
TPC 11. ADR380 Minimum Input/Output
Voltage Differential vs. Load Current
REV. A
TPC 14. ADR381 Typical Noise Voltage 0.1 Hz to 10 Hz
–7–
ADR380/ADR381
CL = 0␮F
VOUT
100␮V/DIV
1V/DIV
LOAD OFF
VLOAD ON
2V/DIV
LOAD = 1mA
TIME (200␮s/DIV)
TIME (10ms/DIV)
TPC 15. ADR381 Typical Noise Voltage 10 Hz to 10 kHz
TPC 18. ADR381 Load Transient Response with
CL = 0 µ F
CL = 1nF
CBYPASS = 0␮F
VOUT
VOUT
1V/DIV
1V/DIV
LOAD OFF
LINE INTERRUPTION
VIN
0.5V/DIV
VLOAD ON
0.5V/DIV
2V/DIV
LOAD = 1mA
TIME (10␮s/DIV)
TIME (200␮s/DIV)
TPC 16. ADR381 Line Transient Response
TPC 19. ADR381 Load Transient Response with
CL = 1 nF
CL = 100nF
CBYPASS = 0.1␮F
VOUT
VOUT
1V/DIV
1V/DIV
LOAD OFF
LINE INTERRUPTION
0.5V/DIV
VLOAD ON
0.5V/DIV
2V/DIV
LOAD = 1mA
TIME (10␮s/DIV)
TIME (200␮s/DIV)
TPC 17. ADR381 Line Transient Response
TPC 20. ADR381 Load Transient Response with
CL = 100 nF
–8–
REV. A
ADR380/ADR381
150
RL = 500⍀
100
VOUT
50
DRIFT (ppm)
2V/DIV
0
–50
VIN
5V/DIV
–100
CONDITIONS: VIN = 6V IN A CONTROLLED
ENVIRONMENT 50ⴗC ⴞ1ⴗC
–150
0
TIME (200␮s/DIV)
TPC 21. ADR381 Turn-On/Turn-Off Response at 5 V
100
200
300
400
500 600
HOURS
700
800
900
1000
TPC 23. ADR380 Long-Term Drift
150
CB = 0.1␮F
100
50
DRIFT (ppm)
ZOUT (10⍀/DIV)
CL = 40pF
CL = 0.1␮F
CL = 1␮F
0
–50
–100
CONDITIONS: VIN = 6V IN A CONTROLLED
ENVIRONMENT 50ⴗC ⴞ1ⴗC
10
100
1k
10k
FREQUENCY (Hz)
100k
–150
0
1M
TPC 22. ADR381 Output Impedance vs. Frequency
REV. A
100
200
300
400
500 600
HOURS
700
800
TPC 24. ADR381 Long-Term Drift
–9–
900
1000
ADR380/ADR381
THEORY OF OPERATION
Band gap references are the high performance solution for low
supply voltage and low power voltage reference applications,
and the ADR380/ADR381 are no exception. But the uniqueness of this product lies in its architecture. By observing Figure
1, the ideal zero TC band gap voltage is referenced to the
output, not to ground. The band gap cell consists of the PNP
pair Q51 and Q52, running at unequal current densities. The
difference in VBE results in a voltage with a positive TC which is
amplified up by the ratio of 2 × R58/R54. This PTAT voltage,
combined with VBEs of Q51 and Q52, produce the stable band
gap voltage. Reduction in the band gap curvature is performed
by the ratio of the two resistors R44 and R59. Precision laser
trimming and other patented circuit techniques are used to
further enhance the drift performance.
degrade by putting an output capacitor here is turn-on time.
(This will vary depending on the size of the capacitor.) Load
transient response is also improved with an output capacitor. A
capacitor will act as a source of stored energy for a sudden increase in load current.
APPLICATIONS
Stacking Reference ICs for Arbitrary Outputs
Some applications may require two reference voltage sources
which are a combined sum of standard outputs. The following
circuit shows how this stacked output reference can be implemented:
1
VIN
Q1
C2
1␮F
R44
R58
1
R49
R54
C3
0.1␮F
Q51
VOUT2
3
VOUT
–
2
GND
R59
+
VOUT
U2
ADR380/
ADR381
C1
0.1␮F
VIN
VIN
R53
Q52
VOUT
VIN
U1
ADR380/
ADR381
2
VOUT1
C4
1␮F
R1
3.9k⍀
GND
3
R48
R61
R60
Figure 2. Stacking Voltage References with the
ADR380/ADR381
GND
Figure 1. Simplified Schematic
Device Power Dissipation Considerations
The ADR380/ADR381 are capable of delivering load currents
to 5 mA with an input voltage that ranges from 2.8 V (ADR381
only) to 15 V. When this device is used in applications with
large input voltages, care should be taken to avoid exceeding the
specified 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 – TA
θ JA
where:
PD is the device power dissipation,
TJ and TA are junction and ambient temperatures,
respectively, and
θJA is the device package thermal resistance.
Input Capacitor
Input capacitor is not required on the ADR380/ADR381. There
is no limit for the value of the capacitor used on the input, but a
capacitor on the input will improve transient response in applications where the load current suddenly increases.
Output Capacitor
The ADR380/ADR381 do not need an output capacitor for
stability under any load condition. An output capacitor, typically
0.1 µF, will take out any very low level noise voltage, and will
not affect the operation of the part. The only parameter that will
Two ADR380s or ADR381s are used; the outputs of the individual references are simply cascaded to reduce the supply
current. Such configuration provides two output voltages—
VOUT1 and VOUT2. VOUT1 is the terminal voltage of U1, while
VOUT2 is the sum of this voltage and the terminal voltage of U2.
U1 and U2 can be chosen for the two different voltages that
supply the required outputs.
While this concept is simple, a precaution is in order. Since the
lower reference circuit must sink a small bias current from U2,
plus the base current from the series PNP output transistor in
U2, the external load of either U1 or R1 must provide a path for
this current. If the U1 minimum load is not well-defined, the
resistor R1 should be used, set to a value that will conservatively
pass 600 µA of current with the applicable VOUT1 across it. Note
that the two U1 and U2 reference circuits are locally treated as
macrocells, each having its own bypasses at input and output for
optimum stability. Both U1 and U2 in this circuit can source dc
currents up to their full rating. The minimum input voltage, VS,
is determined by the sum of the outputs, VOUT2, plus the
300 mV dropout voltage of U2.
A Negative Precision Reference Without Precision Resistors
In many current-output CMOS DAC applications where the
output signal voltage must be of the same polarity as the reference voltage, it is often required to reconfigure a current-switching
DAC into a voltage-switching DAC through the use of a 1.25 V
reference, an op amp, and a pair of resistors. Using a currentswitching DAC directly requires an additional operational
amplifier at the output to reinvert the signal. A negative voltage
–10–
REV. A
ADR380/ADR381
reference is then desirable from the point that an additional
operational amplifier is not required for either reinversion
(current-switching mode) or amplification (voltage-switching
mode) of the DAC output voltage. In general, any positive
voltage reference can be converted into a negative voltage reference through the use of an operational amplifier and a pair of
matched resistors in an inverting configuration. The disadvantage to this approach is that the largest single source of error in
the circuit is the relative matching of the resistors used.
C1
1␮F
VIN
C1
1␮F
C2
0.1␮F
R4
1k⍀
GND
R3
100k⍀
3
C3
1␮F
A1
+V
–V
R5
100⍀
2
U1
ADR380
C2
0.1␮F
C3
1␮F
ISY
ADJUST
P1
IOUT
Figure 4. A Precision Current Source
Precision High Current Voltage Source
In some cases, the user may want higher output current delivered
to a load and still achieve better than 0.5% accuracy out of the
ADR380/ADR381. The accuracy for a reference is normally
specified on the data sheet with no load. However, the output
voltage changes with load current.
The circuit in Figure 5 provides high current without compromising the accuracy of the ADR380/ADR381. By op amp action,
VO follows VREF with very low drop in R1. To maintain circuit
equilibrium, the op amp also drives the N-Ch MOSFET Q1 into
saturation to maintain the current needed at different loads. R2
is optional to prevent oscillation at Q1. In such an approach, hundreds of milliamps of load current can be achieved and the current
is limited by the thermal limitation of Q1. VIN = VO + 300 mV.
VIN
R1
100k⍀
–VREF
OP195
+8 –15V
–5V
C1
0.001␮F
+V
1
Figure 3. A Negative Precision Voltage Reference
Uses No Precision Resistors
VIN
VOUT
U1
ADR380/
ADR381
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, the ADR380/ADR381 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 (R1 + P1), 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 90 µA to approximately 5 mA.
REV. A
R1
RL
+5V
U2
VOUT
3
C4
1␮F
U1
ADR380
VIN
GND
The circuit 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. A precaution should be noted with
this approach: 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.
2
1 V
IN VOUT
1
VIN
–11–
2
A1
–V
AD820
Q1
2N7002
R2
100⍀
VO
RL
GND
3
Figure 5. ADR380/ADR381 for Precision High
Current Voltage Source
ADR380/ADR381
OUTLINE DIMENSIONS
3-Lead Small Outline Transistor Package [SOT-23-3]
(RT-3)
C02175–0–7/04(A)
Dimensions shown in millimeters
3.04
2.90
2.80
1.40
1.30
1.20
3
1
2.64
2.10
2
PIN 1
0.95 BSC
1.90 BSC
1.12
0.89
0.10
0.01
SEATING
PLANE
0.50
0.30
0.20
0.08
0.60
0.50
0.40
COMPLIANT TO JEDEC STANDARDS TO-236AB
Tape and Reel Dimensions
Dimensions shown in millimeters
4.10
4.00
3.90
1.55
1.50
1.50
2.05
2.00
1.95
8.30
8.00
7.70
7" REEL 100.00
OR
13" REEL 330.00
1.10
1.00
0.90
1.85
1.75
1.65
0.35
0.30
0.25
2.80
2.70
2.60
1.50 MIN
20.20
MIN
14.40 MAX
13.20
13.00
12.80
7" REEL 50.00 MIN
OR
13" REEL 100.00 MIN
3.55
3.50
3.45
3.20
3.10
2.90
1.00 MIN
0.75 MIN
9.90
8.40
8.40
DIRECTION OF UNREELING
Revision History
Location
Page
7/04—Data Sheet Changed from Rev. 0 to Rev. A.
Updated format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal
Changes to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
–12–
REV. A