ETC ADR390ART

a
Precision Low Drift 2.048 V/2.500 V
SOT-23 Voltage References with Shutdown
ADR390/ADR391
PIN CONFIGURATION
5-Lead SOT-23
(RT Suffix)
FEATURES
Load Regulation: 60 ppm/mA
Line Regulation: 25 ppm/V
Wide Operating Range:
2.4 V–18 V for ADR390
2.8 V–18 V for ADR391
Low Power: 120 ␮A Max
Shutdown to Less than 3 ␮A Max
High Output Current: 5 mA Min
Wide Temperature Range: ⴚ40ⴗC to +85ⴗC
Tiny SOT-23-5 Package
APPLICATIONS
Battery-Powered Instrumentation
Portable Medical Instruments
Data Acquisition Systems
Industrial and Process Control Systems
Hard Disk Drives
Automotive
SHDN 1
VIN
2
5
GND
4
VOUT (FORCE)
ADR390/
ADR391
(Not to Scale)
VOUT (SENSE) 3
Table I. ADR39x Products
Part
Number
Output
Voltage (V)
Initial Accuracy
mV
%
Tempco
ppm/ⴗC, Max
ADR390
ADR391
2.048
2.500
±6
±6
25
25
± 0.29
± 0.24
GENERAL DESCRIPTION
The ADR390 and ADR391 are precision 2.048 V and 2.5 V
bandgap voltage references featuring high accuracy and 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 with additional shutdown capability
make them ideal for 3 V to 5 V battery-powered applications.
The VOUT Sense Pin enables greater accuracy by supporting full
Kelvin operation in systems using very fine or long circuit traces.
The ADR390 and ADR391 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. Each is available
in the tiny 5-lead SOT-23 package.
The combination of VOUT sense and shutdown functions also
enables a number of unique applications combining precision
reference/regulation with fault decision and overcurrent protection. Details are provided in the Applications section.
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
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: www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001
ADR390/ADR391
ADR390 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
(@ VIN = 5 V, TA = 25ⴗC unless otherwise noted.)
Parameter
Symbol
Output Voltage
Initial Accuracy
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
∆VO/∆VIN
Load Regulation
∆VO/∆ILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
Shutdown Supply Current
Shutdown Logic Input Current
Shutdown Logic Low
Shutdown Logic High
eN
tR
∆VO
VO_HYS
RRR
ISC
ISHDN
ILOGIC
VINL
VINH
Conditions
Min
Typ
2.042
–6
–0.29
2.048 2.054
+6
+0.29
5
25
3
21
300
V
mV
%
ppm/°C
ppm/°C
mV
10
25
ppm/V
100
60
120
140
ppm/mA
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
µA
nA
V
V
–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
Max
5
20
50
40
85
30
See Figure 1
fIN = 60 Hz
3
500
0.8
2.4
Unit
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS
(@ VIN = 15 V, TA = 25ⴗC unless otherwise noted.)
Parameter
Symbol
Output Voltage
Initial Accuracy
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
∆VO/∆VIN
Load Regulation
∆VO/∆ILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
Shutdown Supply Current
Shutdown Logic Input Current
Shutdown Logic Low
Shutdown Logic High
eN
tR
∆VO
VO_HYS
RRR
ISC
ISHDN
ILOGIC
VINL
VINH
Conditions
Min
Typ
2.042
–6
–0.29
2.048 2.054
+6
+0.29
5
25
3
21
300
V
mV
%
ppm/°C
ppm/°C
mV
10
25
ppm/V
100
60
120
140
ppm/mA
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
µA
nA
V
V
–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
Max
5
20
50
40
85
30
See Figure 1
fIN = 60 Hz
3
500
0.8
2.4
Unit
Specifications subject to change without notice.
–2–
REV. A
ADR390/ADR391
ADR391 SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (@ V
IN
= 5 V, TA = 25ⴗC unless otherwise noted).
Parameter
Symbol
Output Voltage
Initial Accuracy
VO
∆VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
∆VO/∆VIN
Load Regulation
∆VO/∆ILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
Shutdown Supply Current
Shutdown Logic Input Current
Shutdown Logic Low
Shutdown Logic High
eN
tR
∆VO
VO_HYS
RRR
ISC
ISHDN
ILOGIC
VINL
VINH
Conditions
Min
Typ
Max
Unit
2.494
–6
–0.24
2.5
2.506
+6
+0.24
25
21
V
mV
%
ppm/°C
ppm/°C
mV
10
25
ppm/V
100
60
120
140
ppm/mA
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
µA
nA
V
V
–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
5
3
300
5
20
50
75
85
25
See Figure 1
fIN = 60 Hz
3
500
0.8
2.4
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS
(@ VIN = 15 V, TA = 25ⴗC unless otherwise noted.)
Parameter
Symbol
Output Voltage
Initial Accuracy
VO
VOERR
Temperature Coefficient
TCVO
Minimum Supply Voltage Headroom
Line Regulation
VIN – VO
∆VO/∆VIN
Load Regulation
∆VO/∆ILOAD
Quiescent Current
IIN
Voltage Noise
Turn-On Settling Time
Long-Term Stability
Output Voltage Hysteresis
Ripple Rejection Ratio
Short Circuit to GND
Shutdown Supply Current
Shutdown Logic Input Current
Shutdown Logic Low
Shutdown Logic High
eN
tR
∆VO
VO_HYS
RRR
ISC
ISHDN
ILOGIC
VINL
VINH
Conditions
Typ
Max
Unit
2.494
–6
–0.24
2.5
2.506
+6
+0.24
25
21
V
mV
%
ppm/°C
ppm/°C
mV
10
25
ppm/V
100
60
120
140
ppm/mA
µA
µA
µV p-p
µs
ppm
ppm
dB
mA
µA
nA
V
V
–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
5
3
300
5
20
50
75
85
30
See Figure 1
fIN = 60 Hz
3
500
0.8
2.4
Specifications subject to change without notice.
REV. A
Min
–3–
ADR390/ADR391
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
Shutdown Logic Level . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V
Or Supply Voltage, Whichever is Lower . . . . . . . . . . . . 18 V
Output Short-Circuit Duration to GND . . . . . . . . . . Indefinite
Storage Temperature Range
RT Package . . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Operating Temperature Range
ADR390/ADR391 . . . . . . . . . . . . . . . . . . –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
␪JA*
␪JC
Unit
5-Lead SOT-23 (RT)
230
–
°C/W
*θJA is specified for worst-case conditions, i.e., θJA is specified for device in
socket for SOT packages.
*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 listed in the operational sections
of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ORDERING GUIDE
Model
Temperature
Range
Package
Description
Package
Option
Top
Mark
Output
Voltage
Number of
Parts Per Reel
ADR390ART–REEL7
ADR390ART–REEL
–40⬚C to +85⬚C
–40⬚C to +85⬚C
5-Lead SOT
5-Lead SOT
RT-5
RT-5
R0A
R0A
2.048
2.048
3,000
10,000
ADR391ART–REEL7
ADR391ART–REEL
–40⬚C to +85⬚C
–40⬚C to +85⬚C
5-Lead SOT
5-Lead SOT
RT-5
RT-5
R1A
R1A
2.500
2.500
3,000
10,000
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 ADR390/ADR391 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–
WARNING!
ESD SENSITIVE DEVICE
REV. A
ADR390/ADR391
transient response can be improved with an additional 1 µF to
10 µF output capacitor in parallel. A capacitor here will act as a
source of stored energy for sudden increase in load current. The
only parameter that will degrade, by adding an output capacitor,
is turn-on time and it depends on the size of the capacitor chosen.
PARAMETER DEFINITION
Temperature Coefficient (TCV O)
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 =
( ) ( ) × 10
(25°C ) × (T − T )
VO T2 − VO T1
VO
Where:
2
Long Term Stability
6
Typical shift in output voltage over 1000 hours at a controlled
temperature. Figure 1 shows a sample of parts measured at
different intervals in a controlled environment of 50°C for
1000 hours.
1
VO(25⬚C) = VO at 25⬚C.
∆VO = VO (t0 ) − VO (t1 )
VO(T1) = VO at temperature1.
VO(T2) = VO at temperature2.
[
]
∆VO ppm =
Line Regulation (∆VO /∆VIN)
VO (t0 ) − VO (t1 )
VO (t0 )
Where:
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.
VO(t0) = VO at at time 0.
VO(t1) = VO after 1000 hours operation at a controlled
temperature.
Load Regulation (∆VO /∆ILOAD)
Thermal Hysteresis (VO_HYS)
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-per-million
per milliampere, or Ω of dc output resistance.
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.
VO _ HYS = VO 25o C − VO _ TC
Input Capacitor
Input capacitors are not required on the ADR390/ADR391. 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 will improve transient
response in applications where the supply suddenly changes. An
additional 0.1 µF in parallel will also help reducing noise from
the supply.
VO _ HYS
( )
V (25°C ) − V
[ ppm] = V (25°C )
O
VO_TC = VO at 25⬚C after temperature cycle at +25⬚C to
–40⬚C to +85⬚C and back to +25⬚C.
200
DATA TAKEN IN CONTROLLED
ENVIRONMENT @ 50ⴗC ⴞ 1ⴗC
150
DRIFT – ppm
100
50
0
ⴚ50
ⴚ100
86
176
250
324
440
TIME – Hours
640
840
1040
Figure 1. ADR391 Typical Long-Term Drift over 1000 Hours
REV. A
× 106
VO(25⬚C) = VO at 25⬚C.
The ADR390/ADR391 does not need output capacitors for
stability under any load condition. An output capacitor, typically 0.1 µF, will filter out any low-level noise voltage and will
not affect the operation of the part. On the other hand, the load
0
O _ TC
O
Where:
Output Capacitor
ⴚ150
× 106
–5–
ADR390/ADR391–Typical Performance Characteristics
140
2.054
SAMPLE 1
2.052
SUPPLY CURRENT – ␮A
120
VOUT – V
2.050
2.048
SAMPLE 2
2.046
2.044
2.042
ⴚ40
+85ⴗC
100
+25ⴗC
ⴚ40ⴗC
80
60
SAMPLE 3
ⴚ15
10
35
TEMPERATURE – ⴗC
60
40
2.5
85
5.0
7.5
10.0
INPUT VOLTAGE – V
12.5
15.0
TPC 4. ADR391 Supply Current vs. Input Voltage
TPC 1. ADR390 Output Voltage vs. Temperature
2.506
40
IL= 0mA TO 5mA
LOAD REGULATION – ppm/mA
2.504
SAMPLE 1
VOUT – V
2.502
SAMPLE 2
2.500
2.498
SAMPLE 3
2.496
2.494
ⴚ40
35
30
VIN = 3.0V
25
VIN = 5.0V
20
15
ⴚ15
10
35
TEMPERATURE – ⴗC
60
10
ⴚ40
85
TPC 2. ADR391 Output Voltage vs. Temperature
ⴚ15
10
35
TEMPERATURE – ⴗC
60
85
TPC 5. ADR390 Load Regulation vs. Temperature
140
40
IL= 0mA TO 5mA
LOAD REGULATION – ppm/mA
SUPPLY CURRENT – ␮A
120
+85ⴗC
100
+25ⴗC
ⴚ40ⴗC
80
60
40
2.5
35
30
VIN = 3.5V
25
VIN = 5.0V
20
15
5.0
7.5
10.0
INPUT VOLTAGE – V
12.5
10
ⴚ40
15.0
TPC 3. ADR390 Supply Current vs. Input Voltage
ⴚ15
10
35
TEMPERATURE – ⴗC
60
85
TPC 6. ADR391 Load Regulation vs. Temperature
–6–
REV. A
ADR390/ADR391
0.8
5
4
DIFFERENTIAL VOLTAGE – V
LINE REGULATION – ppm/V
VIN = 2.5V TO 15V
3
2
1
0
ⴚ40
ⴚ15
0.6
+85ⴗC
+25ⴗC
0.4
ⴚ40ⴗC
0.2
0
10
35
TEMPERATURE – ⴗC
60
85
0
1
2
3
LOAD CURRENT – mA
TPC 10. ADR391 Minimum Input-Output Voltage
Differential vs. Load Current
TPC 7. ADR390 Line Regulation vs. Temperature
60
5
TEMPERATURE: +25ⴗC
VIN = 2.8V TO 15V
ⴚ40ⴗC
+85ⴗC
+25ⴗC
50
4
40
3
FREQUENCY
LINE REGULATION – ppm/V
5
4
2
30
20
1
10
0
ⴚ40
ⴚ15
10
35
TEMPERATURE – ⴗC
60
0
ⴚ0.24 ⴚ0.18 ⴚ0.12 ⴚ0.06
0
0.06 0.12
VOUT DEVIATION – mV
85
TPC 8. ADR391 Line Regulation vs. Temperature
0.18
0.24
0.30
TPC 11. ADR390 VOUT Hysteresis Distribution
70
0.8
TEMPERATURE: +25ⴗC
ⴚ40ⴗC
+85ⴗC
+25ⴗC
0.6
50
FREQUENCY
DIFFERENTIAL VOLTAGE – V
60
ⴚ40ⴗC
0.4
+85ⴗC
+25ⴗC
40
30
20
0.2
10
0
0
1
2
3
LOAD CURRENT – mA
4
0
ⴚ0.56
5
ⴚ0.26
ⴚ0.11
0.04
VOUT DEVIATION – mV
0.19
0.34
TPC 12. ADR391 VOUT Hysteresis Distribution
TPC 9. ADR390 Minimum Input-Output Voltage
Differential vs. Load Current
REV. A
ⴚ0.41
–7–
ADR390/ADR391
0
1k
VIN = 5V
CBYPASS = 0␮F
VOLTAGE NOISE DENSITY – nV/ Hz
0
0
LINE
INTERRUPTION
0.5V/DIV
VOLTAGE
0
ADR391
0
VOUT
ADR390
1V/DIV
0
0
100
0
10
100
1k
FREQUENCY – Hz
10k
TIME – 10␮s/DIV
TPC 16. ADR391 Line Transient Response
TPC 13. Voltage Noise Density vs. Frequency
0
0
0
0
0
0
0
0
VOLTAGE
VOLTAGE – 2␮V/DIV
CBYPASS = 0.1␮F
0
0.5V/DIV
LINE
INTERRUPTION
0
0
0
0
0
0
0
VOUT
1V/DIV
0
0
TIME – 10␮s/DIV
TIME – 1 Sec/DIV
TPC 14. ADR391 Typical Voltage Noise 0.1 Hz to 10 Hz
TPC 17. ADR391 Line Transient Response
0
0
0
0
0
0
VOLTAGE – 1V/DIV
VOLTAGE – 100␮V/DIV
CL = 0nF
0
0
0
VOUT
0
0
VLOAD ON
LOAD OFF
0
0
0
0
0
0
0
TIME – 10ms/DIV
TIME – 200␮s/DIV
TPC 18. ADR391 Load Transient Response
TPC 15. ADR391 Voltage Noise 10 Hz to 10 kHz
–8–
REV. A
ADR390/ADR391
0
0
CL = 1nF
VIN = 15V
VOUT
0
0
0
0
0
VOLTAGE
VOLTAGE – 1V/DIV
0
0
LOAD OFF
0
5V/DIV
VOUT
2V/DIV
0
0
VLOAD ON
0
0
0
0
0
VIN
0
TIME – 200␮s/DIV
TIME – 40␮s/DIV
TPC 19. ADR391 Load Transient Response
TPC 22. ADR391 Turn-Off Response at 15 V
0
0
CL = 100nF
0
CBYPASS = 0.1␮F
VOUT
0
0
2V/DIV
VOUT
0
VOLTAGE
VOLTAGE – 1V/DIV
0
0
LOAD OFF
0
0
0
0
VLOAD ON
VIN
0
0
0
0
0
5V/DIV
0
TIME – 200␮s/DIV
TIME – 200␮s/DIV
TPC 20. ADR391 Load Transient Response
TPC 23. ADR391 Turn-On/Turn-Off Response at 5 V
0
0
VIN = 15V
RL = 500⍀
0
0
5V/DIV
0
0
2V/DIV
0
VOLTAGE
VOLTAGE
VOUT
VIN
0
0
VOUT
2V/DIV
0
0
0
VIN
0
0
0
0
0
0
TIME – 20␮s/DIV
TIME – 200␮s/DIV
TPC 21. ADR391 Turn-On Response Time at 15 V
REV. A
5V/DIV
TPC 24. ADR391 Turn-On/Turn-Off Response at 5 V
–9–
ADR390/ADR391
THEORY OF OPERATION
0
0
VOLTAGE – 5V/DIV
Bandgap references are the high-performance solution for low
supply voltage and low power voltage reference applications,
and the ADR390/ADR391 is no exception. The uniqueness of
this product lies in its architecture. By observing Figure 2, the
ideal zero TC bandgap voltage is referenced to the output, not to
ground. Therefore, if noise exists on the ground line, it will be
greatly attenuated on VOUT. The bandgap 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
RL = 500⍀
CL = 100nF
0
2V/DIV
VOUT
0
0
0
5V/DIV
VIN
0
R58
. This PTAT
R54
voltage, combined with VBEs of Q51 and Q52 produce the stable
bandgap voltage.
which is amplified up by the ratio of 2 ×
0
0
TIME – 200␮s/DIV
TPC 25. ADR391 Turn-On/Turn-Off Response at 5 V
Reduction in the bandgap curvature is performed by the ratio of
the resistors R44 and R59, one of which is linearly temperature
dependent. Precision laser trimming and other patented circuit
techniques are used to further enhance the drift performance.
80
VIN
60
Q1
RIPPLE REJECTION – dB
40
VOUT (FORCE)
VOUT (SENSE)
20
R59
R44
0
ⴚ20
R58
R49
ⴚ40
R54
ⴚ60
ⴚ80
SHDN
Q51
ⴚ100
R53
Q52
ⴚ120
10
100
1k
10k
FREQUENCY – Hz
100k
1M
R48
R60
R61
TPC 26. Ripple Rejection vs. Frequency
GND
Figure 2. Simplified Schematic
Device Power Dissipation Considerations
100
The ADR390/ADR391 is capable of delivering load currents to
5 mA with an input voltage that ranges from 2.8 V (ADR391 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:
90
OUTPUT IMPEDANCE – ⍀
80
70
60
CL = 0␮F
50
40
PD =
30
20
CL = 1␮F
10
0
10
100
1k
10k
FREQUENCY – Hz
CL = 0.1␮F
100k
TPC 27. Output Impedance vs. Frequency
1M
TJ − TA
θ JA
In this equation, TJ and TA are, respectively, the junction and
ambient temperatures, PD is the device power dissipation, and
θJA is the device package thermal resistance.
Shutdown Mode Operation
The ADR390/ADR391 includes a shutdown feature that is TTL/
CMOS level compatible. A logic LOW or a zero volt condition on
the SHDN pin is required to turn the device off. During shutdown,
the output of the reference becomes a high impedance state where
its potential would then be determined by external circuitry. If the
shutdown feature is not used, the SHDN pin should be connected
to VIN (Pin 2).
–10–
REV. A
ADR390/ADR391
APPLICATIONS
BASIC VOLTAGE REFERENCE CONNECTION
The circuit in Figure 3 illustrates the basic configuration for the
ADR39x family. Decoupling capacitors are not required for circuit stability. The ADR39x family is capable of driving capacitive
loads from 0 µF to 10 µF. However, a 0.1 µF ceramic output
capacitor is recommended to absorb and deliver the charge as is
required by a dynamic load.
SHUTDOWN
SHDN
GND
ADR39x
INPUT
CB
VIN
*
0.1␮F
VOUT(S) VOUT(F)
OUTPUT
*
CB
* NOT REQUIRED
0.1␮F
Figure 3.
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:
ADR390/ADR390
ADR391/ADR391
VIN
C1
0.1␮F
VOUT1 (V) VOUT2 (V)
2.048
2.5
4.096
5.0
2 U2
VIN
1
VOUT(F) 4
SHDN
VOUT(S)
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 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 (currentswitching 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.
A Negative Precision Reference without Precision Resistors
OUTPUT TABLE
U1/U2
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 best
stability. Both U1 and U2 in this circuit can source dc currents up to
their full rating. The minimum input voltage, VIN, is determined by
the sum of the outputs, VOUT2, plus the dropout voltage of U2.
A negative reference can be easily generated by adding an op
amp, A1 and configured as Figure 5 below. VOUTF and VOUTS
are 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.
VOUT2
VDD
3
GND
2
5
VIN
4 V
OUT(F)
2 U1
VIN
C2
0.1␮F
1
VOUT(F) 4
3
VOUT(S)
VOUT1
SHDN
VOUT(S) 3
SHDN
ADR39x
GND
5
R1
3.9k⍀
GND
–VDD
Figure 4. Stacking Voltage References with the ADR390/
ADR391
Two reference ICs are used, fed from an unregulated input,
VIN. The outputs of the individual ICs are simply connected in
series which 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 are simply
chosen for the two voltages that supply the required outputs (see
Output Table). For example, if both U1 and U2 are ADR391s,
VOUT1 is 2.5 V and VOUT2 is 5.0 V.
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, either the external load of U1 or R1 must provide a path for
this current. If the U1 minimum load is not well defined, the
REV. A
–VREF
A1
5
A1 = OP777, OP193
Figure 5.
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 the following figure, the ADR390/ADR391 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 90 µA to approximately 5 mA.
–11–
ADR390/ADR391
The transistor Q2 protects Q1 during short circuit limit faults by
robbing its base drive. The maximum current is ILMAX ≈ 0.6 V/RS.
R1
4.7k⍀
VIN
U1
SHDN
GND
VIN
VOUT (FORCE)
VIN
VOUT (SENSE)
ADR390/ADR391
Q1
Q2N4921
Q2
Q2N2222
RS
SHDN
VOUT
RL
ADR39x
VIN
VOUT
R1
R1
GND
ISY
ADJUST
P1
IOUT
}
IL
C00419–2.5–4/01(A)
The ADR390/ADR391 includes a shutdown feature that is
TTL/CMOS level compatible. A logic LOW or a zero volt
condition on the SHDN pin is required to turn the device off.
During shutdown, the output of the reference becomes a highimpedance state where its potential would then be determined
by the external circuitry. If the shutdown feature is not used, the
SHDN pin should be connected to VIN (Pin 2).
Figure 7. ADR390/ADR391 for High-Power Performance
with Current Limit
A similar circuit function can also be achieved with the Darlington
transistor configuration, see Figure 8.
RSET
R1
4.7k⍀
VIN
RL
U1
SHDN
GND
VIN
Figure 6. A Precision Current Source
Q2N2222
VOUT (FORCE)
High-Power Performance with Current Limit
Q1
Q2
VOUT (SENSE)
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
ADR390/ADR391. The accuracy for a reference is normally
specified on the data sheet with no load. However, the output
voltage changes with load current.
ADR390/ADR391
Q2N4921
RS
RL
Figure 8. ADR390/ADR391 High Output Current with
Darlington Drive Configuration
The circuit below provides high current without compromising
the accuracy of the ADR390/ADR391. The series pass transistor Q1 provides up to 1 A load current. The ADR390/ADR391
delivers only the base drive to Q1 through the force pin. The
sense pin of the ADR390/ADR391 is a regulated output and is
connected to the load.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
PRINTED IN U.S.A.
5-Lead SOT-23
(RT Suffix)
0.1181 (3.00)
0.1102 (2.80)
0.0669 (1.70)
0.0590 (1.50)
5
1
4
2
0.1181 (3.00)
0.1024 (2.60)
3
PIN 1
0.0374 (0.95) BSC
0.0748 (1.90)
BSC
0.0512 (1.30)
0.0354 (0.90)
0.0059 (0.15)
0.0019 (0.05)
0.0079 (0.20)
0.0031 (0.08)
0.0571 (1.45)
0.0374 (0.95)
0.0197 (0.50)
0.0138 (0.35)
SEATING
PLANE
–12–
10ⴗ
0ⴗ
0.0217 (0.55)
0.0138 (0.35)
REV. A