©2011 Fairchild Semiconductor Corporation
www.fairchildsemi.com
Rev. 1.0.1
Features
• Programmable Output Voltage to 36 Volts
• Low Dynamic Output Impedance 0.2Ω Typical
• Sink Current Capability of 1.0 to 100mA
• Equivalent Full-Range Temperature Coefficient of
50ppm/°C Typical
• Temperature Compensated for Operation Over Full Rated
Operating Temperature Range
• Low Output Noise Voltage
• Fast T urn-on Response
Description
The LM431SAI is three terminal output adjustable regulator
with thermal stability over operating temperature range from
-40°C to +85°C. The output voltage can be set any value
between VREF (approximately 2.5 volts) and 36 volts with
two external resistors. This device has a typical dynamic out-
put impedance of 0.2Ω. Active output circuit provides a
sharp turn-on characteristic, making this device excellent
replacement for Zener Diodes in many applications.
SOT-23F
12
3
1. Cathode 2. Ref 3. Anode
Internal Block Diagram
+
-
LM431SAI
Programmable Shunt Regulator
LM431SAI
2
Absolute Maximum Ratings
(Operating temperature range applies unless otherwise specified.)
Note:
1. Thermal resistance test board
Size: 76.2mm * 114.3mm * 1.6mm (1S0P)
JEDEC Standard: JESD51-3, JESD51-7
2. Assume no ambient airflow.
3. TJMAX = 150°C, Ratings apply to ambient temperature at 25°C
4. Power dissipation calculation: PD = (TJ - TA)/RθJA
Recommended Operating Conditions
Parameter Symbol Value Unit
Cathode Voltage VKA 37 V
Cathode current Range (Continuous) IKA -100 ~ +150 mA
Reference Input Current Range IREF -0.05 ~ +10 mA
Thermal Resistance Junction-Air (Note1,2)
MF Suffix Package RθJA 350 °C/W
Power Dissipation (Note3,4)
MF Suffix Package PD350 mW
Junction Temperature TJ150 °C
Operating Temperature Range TOPR -40 ~ +85 °C
Storage Temperature Range TSTG -65 ~ +150 °C
Parameter Symbol Min. Typ. Max. Unit
Cathode Voltage VKA VREF -36V
Cathode Current IKA 1.0 - 100 mA
LM431SAI
3
Electrical Characteristics
(TA = +25°C, unless otherwise specified)
Note:
1. TMIN = -40°C, TMAX = +85°C
2. The deviation parameters VREF(dev) and IREF(dev)are defined as the differences between the maximum and minimum values
obtained over the rated temperature range. The average full-range temperature coefficient of the reference input voltage,
αVREF, is defined as:
where TMAX -TMIN is the rated operating free-air temperature range of th e device.
αVREF can be positive or negative depending on whether minimum VREF or maximum VREF, respectively , occurs at the lower
temperature.
Example: VREF(dev) = 4.5mV, VREF = 2500 mV at 25 °C, TMAX -TMIN = 125 °C for LM431SAI.
Because minimum VREF occurs at the lower temperature, the coefficient is positive.
Parameter Symbol Conditions LM431SAI Unit
Min. Typ. Max.
Reference Input Voltage VREF VKA=VREF, IKA=10mA 2.450 2.500 2.550 V
Deviation of Reference
Input Voltage Over-
Temperature VREF(dev) VKA=VREF, IKA=10mA
TMIN≤TA≤TMAX -520mV
Ratio of Change in
Reference Input Voltage
to the Change in
Cathode Voltage
Δ
VREF/
Δ
VKA IKA =10mA
Δ
VKA=10V-VREF - -1.0 -2.7
mV/V
Δ
VKA=36V-10V - -0.5 -2.0
Reference Input Current IREF IKA=10mA,
R1=10KΩ,R2=∞-1.54
μ
A
Deviation of Reference
Input Current Over Full
Temperature Range IREF(dev)
IKA=10mA,
R1=10KΩ,R2=∞
TMIN≤TA≤TMAX -0.82
μ
A
Minimum Cathode
Current for Regulation IKA(MIN) VKA=VREF - 0.45 1.0 mA
Off -Stage Cathode
Current IKA(OFF) VKA=36V, VREF=0 - 0.05 1.0
μ
A
Dynamic Impedance ZKA VKA=VREF,
IKA=1 to 100mA ,f ≥1.0kHz - 0.15 0.5 Ω
αVREF ppm
°C
------------
⎝⎠
⎛⎞
VREF dev()
VREF at25°C()
--------------------------------------
⎝⎠
⎛⎞
106
⋅
TMAX TMIN
–
----------------------------------------------------------
=
αVREF
4.5mV
2500mV
-----------------------
⎝⎠
⎛⎞
106
⋅
125°C
------------------------------------------ 14.4ppm °C⁄==
VREF(min)
VREF(max)
TMAX -TMIN
VREF(dev)
LM431SAI
4
Test Circuits
Figure 1. Test Circuit for VKA=VREF Figure 2. Test Circuit for VKA≥VREF
LM431SAI
LM431SAI
LM431SAI
Figure 3. Test Circuit for lKA(OFF)
LM431SAI
5
Typical Performance Characteristics
-2 -1 0 1 2 3
-100
-50
0
50
100
150
VKA = VREF
TA = 25oC
IK, Cathode Current (mA)
VKA, Cathode Voltage (V)
1k 10k 100k 1M 10M
-10
0
10
20
30
40
50
60
TA = 25oC
IKA = 10mA
Open Loop Voltage Gain (dB)
Frequency (Hz)
-10123
-200
0
200
400
600
800
IKA(MIN)
VKA = VREF
TA = 25oC
IKA, CATHODE CURRENT (uA)
VKA, CATHODE VOLTAGE (V)
0 4 8 12 16 20
0
1
2
3
4
5
6
TA=25oC
OUTPUT
INPUT
Voltage Swing (V)
Time (us)
Figure 4. Cathode Current vs. Cathode Voltage Figure 5. Cathode Current vs. Cathode Voltage
Figure 6. Reference Input Voltage vs.
Ambient Temperature Figure7. Reference Input Current vs.
Ambient Temperature
Figure 8. Small Signal Voltage Amplification vs. Frequency Figure 9. Pulse Response
LM431SAI
6
Typical Performance Characteristics (Continued)
100p 1n 10n 100n 1ٛ10
0
20
40
60
80
100
120
140
B
A
A VKA = Vref
B VKA = 5.0 V @ IK = 10mA
TA = 25oC
IK, CATHODE CURRENT(mA)
CL, LOAD CAPACITANCE
Figure 10. Stability Boundary Conditions Figure 11. Anode-Reference Diode Curve
Figure 12. Reference-Cathode Diode Curve
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
1
2
3
4
5
Current(mA)
Anode-Ref. Voltage(V)
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
1
2
3
4
5
Current(mA)
Ref.-Cathode Voltage(V)
stable stable
LM431SAI
7
Typical Application
VO1R1
R2
-------
+
⎝⎠
⎛⎞
Vref
=
LM431SAI
VOVref 1R1
R2
-------
+
⎝⎠
⎛⎞
=
LM431SAI
LM7805/MC7805
VO1R1
R2
-------
+
⎝⎠
⎛⎞
Vref
=
LM431SAI
LM431SAI LM431SAI
Figure 13. Shunt Regulator Figure 14. Output Control for
-Three-Termianl Fixed Regulator Figure 15. High Current Shunt Regulator
Figure 16. Current Limit or Current Source Figure 17. Constant-Current Sink
LM431SAI
8
Mechanical Dimensions
Package Dimensions in millimeters
Marking
SOT-23F
43A
2% tolerance
I
LM431SAI
2/22/11 0.0m 001
Stock#DS400510
© 2011 Fairchild Semiconductor Corporation
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OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body,
or (b) support or sustain life, and (c) whose failure to
perform when properly used in accordance with
instructions for use provided in the labeling, can be
reasonably expected to result in a significant injury of the
user.
2. A critical component in any component of a life support
device or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
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PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRC HILD DOES NOT ASSUME ANY
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Ordering Information
Product Number Output Voltage Tolerance Package Operating Temperature
LM431SAIMFX 2% SOT-23F -40 ~ +85°C
