LM431 Adjustable Precision Zener Shunt Regulator
March 2002
LM431 Adjustable Precision Zener Shunt Regulator
General Description
The LM431 is a 3-terminal adjustable shunt regulator with guaranteed temperature stability over the entire temperature range of operation. It is now available in a chip sized package (4-Bump micro SMD) using National’s micro SMD package technology. The output voltage may be set at any level greater than 2.5V (VREF) up to 36V merely by selecting two external resistors that act as a voltage divided network. Due to the sharp turn-on characteristics this device is an excellent replacement for many zener diode applications.
Features
n Average temperature coefficient 50 ppm/˚C n Temperature compensated for operation over the full temperature range n Programmable output voltage n Fast turn-on response n Low output noise n LM431 in micro SMD package n See AN-1112 for micro SMD considerations
Connection Diagrams
TO-92: Plastic Package SOT-23: 3-Lead Small Outline
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Top View 4-Bump micro SMD
Top View SO-8: 8-Pin Surface Mount
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Top view
Top View (bump side down)
Note: *NC = Not internally connected. Must be electrically isolated from the rest of the circuit for the microSMD package.
© 2002 National Semiconductor Corporation
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LM431
Ordering Information
Package TO-92 Typical Accuracy Order Number/Package Marking 0.5% LM431CCZ/ LM431CCZ LM431CIZ/ LM431CIZ SO-8 LM431CCM/ 431CCM LM431CIM/ 431CIM SOT-23 LM431CCM3/ N1B LM431CIM3 N1A micro SMD – 1% LM431BCZ/ LM431BCZ LM431BIZ/ LM431BIZ LM431BCM/ 431BCM LM431BIM/ 431BIM LM431BCM3/ N1D LM431BIM3 N1C – 2% LM431ACZ/ LM431ACZ LM431AIZ/ LM431AIZ LM431ACM/ LM431ACM LM431AIM/ LM431AIM LM431ACM3/ N1F LM431AIM3 N1E LM431AIBP LM431AIBPX(Note 1) Temperature Range 0˚C to +70˚C Rails −40˚C to +85˚C 0˚C to +70˚C Rails and Tape &Reel −40˚C to +85˚C 0˚C to +70˚C Rails and Tape &Reel −40˚C to +85˚C −40˚C to +85˚C 250 Units Tape and Reel BPA04AFB 3k Units Tape and Reel MF03A M08A Z03A Transport Media NSC Drawing
Note 1: The micro SMD package marking is a 1 digit manufacturing Date Code only
micro SMD Top View Marking Example
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Symbol and Functional Diagrams
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DC Test Circuits
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FIGURE 1. Test Circuit for VZ = VREF
Note: VZ = VREF (1 + R1/R2) + IREF • R1
FIGURE 2. Test Circuit for VZ > VREF
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FIGURE 3. Test Circuit for Off-State Current
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LM431
Absolute Maximum Ratings (Note 2)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range Operating Temperature Range Industrial (LM431xI) Commercial (LM431xC) Soldering Information Infrared or Convection (20 sec.) Wave Soldering (10 sec.) Cathode Voltage Continuous Cathode Current −65˚C to +150˚C −40˚C to +85˚C 0˚C to +70˚C 235˚C 260˚C (lead temp.) 37V −10 mA to +150 mA
Reference Voltage Reference Input Current Internal Power Dissipation (Notes 3, 4) TO-92 Package SO-8 Package SOT-23 Package micro SMD Package
−0.5V 10 mA 0.78W 0.81W 0.28W 0.30W
Operating Conditions
Cathode Voltage Cathode Current Min VREF 1.0 mA Max 37V 100 mA
LM431 Electrical Characteristics
TA = 25˚C unless otherwise specified Symbol VREF Parameter Reference Voltage Conditions VZ = VREF, II = 10 mA LM431A (Figure 1 ) VZ = VREF, II = 10 mA LM431B (Figure 1 ) VZ = VREF, II = 10 mA LM431C (Figure 1 ) VDEV Deviation of Reference Input Voltage Over Temperature (Note 5) Ratio of the Change in Reference Voltage to the Change in Cathode Voltage IREF ∝IREF Reference Input Current Deviation of Reference Input Current over Temperature IZ(MIN) IZ(OFF) rZ Minimum Cathode Current for Regulation Off-State Current Dynamic Output Impedance (Note 6) VZ = VREF, II = 10 mA, TA = Full Range (Figure 1 ) IZ = 10 mA VZ from VREF to 10V VZ from 10V to 36V −1.4 −1.0 2.0 −2.7 −2.0 4.0 µA mV/V 8.0 17 mV 2.485 2.500 2.510 V 2.470 2.495 2.520 V Min 2.440 Typ 2.495 Max 2.550 Units V
(Figure 2 )
R1 = 10 kΩ, R2 = ∞, II = 10 mA (Figure 2 ) R1 = 10 kΩ, R2 = ∞, II = 10 mA, TA = Full Range (Figure 2 ) VZ = VREF (Figure 1 ) VZ = 36V, VREF = 0V (Figure 3 ) VZ = VREF, LM431A, Frequency = 0 Hz (Figure 1 ) VZ = VREF, LM431B, LM431C Frequency = 0 Hz (Figure 1 )
0.4 0.4 0.3
1.2 1.0 1.0 0.75 0.50
µA mA µA Ω Ω
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its rated operating conditions. Note 3: TJ Max = 150˚C. Note 4: Ratings apply to ambient temperature at 25˚C. Above this temperature, derate the TO-92 at 6.2 mW/˚C, the SO-8 at 6.5 mW/˚C, the SOT-23 at 2.2 mW/˚C and the micro SMD at 3mW/˚C. Note 5: Deviation of reference input voltage, VDEV, is defined as the maximum variation of the reference input voltage over the full temperature range.
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LM431
LM431 Electrical Characteristics
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The average temperature coefficient of the reference input voltage, ∝VREF, is defined as:
Where: T2 − T1 = full temperature change (0-70˚C). ∝VREF can be positive or negative depending on whether the slope is positive or negative. Example: VDEV = 8.0 mV, VREF = 2495 mV, T2 − T1 = 70˚C, slope is positive.
Note 6: The dynamic output impedance, rZ, is defined as:
When the device is programmed with two external resistors, R1 and R2, (see Figure 2 ), the dynamic output impedance of the overall circuit, rZ, is defined as:
Equivalent Circuit
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LM431
Typical Performance Characteristics
Input Current vs VZ Thermal Information Input Current vs VZ
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Dynamic Impedance vs Frequency
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Stability Boundary Conditions
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Note: The areas under the curves represent conditions that may cause the device to oscillate. For curves B, C, and D, R2 and V+ were adjusted to establish the initial VZ and IZ conditions with CL = 0. V+ and CL were then adjusted to determine the ranges of stability.
Test Circuit for Curve A Above
Test Circuit for Curves B, C and D Above
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Typical Applications
Shunt Regulator Single Supply Comparator with Temperature Compensated Threshold
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Series Regulator
Output Control of a Three Terminal Fixed Regulator
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Higher Current Shunt Regulator
Crow Bar
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LM431
Typical Applications
(Continued) Over Voltage/Under Voltage Protection Circuit
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Voltage Monitor
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Typical Applications
(Continued) Current Limiter or Current Source
Delay Timer
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Constant Current Sink
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Application Info
1.0 Mounting To ensure that the geometry of the micro SMD package maintains good physical contact with the printed circuit board, pin A1 (NC) must be soldered to the pcb. Please see AN-1112 for more detailed information regarding board mounting techniques for the micro SMD package.
2.0 LM431 micro SMD Light Sensitivity When the LM431 micro SMD package is exposed to bright sunlight, normal office fluorescent light, and other LED’s and lasers, it operates within the guaranteed limits specified in the electrical characteristics table.
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LM431
Physical Dimensions
inches (millimeters) unless otherwise noted
NS Package Number M08A
SOT-23 Molded Small Outline Transistor Package (M3) NS Package Number MF03A
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LM431
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
NS Package Number Z03A
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LM431 Adjustable Precision Zener Shunt Regulator
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
NOTES: UNLESS OTHERWISE SPECIFIED 1. EPOXY COATING 2. 63Sn/37Pb EUTECTIC BUMP 3. RECOMMEND NON-SOLDER MASK DEFINED LANDING PAD. 4. PIN A1 IS ESTABLISHED BY LOWER LEFT CORNER WITH RESPECT TO TEXT ORIENTATION. REMAINING PINS ARE NUMBERED. 5. XXX IN DRAWING NUMBER REPRESENTS PACKAGE SIZE VARIATION WHERE X1 IS PACKAGE WIDTH, X2 IS PACKAGE LENGTH AND X3 IS PACKAGE HEIGHT. 6. REFERENCE JEDEC REGISTRATION MO-211, VARIATION BA. 4-Bump micro SMD X1 = 0.777 X2 = 0.904 X3 = 0.850 NS Package Number BPA04AFB
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