LM431: 3-Terminal Adjustable Shunt Regulator

Overview

The LM431 is a precision 3-terminal adjustable shunt regulator designed to provide excellent temperature stability and performance across its entire operating range. This component allows the output voltage to be set to any value greater than 2.5V (V_REF) up to 36V by using an external resistor divider network. The LM431 is an ideal replacement for zener diodes in many applications due to its sharp turn-on characteristics and superior performance.

This device is widely used in power supplies, voltage references, and other precision regulation applications where stable and accurate voltage control is required. Its temperature-compensated design ensures reliable operation in varying environmental conditions.

Features

• Adjustable Output Voltage: Programmable from 2.5V to 36V using external resistors.
• Temperature Stability: Average temperature coefficient of 50 ppm/°C ensures consistent performance over a wide temperature range.
• Low Output Noise: Provides clean and stable voltage regulation for sensitive circuits.
• Fast Turn-On Response: Sharp switching characteristics make it suitable for dynamic applications.
• High Accuracy: Available in multiple tolerance grades (0.5%, 1%, and 2%) to meet precision requirements.
• Wide Operating Range: Functions reliably across industrial and commercial temperature ranges.
• Multiple Package Options: Available in TO-92, SO-8, and SOT-23 packages for flexibility in design.

Applications

The LM431 is a versatile component suitable for a wide range of applications, including:

• Voltage Regulation: Used in power supplies to provide stable reference voltages.
• Switching Power Supplies: Enhances efficiency and accuracy in DC-DC converters.
• Precision References: Ideal for analog circuits requiring stable voltage references.
• Battery Chargers: Ensures accurate voltage control in charging circuits.
• Error Amplifiers: Provides feedback control in regulation loops.
• Zener Diode Replacement: Offers superior performance compared to traditional zeners.

Electrical Characteristics

Absolute Maximum Ratings

• Cathode Voltage (V_KA): 37V
• Cathode Current (I_KA): 100mA (continuous), 200mA (peak)
• Reference Input Current (I_REF): 10mA
• Operating Temperature Range: 0°C to +70°C (commercial), -40°C to +85°C (industrial)
• Storage Temperature Range: -65°C to +150°C

Typical Performance Characteristics

• Reference Voltage (V_REF): 2.495V (typical)
• Temperature Coefficient: 50 ppm/°C (average)
• Dynamic Impedance: 0.2Ω (typical at I_KA = 10mA)
• Minimum Cathode Current for Regulation (I_KA(min)): 1mA
• Output Noise Voltage: 20μV (typical, 10Hz to 10kHz)

Package Information

The LM431 is available in multiple package options to suit various design requirements:

TO-92 (Plastic Package)

• Order Numbers: LM431ACZ, LM431AIZ, LM431BCZ, LM431BIZ, LM431CCZ, LM431CIZ
• Package Type: Through-hole, 3-pin
• Dimensions: Standard TO-92 outline

SO-8 (8-Pin Surface Mount)

• Order Numbers: LM431ACM, LM431AIM, LM431BCM, LM431BIM, LM431CCM, LM431CIM
• Package Type: Surface-mount, 8-pin
• Dimensions: Standard SO-8 outline

SOT-23 (3-Lead Small Outline)

• Order Numbers: LM431ACM3, LM431AIM3, LM431BCM3, LM431BIM3, LM431CCM3, LM431CIM3
• Package Type: Surface-mount, 3-pin
• Dimensions: Compact SOT-23 outline

Ordering Information

The LM431 is available in different accuracy grades and temperature ranges:

• 0.5% Accuracy: LM431ACZ (TO-92, 0°C to +70°C), LM431AIM (SO-8, -40°C to +85°C)
• 1% Accuracy: LM431BCZ (TO-92, 0°C to +70°C), LM431BIM (SO-8, -40°C to +85°C)
• 2% Accuracy: LM431CCZ (TO-92, 0°C to +70°C), LM431CIM (SO-8, -40°C to +85°C)

Conclusion

The LM431 is a highly reliable and flexible shunt regulator that offers precision voltage regulation, excellent temperature stability, and a wide range of applications. Its adjustable output, low noise, and fast response make it a preferred choice for designers seeking robust voltage control solutions. With multiple package options and accuracy grades, the LM431 can be tailored to meet the specific needs of various electronic systems.