Texas Instruments LM3940 LDO Fixed Voltage Regulator 3.3V 1A TO-220

Texas Instruments LM3940 is a 1A fixed 3.3V low-dropout (LDO) voltage regulator in a TO-220 package, designed to deliver a stable 3.3V output from a standard 5V power supply.

Overview

The LM3940 suits mixed-voltage systems that operate with both 5V and 3.3V logic, particularly where primary power is sourced from a 5V bus. As a low-dropout regulator, it maintains 3.3V output regulation with input voltages as low as 4.5V, helping to keep the output stable as the supply voltage sags. The product specifies minimum and maximum output voltage error relative to the nominal 3.3V, along with load regulation across varying conditions.

Key Features

• Internal current limit circuit protects against high-load current faults and short-circuit events, during which it sources a constant current
• Thermal shutdown protection disables the output when excessive heat is dissipated
• If the thermal limit is sustained, the regulator cycles on and off at a high duty cycle until power dissipation is reduced
• Requires only one external component for operation
• Through-hole TO-220 package for straightforward mounting and heat dissipation

Specifications

• Output Type: Fixed
• Output Voltage: 3.3V
• Maximum Output Current: 1A
• Input Voltage Range: 0V to 7.5V (4.5V to 5.5V for specified 3.3V operation)
• Typical Dropout Voltage: 500mV
• Operating Temperature Range: -40°C to +125°C
• Weight: 5.443 g
• Dimensions (Width x Depth x Height): 3.3 x 1.5 x 4.3

Applications

The regulator is intended for mixed-voltage designs that need a 3.3V rail derived from a 5V bus, including systems operating with both 5V and 3.3V logic. Its through-hole TO-220 package suits applications where straightforward mounting and heat dissipation are required. Choose the Texas Instruments LM3940 when a regulated 3.3V supply is needed from a 5V source in a design that requires internal current limit and thermal shutdown protection.