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LM3940IMP-3.3/NOPB

1A LDO Regulator for 5V-to-3.3V Conversion, 310mV Dropout, SOT-223-4

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Manufacturer Part：

LM3940IMP-3.3/NOPB

Package：

SOT-223-4 (DCY), 6.5mm x 3.5mm

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Description

Product Overview

The LM3940IMP-3.3/NOPB from Texas Instruments is a 1A low-dropout voltage regulator specifically designed for 5V to 3.3V conversion. With a typical dropout voltage of only 310mV at 1A, the device maintains 3.3V output regulation with input voltages as low as 4.5V. Packaged in a SOT-223-4 surface mount format, it requires only two external capacitors for operation and includes built-in thermal overload and short-circuit protection.

Key Specifications

Output Voltage 3.3V (fixed)
Output Current 1A (guaranteed)
Input Voltage Range 4.5V to 5.5V (up to 7.5V abs max)
Dropout Voltage 310mV typical @ 1A
Output Accuracy ±2.5%
Quiescent Current 110uA typical
PSRR 32dB @ 100kHz
Output Noise 150uVrms
Operating Temperature -40°C to +125°C

Features

  • Specifically designed for 5V to 3.3V conversion
  • True LDO: maintains regulation down to 4.5V input
  • Guaranteed 1A output current
  • Requires only one 33uF output capacitor
  • Built-in thermal overload protection
  • Short-circuit current limit protection

Applications

  • 5V to 3.3V logic level conversion
  • Laptop and desktop computers
  • Embedded systems with dual-voltage logic
  • USB-powered 3.3V devices
  • Industrial control systems

The LM3940IMP-3.3/NOPB from Texas Instruments is a 1A low-dropout regulator specifically designed to provide 3.3V from a 5V supply. With a typical dropout voltage of only 310mV at full 1A load, it maintains output regulation with input voltages as low as 4.5V. The SOT-223-4 surface mount package provides excellent power dissipation when soldered to a copper plane on the PCB. Output voltage accuracy is specified at ±2.5% over temperature. The device requires only a 33uF output capacitor for stability and includes comprehensive protection against thermal overload and output short circuits.

The LM3940 uses a PNP pass transistor in a low-dropout configuration. Unlike traditional NPN-based regulators that require the input voltage to be at least 2V above the output, the PNP pass element allows the regulator to operate with only 310mV of headroom at 1A. The internal bandgap reference provides a stable 1.23V reference voltage, which is compared against a divided-down version of the output voltage by the error amplifier. The error amplifier drives the PNP pass transistor to maintain the output at 3.3V. Thermal shutdown activates at approximately 165°C junction temperature, and short-circuit current limit protects against overload conditions.

Pin Name Function
1 OUT Regulated 3.3V output
2 GND Ground (2 tabs internally connected)
3 IN Unregulated input (4.5V to 5.5V)
4 Tab GND (thermal pad, electrically ground)
  • 5V to 3.3V logic voltage conversion in dual-voltage systems
  • Laptop and desktop computer motherboard 3.3V rail generation
  • USB-powered devices requiring stable 3.3V from 5V bus
  • Embedded systems with mixed 5V/3.3V logic families
  • Industrial control equipment power management
Model Notes
LM1117-3.3 800mA alternative, slightly higher dropout
LD1117S33 ST equivalent 800mA LDO
AMS1117-3.3 1A alternative, popular low-cost option
TLV1117-33 TI improved version, 800mA, better accuracy
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