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L4940D2T5-TR

1.5A 5V LDO, 450mV Vdo@1A, D2PAK, reverse polarity, thermal shutdown, 68dB PSRR

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Manufacturer Part：

L4940D2T5-TR

Package：

D2PAK / TO-263-3 (10.30 x 8.70 x 4.50 mm, exposed tab)

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Description

Product Overview

The L4940D2T5-TR from STMicroelectronics is a 1.5A, 5V fixed-output very low dropout voltage regulator in a D2PAK (TO-263) package. With 450mV typical dropout at 1A and reverse polarity protection, it targets battery-powered and automotive power supply applications.

Key Specifications

Output Voltage 5.0 V (+/-2% over line, load, temperature)
Output Current 1.5 A
Input Voltage Up to 17 V
Dropout Voltage 450 mV typical at 1 A, 900 mV max at 1.5 A
Quiescent Current 5 mA typical at light load
PSRR 68 dB typical at 120Hz, 1A
Short-Circuit Current 2.7 A typical
Operating Temperature -40C to +150C (junction)

Features

  • 5V fixed output at 1.5A in D2PAK surface-mount package
  • 450mV typical dropout at 1A for efficient battery-powered operation
  • +/-2% output voltage tolerance over line, load, and temperature
  • Internal current limiting, anti-saturation circuit, and thermal shutdown
  • Reverse polarity protection for automotive battery installation safety
  • 68dB PSRR at 120Hz for clean output from rectified AC sources

Applications

  • Automotive 5V power supply with reverse polarity protection
  • Battery-powered equipment 5V regulation with low dropout
  • Industrial control 5V supply from 12V/24V input
  • Post-regulation after switching converter for clean 5V output

The L4940D2T5-TR from STMicroelectronics is a 1.5A, 5V fixed-output very low dropout positive voltage regulator in a D2PAK (TO-263-3) surface-mount package. The L4940 series is specifically designed for battery-powered equipment, offering very low input-to-output voltage drop to reduce consumption and prolong battery life. The 450mV typical dropout voltage at 1A output current allows the regulator to maintain 5V output from input voltages as low as 5.45V, making efficient use of battery capacity. The D2PAK package with exposed thermal tab provides excellent thermal performance, enabling full 1.5A output current with appropriate PCB copper heatsinking. The device employs internal current limiting with anti-saturation circuit to protect against output overload and short circuits. The thermal shutdown circuit disables the regulator when the junction temperature exceeds the safe limit, providing protection against excessive power dissipation. Reverse polarity protection prevents damage from incorrect battery installation. The 68dB PSRR at 120Hz effectively rejects input ripple from rectified AC sources. The +/-2% output voltage accuracy is maintained over the full input voltage, output current, and temperature range.

The L4940D2T5-TR uses a PNP pass transistor low-dropout regulator topology. (1) PNP Pass Element: The PNP transistor connects between input and output. Unlike NPN-pass regulators that require at least 2-3V headroom (VBE + VCEsat + VBE), the PNP pass element requires only the VCEsat voltage, achieving the low 450mV typical dropout. (2) Voltage Regulation: An internal bandgap reference generates a stable voltage. The error amplifier compares a fraction of the output voltage with the reference and drives the PNP base to maintain regulation. (3) Anti-Saturation Circuit: When the input-to-output differential is very low, the PNP transistor approaches saturation, which can cause excessive ground current. The anti-saturation circuit limits the base drive to prevent deep saturation, controlling the ground current increase in dropout conditions. (4) Current Limiting: An internal current-sensing circuit monitors the output current and limits it to approximately 2.7A during overload conditions. (5) Thermal Shutdown: A temperature sensor monitors the junction temperature. When it exceeds approximately 150C, the pass transistor is turned off. After cooling below the hysteresis threshold, regulation resumes. (6) Reverse Polarity: An internal circuit blocks reverse current flow when the input voltage is negative, protecting the regulator and the load.

Pin Name Type Function
1 IN Power Input supply (up to 17V)
2 GND Ground Ground (tab, thermal contact)
3 OUT Output Regulated 5V output
  • Automotive 5V power supply with reverse polarity protection in D2PAK
  • Battery-powered equipment 5V regulation with 450mV low dropout at 1A
  • Industrial control 5V supply from 12V/24V input at 1.5A with 68dB PSRR
  • Post-regulation after switching converter for clean 5V output at +/-2%
Manufacturer Part Number Package Notes
ST L4940V5 TO-220 Through-hole version
ST L4940D2T12-TR D2PAK 12V output version
TI LM2940T-5.0 TO-220 1A, 5V, similar LDO
onsemi NCP1117DT50RKG DPAK 1A, 5V, LDO
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