STMicroelectronics L4940D2T5

Overview

L4940D2T5 from STMicroelectronics is a fixed +5V, 1.5A low-dropout linear voltage regulator in D2PAK package, featuring 500mV typical dropout at full load, 5–8mA quiescent current, and integrated thermal shutdown, short-circuit, reverse-polarity, and safe-area protection. It enables efficient battery-powered industrial control modules requiring stable 5V rail with minimal input overhead.

For engineers reviewing the L4940D2T5 datasheet, L4940D2T5 pinout, L4940D2T5 application, or L4940D2T5 equivalent, key selection criteria include dropout voltage at 1.5A, output voltage accuracy over temperature (±0.2V), thermal resistance (3°C/W junction-to-case), reverse polarity tolerance (−15V), and SOA-protected current limiting behavior under transient overload.

Technical Context

The L4940D2T5 implements a monolithic bipolar-based series pass architecture with antisaturation circuitry to minimize saturation voltage and sustain regulation down to 500mV input-output differential. Its internal current limiting operates in foldback mode, and thermal shutdown activates at ~150°C junction temperature with hysteresis for safe recovery.

It delivers ±1% initial output voltage accuracy (4.9–5.1V at 500mA) and maintains load regulation within ±25mV across 5mA–1.5A. Line regulation is ±10mV over VI = 6–17V, and supply voltage rejection exceeds 58dB at 120Hz - critical for noise-sensitive analog subsystems powered from noisy DC-DC pre-regulators.

Key Specifications

Pinout & Package

D2PAK (TO-263) surface-mount package with exposed thermal pad; 3-terminal configuration: Input (Pin 1), Ground (Pin 2), Output (Pin 3).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output LDO regulator applications.

Compared with LD1085V50 and TLV1117-50, the L4940D2T5 uniquely combines 1.5A capability, 500mV dropout, and −15V reverse polarity tolerance in D2PAK - making it the sole choice for robust, high-current 5V regulation in battery-backed or field-deployed equipment.

Availability

L4940D2T5 is available at Aetrix Electronics and suitable for industrial PLC I/O modules, portable medical monitors, automotive body control units, and point-of-sale terminals requiring stable component supply with long lifecycle visibility and traceable sourcing.

Supply support for L4940D2T5 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The L4940 series belongs to ST's legacy linear regulator product line, engineered specifically for high-reliability, medium-current applications where fault tolerance, thermal robustness, and minimal dropout are prioritized over ultra-low quiescent current.

FAQ

What is the minimum input voltage required for regulation at 1.5A load?

The L4940D2T5 requires a minimum input voltage of 5.5V to maintain 5.0V output at 1.5A, based on its 500mV typical dropout voltage. At elevated temperatures or worst-case process corners, design margin should allow up to 5.9V input to guarantee regulation across full operating conditions.

Does L4940D2T5 require an external capacitor on the output pin?

Yes - a minimum 22µF low-ESR capacitor (tantalum or ceramic) is mandatory at the output for stability and transient response, per ST's test circuit and application notes. Omitting it risks oscillation or poor load-step recovery, especially under dynamic loads like microcontroller wake-up events.

Can L4940D2T5 be used without a heatsink in free-air conditions?

No - at 1.5A with 2V input-output differential (7V in → 5V out), power dissipation reaches 3W. With D2PAK's 62.5°C/W junction-to-ambient thermal resistance, junction temperature would exceed 200°C. A heatsink reducing R_th(j-a) to ≤25°C/W is required for continuous 1.5A operation.

How does the reverse polarity protection function internally?

The L4940D2T5 integrates a series PNP transistor between IN and the internal pass element. When input is reversed, this transistor remains off, blocking current flow and preventing damage - verified by −15V absolute maximum rating with no external components needed.