STMicroelectronics L4947L

Overview

L4947L from STMicroelectronics is a monolithic 5V/0.5A very low-dropout linear voltage regulator in Pentawatt package, featuring integrated power-on reset with externally programmable delay, ±80V load dump protection, reverse voltage protection (–18V), and thermal shutdown with hysteresis-designed for microprocessor supply in automotive engine control units during cranking (Vi ≥ 6V).

For engineers reviewing the L4947L datasheet, L4947L pinout, L4947L application, or L4947L equivalent, key selection considerations include dropout voltage ≤0.75V at 500mA over –40°C to +125°C, reset threshold hysteresis of 50mV, output voltage accuracy of ±4%, 80V transient immunity, and external capacitor–programmed reset delay timing.

Technical Context

The L4947L uses a lateral PNP pass transistor to achieve ultra-low dropout (0.4V typ. at 25°C, 0.75V max. over full temperature range at 500mA), enabling stable operation during automotive battery cranking. Its internal architecture integrates error amplifier, reference, driver stage, and dedicated reset comparator with programmable delay via external capacitor Cd.

Protection functions are hardware-asserted: load dump clamping at ±80V (5ms rise/fall), field decay suppression (±80V, τr = 33ms), reverse polarity blocking up to –18V, short-circuit current limiting (0.5–1.5A), and thermal shutdown with hysteresis. Reset logic asserts active-low signal when Vo drops below VRT(off) (4.70V for L4947 variant) and releases after delay upon crossing VRT(on).

Key Specifications

Pinout & Package

Supplied in Pentawatt (5-pin, single-in-line) package with heat sink tab (pin 3). Package dimensions comply with STMicroelectronics mechanical drawing: L ≈ 17.7mm, W ≈ 6.7mm, H ≈ 4.5mm, lead pitch 2.54mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar automotive LDO with reset applications.

Compared with TL750L05ACD and MAX6495ATA+T, the L4947L uniquely combines ±80V load dump, –18V reverse polarity tolerance, and 0.75V max dropout in a through-hole Pentawatt package-making it the only option qualified for direct replacement in legacy automotive ECU designs requiring cranking compatibility and minimal BOM count.

Availability

L4947L is available at Aetrix Electronics and suitable for Engine Control Units, Body Control Modules, Transmission Control Units, and ADAS Sensor Hubs requiring stable component supply across extended temperature and harsh electrical environments.

Supply support for L4947L 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, Switzerland, specializing in automotive, industrial, and power management ICs with vertical manufacturing and AEC-Q100 qualification expertise.

The L4947L belongs to ST's automotive-grade linear regulator family, engineered specifically for engine bay–mounted electronic control units needing cranking resilience, transient robustness, and integrated system supervision.

FAQ

What is the minimum input voltage required for regulation at full 500mA load?

The L4947L maintains 5V regulation down to 5.75V input (5.0V + 0.75V dropout) across –40°C to +125°C. At 25°C, dropout is typically 0.4V, allowing regulation from 5.4V. This enables reliable operation during automotive cranking when battery voltage dips to 6V, with margin for line drop and ripple.

How is the power-on reset delay time determined and what capacitor value yields 20ms?

The reset delay T_d is set by an external capacitor C_d connected between RESET pin and ground. For T_d = 20ms (typical mid-range), a 100nF capacitor is specified at 25°C. The delay scales linearly with capacitance; doubling C_d doubles T_d. Temperature variation adds ±30% tolerance over full range.

Does the L4947L require an input capacitor, and what are the stability requirements for the output capacitor?

No input capacitor is mandatory, but a 1µF ceramic is recommended for high-frequency decoupling. The output capacitor must be ≥47µF with ESR <10Ω (ideally <3Ω) to ensure loop stability. Aluminum or tantalum types meeting these specs are acceptable; low-ESR polymer capacitors are preferred for extended life at high temperature.

Can the RESET pin drive a microcontroller directly, and what pull-up configuration is required?

Yes, the RESET pin is an open-collector NPN output rated for 1.6mA sink at 0.4V saturation. It requires an external pull-up resistor to V_OUT; 1kΩ is standard per datasheet test conditions. Driving 3.3V or 5V logic is supported, but the pull-up must connect to the same regulated rail used by the MCU to maintain valid voltage referencing during brown-out.