STMicroelectronics L4947

Overview

L4947 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 L4947 datasheet, L4947 pinout, L4947 application, or L4947 equivalent, key selection considerations include dropout voltage ≤0.75V at 500mA over –40°C to +125°C, reset threshold hysteresis of 50mV, 47µF minimum output capacitor with ESR <10Ω, and compatibility with 100nF external delay capacitor for 10–30ms power-on reset timing.

Technical Context

The L4947 employs a lateral PNP pass transistor to achieve ultra-low dropout (0.4V typ. at 25°C, 0.75V max over full temperature range), enabling stable 5V regulation even when input drops to 6V during automotive cranking. Its internal three-stage gain structure (reference, error amplifier, driver) requires external output capacitance ≥47µF with ESR <10Ω for loop stability.

Reset functionality is implemented via dual-threshold comparators: VRT(on) = VO – 0.04V (L4947) and VRT(off) = VO – 0.15V, yielding 50mV hysteresis; delay time (10–30ms @ Cd = 100nF) is set by charging current Id = 20µA into an external capacitor, with discharge voltage clamped to 0.55–1.20V during power-off.

Key Specifications

Pinout & Package

Package: Pentawatt (5-pin, single-in-line, through-hole). Thermal resistance R_{th j-case} = 3.5°C/W supports 500mA continuous output with minimal heatsinking in automotive PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TL750L05 and MC78T05ABD2TR4, the L4947 delivers unique value through its 0.75V dropout, built-in reset with programmable delay, and certified ±80V load dump resilience-enabling single-chip microprocessor supply in harsh automotive domains without supplemental protection circuitry.

Availability

L4947 is available at Aetrix Electronics and suitable for Engine Control Units, Body Control Modules, Transmission Control Modules, and ADAS Camera ECUs requiring stable component supply under AEC-Q100-aligned manufacturing and traceable sourcing.

Supply support for L4947 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 automotive-grade ICs with vertical fabrication capability.

The L4947 belongs to ST's automotive linear regulator product line, engineered specifically for robust 5V microprocessor supply in engine bay and chassis-mounted ECUs subject to ISO 7637-2 transients and wide thermal excursions.

FAQ

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

The L4947 maintains 5V regulation down to 6V input at 500mA load due to its 0.75V max dropout voltage. Below 6V, output collapses linearly; operation below 6V is not guaranteed per datasheet absolute maximums and electrical characteristics tables.

Can the reset delay be adjusted beyond 30ms?

Yes-delay scales linearly with capacitor value: Td ≈ Cd × 50kΩ. Using 220nF yields ~22–66ms delay; 470nF extends to ~47–141ms. Ensure Cd has low leakage (<100pA) and stable dielectric (e.g., C0G/NP0 ceramic) to maintain accuracy over temperature.

Is an external output capacitor mandatory, and what type is recommended?

Yes-minimum 47µF with ESR <10Ω is mandatory for stability. ST recommends low-ESR tantalum or polymer aluminum capacitors; ceramic capacitors require ≥100µF due to lower effective capacitance at bias. The 20µF minimum cited in some sections applies only to transient stability, not full-loop compensation.

Does the L4947 meet AEC-Q100 qualification requirements?

The L4947 is designed to automotive stress standards including ±80V load dump (ISO 7637-2 Pulse 5), –40°C to +125°C operation, and ESD protection per MIL-STD-883C, but official AEC-Q100 certification status is not declared in the 2000 datasheet. Customers requiring formal AEC-Q100 documentation should consult ST's current automotive product roadmap or contact ST support directly.