STMicroelectronics L4947H

Overview

L4947H 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, thermal shutdown with hysteresis, and short-circuit protection-designed for automotive microprocessor supply during cranking (down to 6V input).

For engineers reviewing the L4947H datasheet, L4947H pinout, L4947H application, or L4947H equivalent, key selection considerations include dropout voltage ≤0.75V at 500mA over –40°C to +125°C, reset threshold hysteresis of 50mV, 5V ±4% output accuracy, and compatibility with 20µF minimum output capacitor (ESR <10Ω) for stability.

Technical Context

The L4947H uses a lateral PNP pass transistor to achieve ultra-low dropout (typ. 0.4V at 25°C, max. 0.75V across full temperature range at 500mA), enabling reliable operation during automotive battery cranking. Its internal three-stage gain structure (reference, error amplifier, driver) requires external output capacitance ≥20µF with ESR <10Ω for loop stability.

The reset function implements dual-threshold supervision: power-on reset triggers when V_O crosses V_RT(on) = V_O − 0.04V (L4947 variant), followed by a capacitor-programmable delay; power-off reset asserts low at V_RT(off) = V_O − 0.15V, with 50mV hysteresis. Delay timing is set by external capacitor C_d, with charging current fixed at 20µA.

Key Specifications

Pinout & Package

Package: Pentawatt (5-pin, single-in-line, through-hole). Thermal resistance junction-to-case is 3.5°C/W, enabling direct heatsinking via mounting tab.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TL750L05 and MC78T05BD2TR4, the L4947H integrates reset timing, ±80V load dump immunity, and 0.75V dropout-reducing component count by three devices while enabling cranking-down-to-6V operation essential for modern automotive ECUs.

Availability

L4947H is available at Aetrix Electronics and suitable for engine control units, body control modules, instrument clusters, and telematics control units requiring stable component supply across automotive production lifecycles.

Supply support for L4947H 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, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets.

The L4947H belongs to ST's automotive-grade linear regulator product line, engineered specifically for microprocessor power supply in harsh environments where cranking resilience, transient immunity, and integrated supervision are mandatory.

FAQ

What is the minimum output capacitor required for stable operation?

The L4947H requires a minimum 20µF output capacitor with ESR <10Ω over the full temperature range. ST recommends 47µF tantalum or low-ESR aluminum electrolytic capacitors to ensure phase margin >45° across –40°C to +125°C and all load conditions.

How is the power-on reset delay time calculated?

Reset delay T_d is determined by external capacitor C_d and internal 20µA charging current: T_d ≈ C_d × V_d / 20µA, where V_d is the delay comparator threshold (3.65–4.35V). For C_d = 100nF, typical delay is 20ms at 25°C, varying ±15% over temperature.

Does the L4947H support reverse battery connection?

Yes-the L4947H incorporates reverse voltage protection up to –18V DC. When input polarity is reversed, internal circuitry blocks conduction, preventing damage to the regulator and downstream loads without requiring external diodes or MOSFETs.

What thermal derating applies above 125°C junction temperature?

The L4947H features thermal shutdown with hysteresis and is rated for junction temperatures up to +150°C. Above +125°C, output current must be reduced linearly: at +150°C, maximum safe output is 300mA with R_th(j-case) = 3.5°C/W and case temperature held ≤100°C via heatsink.