STMicroelectronics L4979D

Overview

L4979D from STMicroelectronics is an AEC-Q100 qualified automotive low-dropout linear voltage regulator with integrated microprocessor supervisory functions - including voltage reset, watchdog timer, and enable control - delivering 5.0 V ±2% output at up to 150 mA. It operates from 5.6 V to 31 V input, achieves <400 mV dropout at full load, and features 6 µA quiescent current in shutdown mode. Used in engine control units (ECUs) for stable MCU power and fault monitoring.

For engineers reviewing the L4979D datasheet, L4979D pinout, L4979D application, or L4979D equivalent, key selection criteria include its automotive-grade thermal range (−40 °C to 150 °C junction), programmable reset delay via external capacitor, watchdog timeout adjustability, and SO-8 package compatibility with space-constrained ECU PCB layouts.

Technical Context

The L4979D integrates a p-channel MOSFET pass element enabling low dropout (<400 mV at 150 mA) while maintaining regulation across wide input (5.6–31 V) and temperature (−40 °C to 150 °C) ranges. Its on-chip trimmed bandgap reference ensures ±2% output accuracy over line, load, and temperature.

Reset functionality monitors Vo with a threshold set at 6–10% below nominal output; delay is programmable via external capacitor on Vcr. Watchdog operation relies on Wi edge detection and Vcw-based timing, where discharge/charge currents (8–30 µA) define timeout windows scalable from milliseconds to hundreds of milliseconds.

Key Specifications

Pinout & Package

Available in SO-8 package (ECOPACK® compliant), with exposed thermal pad connected to GND pins (pins 2, 5, 6, 15, 16 in SO-20 variant). Pin 1 is Enable (En); pin 3 is open-drain Reset (Res); pins 4 and 5 are Vcr and Vcw for reset/watchdog timing capacitors; pin 7 is Vo; pin 8 is Vs. Ground pins serve dual role as electrical reference and thermal conduction paths.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV70733PDRVR and MAX6326US31D3+, the L4979D uniquely combines 5 V LDO regulation, AEC-Q100 qualification, programmable reset, and watchdog in a single SO-8 package - eliminating BOM count, layout area, and inter-IC timing uncertainty in automotive ECUs.

Availability

L4979D is available at Aetrix Electronics and suitable for engine control units, body control modules, and transmission control units requiring stable component supply with automotive-grade reliability and long-term lifecycle support.

Supply support for L4979D 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 analog, microcontroller, power, and automotive ICs since 1987.

The L4979D belongs to ST's automotive power management portfolio, engineered specifically for intelligent, fault-tolerant voltage regulation in engine, chassis, and safety-critical electronic control units.

FAQ

What is the maximum allowable input voltage for continuous operation?

The L4979D supports continuous DC input up to 31 V per operating specifications. Its absolute maximum rating is 40 V, allowing brief exposure to automotive load-dump transients without damage - however sustained operation above 31 V risks thermal overload and is outside guaranteed performance limits.

How does the reset function respond when output voltage falls below 1 V?

The reset circuit remains fully functional down to Vo = 1 V, guaranteeing Res assertion. Below 1 V, the reset reaction time accelerates to 2 µs (vs. typical 100–700 µs), ensuring rapid fault signaling during severe undervoltage conditions such as battery disconnection or catastrophic short circuits.

Can the watchdog timer be disabled independently of the voltage regulator?

No - the watchdog circuit is enabled or disabled synchronously with the regulator via the En pin. When En = low, both regulator output and watchdog monitoring are shut down, reducing total current to 6 µA. There is no separate watchdog disable control.

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

Yes - a minimum 100 nF ceramic capacitor is required between Vo and GND for stability. ST recommends X7R or C0G dielectric types with low ESR (<100 mΩ) placed within 5 mm of Vo and GND pins; larger values (e.g., 1–10 µF) improve transient response but do not replace the mandatory 100 nF unit.