STMicroelectronics L4979MD

Overview

L4979MD from STMicroelectronics is an AEC-Q100 qualified automotive low-dropout linear voltage regulator with integrated microprocessor supervisory functions - including voltage reset, programmable watchdog timer, and enable-controlled shutdown. It delivers a precise 5.0 V ±2% output at up to 150 mA, operates from 5.6 V to 31 V input, achieves <400 mV dropout at full load, and features 6 µA quiescent current in disable mode. It is used in engine control units (ECUs) and body control modules requiring robust power sequencing and fault monitoring.

For engineers reviewing the L4979MD datasheet, L4979MD pinout, L4979MD application, or L4979MD equivalent, this page provides verified technical context, SO-20 package mapping, reset/watchdog timing design values, thermal derating guidance, and validated automotive-grade alternatives for functional safety-critical power management.

Technical Context

The L4979MD integrates a p-channel MOSFET pass element enabling low-dropout operation (<400 mV at 150 mA) while maintaining regulation across 5.6–31 V input and -40 °C to 150 °C junction temperature. Its internal bandgap reference and on-chip trimming ensure ±2% output accuracy over line, load, and temperature.

Reset functionality monitors Vo down to 1 V with programmable delay (via external C_tr), while the watchdog circuit responds to missing Wi pulses using a sawtooth waveform generated by constant-current charge/discharge of C_tw. Both RES and EN are fully compatible with 5 V logic interfaces.

Key Specifications

Pinout & Package

Package: SO-20 (ECOPACK®, RoHS-compliant, 10.0–10.65 mm × 7.4–7.6 mm × 2.35–2.65 mm height). Thermal resistance R_{th j-amb} = 50–80 °C/W depending on PCB copper area (up to 6 cm²).

Key Features

Applications

Equivalent & Alternatives

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

Compared with NCP380LSN33T2G and TLE42754G, the L4979MD uniquely combines 5 V precision regulation, programmable reset delay, and configurable watchdog in a single SO-20 package - reducing BOM count and enabling higher diagnostic coverage for ISO 26262 ASIL-B systems.

Availability

L4979MD is available at Aetrix Electronics and suitable for engine control units, body control modules, ADAS camera ECUs, and electric power steering controllers requiring stable component supply with automotive-grade lifecycle assurance.

Supply support for L4979MD 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 broad AEC-Q100 product portfolios.

The L4979MD belongs to ST's automotive power management family, designed specifically for intelligent voltage regulation and functional safety supervision in harsh-temperature vehicle subsystems.

FAQ

What is the maximum allowable input voltage for continuous operation?

The L4979MD supports continuous DC input from 5.6 V to 31 V. Its absolute maximum rating is 40 V, allowing it to survive automotive load-dump transients without external protection. Operation above 31 V is not recommended for sustained use due to thermal limits and reduced dropout margin.

How does the reset circuit respond when output voltage drops below 1 V?

The reset circuit guarantees activation only down to Vo = 1 V. Below that threshold, the internal comparator may not operate reliably, and RES behavior is unspecified. For systems requiring reset assertion below 1 V, external supervision or a secondary reset IC is necessary.

Can the watchdog timer be disabled while keeping the regulator active?

No - the EN pin controls all functions simultaneously. When EN is high, regulator, reset, and watchdog are all enabled. There is no independent watchdog disable mode; disabling EN halts all three functions and reduces quiescent current to 6 µA.

What is the minimum output capacitance required for stability?

A minimum 100 nF ceramic capacitor is required between Vo and GND for regulator stability. ST recommends ≥1 µF for improved transient response and noise rejection, especially in noisy automotive environments with CAN/LIN bus coupling.