STMicroelectronics L4938ED

Overview

L4938ED from STMicroelectronics is a monolithic dual-voltage regulator IC designed for automotive microcomputer power supply systems, featuring two low-dropout outputs (5 V ±1% @ 100 mA and 5 V ±2% @ 400 mA), adjustable reset threshold (3.8–4.7 V), and integrated sense comparator with -5 V transient protection on EN/SI pins.

For engineers reviewing the L4938ED datasheet, L4938ED pinout, L4938ED application, or L4938ED equivalent, this device supports critical automotive subsystems requiring stable dual-rail regulation, programmable reset supervision, and robust input transient immunity under 40 V transients and -5 V negative spikes.

Technical Context

The L4938ED integrates two independent linear regulators: a 100 mA standby regulator (OUT1) with dropout maintained down to 3 V input and thermal shutdown at ~165 °C, and a 400 mA main regulator (OUT2) with enable-controlled activation and ADJ-pin feedback for fixed or adjustable output configuration. Both regulators share internal reference circuitry supplied by OUT1 above 4.5 V, reducing sensitivity to input transients.

Its functional blocks include a voltage-sense comparator (threshold 1.16 V typ, hysteresis 30 mV), a programmable reset generator (delay 60–140 ms with 47 nF CT), and input protection clamping EN/SI to -5 V. The SO-20 package provides eight GND pins for low-impedance thermal and noise paths, supporting automotive-grade reliability across -40 °C to +150 °C junction temperature.

Key Specifications

Pinout & Package

Package: SO-20 (ECOPACK® compliant, surface-mount, 1.27 mm pitch). Eight dedicated GND pins (pins 4–7, 14–17) provide low-inductance return paths and enhanced thermal dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-output automotive regulator applications.

Compared with TLF49400ESV50 and MAX16910ATP+, the L4938ED uniquely combines dual independently controllable LDOs, programmable reset timing, and integrated sense comparator-enabling consolidated power + supervision functionality in space-constrained automotive ECUs without sacrificing design flexibility.

Availability

L4938ED is available at Aetrix Electronics and suitable for automotive body electronics, instrument cluster systems, and engine control units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for L4938ED 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 qualification coverage.

The L4938ED belongs to ST's automotive power management portfolio, engineered specifically for microcontroller-based vehicle subsystems demanding dual-rail regulation, robust fault supervision, and extended temperature operation.

FAQ

What is the maximum allowable input voltage for continuous operation?

The L4938ED supports continuous DC supply voltage from 5 V to 28 V on VS1 and VS2 pins. Transient operation up to 40 V is permitted for durations ≤400 ms per ISO 7637-2 Pulse 5a, verified in absolute maximum ratings (Table 3). Exceeding 28 V continuously risks thermal overstress and reduced lifetime.

Can OUT2 be configured for an output voltage other than 5 V?

Yes. When the ADJ pin is connected to an external resistor divider between OUT2 and GND, OUT2 becomes adjustable. The datasheet specifies RADJ = 60 kΩ to 150 kΩ range and confirms programmability across typical automotive voltages (e.g., 3.3 V). Fixed 5 V operation requires direct ADJ-to-OUT2 connection.

How does the sense comparator (SI pin) interface with a 12 V battery rail?

The SI pin accepts -20 V to +20 V input but triggers at ~1.16 V internal threshold. To monitor a 12 V battery, a resistor divider (e.g., 100 kΩ/12 kΩ) scales 12 V to ~1.29 V at SI. This enables low-battery detection before MCU brown-out, with SO output signaling status to a GPIO pin.

Is thermal derating required when operating at 400 mA output current?

Yes. With R_thj-amb = 50 °C/W (SO-20), 400 mA at 5 V output into 28 V input yields ~9.2 W dissipation - exceeding the 875 mW ambient-rated limit. Derating requires PCB copper area ≥8 cm², forced airflow, or lowering input voltage. PowerSO-20 package (R_thj-case < 2 °C/W) is recommended for full 400 mA continuous operation.