STMicroelectronics L4938E

Overview

L4938E from STMicroelectronics is a monolithic dual-output automotive voltage regulator IC with 100mA and 400mA low-dropout outputs, adjustable reset threshold (3.8–4.7V), -5V negative transient protection on EN/SI inputs, and standby quiescent current of 65µA. It supplies microcomputer systems in engine control units and body electronics where dual-rail stability and robust fault supervision are required.

For engineers reviewing the L4938E datasheet, L4938E pinout, L4938E application, or L4938E equivalent, this device supports critical power sequencing, supply monitoring, and fail-safe reset generation in 5V/12V automotive subsystems - especially where input transients, thermal margin, and low-power standby operation must be concurrently managed.

Technical Context

The L4938E integrates two independent LDO regulators: Output 1 (100mA, 5V ±1%) uses an isolated-collector vertical PNP pass element enabling dropout down to 3V input; Output 2 (400mA, 5V ±2% or adjustable via ADJ) shares the same topology but includes enable-controlled shutdown. Both outputs feature internal thermal shutdown with Output 2 deactivating ~10K before Output 1.

Its supervisory functions include a programmable reset circuit (threshold set by PR-to-GND resistor, delay set by CT capacitor), a sense comparator (1.23V reference, ±20V SI input range), and ESD-protected EN/SI inputs rated for -5V negative transients. The reference is supplied from either VS or VOUT1, reducing sensitivity during input transients.

Key Specifications

Pinout & Package

Package: DIP-16 (12+2+2 lead count configuration), 20-pin PowerSO20 and SO20 variants exist but L4938E specifically denotes the DIP package per ordering number.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLF49412GS and MC33FS4500, the L4938E uniquely balances dual independent LDOs, programmable reset, and sense monitoring in a compact DIP package - making it optimal for cost-sensitive, thermally constrained automotive modules needing precise rail separation and fault supervision without communication layers.

Availability

L4938E is available at Aetrix Electronics and suitable for engine control units, body control modules, transmission control units, and ADAS camera ECUs requiring stable component supply across extended temperature and automotive qualification lifecycles.

Supply support for L4938E 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 L4938E belongs to ST's automotive power management portfolio, designed specifically for microcomputer-supplied systems in harsh environments - emphasizing transient resilience, thermal robustness, and integrated supervision for functional safety compliance.

FAQ

What is the maximum allowable input voltage for continuous operation?

The L4938E supports DC operating supply voltage from 5V to 28V continuously. Its transient rating allows up to 40V for durations ≤400ms, covering ISO 7637-2 Pulse 5a load-dump events. Exceeding 28V continuously risks thermal overload and reduced lifetime, even if within absolute maximum ratings.

Can Output 2 be adjusted to voltages other than 5V?

Yes - Output 2 voltage is adjustable using an external resistor divider between ADJ and OUT2. With RADJ (internal) of 60–150kΩ and VOUT1 ≈ 5V, VOUT2 can be set from ~3.3V to ~12V. The formula is VOUT2 = VOUT1 × (1 + R1E(R2E + RADJ)/(R2E × RADJ)), and ADJ must remain capacitively unloaded to preserve loop stability.

How does the sense comparator function in system-level monitoring?

The SI pin connects to an external voltage divider from the main battery rail, comparing the scaled input to a 1.23V internal reference. When SI drops below ~1.16V (falling edge), SO goes low - signaling low-battery condition to the MCU before reset triggers. This enables predictive shutdown, not just fault response.

Is the L4938E still in active production?

No - STMicroelectronics has marked the L4938E series as obsolete (as noted on page 1 of the datasheet). However, Aetrix Electronics maintains legacy inventory with full traceability and offers engineering support for design-in continuity, including cross-reference guidance and long-term supply planning for existing platforms.