STMicroelectronics L387A

Overview

L387A from STMicroelectronics is a very low dropout 5 V linear voltage regulator with integrated reset generator, designed for microprocessor supply and supervision in battery-powered and industrial systems. It delivers ≥500 mA output current, maintains ±4% output accuracy (4.75–5.25 V) over –40°C to +125°C, features 0.40 V dropout at 350 mA, and provides programmable power-on reset delay via external capacitor.

For engineers reviewing the L387A datasheet, L387A pinout, L387A application, or L387A equivalent, this page details its regulated 5 V output, reset timing behavior, thermal performance in Pentawatt® package, and suitability for embedded microcontroller power sequencing where low quiescent current (5–160 mA) and high noise immunity on reset delay are critical.

Technical Context

The L387A integrates a precision bandgap-referenced 5 V regulator and an independent reset circuit with hysteresis on the delay capacitor node to reject ground bounce. Its internal architecture includes a current-limited pass transistor, temperature-compensated error amplifier, and comparator-based reset generator with dual thresholds (VRT(on)/VRT(off)) and 450 mV hysteresis.

Reset assertion occurs at power-on after a capacitor-programmable delay (e.g., 25 ms with 100 nF), and deasserts at power-off when output falls below VRT(off). The device operates across 6.2 V to 26 V input, supports up to 35 V absolute max input, and maintains regulation down to 0.65 V dropout at 500 mA.

Key Specifications

Pinout & Package

The L387A is housed in a Pentawatt® (5-pin, single-in-line) thermally enhanced package with exposed metal tab for heatsinking. Pin 1 is Input, Pin 2 is Ground, Pin 3 is Output, Pin 4 is Reset Delay Capacitor (CD), Pin 5 is Reset Output (RESET).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 5 V LDO-with-reset applications.

Compared with TPS76350 and MAX809, the L387A uniquely combines ≥500 mA regulation, programmable reset delay, and power-off reset in one Pentawatt® package - eliminating BOM count and layout complexity in space-constrained microprocessor systems.

Availability

L387A is available at Aetrix Electronics and suitable for industrial PLC I/O modules, portable medical monitors, automotive body control units, and smart energy meters requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for L387A 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, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The L387A belongs to ST's legacy linear regulator portfolio targeting cost-sensitive, high-reliability embedded systems where integration of regulation and reset simplifies power architecture and improves robustness.

FAQ

What is the minimum input voltage required for regulation at full 500 mA load?

The L387A requires Vi ≥ Vo + dropout = 5.0 V + 0.65 V = 5.65 V to maintain regulation at 500 mA. Its specified operating input range starts at 6.2 V to guarantee performance across temperature and process variation, with 0.40 V dropout confirmed at 350 mA and 25°C.

Can the reset delay be adjusted beyond the 25 ms typical value shown in the datasheet?

Yes - delay time scales linearly with capacitor value on Pin 4 (CD). With td ≈ 0.25 × Cd (ms/nF), a 470 nF capacitor yields ~118 ms delay. The internal charging current (10–30 µA) varies with temperature, so design margins should account for ±20% timing variation over –40°C to +125°C.

Is the RESET output compatible with 3.3 V logic microcontrollers?

Yes - RESET is open-collector with 0.5 V max saturation voltage at 3 mA sink current. When pulled up to 3.3 V via external resistor, it delivers valid low-level signaling to 3.3 V I/O. Leakage remains ≤50 µA when high, ensuring compatibility with weak pull-ups.

Does the L387A require an input bypass capacitor?

While not explicitly mandated, ST recommends ≥1 µF ceramic capacitor at the IN pin to suppress high-frequency noise and improve transient response. This is especially critical when using long PCB traces or high-impedance sources like batteries or unregulated switchers, as instability may occur without local decoupling.