STMicroelectronics L387AH

Overview

L387AH from STMicroelectronics is a very low dropout 5 V linear voltage regulator with integrated reset function, housed in a Pentawatt® package. It delivers ≥500 mA output current, maintains ±4% output accuracy (4.75–5.25 V) over –40°C to +125°C, and features a programmable reset delay via external capacitor. It is used in microprocessor-based systems requiring reliable power-on reset and battery-efficient operation.

For engineers reviewing the L387AH datasheet, L387AH pinout, L387AH application, or L387AH equivalent, key selection criteria include dropout voltage at 500 mA (≤0.8 V), reset threshold hysteresis (450 mV), thermal resistance (4°C/W), and compatibility with low-ESR output capacitors (≤3 Ω).

Technical Context

The L387AH integrates a precision 5 V bandgap reference, low-dropout pass transistor, and a dual-threshold reset comparator with hysteresis on the V4 input pin. Its reset logic asserts low during power-off and transitions high after a user-programmable delay (e.g., 25 ms with 100 nF) upon power-up.

It operates across 6.2 V to 26 V input range, sustains full load (500 mA) with ≤0.8 V dropout, and achieves 60 dB supply voltage rejection at 120 Hz. The device uses internal current limiting and thermal shutdown for fault protection.

Key Specifications

Pinout & Package

Packaged in Pentawatt® (5-pin, single-in-line, through-hole), with heatsink tab connected to Pin 2 (GND). Package thermal resistance is 4°C/W junction-to-case, enabling >500 mA operation without forced airflow when mounted on ≥2 cm² copper pour.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS76350QDBVRQ1 and MAX809SEUR+T, the L387AH uniquely combines ≥500 mA regulation, sub-0.8 V dropout, and user-adjustable reset delay in one Pentawatt® package-enabling compact, battery-optimized designs without external components.

Availability

L387AH is available at Aetrix Electronics and suitable for industrial PLC I/O modules, automotive body control units, portable medical monitors, and smart energy meters requiring stable component supply and long-term lifecycle support.

Supply support for L387AH 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 sensing solutions for industrial, automotive, and consumer markets.

The L387AH belongs to ST's legacy linear regulator family targeting cost-sensitive, reliability-critical embedded systems where integration of reset and regulation reduces BOM count and board space.

FAQ

What is the minimum output capacitor value required for stability?

The L387AH requires a minimum 33 µF aluminum or tantalum capacitor with ESR ≤3 Ω across the operating temperature range. Ceramic capacitors are not recommended unless series resistance is added to meet ESR requirements, as low-ESR ceramics may cause instability per the datasheet test conditions.

How does the reset delay time scale with capacitor value?

Reset delay (t_d) scales approximately linearly with capacitor value on Pin 4: t_d ≈ 0.25 × C_d (ms/nF). For example, 100 nF yields ~25 ms, 470 nF yields ~118 ms. This relationship holds across –40°C to +125°C, with ±20% tolerance due to process variation.

Can the L387AH be used with input voltages below 6.2 V?

No. The L387AH requires a minimum input voltage of 6.2 V to maintain regulation and reset functionality. Below this, output voltage collapses and reset behavior becomes undefined. For lower-input applications, consider ultra-low-V_in regulators like the AP2112K-5.0.

Is the reset output compatible with 3.3 V logic interfaces?

Yes. The open-collector VR pin can sink up to 16 mA and is rated for 0.5–0.8 V low-level output when loaded with a 3.3 V pull-up. It directly interfaces with 3.3 V CMOS/TTL reset inputs without level-shifting, provided the pull-up resistor is sized for ≤16 mA total current.