STMicroelectronics L4989D

Overview

L4989D from STMicroelectronics is an AEC-Q100-qualified automotive 5 V low-dropout linear voltage regulator with integrated reset and watchdog functions, delivering up to 150 mA output current, 180 mV typical dropout at 150 mA, ±3% output voltage accuracy, and operation across 5.6 V–31 V input range - used to power microcontroller subsystems in engine control units and body electronics.

For engineers reviewing the L4989D datasheet, L4989D pinout, L4989D application, or L4989D equivalent, this device supports critical automotive safety monitoring via programmable reset delay (via external capacitor on Vcr), adjustable watchdog timeout (via Vcw), and robust thermal/short-circuit protection - all within a compact SO-8 package rated for −40°C to +150°C junction temperature.

Technical Context

The L4989D uses a p-channel MOSFET as its pass element, enabling regulation independent of input transients up to 40 V and maintaining stable 5 V output even during load steps from 1 mA to 150 mA. Its pre-trimmed bandgap reference ensures ±3% output accuracy without external trimming.

Reset functionality monitors Vo down to 1 V with a reaction time as fast as 2 µs below 4 V, while the watchdog circuit responds to missing Wi pulses by discharging an external capacitor (Ctw) with a constant 1.25–5 µA current - generating reset when Vcw crosses programmable thresholds (10–16% and 44–50% of Vo_ref).

Key Specifications

Pinout & Package

Package: SO-8 (8-pin small outline, ECOPACK® compliant, 1.27 mm pitch, 5.0 × 6.0 mm body).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar automotive voltage regulation and supervision applications.

Compared with NCP380LSN33T2G and TLE42754G, the L4989D uniquely integrates AEC-Q100 Grade 0 qualification, 5 V regulation, programmable reset, and watchdog in a single SO-8 package - reducing system-level complexity and enabling ASIL-B–capable supervision without external components.

Availability

L4989D is available at Aetrix Electronics and suitable for engine control units, body control modules, and transmission control units requiring stable component supply across automotive production lifecycles.

Supply support for L4989D 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The L4989D belongs to ST's automotive analog power portfolio, engineered specifically for functional safety-critical 5 V supply and supervision in engine, transmission, and chassis control systems.

FAQ

What is the minimum input voltage required for regulation at full 150 mA load?

The L4989D maintains 5 V regulation at 150 mA with a minimum input voltage of 5.18 V, calculated from its 180 mV typical dropout voltage (Vo + Vdp = 5.0 V + 0.18 V). This enables reliable operation during automotive cold-crank events where battery voltage may dip to 6 V - well within the 5.6 V absolute minimum specified in the datasheet.

How does the reset circuit behave when output voltage falls below 1 V?

The reset output (Res) is guaranteed to remain low only when Vo is above 1 V; below that threshold, the internal comparator is no longer functional and Res behavior is undefined. However, the datasheet specifies a fast 2 µs reset reaction time when Vo drops below 4 V - ensuring rapid fault detection during brownout conditions common in start-stop systems.

Can the watchdog timer be disabled without affecting the reset function?

Yes - asserting WEn low disables only the watchdog circuit while leaving the reset function fully operational. The reset circuit monitors Vo continuously and asserts Res low whenever Vo falls below the threshold (Vo_th), independent of WEn state. This allows designers to retain power-supply supervision while disabling MCU heartbeat monitoring during debug or low-power modes.

What is the recommended capacitor value for Vcr to achieve a 100 ms reset delay?

A 1 nF capacitor on Vcr yields a typical reset delay of 115 ms (within the 65–165 ms range), matching the target 100 ms requirement closely. The delay is calculated as trd = 512 × Tosc, where Tosc depends on internal charge/discharge currents (8–30 µA) and Vcr threshold ratios - making 1 nF the standard value used in ST's reference designs and evaluation schematics.