STMicroelectronics L9777A

Overview

L9777A from STMicroelectronics is a monolithic low-dropout voltage regulator delivering up to 200 mA on VCC (5 V ±2 %) and up to 100 mA on switchable VDD, with integrated dual reset (NMI and RESET), adjustable undervoltage threshold, watchdog monitoring, and overtemperature/short-circuit protection - designed for automotive microprocessor power supply under harsh conditions (VI = 5.6 V to 31 V, TJ = −40 °C to +150 °C).

For engineers reviewing the L9777A datasheet, L9777A pinout, L9777A application, or L9777A equivalent, this device supports critical automotive subsystems requiring stable 5 V regulation, programmable reset timing, fault-tolerant watchdog supervision, and robust thermal/electrical protection across wide input voltage and temperature ranges.

Technical Context

The L9777A implements a primary 5 V LDO regulator (VCC) with 2 % accuracy and <400 mV dropout at full load, plus a tracking VDD regulator enabled via VDD_EN pin. Its reset architecture features two independent outputs: NMI (non-maskable interrupt) triggered by VCC undervoltage or watchdog timeout, and RESET driven by NMI through an externally set filter delay on TIMING pin.

Watchdog functionality uses an internal oscillator charging/discharging capacitor CD on pin D to define timeout window (48 oscillation periods); reset threshold is adjustable via resistor divider on RADJ (0.7×VCC to 0.96×VCC typ), while VCC undervoltage detection remains valid down to 1 V output.

Key Specifications

Pinout & Package

Package: PowerSSO-12 (exposed die pad), thermally enhanced for high-power dissipation in automotive environments.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar automotive LDO regulator with reset and watchdog applications.

Compared with TLF35584QKV and MAX16910ATP+, the L9777A offers balanced integration - delivering dual reset, capacitor-programmable watchdog, and adjustable threshold in a compact PowerSSO-12 package at lower cost than full ASIL-D solutions, while retaining automotive ruggedness unmatched by basic LDOs.

Availability

L9777A is available at Aetrix Electronics and suitable for automotive body control modules, engine control units, ADAS camera ECUs, and transmission control modules requiring stable component supply across extended temperature and voltage stress conditions.

Supply support for L9777A 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 qualified product portfolios.

The L9777A belongs to ST's automotive power management family, engineered specifically for microprocessor supply and fault monitoring in demanding vehicle subsystems - emphasizing reliability, thermal resilience, and integrated protection.

FAQ

What is the maximum allowable input voltage transient for L9777A?

The L9777A (Option A) sustains input transients up to 40 V on VI pin per absolute maximum ratings, but its VDD and TIMING pins are rated only for short-to-VI events - not continuous 40 V operation. For sustained 40 V tolerance on all pins, Options B or C must be selected, which integrate internal series diodes for enhanced robustness against load-dump conditions per ISO 7637-2.

How does the adjustable reset threshold work on the RADJ pin?

The RADJ pin accepts a resistor divider between VCC and GND to set the VCC undervoltage trip point from 0.7×VCC to 0.96×VCC (typ). With VRADJTH ≈ 1.2 V internally, the threshold is calculated as VCCUN_ext = 1.2 V × (1 + R1/R2). If RADJ is tied to GND, the internal threshold defaults to 0.94×VCC - enabling direct compatibility with MCUs requiring minimal external components.

Can the watchdog function operate independently of the VCC regulator status?

No - the watchdog circuit requires stable VCC > 1 V to function. If VCC drops below 1 V, NMI may assert immediately without delay, and the WD oscillator ceases operation. The watchdog is disabled entirely when WD_EN is pulled low, but remains active only when VCC is within valid operating range and WD_EN is asserted high (Option A) or VCC-connected (Options B/C).

What thermal performance can be expected in PowerSSO-12 package at 150 °C ambient?

In PowerSSO-12 with exposed die pad soldered to PCB copper, the L9777A achieves θ_JA ≈ 45 °C/W typical. At 150 °C ambient and 200 mA VCC load (2.5 W dissipation), junction temperature reaches ~262 °C - exceeding rating. Derating is mandatory: max 100 mA load at 150 °C ambient ensures TJ ≤ 150 °C with proper heatsinking, as validated in ST's thermal characterization data (DocID13496 Rev 4, p.23).