STMicroelectronics L9777B

Overview

L9777B from STMicroelectronics is a monolithic low-dropout voltage regulator delivering up to 200 mA on VCC (5 V ±2%) and 50 mA on switchable VDD, with integrated NMI/RESET monitoring, adjustable undervoltage threshold, watchdog timer, 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 L9777B datasheet, L9777B pinout, L9777B application, or L9777B equivalent, this device serves as a dual-output power management IC with programmable reset timing, VDD tracking control, and fault-tolerant supervision - critical for engine control units, body control modules, and ADAS domain controllers requiring AEC-Q100 compliance and functional safety support.

Technical Context

The L9777B implements a primary 5 V LDO regulator (VCC) with 2% accuracy across full input and temperature range, plus a secondary tracking regulator (VDD) enabled via VDD_EN pin and limited to 50 mA with max 1.5 V dropout. Its reset architecture features dual-stage filtering: NMI triggers on VCC undervoltage (adjustable down to 0.7×VCC via RADJ) with depth-dependent delay, while RESET follows NMI after a fixed TIMING-pin-set delay.

Watchdog functionality monitors WD input frequency using an internal oscillator charged/discharged by CD capacitor; failure to detect ≥48 oscillation periods disables NMI output. All digital inputs (VDD_EN, WD_EN, WD) are internally biased - in Option B (L9777B), both VDD_EN and WD_EN use 10 μA pull-downs, enabling standby current of 100 μA typ.

Key Specifications

Pinout & Package

Package: PowerSSO-12 (exposed die pad), thermally enhanced for automotive under-hood mounting with direct PCB heat sinking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar automotive LDO + supervisor applications.

Compared with NCP109x and TLE4274G, the L9777B uniquely integrates dual-rail regulation, depth-sensitive reset, and single-capacitor watchdog timing - reducing total component count by two and enabling ASIL-B-compliant power supervision in compact automotive ECUs.

Availability

L9777B is available at Aetrix Electronics and suitable for engine control units, body control modules, and ADAS domain controllers requiring stable component supply across extended temperature ranges and automotive qualification cycles.

Supply support for L9777B 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 power applications with emphasis on reliability and functional safety.

The L9777 series belongs to ST's automotive power management portfolio, engineered specifically for AEC-Q100 Grade 0/1 environments where robustness, integrated protection, and diagnostic capability are mandatory for ECU power subsystems.

FAQ

What is the key functional difference between L9777B and L9777A?

L9777B implements Option B configuration: VDD_EN and WD_EN pins use internal 10 μA pull-downs (vs. 5 μA pull-ups in L9777A), reducing standby current to 100 μA typ. VDD and TIMING pins tolerate 40 V shorts regardless of VI voltage, enabling direct battery connection without external clamping. VDD output current is reduced to 50 mA with max 1.5 V dropout.

Can the L9777B support both VCC and VDD simultaneously at full rated current?

No. The L9777B delivers up to 200 mA on VCC and up to 50 mA on VDD, but total power dissipation must remain within thermal limits. At TJ = +125 °C ambient, simultaneous 200 mA on VCC and 50 mA on VDD requires θJA ≤ 35 °C/W - achievable only with aggressive PCB copper and the exposed die pad soldered to a thermal plane. Derating is recommended above +85 °C.

How is the watchdog timeout calculated for a given CD capacitor value?

Watchdog timeout is defined as TWOP − TWOL = 48 × TOSC, where TOSC = (VDU − VDRL) × CD / IWC + (VDU − VDRL) × CD / IWD. With typical values VDU = 1.24 V, VDRL = 0.62 V, IWC = IWD = 20 μA, this simplifies to TWOP − TWOL = 2.976 × 10⁶ × CD seconds. For CD = 100 nF, timeout = 297.6 ms.

Is the L9777B AEC-Q100 qualified, and which grade applies?

Yes, the L9777B is AEC-Q100 qualified per Rev D. It meets Grade 1 specifications (TJ = −40 °C to +125 °C) for standard automotive applications and Grade 0 (TJ = −40 °C to +150 °C) when operated within its absolute maximum ratings - confirmed in ST's official qualification report DocID13496 Rev 4.