STMicroelectronics L9651

Overview

L9651 from STMicroelectronics is a quad low-side power switch IC with integrated diagnostic serial interface, designed for automotive and industrial load control. It features four 2.2 A-rated VDMOS outputs (RDSON < 500 mΩ at 25°C), 70 V internal output clamping, CMOS-compatible inputs, and wide 4.7–30 V supply operation - used in body control modules for driving solenoids, relays, and lamps.

For engineers reviewing the L9651 datasheet, L9651 pinout, L9651 application, or L9651 equivalent, key selection criteria include its daisy-chainable 500 kHz serial diagnostic interface, per-channel open-load/short-to-battery/short-to-ground detection with 100 µs filtering, and fault storage in an 8-bit serial register without host polling.

Technical Context

The L9651 implements four independent low-side switches using modified VDMOS technology with undervoltage lockout (VBATDU = 4.7 V) and thermal shutdown (TJ = 175°C). Each channel supports up to 2.2 A continuous current and clamps inductive kickback to 70 V with 10 mJ energy rating.

Its synchronous serial diagnostic interface uses SY (synchronization), CL (clock), DI (data in), and DO (data out) pins to report real-time fault status - including bit-mapped open-load, short-to-ground, short-to-battery, and overtemperature events - with fault latching and external pull-up required on DO.

Key Specifications

Pinout & Package

Package: PowerSO-20 (JEDEC MO-166), thermally enhanced surface-mount package with exposed slug for improved heat dissipation (Rth j-case = 2.5 °C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad low-side switch with serial diagnostics applications.

Compared with TPS4H160-Q1 and VNQ7E100AJ, the L9651 uniquely combines daisy-chain serial diagnostics, 8-bit fault memory, and 70 V clamping in a single PowerSO-20 package - optimizing for space-constrained automotive ECUs requiring minimal MCU overhead and robust inductive load handling.

Availability

L9651 is available at Aetrix Electronics and suitable for automotive body control modules, industrial PLC output stages, truck lighting control units, and off-highway equipment harness monitors requiring stable component supply across extended temperature and voltage ranges.

Supply support for L9651 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 microcontrollers, power ICs, sensors, and automotive-grade analog products.

The L9651 belongs to ST's "Smart Power" product line, engineered specifically for automotive and industrial load switching applications demanding integrated protection, diagnostics, and high reliability under harsh electrical conditions.

FAQ

What is the purpose of the SY (synchronization) pin on the L9651?

The SY pin resets the internal shift register and initiates a new diagnostic frame. When asserted high, it aligns all daisy-chained L9651 devices to begin serial output simultaneously - ensuring synchronized fault reporting across multiple ICs without timing skew or data corruption.

Does the L9651 require an external pull-up resistor on the DO pin?

Yes, the DO pin is an open-drain output and requires an external pull-up resistor (typically 4.7 kΩ to VCC) to generate valid logic-high levels. Without it, serial data cannot be correctly read by the host controller, and fault status will appear indeterminate or stuck low.

How does the L9651 detect short-to-battery faults?

The L9651 detects short-to-battery when the output is actively driven ON and the measured output voltage remains near VBAT (indicating no voltage drop across the load). This condition triggers a fault bit in the serial register, distinguishing it from normal operation or open-load states.

Can the L9651 drive inductive loads without external flyback components?

Yes - its internal clamp limits output voltage to 70 V during turn-off transients, and it is rated for 10 mJ clamping energy per pulse (repetition rate < 100 Hz). This allows direct connection to solenoids and relays in most 12 V/24 V systems without external diodes or RC snubbers.