STMicroelectronics L7981

Overview

L7981 from STMicroelectronics is a 3 A step-down switching regulator with integrated P-channel MOSFET, designed for high-efficiency DC-DC conversion in space-constrained power supplies. It operates from 4.5 V to 28 V input, delivers adjustable output down to 0.6 V, features 250 kHz–1 MHz programmable switching frequency, internal soft-start and enable, and supports zero-load operation - used in FPGA core supplies, LCD TV power rails, and industrial DC-DC modules.

For engineers reviewing the L7981 datasheet, L7981 pinout, L7981 application, or L7981 equivalent, key selection criteria include its voltage-mode control architecture, 3.7 A current limit, thermal shutdown at 150 °C, VFQFPN3x3-8L/HSOP8 package options, and feed-forward compensation for line/load transient stability.

Technical Context

The L7981 implements voltage-mode PWM control using an internal 0.6 V reference and error amplifier with 100 dB open-loop gain and 4.5 MHz GBWP. Its oscillator supports free-running (250 kHz) or resistor-programmed operation up to 1 MHz, with voltage and frequency feed-forward to maintain constant PWM gain across input and frequency variations.

Synchronization is achieved via the SYNCH pin, enabling master/slave phase-shifted operation when two devices are connected - reducing input capacitor RMS current. Overcurrent protection uses blanking-time–gated peak-current sensing with hiccup-mode recovery under sustained overload and pulse-skipping during soft-start.

Key Specifications

Pinout & Package

Available in VFQFPN 3 × 3 mm – 8L (exposed pad, R_thJA = 60 °C/W) and HSOP8 (exposed pad, R_thJA = 40 °C/W) packages - both optimized for thermal performance in high-power density designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM5164QPWPRQ1 and TPS54332DR, the L7981 uniquely combines 3 A output, feed-forward compensation, and master/slave synchronization in a thermally enhanced dual-package option - making it optimal for industrial and consumer multi-rail power systems requiring tight transient response and thermal headroom.

Availability

L7981 is available at Aetrix Electronics and suitable for FPGA core supplies, LCD TV power rails, and industrial DC-DC modules requiring stable component supply, long-term lifecycle support, and dual-package flexibility (VFQFPN3x3-8L and HSOP8).

Supply support for L7981 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L7981 belongs to ST's high-current monolithic buck regulator product line, engineered for compact, thermally robust DC-DC conversion in cost-sensitive, high-volume applications such as consumer displays and industrial control units.

FAQ

What is the minimum output voltage achievable with the L7981?

The L7981 regulates output down to 0.6 V, set by its internal bandgap reference. This value is guaranteed across temperature (−40 °C to +125 °C) and line conditions, with ±1.2% tolerance. To achieve lower voltages, external circuitry such as a resistive divider with offset or a secondary LDO is required - the IC itself cannot regulate below 0.6 V.

Can the L7981 operate in dropout mode, and how is it implemented?

Yes - the L7981 supports 100% duty cycle operation, enabling dropout mode when V_IN approaches V_OUT. This is achieved via its P-channel MOSFET high-side switch and adaptive gate driver, which maintains regulation even with minimal headroom. Dropout behavior is confirmed in datasheet Figure 32 and validated across input ranges down to 4.5 V.

How does the SYNCH pin function when used for master-slave interleaving?

When two L7981 devices have their SYNCH pins tied together, the higher-frequency unit becomes master and forces the other into slave mode with 180° phase shift. No external clock source is needed - synchronization occurs automatically via internal signal routing. This reduces input ripple current by up to 30% compared to parallel non-interleaved operation.

What compensation topology is recommended for ceramic-output-capacitor designs?

For low-ESR ceramic output capacitors, a Type II compensation network is recommended - it introduces one pole and one zero to stabilize the loop against the LC double-pole and ESR zero. The L7981's error amplifier (100 dB gain, 4.5 MHz GBWP) supports this configuration, and design equations are provided in Section 6.4.2 of the datasheet (pages 24–26).