STMicroelectronics L7981ATR

Overview

L7981ATR from STMicroelectronics is a 3 A synchronous step-down DC-DC switching regulator with integrated P-channel MOSFET, designed for mid-power point-of-load conversion in space-constrained systems. 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 supports 100% duty cycle for low-dropout operation - used in FPGA core supplies, LCD TV power rails, and industrial DC-DC modules.

For engineers reviewing the L7981ATR datasheet, L7981ATR pinout, L7981ATR application, or L7981ATR equivalent, key selection criteria include verified 3.7 A current limit, VFQFPN3x3-8L thermal resistance (60°C/W), voltage-mode control architecture, feed-forward compensation capability, and EN/FSW/SYNCH pin functionality for system-level synchronization and sequencing.

Technical Context

The L7981ATR implements voltage-mode PWM control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage feed-forward (input-dependent) and frequency feed-forward (FSW-resistor dependent) to maintain constant loop gain across operating conditions. Its error amplifier features 100 dB DC gain, 4.5 MHz GBWP, and rail-to-rail output swing (0–3.3 V) for robust loop compensation.

Overcurrent protection uses blanking-time–gated peak-current sensing (200 ns mask) with hiccup-mode recovery under sustained overload and pulse-skipping during soft-start to enforce constant-current behavior. Thermal shutdown activates at 150°C with 30°C hysteresis, and the enable function supports <30 µA standby current with 0.3 V / 1.2 V logic thresholds.

Key Specifications

Pinout & Package

Package: VFQFPN 3 × 3 mm, 8-lead, exposed pad (RoHS-compliant, moisture sensitivity level 3).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2678SD-ADJ/NOPB and MP2315GJ-Z, the L7981ATR uniquely combines programmable frequency, synchronization I/O, voltage/frequency feed-forward, and VFQFPN thermal performance - making it optimal for compact, multi-rail, noise-sensitive industrial and consumer power systems.

Availability

L7981ATR 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 RoHS-compliant packaging.

Supply support for L7981ATR 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 power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L7981 belongs to ST's high-efficiency monolithic buck regulator product line, engineered for space-constrained, thermally demanding applications requiring precise voltage regulation, robust fault protection, and system-level timing flexibility.

FAQ

What is the maximum allowable junction temperature for continuous operation?

The L7981ATR has a guaranteed junction temperature range of –40°C to +150°C. Thermal shutdown activates at +150°C with +30°C hysteresis, meaning normal operation resumes at approximately +120°C. For continuous 3 A output, PCB layout must ensure junction temperature remains below 150°C - achievable using the VFQFPN package's 60°C/W R_thJA with ≥2 cm² of 2-oz copper connected to the exposed pad.

Can the L7981ATR operate with an input voltage lower than 4.5 V?

No. The absolute maximum rating specifies V_CC ON threshold at 4.4 V (typical), with 0.12–0.35 V hysteresis. Operation below 4.5 V violates the specified operating input voltage range (4.5 V to 28 V) and risks UVLO-induced instability or failure to start. For sub-4.5 V inputs, consider ST's L6926 or similar low-V_IN buck regulators.

How does the SYNCH pin behave when left unconnected?

When the SYNCH pin is left floating, it outputs a square wave synchronized to the internal oscillator with ~180° phase shift relative to the power switch turn-on. This inherent phase inversion enables natural interleaving when two L7981ATRs have their SYNCH pins tied together - the higher-frequency unit becomes master, and the other synchronizes with half-period delay, reducing input capacitor RMS current.

Is an external freewheeling diode required for the L7981ATR?

No. The L7981ATR integrates a P-channel MOSFET as the high-side switch but does not integrate the low-side freewheeling element. An external Schottky diode (or synchronous MOSFET driver + N-channel MOSFET) is required between OUT and GND. Diode selection must account for peak reverse voltage ≥V_IN, average current ≥I_OUT, and low forward voltage to minimize conduction loss and thermal stress.