STMicroelectronics L5981TR

Overview

L5981TR from STMicroelectronics is a 1.5 A (min) integrated step-down switching regulator with internal P-channel MOSFET, operating from 2.9 V to 18 V input and delivering adjustable output down to 0.6 V. It features 250 kHz–1 MHz programmable switching frequency, internal soft-start, 100% duty-cycle low-dropout operation, and thermal/overcurrent protection in a VFQFPN8 3 mm × 3 mm package-used in LCD TV power rails, FPGA core supplies, and XDSL DC-DC modules.

For engineers reviewing the L5981TR datasheet, L5981TR pinout, L5981TR application, or L5981TR equivalent, key selection criteria include input voltage range (2.9–18 V), feedback reference (0.6 V), adjustable switching frequency (250 kHz–1 MHz), thermal shutdown threshold (150 °C), and VFQFPN8 thermal resistance (60 °C/W).

Technical Context

The L5981TR implements voltage-mode PWM control with feedforward compensation: input voltage feedforward adjusts sawtooth slope to maintain constant PWM gain across VIN, while frequency feedforward preserves gain when FSW is adjusted via external resistor. Its oscillator supports master/slave synchronization via the SYNCH pin, enabling phase-shifted operation for reduced input ripple in multi-rail systems.

Functional blocks include a high-side P-MOSFET driver, error amplifier with 100 dB open-loop gain and 4.5 MHz GBWP, peak-current-limit sensing with 200 ns blanking time, and hysteretic thermal shutdown (150 °C trip, ~130 °C recovery). The COMP pin provides direct access to error amplifier output for Type II or Type III loop compensation networks.

Key Specifications

Pinout & Package

VFQFPN8 3 mm × 3 mm package with exposed thermal pad (pin 1–8 top view); 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 MP2307DN-LF-Z and TPS54202DRCT, the L5981TR uniquely combines voltage/frequency feedforward, master/slave sync, and 60 °C/W thermal performance in a 3 mm × 3 mm VFQFPN8-making it optimal for space-constrained, multi-rail industrial and telecom designs requiring robust transient response and thermal management.

Availability

L5981TR is available at Aetrix Electronics and suitable for LCD TV power rails, FPGA core supplies, and XDSL line card DC-DC modules requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for L5981TR 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, designing and manufacturing microcontrollers, power ICs, sensors, and analog chips for automotive, industrial, and consumer markets.

The L5981TR belongs to ST's high-efficiency monolithic buck regulator product line, engineered for compact, thermally robust DC-DC conversion in space- and reliability-critical applications such as set-top boxes, networking equipment, and industrial PLCs.

FAQ

What is the minimum input voltage required for L5981TR startup?

The L5981TR requires a minimum input voltage of 2.9 V to initiate operation, as defined by its V_CCON UVLO threshold. This allows reliable startup from nominal 3.3 V buses-even during brown-out conditions-and supports automotive cold-cranking scenarios where battery voltage dips to ~3.0 V. The 175 mV hysteresis prevents oscillation near the threshold.

How does the SYNCH pin enable multi-device synchronization?

The SYNCH pin supports three modes: floating (internal 180° phase-shifted clock), externally driven (zero-phase sync at higher frequency), or tied to another L5981TR (master/slave configuration). When two devices are connected, the higher-frequency unit becomes master, and the slave switches half-a-cycle delayed-reducing total input capacitor RMS current by distributing switching events across the period.

Can L5981TR operate with zero load current?

Yes-the L5981TR maintains regulation with zero load current, drawing only ≤30 µA in standby (IQST-BY). Its error amplifier remains active, COMP pin retains control authority, and feedback loop stays closed. This enables use in always-on system rails (e.g., real-time clocks, memory retention) without requiring auxiliary LDOs or external disable circuitry.

What compensation network type is recommended for ceramic output capacitors with low ESR?

For ceramic output capacitors with very low ESR (e.g., <5 mΩ), a Type II compensation network is recommended. It introduces one pole and one zero to counteract the LC double-pole and cancel the ESR zero, achieving sufficient phase margin (>45°) without excessive component count. Type III is reserved for higher-ESR electrolytics where an additional zero is needed to compensate the output capacitor's ESR-related phase lag.