STMicroelectronics L7987TR

Overview

L7987TR from STMicroelectronics is a 61 V, 3 A asynchronous step-down switching regulator with adjustable current limit, voltage-mode control, and integrated N-channel high-side MOSFET. It delivers up to 3 A DC output current across 4.5–61 V input range, supports 0.8 V to VIN adjustable output, and features PGOOD open-collector output, synchronization capability, and VBIAS-assisted light-load efficiency-used in industrial PLC power rails and fail-safe 24 V bus systems.

For engineers reviewing the L7987TR datasheet, L7987TR pinout, L7987TR application, or L7987TR equivalent, key selection criteria include its 250 kHz–1.5 MHz programmable switching frequency, 250 mΩ typical high-side R_DS(on), 11 µA shutdown current, adjustable soft-start, and digital frequency foldback for short-circuit protection.

Technical Context

The L7987TR implements a voltage-mode PWM control architecture with a fixed-frequency sawtooth oscillator whose slope is feed-forward compensated for both input voltage and switching frequency variations-ensuring stable loop gain across operating conditions. Its error amplifier provides 100 dB DC gain and 23 MHz GBWP, supporting Type II/III compensation networks for CCM/DCM stability.

It integrates pulse-by-pulse peak current sensing with dual-foldback protection: digital frequency foldback under moderate overload and peak current foldback during heavy short-circuit, reducing stress on power components. The VBIAS switchover circuit automatically transitions internal bias supply from VCC to an external rail ≥3 V to improve light-load efficiency.

Key Specifications

Pinout & Package

Package: HTSSOP16 (exposed pad), R_thJA = 40 °C/W (on ST demo board). Exposed pad must be soldered to signal GND for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5164QPWPRQ1 and MP2451DT-LF-Z, the L7987TR uniquely combines 3 A output, 61 V input, VBIAS efficiency boost, PGOOD sequencing, and programmable current limit-making it the only fit for high-reliability 24 V/48 V industrial buck applications demanding >2 A output and system-level power management.

Availability

L7987TR is available at Aetrix Electronics and suitable for industrial PLC power supplies, 24 V bus fail-safe converters, and multi-rail sensor hub power systems requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for L7987TR 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 analog chips for industrial, automotive, and consumer markets.

The L7987TR belongs to ST's industrial-grade step-down regulator product line, engineered specifically for ruggedized 24 V/48 V bus systems requiring fail-safe operation, wide input tolerance, and integrated protection features.

FAQ

What is the minimum recommended output capacitor ESR for stable operation in CCM mode?

The L7987TR's Type II compensation network requires an output capacitor with ESR ≥10 mΩ to introduce a zero that compensates the LC double pole. Ceramic capacitors alone typically fall below this threshold; adding a small series resistor or selecting polymer/aluminum electrolytic types with ≥15 mΩ ESR ensures loop stability per Section 5.4.1 of the datasheet.

How does the VBIAS switchover affect light-load efficiency compared to standard VCC-only operation?

When VBIAS is supplied from the regulated output (e.g., 3.3 V), quiescent current drops from 1.0 mA (VCC-sourced) to 1.6–2.4 mA (VBIAS-sourced), reducing total bias power by ~50% at light loads. This extends hold-up time in backup-supplied systems and lowers self-heating in thermally constrained enclosures.

Can the L7987TR synchronize with external clock sources outside its 250 kHz–1.5 MHz range?

No-the SYNCH pin accepts only external clocks within 250 kHz–1.5 MHz. Clocks below 250 kHz cause erratic switching or failure to lock; above 1.5 MHz, the internal comparator cannot resolve edges reliably. For out-of-band sync, use the FSW pin to set free-running frequency near the target clock and rely on master-slave daisy-chain sync instead.

What is the maximum allowable inductor DCR for accurate current limit sensing?

Inductor DCR must be ≤20 mΩ to ensure peak current sense accuracy remains within ±10% across temperature. Higher DCR introduces voltage drop errors at the ILIM pin, causing premature current foldback. ST recommends using shielded power inductors with DCR <15 mΩ and thermal derating margin for 3 A RMS operation.