STMicroelectronics L5987A

Overview

L5987A from STMicroelectronics is a 3 A synchronous step-down switching regulator with integrated P-channel MOSFET, designed for high-efficiency DC-DC conversion in space-constrained power rails. It operates from 2.9 V to 18 V input, delivers adjustable output down to 0.6 V, features 250 kHz–1 MHz programmable switching frequency, internal soft-start, and 100% duty-cycle low-dropout operation - enabling use on 3.3 V bus systems in LCD TV, FPGA core supplies, and industrial chargers.

For engineers reviewing the L5987A datasheet, L5987A pinout, L5987A application, or L5987A equivalent, key selection criteria include thermal resistance (HSOP8: 40 °C/W), current-limit accuracy (3.5–4.4 A), feedback voltage tolerance (±1.17%), synchronization capability via SYNCH pin, and zero-load quiescent current (20–30 µA) for always-on subsystems.

Technical Context

The L5987A implements voltage-mode PWM control with feedforward compensation: input voltage feedforward maintains constant PWM gain across VIN variations, while frequency feedforward preserves gain stability when FSW resistor adjusts switching frequency. Its error amplifier features 100 dB open-loop gain and 4.5 MHz GBWP, supporting Type II or Type III compensation depending on output capacitor ESR.

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. Thermal shutdown activates at 150 °C with 30 °C hysteresis, and the INH pin provides logic-level enable/disable with <30 µA standby current.

Key Specifications

Pinout & Package

Available in HSOP8 package with exposed thermal pad (40 °C/W R_thJA) - optimized for high-current, thermally demanding applications. Pinout validated per STMicroelectronics DocID14972 Rev 4, Section 1.2.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315DJ-LF-Z and TPS563201, the L5987A uniquely combines 3 A capability, 2.9 V minimum input, 100% duty cycle, and dual feedforward - making it optimal for low-VIN, thermally constrained, and high-transient-performance applications.

Availability

L5987A is available at Aetrix Electronics and suitable for LCD TV power rails, FPGA core supplies, industrial battery chargers, and networking DC-DC modules requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for L5987A 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 L5987A belongs to ST's high-current monolithic buck regulator product line, engineered for space- and thermally constrained applications requiring robust protection, wide input range, and precise output regulation without external MOSFETs.

FAQ

What is the maximum continuous output current of the L5987A in HSOP8 package?

The L5987A in HSOP8 package delivers up to 3 A DC output current continuously, enabled by its 3.5 A minimum current-limited internal P-channel MOSFET and 40 °C/W thermal resistance. This rating holds at +85 °C ambient with proper PCB copper pour on the exposed pad; derating applies above that temperature per the thermal curve in Figure 9 of DocID14972 Rev 4.

How does the SYNCH pin function in master-slave configuration?

When two L5987A devices have their SYNCH pins connected, the unit with higher oscillator frequency becomes the master and the other the slave. The slave synchronizes with zero phase shift to the master's clock, resulting in 180° phase-shifted power switch turn-on - reducing total input capacitor RMS current by interleaving. No external clock source is required for this mode.

Can the L5987A operate with input voltage as low as 3.3 V?

Yes - the L5987A supports input voltages from 2.9 V to 18 V, making it fully compatible with 3.3 V intermediate buses. Its 100% duty-cycle capability allows regulation down to V_OUT ≈ V_IN, and the 2.9 V UVLO threshold ensures reliable startup even with marginal 3.3 V rails under load.

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 stabilize the loop, matching the single ESR zero and double LC pole of the power stage. Type III is required only when the output capacitor's ESR zero is insufficient to compensate the LC double pole, such as with bulk electrolytic capacitors.