STMicroelectronics L5987

Overview

L5987 from STMicroelectronics is a 3 A synchronous step-down switching regulator with integrated P-channel MOSFET, designed for point-of-load DC-DC conversion in space-constrained systems. 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 rails in consumer and industrial power supplies.

For engineers reviewing the L5987 datasheet, L5987 pinout, L5987 application, or L5987 equivalent, key selection criteria include its VFQFPN3x3-8L/HSOP8 thermal performance (R_thJA = 60 °C/W and 40 °C/W), voltage feedforward architecture for line transient immunity, hiccup-mode overcurrent protection, and zero-load quiescent current of 20–30 µA - critical for always-on embedded systems.

Technical Context

The L5987 implements voltage-mode PWM control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage feedforward (input-dependent) and frequency feedforward (FSW-resistor dependent), maintaining constant PWM gain across VIN and switching frequency variations. Its error amplifier features 100 dB open-loop gain, 4.5 MHz GBWP, and externally accessible COMP/FB pins for Type II or Type III compensation.

Internal protection includes cycle-by-cycle peak current limiting with 200 ns blanking time, hysteretic thermal shutdown (150 °C trip, 130 °C recovery), UVLO with 0.175–0.3 V hysteresis, and active-high inhibit (INH) with 0.6 V ON / 1.9 V OFF thresholds. The device supports master/slave synchronization via the SYNCH pin, enabling phase-shifted parallel operation to reduce input ripple RMS current.

Key Specifications

Pinout & Package

The L5987 is available in two thermally enhanced packages: VFQFPN 3 × 3 mm, 8-lead with exposed pad (R_thJA = 60 °C/W), and HSOP8 with exposed pad (R_thJA = 40 °C/W). Both packages support high-power density layouts and require proper thermal pad soldering per ST's AN4405 guidelines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315GJ-Z and TPS54332DR, the L5987 offers unique voltage feedforward for superior line regulation, true 100% duty cycle for ultra-low dropout, and dual-package thermal options - making it optimal for compact, thermally constrained, and line-sensitive 3 A buck applications.

Availability

L5987 is available at Aetrix Electronics and suitable for consumer audio systems, FPGA power delivery, DSL modems, and hard disk drive power rails requiring stable component supply, long-term lifecycle assurance, and consistent thermal performance across VFQFPN and HSOP8 variants.

Supply support for L5987 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 automotive, industrial, and consumer markets.

The L5987 belongs to ST's high-efficiency monolithic DC-DC converter product line, engineered for space-constrained, thermally demanding point-of-load applications where integration, thermal resilience, and transient performance are critical.

FAQ

What is the minimum input voltage required for L5987 startup and regulation?

The L5987 requires a minimum input voltage of 2.9 V to initiate startup and sustain regulation, verified by its V_CCON threshold and UVLO hysteresis of 0.175–0.3 V. This allows direct operation from a nominal 3.3 V bus without pre-regulation, and the device maintains regulation down to V_IN = V_OUT + V_DS(on) due to 100% duty-cycle capability.

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

When two L5987 devices have their SYNCH pins connected, the unit with the higher oscillator frequency automatically becomes the master and the other the slave. The slave synchronizes with zero phase shift to the master's clock, resulting in a 180° phase shift between their power switch turn-on events - reducing total input capacitor RMS current by up to 30% in interleaved operation.

Can L5987 operate with zero load current while maintaining regulation?

Yes - the L5987 supports zero-load operation with stable output regulation and ultra-low standby current of 20–30 µA. This is enabled by its optimized bias circuitry and low-I_Q error amplifier design, making it suitable for always-on subsystems such as real-time clocks, sensor wake-up logic, or standby power domains in consumer electronics.

What is the difference between L5987 and L5987A part numbers?

The L5987 (VFQFPN3x3-8L) and L5987A (HSOP8) share identical electrical specifications and functional blocks but differ in package thermal performance: the HSOP8 variant has lower R_thJA (40 °C/W vs. 60 °C/W), enabling full 3 A output with less board area and no heatsink, while the VFQFPN offers smaller footprint and compatibility with automated optical inspection in high-density layouts.