STMicroelectronics L5986A

Overview

L5986A from STMicroelectronics is a 2.5 A synchronous step-down switching regulator with integrated P-channel MOSFET, designed for mid-power 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, and supports 100% duty cycle for low-dropout operation - used in LCD TV power rails and FPGA core supplies.

For engineers reviewing the L5986A datasheet, L5986A pinout, L5986A application, or L5986A equivalent, key selection criteria include its voltage-mode control architecture, thermal shutdown hysteresis (30 °C), soft-start duration (7.4–9.1 ms), and dual-package support (VFQFPN 3×3 mm–8L and HSOP8) with exposed thermal pads.

Technical Context

The L5986A implements voltage-mode PWM control with internal 0.6 V reference and feedforward compensation: input voltage and switching frequency modulate sawtooth slope to maintain constant PWM gain. Its oscillator supports free-running (250 kHz) or resistor-programmed operation up to 1 MHz via the FSW pin.

Functional blocks include a 3.0 A min. current-limited P-channel MOSFET, error amplifier with 100 dB open-loop gain and 4.5 MHz GBWP, hiccup-mode overcurrent protection with 200 ns blanking time, and thermal shutdown at 150 °C with 30 °C hysteresis - all enabled by a single VCC supply and minimal external components.

Key Specifications

Pinout & Package

Available in VFQFPN 3 × 3 mm – 8L (exposed pad, R_thJA = 60 °C/W) and HSOP8 (exposed pad, R_thJA = 40 °C/W) packages. Both support high-power density layout with direct thermal path to PCB.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315GJ-Z and TPS54202DDCR, the L5986A uniquely combines 2.5 A capability, 2.9 V minimum input, 100% duty cycle, and master/slave synchronization - making it optimal for multi-rail systems requiring coordinated switching and ultra-low dropout.

Availability

L5986A is available at Aetrix Electronics and suitable for LCD TV power supplies, FPGA core rails, industrial PLC I/O modules, and automotive infotainment systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for L5986A 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 L5986A belongs to ST's high-efficiency monolithic DC-DC regulator product line, engineered for robustness in noisy environments and ease of integration into compact, thermally demanding power architectures.

FAQ

What is the minimum input voltage required for L5986A to start switching?

The L5986A has a turn-on V_CC threshold of 2.9 V with 175–300 mV hysteresis. Below 2.9 V, the UVLO circuit holds the device disabled; operation begins reliably once V_CC exceeds this threshold and remains above 2.725 V due to hysteresis. This enables compatibility with 3.3 V bus systems even under droop conditions.

Can L5986A operate without an external feedback resistor divider?

Yes - connecting the FB pin directly to the OUT pin configures the regulator for 0.6 V output. For any higher output voltage, a resistor divider (R1 from OUT to FB, R2 from FB to GND) is mandatory to scale the feedback voltage to 0.6 V. The internal reference is fixed and non-adjustable.

How does the SYNCH pin behave when left unconnected?

When floating, the SYNCH pin outputs a square wave at the internal switching frequency with 180° phase shift relative to the power switch turn-on edge. This allows natural interleaving when two L5986A devices are synchronized by connecting their SYNCH pins - the higher-frequency unit becomes master, the other slave, achieving half-cycle phase offset.

What thermal performance difference exists between VFQFPN and HSOP8 packages?

The HSOP8 package achieves R_thJA = 40 °C/W (on demo board), while VFQFPN 3×3 mm–8L achieves 60 °C/W. This 20 °C/W difference means HSOP8 dissipates heat ~33% more effectively under identical conditions - critical for 2.5 A loads in enclosed industrial enclosures where ambient exceeds 70 °C.