STMicroelectronics L5986

Overview

L5986 from STMicroelectronics is a 2.5 A synchronous step-down switching regulator with integrated high-side 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, internal soft-start, and 100% duty-cycle low-dropout capability - used in LCD TV power rails and FPGA core supplies.

For engineers reviewing the L5986 datasheet, L5986 pinout, L5986 application, or L5986 equivalent, key selection criteria include its voltage-mode control architecture, SYNCH pin synchronization capability, thermal shutdown hysteresis (30 °C), VFQFPN3x3 and HSOP8 package options, and zero-load current operation for always-on subsystems.

Technical Context

The L5986 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) to maintain constant PWM gain across line and frequency variations. Its error amplifier has 100 dB open-loop gain, 4.5 MHz GBWP, and rail-to-rail output swing (0–3.3 V).

Synchronization is achieved through the bidirectional SYNCH pin: when floating, it outputs a 180° phase-shifted clock; when driven externally, it locks the device to an external master clock with zero phase shift. Overcurrent protection uses blanking time (~200 ns) and implements hiccup mode under sustained overload and pulse-skipping during soft-start.

Key Specifications

Pinout & Package

Available in VFQFPN 3 × 3 mm – 8L and HSOP8 packages, both with exposed thermal pads for enhanced heat dissipation. The VFQFPN variant achieves R_thJA = 60 °C/W; HSOP8 achieves 40 °C/W on demonstration board mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315 and TPS54202, the L5986 uniquely combines 2.5 A capability, 0.6 V reference precision, SYNCH-enabled multi-phase scalability, and 100% duty-cycle operation - making it optimal for industrial FPGA and automotive DSP power where input range, thermal robustness, and system-level timing coordination are critical.

Availability

L5986 is available at Aetrix Electronics and suitable for LCD TV power supplies, FPGA core rails, car audio DSP power, and XDSL line card DC-DC modules requiring stable component supply across extended temperature and long product lifecycles.

Supply support for L5986 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 automotive ICs with vertical manufacturing and broad industrial qualification coverage.

The L5986 belongs to ST's high-efficiency monolithic buck regulator product line, engineered for space-constrained industrial and consumer power systems demanding robust thermal performance, wide input range, and flexible system integration via synchronization and programmable frequency.

FAQ

What is the minimum input voltage required for L5986 startup?

The L5986 turns on when V_CC exceeds 2.9 V (typical), with 0.175 V hysteresis to prevent oscillation during brown-out. Startup is guaranteed down to 2.9 V at -40 °C to +125 °C junction temperature, enabling reliable operation from 3.3 V system rails even under worst-case tolerances and temperature extremes.

Can L5986 operate in 100% duty cycle mode, and under what conditions?

Yes - the L5986 supports 100% duty cycle operation when the input voltage approaches the output voltage, allowing regulation down to V_OUT = V_IN − V_SW (where V_SW ≈ 0.3 V at 2.5 A). This occurs automatically when feedback demands maximum on-time, enabling dropout operation during low-input or high-load transients without dropout reset.

How does the SYNCH pin function when two L5986 devices are connected together?

When SYNCH pins of two L5986 devices are tied together, the unit with the higher free-running or programmed switching frequency becomes the master; the other synchronizes as a slave with 180° phase shift. This interleaving reduces input capacitor RMS current by up to 30%, lowering thermal stress and EMI in multi-rail systems like LCD TV mainboards.

What is the purpose of the masking time in L5986 overcurrent protection?

The L5986 employs a 200 ns blanking (masking) time after each high-side switch turn-on to ignore current-sense noise from MOSFET switching transients. This prevents false overcurrent triggering while preserving accurate peak-current detection - essential for stable pulse-by-pulse limiting during soft-start and hiccup recovery under short-circuit conditions.