STMicroelectronics L6985F

Overview

L6985F from STMicroelectronics is a 38 V, 500 mA synchronous step-down switching regulator with peak-current-mode control, 30 µA quiescent current in low-consumption mode (LCM), adjustable output voltage (0.85 V to VIN), and dual operating modes (LCM/LNM) for light-load efficiency or constant-frequency low-noise operation. It integrates P-channel high-side and N-channel low-side MOSFETs (R_DS(on) = 360 mΩ / 150 mΩ), embedded voltage supervisor with open-drain RST, and synchronization capability - deployed in industrial PLCs and decentralized sensor nodes powered from 12 V/24 V buses.

For engineers reviewing the L6985F datasheet, L6985F pinout, L6985F application, or L6985F equivalent, key selection criteria include its 4–38 V input range, 250 kHz–2 MHz adjustable f_SW, 8 µA shutdown current, thermal shutdown at 165 °C, and HTSSOP16 package with exposed pad for thermal management.

Technical Context

The L6985F employs peak-current-mode architecture with pulse-by-pulse high-side/low-side current sensing for overcurrent protection and foldback under short-circuit. Its switchover feature dynamically shifts internal bias supply from VIN to VBIAS (3–5.5 V) to reduce effective I_Q at light load.

Two configurable operating modes are implemented via MLF pinstrapping: Low Noise Mode (LNM) enforces fixed-frequency PWM across full load range for EMI-sensitive applications; Low Consumption Mode (LCM) enables frequency skipping to maintain >85% efficiency at 1 mA output while controlling ripple.

Key Specifications

Pinout & Package

Package: HTSSOP16 (exposed pad), R_thJA = 40 °C/W, requires SGND/PGND connection to exposed pad per STMicroelectronics layout guidelines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMR36506R and TPS54560B, the L6985F uniquely combines industrial-grade input range (4–38 V), integrated RST supervision with programmable delay, and dual LCM/LNM modes - making it optimal for space-constrained, noise-sensitive, or sequenced-power industrial embedded systems where both efficiency and reliability are co-prioritized.

Availability

L6985F is available at Aetrix Electronics and suitable for industrial PLCs, decentralized sensor nodes, low-noise imaging subsystems, and FPGA core voltage regulation requiring stable component supply across extended temperature and lifecycle requirements.

Supply support for L6985F 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 embedded markets.

The L6985F belongs to ST's high-reliability DC-DC converter product line, designed specifically for robust, low-noise, and low-quiescent-current power conversion in harsh industrial environments with wide input voltage variation.

FAQ

What is the purpose of the VBIAS pin on the L6985F?

The VBIAS pin enables switchover of the internal LDO bias supply from VIN to an external 3–5.5 V source (typically the regulated output). When active, this reduces the effective quiescent current drawn from VIN - critical for battery-powered or energy-harvested systems where every microamp counts. The switchover thresholds are 2.85 V (VIN→VBIAS) and 2.78 V (VBIAS→VIN), with hysteresis ensuring stable transition.

How does the L6985F implement output voltage sequencing?

Sequencing is achieved using the open-drain RST output and DELAY pin. After V_OUT reaches its target, an external capacitor on DELAY charges at 1–3 µA until voltage crosses 1.234 V, releasing RST. This delay can be cascaded: RST from one L6985F can enable the SS/INH of a second regulator, enforcing strict power-up order - essential for FPGAs, processors, and multi-rail ASICs.

Can the L6985F operate with 100% duty cycle, and how is this enabled?

Yes - the L6985F supports 100% duty cycle operation due to its integrated P-channel high-side MOSFET. Unlike N-channel-based regulators requiring bootstrap circuitry, the P-channel device eliminates the need for a floating gate drive, allowing continuous conduction when V_OUT approaches V_IN. This is vital for low-dropout applications such as post-regulation from 5 V or 3.3 V sources where minimal headroom is available.

What protection features are built into the L6985F?

The L6985F integrates six hardware protections: (1) Overcurrent protection with pulse-by-pulse high-side/low-side current sensing and foldback under short-circuit; (2) Overvoltage protection that actively discharges the output capacitor; (3) Thermal shutdown at 165 °C with 30 °C hysteresis; (4) Input UVLO with 2.7 V rising / 2.4 V falling thresholds; (5) Output voltage supervisor with programmable RST assertion; and (6) Internal current limiting on COMP pin (±25 µA) to prevent compensation network saturation.