STMicroelectronics L6591

Overview

L6591 from STMicroelectronics is a double-ended PWM controller optimized for zero-voltage-switching (ZVS) half-bridge topologies in high-efficiency AC-DC power supplies. It delivers complementary gate drive with programmable deadtime, integrates a 600 V-rail-compatible high-side driver with synchronous bootstrap diode, supports up to 500 kHz switching, and features adaptive UVLO, pulse-by-pulse OCP, and transformer saturation detection - deployed in telecom SMPS and desktop PC power supplies.

For engineers reviewing the L6591 datasheet, L6591 pinout, L6591 application, or L6591 equivalent, this page provides verified technical context, SO16N package mapping, soft-switching timing behavior, PFC interface logic, and validated alternative options for ZVS half-bridge control designs.

Technical Context

The L6591 implements a T-flip-flop–limited PWM architecture where oscillator frequency is halved to set switching frequency (e.g., 180 kHz oscillator → 90 kHz bridge operation), with deadtime programmed via external capacitor on OSC pin. Its high-voltage startup generator delivers 0.75 mA typical charge current to Vcc from HVSTART, enabling direct rectified-line connection without auxiliary winding.

Adaptive UVLO dynamically adjusts turn-on/turn-off thresholds (VccOn = 13–15 V, VccOff = 8.2–11.3 V) based on COMP voltage level, improving light-load stability. The dual-level OCP includes leading-edge blanking (200 ns), 0.8 V pulse-by-pulse trip, and 1.5 V hiccup-mode shutdown triggered by transformer saturation or secondary diode failure.

Key Specifications

Pinout & Package

Package: SO16N (SOIC-16 narrow, 150 mil width), RoHS-compliant, ECOPACK® certified.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar ZVS half-bridge PWM control applications.

Compared with UCC28950 and ICE2PCS01, the L6591 uniquely combines ZVS-optimized deadtime programming, onboard 600 V high-side driver with synchronous bootstrap, and dedicated PFC_STOP signaling - making it the only option among the three that fully supports self-contained, high-efficiency ZVS half-bridge designs without auxiliary components.

Availability

L6591 is available at Aetrix Electronics and suitable for telecom SMPS, desktop PC power supplies, and high-power AC-DC adapters requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for L6591 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, Switzerland, designing and manufacturing analog, microcontroller, power, and automotive ICs with focus on energy efficiency and system integration.

The L6591 belongs to ST's high-voltage power management IC product line, engineered specifically for resonant and soft-switched AC-DC converters targeting telecom, computing, and industrial power supplies.

FAQ

What is the maximum recommended oscillator frequency for stable L6591 operation?

The L6591 datasheet specifies an oscillator frequency range of 168–192 kHz at full temperature and supply range. While the device supports up to 500 kHz switching (i.e., 1 MHz oscillator), operation above 192 kHz risks timing margin violation due to propagation delays in the T-flip-flop and deadtime logic. For robust ZVS performance across line/load, ST recommends limiting oscillator frequency to ≤190 kHz.

Can the L6591 drive GaN FETs directly?

No - the L6591's high-side and low-side gate drivers are rated for 0.3 A source / 0.8 A sink peak current and optimized for silicon MOSFETs with typical Qg ≤ 50 nC. GaN FETs require faster edge rates, tighter timing control, and often negative turn-off bias - none of which the L6591 provides. A dedicated GaN driver (e.g., LM5113) must be used in cascade.

How does the adaptive UVLO improve light-load behavior?

The adaptive UVLO lowers Vcc turn-off threshold from 11.3 V (full load) to 8.2 V (light load) based on COMP voltage level. This prevents premature shutdown during burst-mode valleys when Vcc sags due to reduced auxiliary winding output, ensuring continuous regulation and eliminating audible noise or output instability caused by repeated cycling.

Is the BOOT pin internally clamped, and what is its absolute maximum voltage?

Yes - the BOOT pin has an absolute maximum rating of −1 V to +618 V relative to FGND (Pin 13), as confirmed in Table 2 of the datasheet. No external clamp is required. The internal structure includes robust ESD protection and dV/dt immunity up to 50 V/ns, enabling reliable operation in high dv/dt ZVS environments without additional snubbing.