STMicroelectronics L6598

Overview

L6598 from STMicroelectronics is a high-voltage resonant controller IC designed for half-bridge LLC and series-resonant AC/DC power supplies. It integrates high-side and low-side MOSFET drivers (450 mA sink / 250 mA source), a current-controlled oscillator (60–120 kHz soft-start, up to 400 kHz max), undervoltage lockout (10.7 V turn-on), and a rail-to-rail sense op amp - enabling closed-loop frequency modulation in 50–600 V input adapters.

For engineers reviewing the L6598 datasheet, L6598 pinout, L6598 application, or L6598 equivalent, key selection criteria include dV/dt immunity (±50 V/ns), integrated bootstrap diode, Zener-clamped Vs pin (15.6 V), deadtime control (0.27 µs typ.), and dual enable inputs (latched EN1 @ 0.6 V, unlatched EN2 @ 1.2 V) for robust protection sequencing.

Technical Context

The L6598 implements a dedicated timing architecture where soft-start frequency shifting is achieved by charging CSS to generate a ramped current that subtracts from Ifstart, dynamically adjusting oscillator current from fstart (120 kHz) down to fmin (60 kHz). Its oscillator uses mirrored current sources (x4/x8) to drive Cf, yielding stable triangular waveforms with <±5% variation across temperature.

High-side driving relies on a patented synchronous bootstrap DMOS (RDSon = 150 Ω typ.) with integrated series diode and internal charge pump - eliminating external bootstrap diodes while maintaining VBOOT capability up to 618 V. The sense op amp (GBW = 1 MHz, Vio = ±10 mV) supports direct feedback to Rfmin for real-time frequency regulation during overcurrent or thermal events.

Key Specifications

Pinout & Package

Available in DIP16 (through-hole) and SO16N (surface-mount) packages per ECOPACK® environmental compliance. Both variants share identical pin mapping and thermal resistance (RthJA = 80 °C/W for DIP16, 120 °C/W for SO16N).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage resonant controller applications.

Compared with IR21531 and UCC256301, the L6598 uniquely balances analog simplicity (no programming), precision analog control (op amp + current-mode oscillator), and robust HV integration (600 V rating, dV/dt immunity, bootstrap DMOS) - making it optimal for cost-sensitive yet performance-critical industrial and adapter designs.

Availability

L6598 is available at Aetrix Electronics and suitable for AC/DC adapters, server PSUs, industrial power supplies, and USB PD fast chargers requiring stable component supply and long-term manufacturing continuity.

Supply support for L6598 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, specializing in power management, analog, microcontrollers, and automotive ICs.

The L6598 belongs to ST's high-voltage resonant controller product line, engineered specifically for efficient, compact, and reliable LLC and series-resonant converters in universal-input offline power supplies.

FAQ

What is the maximum allowable VBOOT voltage for continuous operation?

The L6598 supports a maximum repetitive VBOOT voltage of 618 V, verified per absolute maximum ratings (Table 1). This rating applies under steady-state conditions with dVBOOT/dt ≤ ±50 V/ns. Operation above 600 V requires careful PCB layout to minimize parasitic ringing and ensure sufficient creepage/clearance per IEC 62368-1.

How does the integrated bootstrap DMOS affect gate drive loss at 300 kHz?

At 300 kHz, the bootstrap DMOS (RDSon = 150 Ω typ.) introduces ~4.2 V drop when driving a 50 nC MOSFET, calculated as Vdrop ≈ (Qg / Tcharge) × RDSon + Vdiode. This reduces effective gate voltage swing but remains acceptable in resonant topologies where MOSFET conduction losses dominate over switching losses.

Can the sense op amp be used for overvoltage protection without external components?

Yes - the op amp's rail-to-rail output (0–4.6 V) and 3 V common-mode input range allow direct connection of a resistive divider from output to OPin+ and OPin−, with OPout feeding EN1. This creates a fully integrated analog OVP that triggers latched shutdown at a user-defined threshold without comparators or references.

What is the minimum recommended deadtime for safe half-bridge operation?

The L6598 enforces a fixed minimum deadtime of 0.27 µs (typical) between LVG turn-off and HVG turn-on, and vice versa. This value is internally hardwired and cannot be adjusted. It is sufficient for MOSFETs with Qg < 100 nC switching at ≤250 kHz, but external deadtime extension may be needed for very large GaN devices.