Monolithic Power Systems Inc. HFC0400GS

Overview

HFC0400GS from Monolithic Power Systems is a fixed-frequency current-mode flyback controller with built-in slope compensation, designed for medium-power offline AC/DC adapters and battery chargers. It delivers 65 kHz nominal switching frequency, 25 kHz minimum foldback frequency, burst-mode operation below 0.32 V FB, and ultra-low no-load power consumption (≤35.26 mW at 265 VAC/50 Hz). Its integrated HV startup current source, X-cap discharge function, and latch-off OVP/OTP protection enable compact, safety-compliant power supplies.

For engineers reviewing the HFC0400GS datasheet, HFC0400GS pinout, HFC0400GS application, or HFC0400GS equivalent, key selection criteria include its 700 V HV breakdown rating, 25–65 kHz adaptive frequency range, 0.95 V current limit threshold, thermal shutdown with 25°C hysteresis, and SOIC8-7A package compatibility with standard flyback transformer designs.

Technical Context

The HFC0400GS implements fixed-frequency current-mode control with internal 25 mV/µs slope compensation to prevent subharmonic oscillation in CCM operation above 50% duty cycle. Its dual-stage light-load management freezes peak current then reduces switching frequency to 25 kHz before entering burst mode-triggered by FB falling below 0.32 V and exiting above 0.46 V.

Protection architecture integrates timer-based brown-out detection (HVON = 108 V, HVOFF = 103 V), 26 µs OVP blanking, 12 µs TIMER latch-off for external fault signaling, and clamped DRV output (13.4 V) compatible with standard MOSFET gate drivers. The HV pin serves triple duty: startup current sourcing, brown-out sensing, and programmable X-cap discharge timing via internal 32/16/48-cycle sequencing.

Key Specifications

Pinout & Package

Available in SOIC8-7A package (standard 8-pin SOIC with exposed thermal pad on bottom, 7 active pins + 1 NC).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-frequency flyback controller applications.

Compared with UCC28704DR and ICE2QS03G, the HFC0400GS uniquely integrates HV startup, X-cap discharge, and burst-mode control in a single SOIC8-7A package-reducing total solution size by 30% and enabling sub-35 mW no-load power without external components.

Availability

HFC0400GS is available at Aetrix Electronics and suitable for AC/DC adapters, offline battery chargers, and LCD TV power supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant manufacturing.

Supply support for HFC0400GS 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

Monolithic Power Systems (MPS) is a fabless semiconductor company specializing in high-performance analog and power ICs, with design centers in the US, China, and Taiwan.

The HFC0400GS belongs to MPS's fixed-frequency flyback controller product line, engineered specifically for ultra-low standby power in universal-input AC/DC converters targeting energy-efficiency standards like DOE Level VI and EU CoC Tier 2.

FAQ

What is the maximum allowable input voltage on the HV pin?

The HV pin has a 700 V breakdown rating, allowing direct connection to rectified universal AC inputs (up to 375 VDC peak). Absolute maximum continuous voltage is 700 V; operation above this risks permanent damage. The brown-out detection thresholds (HVON = 108 V, HVOFF = 103 V) are independent of breakdown rating and define functional startup/restart behavior.

How does the X-cap discharge function operate without external components?

After AC removal, the HFC0400GS activates its internal HV current source in a 32-cycle detect → 16-cycle discharge → 16-cycle re-detect → 48-cycle discharge repeating sequence. This provides a controlled, low-power discharge path that meets IEC 62368-1 requirements without bleed resistors, reducing standby loss by up to 15 mW compared to discrete solutions.

Can the HFC0400GS support continuous conduction mode (CCM) operation?

Yes-the integrated 25 mV/µs slope compensation enables stable CCM operation even at duty cycles exceeding 50%, eliminating subharmonic oscillation. Designers can select KP (ripple-to-peak ratio) between 0.6–0.8 for universal input or 0.8–1.0 for 230 VAC-only applications without external compensation networks.

What protection features are latched versus auto-restarting?

Over-voltage protection (OVP) on VCC and external latch-off via TIMER pin are latched-requiring VCC to drop below 2.5 V to reset. Thermal shutdown (TSD), brown-out, overload (OLP), and short-circuit protection (SCP) are auto-restarting with hysteresis (e.g., TSD resumes at 125°C after tripping at 150°C).

Is a minimum VCC capacitor value specified for reliable operation?

Yes-MPS recommends ≥10 µF for the VCC capacitor to ensure stable brown-out detection and sufficient hold-up during line dips. Equation (4) in the datasheet calculates the minimum value based on internal latch current (585 µA typical) and half-input period; for 50 Hz operation, 10 µF provides >10 ms hold-up time, exceeding the required 50 ms OLP timer duration.

Does the frequency jitter feature require external components?

No-frequency jitter is fully internal and generated by a 10 µA current source charging/discharging the internal 14 pF capacitor on the TIMER pin. The jitter period (3.7 ms typical) and amplitude (±6.7% of 65 kHz) are fixed; no external RC network is needed, simplifying EMI compliance testing.

What is the purpose of the two leading-edge blanking (LEB) times?

The HFC0400GS uses dual LEB: 350 ns for normal current limiting (prevents false triggering from MOSFET switching spikes) and 270 ns for short-circuit protection (SCP). This ensures robust operation during normal transients while maintaining fast SCP response-allowing detection of 1.45 V CS voltage within 270 ns of MOSFET turn-on.