ON Semiconductor FAN7688 is an advanced pulse frequency modulated (PFM) controller for LLC resonant converters with synchronous rectification (SR) that offers best-in-class efficiency for isolated DC/DC converters. It employs a current mode control technique based on a charge control, where the triangular waveform from the oscillator is combined with the integrated switch current information to determine the switching frequency. This provides a better control-to-output transfer function of the power stage simplifying the feedback loop design while allowing true input power limit capability. Closed-loop soft-start prevents saturation of the error amplifier and allows monotonic rising of the output voltage regardless of load condition. A dual edge tracking adaptive dead time control minimizes the body diode conduction time, thus maximizing efficiency.
Features
- Secondary side PFM controller for LLC resonant converter with synchronous rectifier control
- Charge current control for better transient response and easy feedback loop design
- Adaptive synchronous rectification control with dual edge tracking
- Closed-loop soft-start
- Wide operating frequency (39 kHz to 690 kHz)
- Green functions to improve light-load efficiency
- Symmetric PWM control at light-load to limit the switching frequency while reducing switching losses
- Disabling SR at light-load condition
- Wide operating temperature range: -40°C to +125°C
- Protection functions with auto-restart
- Overcurrent protection (OCP)
- Output-short protection (OSP)
- Non-zero-voltage switching prevention (NZS) by compensation cutback (frequency shift)
- Power limit by compensation cutback (frequency shift)
- Overload protection (OLP) with programmable shutdown delay time
- Over-temperature protection (OTP)
- Programmable dead times for primary side switches and secondary side synchronous rectifiers
- VDD undervoltage lockout (UVLO)
- SOP-16L package
Applications
- Desktop ATX, desktop-derived server, blade server, and telecom power supplies
- Intelligent 100 W to 2 kW+ off-line power supplies
- Industrial power
- High-efficiency isolated DC-DC converters
- Large screen display power