UC2866NG4 Resonant-Mode Power Supply Controllers

FEATURES

-Controls Zero Current Switched (ZCS)or Zero Voltage Switched (ZVS)Quasi-Resonant Converters

-Zero-Crossing Terminated One-ShotTimer

-Precision 1%, Soft-Started 5VReference

-Programmable Restart DelayFollowing Fault

-Voltage-Controlled Oscillator (VCO)with Programmable Minimum and maximum Frequencies from 10kHz to1MHZ

-Low Start-Up Current (150μA typical)Dual 1 Amp Peak FET Drivers

-UVLO Option for Off-Line or DC/DCApplications

DESCRIPTION

The UC1861-1868 family of ICs is optimized for the control of Zero Current Switched and Zero Voltage Switched quasi-resonant converters. Differences between members of this device family result from the various combinations of UVLO thresholds and output options. Additionally, the one-shot pulse steering logic is configured to program either on-time for ZCS systems (UC1865-1868) or off-time for ZVS applications (UC1861-1864).

The primary control blocks implemented include an error amplifier to compensate the overall system loop and to drive a voltage-controlled oscillator(VCO), featuring programmable minimum and maximum frequencies. Triggered by the VCO, the one-shot generates pulses of a programmed maximum width, which can be modulated by the Zero Detection comparator. This circuit facilitates “true” zero current or voltage switching over variousline, load, and temperature changes, and is also able to accommodate the resonant components' initial tolerances.

Under-Voltage Lockout is incorporated to facilitate safe starts upon power-up. The supply current during the under-voltage lockout period is typically less than 150uA, and the outputs are actively forced to the low state.