UC3861 Datasheet | Unitrode

FEATURES DESCRIPTION - Controls Zero Current Switched (ZCS) The UC1861-1868 family of ICs is optimized for the control of Zero Curor Zero Voltage Switched (ZVS) rent Switched and Zero Voltage Switched quasi-resonant converters. Dif Quasi-Resonant Converters ferences between members of this device family result from the various binations of UVLO thresholds and output options. Additionally, the - Zero-Crossing Terminated One-Shot one-shot pulse steering logic is configured to program either on-time for Timer ZCS systems (UC1865-1868), or off-time for ZVS applications (UC1861- Precision 1%, Soft-Started 5V 1864). Reference The primary control blocks implemented include an error amplifier to - Programmable Restart Delay pensate the overall system loop and to drive a voltage controlled oscillator Following Fault (VCO), featuring programmable minimum and maximum frequencies. Triggered by the VCO, the one-shot generates pulses of a programmed maxi- Voltage-Controlled Oscillator (VCO) mum width, which can be modulated by the Zero Detection parator. with Programmable Minimum and Maximum Frequencies from 10k Hz to This circuit facilitates “true” zero current or voltage switching over various line, load, and temperature changes, and is also able to acmodate the 1MHz resonant ponents' initial tolerances. - Low Start-Up Current (150µA typical) Under-Voltage Lockout is incorporated to facilitate safe starts upon - Dual 1 Amp Peak FET Drivers power-up. The supply current during the under-voltage lockout period is typically less than 150µA, and the outputs are actively forced to the low - UVLO Option for Off-Line or DC/DC state. (continued) Applications Device UVLO Outputs “Fixed” 1861 16.5/10.5 Alternating Off Time 1862 16.5/10.5 Parallel Off Time 1863 36014 Alternating Off Time 1864 36014 Parallel Off Time 1865 16.5/10.5 Alternating On Time 1866 16.5/10.5 Parallel On Time 1867 36014 Alternating On Time 1868 36014 Parallel On Time BLOCK DIAGRAM Pin numbers refer to the J and N...