Synchronous rectifier controller enhances overall system efficiency
Texas Instruments UCC24624 SR Controller is dedicated for LLC resonant converters to substitute the lossy diode output rectifiers with SR MOSFETs and enhance the overall system efficiency. The SR controller employs a drain-to-source voltage sensing method to accomplish on and off control of the SR MOSFET. Proportional gate drive is performed to increase the SR conduction time, reduce the body diode conduction time. To compensate for the offset voltage created by the SR MOSFET parasitic inductance, the device implements an alterable positive turn-off threshold to support different SR MOSFET packages. The device has a built-in 475ns on-time blanking and a fixed 650ns off-time blanking to skirt SR false turn-on and turn-off. The device also integrates a two-channel interlock function that stops the two SRs from being on at the same time. With 230V voltage-sensing pins and 28V ABS maximum VDD rating, it can be directly employed in converters with output voltage up to 24.75V. The internal clamp enables the controller to support 36V output voltage simply by attaching an external current limiting resistor on VDD.
With the built-in standby mode detection based on average switching frequency, the device enters the standby mode automatically without employing external components. The low standby mode current of 180µA supports satisfying modern no-load power consumption conditions such as CoC, and DoE regulations. The device can be used with the UCC25630x LLC and UCC28056 PFC controllers to deliver high efficiency while preserving best light load and no-load performances. Other PFC controllers, such as UCC28064A, UCC28180, and UCC28070 can be utilised to deliver higher power levels. A 1.5A peak source and 4A peak sink driving ability enables the device to support LLC converters up to 1kW.