The UCC24624 high-performance synchronous rectifier (SR) controller is dedicated for LLC resonant converters to replace the lossy diode output rectifiers with SR MOSFETs and improve the overall system efficiency.
The UCC24624 SR controller uses drain-to-source voltage sensing method to achieve on and off control of the SR MOSFET. Proportional gate drive is implemented to extend the SR conduction time, minimize the body diode conduction time. To compensate for the offset voltage caused by the SR MOSFET parasitic inductance, the UCC24624 implements an adjustable positive turn-off threshold to accommodate different SR MOSFET packages. UCC24624 has a built-in 475-ns on-time blanking and a fixed 650-ns off-time blanking to avoid SR false turn-on and turn-off. UCC24624 also integrates a two-channel interlock function that prevents the two SRs from being on at the same time. With 230-V voltage-sensing pins and 28-V ABS maximum VDD rating, it can be directly used in converters with output voltage up to 24.75 V. The internal clamp allows the controller to support 36-V output voltage easily by adding an external current limiting resistor on VDD.
With the built-in standby mode detection based on average switching frequency, UCC24624 enters the standby mode automatically without using external components. The low standby mode current of 180 µA supports meeting modern no-load power consumption requirements such as CoC, and DoE regulations. UCC24624 can be used with the UCC25630x LLC and UCC28056 PFC controllers to achieve high efficiency while maintaining excellent light load and no-load performances. Other PFC controllers, such as UCC28064A, UCC28180, and UCC28070 can be used to achieve higher power levels. 1.5-A peak source and 4-A peak sink driving capability allows UCC24624 to support LLC converters up to 1 kW.