TIDUET3 February   2021

 

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2.3.3 UCC24624

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. Two independent SR control channels are integrated into the single package to minimize the external components and allow for easy PCB layout.

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, and improve efficiency. To compensate for the offset voltage caused by the SR parasitic inductance, the UCC24624 implements an adjustable positive turn-off threshold to accommodate different SR MOSFET packages. The UCC24624 has a built-in 450-ns minimum on-time blanking and a fixed 650-ns minimum off-time blanking to avoid SR false turn-on and -off. The UCC24624 also integrates a two-channel interlock function that prevents the two SRs from being on at the same time.

With the built-in standby mode detection based on average switching frequency, the UCC24624 enters the sleep mode automatically without using external components. The low standby mode current of 175 μA supports meeting modern no-load standby power requirements such as CoC and DoE regulations.

With a 1.5-A peak source and 4-A peak sink driving capability, the UCC24624 is able to support LLC converters up to 1-kW. With 230-V voltage-sensing pins and a 26-V maximum VDD rating, it can be directly used in converters with an output voltage of up to 26 V. The internal clamp allows the controller to support a 36-V output voltage easily by adding an external current limiting resistor on VDD.