The UCC25660 implements a high-speed low latency slew-rate detection block to optimize the dead time between high-side and low-side pulses. The adaptive dead-time block adjusts the dead time to prevent shoot through or excessive body diode conduction.

At the core of the adaptive dead time block is the slew rate detector block, capable of detecting slew rates upto 200V/ns, making UCC25660 an excellent choice for use in high frequency resonant converters.

In burst mode, during a ZCS prevention operation or in power stages where the slew rate can be very slow, the resonant tank current polarity signal (Ipolarity comparator output) is used to augment the slew rate detector.

Taking advantage of the natural symmetric operation of LLC, only the dead time between high-side switch turn off and low-side switch turn on is determined by the slew rate detector. This dead time is copied and then applied to the dead time between low-side MOSFET turn off and high-side MOSFET turn on. There are a few exceptions where the dead time is not copied. The conditions are listed below.

• Missing Slew rate detector signal in the previous High to Low transition.
• ZCS detection in the previous cycle.

Under the above-mentioned conditions, the Ipolarity comparator based on the ISNS signal is used to adjust the dead time during low to high transitions.