7.3.12 Frequency Shift

To operate at high switching frequencies and provide protection during overcurrent conditions, the TPS54618 implements a frequency shift. If frequency shift was not implemented, during an overcurrent condition the low-side MOSFET may not be turned off long enough to reduce the current in the inductor, causing a current runaway. With frequency shift, during an overcurrent condition the switching frequency is reduced from 100%, then 50%, then 25%, as the voltage decreases from 0.799 to 0 V on VSENSE pin to allow the low-side MOSFET to be off long enough to decrease the current in the inductor. During start-up, the switching frequency increases as the voltage on VSENSE increases from 0 to 0.799 V.