SLVSAF1E October 2010 – May 2019 TPS54388-Q1
To operate at high switching frequencies and provide protection during overcurrent conditions, the TPS54388-Q1 device implements a frequency shift. Without this frequency shift, during an overcurrent condition the low-side MOSFET might not turn off long enough to reduce the current in the inductor, causing a current runaway. With frequency shift, during an overcurrent condition there is a switching-frequency reduction from 100% to 50%, then 25%, as the voltage decreases from 0.8 V to 0 V on the VSENSE pin. The frequency shift allows 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 V to 0.8 V. See Figure 6 for details.