The TPS564255 is designed with Out-of-Audio™ (OOA) feature that keeps switching frequency above the audible frequency region at light load or no load conditions. Once the converter determines that there is no switching for longer than 30us, it turns on the low-side MOSFET which brings VFB lower than internal VREF and initiates a new Ton cycle. This ensures that the switching frequency doesn’t go lower than 25kHz typical.