Part Number:TPS54540
in tps54540 datasheet, i found below description.
When operating with a low voltage difference from input to output, the high side MOSFET of the TPS54540 will
operate at 100% duty cycle as long as the BOOT to SW terminal voltage is greater than 2.1V. When the voltage
from BOOT to SW drops below 2.1V, the high side MOSFET is turned off and an integrated low side MOSFET
pulls SW low to recharge the BOOT capacitor.
i believe it means when the input voltage below the Vout set point(for example, the Vout set point is 12V, and the input is 11V. The actual output is less than 11V), the TPS54540 will work in 100% duty cycle for some cycles. Then the high side MOS turn off and low side MOS turn on to charge the boot CAP. So it is similar to decrease the switching frequency on some level(decrease the frequency of charing boot cap).
The ''low frequency'' means the device has slow transient response. Do we have other device which have max fixed duty and charge the boot cap in every cycle?
Vin=28~30V, Vout=26~28V, Iout=3A
Thanks.