UCC27201: UCC27201DR Bootstrap Capacitor Value problem

Hello Cheney,
For the bootstrap capacitor value, for 100% duty cycle operation. There is not a value of capacitor that can solve this issue by itself. With 100% duty cycle there has to be a bias voltage available to be able to maintain the HB-HS bias voltage just to maintain the quiescent current of the HB supply.
I posted in a previous similar post the advice below, to use the SN6501 isolated bias transformer driver for the floating HB-HS bias. Please see below.
Hello Cheney,

Thank you for the interest in the UCC27201 half bridge driver. For operation at 100% duty cycle of the high side MOSFET there will be a concern of maintaining the HB-HS high side bias voltage. The bootstrap capacitor is charged when the HS pin of the driver switches close to ground allowing the bootstrap capacitor to be charged from VDD thru the internal boot diode.

For 100% duty cycle operation, there needs to be an isolated bias supply to provide the bias to HB-HS. The SN6501 is a simple solution to drive a small isolation transformer for this application. Information on this device can be found here:
www.ti.com/.../SN6501


Let me know if you have any questions.

Regards,

Richard Herring