UCC21225A: Boostrap Diode Average Current?

Hi Ting,

Thank you for your question. I work on the applications team in the high power drivers group.

The average bootstrap diode current will be much less than IDBoot(peak)/2. The peak bootstrap current occurs at start-up, during the initial charging of the bootstrap capacitor. Once the bootstrap node is charged up to its peak level, only a small amount of current will be needed to top it off every cycle. The average bootstrap current will drop to the approximate average current required to switch the high-side FET on and off every cycle along with the quiescent current of the driver.

You can calculate the average current using the below equation:

Iboot(avg, steadystate) = Qg * Fsw + IDDq

Where:

Qg = total gate charge

Fsw = switching frequency

IDDq = gate driver quiescent current at your selected switching frequency

For example: If driving a FET with 100nC gate charge @ 100kHz.

Iboot(avg, steadystate) = 100nC * 100 kHz + 2mA = 10mA

If this answered your question, could you please press the green button? If not feel, free to ask more questions.

Thanks and best regards,

John                                                                                                                                                                                  

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