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Original question:

TPS65261: Understanding pull-up currents for external cap CEN

TPS65261: Bootstrap capacitor

Michael Rosa
Prodigy 420 points
Part Number: TPS65261

Hi, 

The datasheet recommends a 47nF capacitor between LX and BST pins. My customer is using a 100nF capacitor here.

Could you please tell me what the min/max range for this capacitor value is?

Thank you,

Michael Rosa

  • +1
    TI__Genius 16600 points

    Hi Michael,

    Thanks for reaching out. The range of Cboot is related with your application and key cares, like duty, EMI...And it's better to validate this value based on board.

    It will be good to use a 100nF capacitor here. May i check what's your concern for this cap?

    Thanks!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Prodigy 420 points

    Hi Lucia,

    I was reviewing a customer schematic (the same from our previous email exchange) and noticed the 100nF value instead of the recommended 47nF value from the datasheet. Good to know that it should be okay.

    I ask because I am not familiar with the purpose and selection criteria of the bootstrap cap. This article seems to indicate that it is used with a charge pump circuit to provide the higher gate drive voltage for the switching FET: https://www.ti.com/lit/an/slyt747/slyt747.pdf. I can infer that a higher voltage rating and low leakage are important, as well as temperature stability.

    Thank you,

    Michael

  • 0 in reply to Michael Rosa
    TI__Genius 16600 points

    Hi Rosa,

    Yes, I remembered the customer schematic from the previous email and nice to have a discussion with you again  :) I agree with you that it is used with a charge pump circuit to provide the higher gate driver voltage for the switching FET. 

    Anything further concern, kindly let me know. Thanks!

    BRs

    Lucia