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BQ24610 bootstrap diode selection

BX27
Genius 3900 points

Hi there!

In figure19 of datasheet, there is a diode D1 between BTST and REGN pins. this shematic uses BAT54C.

Why a Schottky diode is required? and how should we choose the forward current(If) rating of this diode?

Thanks!

  • 0
    Genius 3900 points
    Another question is about the boot strap capacitor C6. if the Vin is 19V , is it necessary to use a 50V cap (as EVM board used) ?
    I think 25V rating is enough. thanks!
  • 0 in reply to BX27
    TI__Expert 8690 points
    Hi Yi,

    You want to use a Schottky diode because it can switch faster as the BTST will be charged every cycle. If you want to use a different diode, just find one that has similar properties as the one we have in the EVM.

    As for the Bootstrap capacitor, you want to have VIN + ~6V, and 25V rating would be just in the boundary. You want to use a higher rating to provide margin.

    Thanks,
    Steven
  • 0 in reply to Steven Bangdiwala
    Genius 3900 points

    Hi Steven,

    About the diode, besides of the fast Trr, I am not sure how its Forward Current rating is chosen. the EVM uses D1 : ZLLS350, whose datasheet provides 380mA If parameter while your EVM manual says D1 "1.16A, 40-V" in page 8(BOM page). there  seem to be inconsistency on this component.

    About the cap, I will use higher rating. but in datasheet page30(Table 5) uses C6 0.1uF/16V. this seems to be incorrect.

    Thanks!

  • 0 in reply to BX27
    TI__Expert 8690 points

    Yi,

    You should follow the EVM user guide, which is what our EVM uses. We evaluate our EVMs to make sure they work as we expect, so if you follow those guidelines, then you are good. Use similar diode to the user guide (ZLLS350). This diode will not continuously conduct like a regular diode, only each cycle to charge up the bootstrap.

    As for the bootstrap cap (C16), the user guide uses 50V rating, and I suggest you use that rating as well to leave enough margin.

    Thanks,
    Steven

  • 0 in reply to Steven Bangdiwala
    Genius 3900 points

    Steven,

    I re-consider about the boostrap cap rating and look into some IR application note on NMOS high-side drive. the voltage seen by this cap is just REGN-diode (about 6V) rather than VIN + ~6.

    Please see attachment page5 "3. HOW TO SELECT THE BOOTSTRAP COMPONENTS".