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UCC27712: External bootcap diodes selection for UCC27712

Gabriel Xu
Intellectual 2145 points
Part Number: UCC27712

Hi teams

Customer planning to use UCC27712 in their new design and want to figure it out the spec requirement for external bootcap diodes.

I notice that EVM have select a diode with 600V voltage tolenrance and 1A forward current. Customer use this gate driver in 24V system currently.

My questions:

  1.  100V voltage tolenrance diodes will be enough or not for 24V application?
  2. The diode we currently use only have 150mA forward current, any potential risk?
  3. Any other spec should be caution for this diodes?
  • 0
    TI__Mastermind 23215 points

    Hello Gabriel,

    For the diode voltage rating, I would choose a diode voltage rated to match the Vds rating of the MOSFETs. For 24V DC input, 100V sounds like enough margin but it depends on how much Vds overshoot and ringing exists.

    For the current rating, the average current in the boot diode will not be high, but I would make sure the diode peak rating is adequate to handle the maximum current on the boot diode initial charge. We usually recommend some boot diode series resistance, so the way to determine the maximum peak current  is just VDD/Rboot.

    Select a fast recovery diode of 25-50ns to minimize energy lost from the boot cap from boot diode reverse current.

    Regards,

  • 0 in reply to Richard Herring
    TI__Intellectual 2145 points

    Hi Richard

    Thanks for your reply, currently we didn't plan to add a resistor in series with this bootcap.

    What will happen if the diode peak current is not enough for UCC27712? 

    Any UVLO protection for the bootcap voltage? 

  • 0 in reply to Gabriel Xu
    TI__Mastermind 23215 points

    Hello Gabriel,

    I would recommend having a resistor in series with the boot diode to limit how fast the HB-HS rises during the initial charging of the HB capacitor. The peak current through the boot diode is a concern for the boot diode selection peak current rating. In the datasheet section 8.2.2.4 there is a recommendation to have a boot resistance to limit the HB rise time to 20us or greater.

    Regards,