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UCC21530-Q1: boot strap diode selection

Part Number: UCC21530-Q1

Hi Experts,

Would you tell a selection criteria of boot strap diode? A following diode can be used? (datasheet p31, Figure 41, VDD=12V(this does not come from battery supply))

https://assets.nexperia.com/documents/data-sheet/PNE20020ER.pdf


Best Regards,
Fujiwara

  • Fujiwara-san,

    Thanks for your question.

    The diode you've mentioned will work as a bootstrap diode. It seems specifically targeted towards SMPS applications. You'll just want to confirm that the blocking voltage is high enough.

    The main considerations when selecting the bootstrap diode are are:

    • Forward repetitive peak current rating ( to ensure robustness of the device in the application)
    • Low Forward voltage (to reduce loss in the diode due when recharging the bootstrap capacitor during a half-cycle)
    • Blocking voltage (depending on the system, this needs to be sufficiently high to withstand the repetitive HS/Switch node Voltage + 12V supply)
    • Low-to-zero reverse recovery charge (reduce reverse recovery time and & reduced power consumption)

    Because the bootstrap diode is repeatedly charging the bootstrap every other half-cycle, the reverse recovery charge becomes a big factor, which is why the diode you mention advertises superfast reverse recovery characteristics.

    Another option for bootstrap diodes are Schottky-barrier diodes which have lower forward voltage and 0 reverse recovery compared to conventional diode, which leads to reduced conduction and reverse recovery losses in the diode. UCC21530-Q1 EVM, section 8 .  For example EVM design uses a 2A/600V Schottky diode (Cree C3D02060E 2A/600V schottky -> https://www.wolfspeed.com/c3d02060e)

    The Schottky diode will be significantly more expensive will be significantly more expensive than the one you posted, however. Theres definitely also a cost consideration to choose between the conventional diode and Schottky-barrier.

    In summary, the diode you posted the datasheet will work for the bootstrap diode. Just recommend to check that the rating will be robust enough with the 200V rated part (bus voltage will be <200V). If higher than that, I'd recommend looking at the other diodes in that product family with higher ratings. 

    This technote is another good reference for bootstrap circuits 

    I hope this helps with your question. If I've answered your question, please let me know by clicking the green button. And if you have any additional questions do let us know!



    Best,

    Dimitri