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UCC28064A: External vs Internal Gate Driver for MOSFETs used with UCC28064A

D R
Prodigy 70 points
Part Number: UCC28064A
Other Parts Discussed in Thread: TIDA-010015

I am looking at TIDA-010015 reference design which uses UCC28064A. In this design, two external gate drive ICs are used to drive the two MOSFETs in interleaved boost converters. Why are those external gate drives needed, compared to driving MOSFETs directly from GDA and GDB pins on the UCC28064A? 

Looking at UCC28064A datasheet, GDA and GDB voltage is 12.4V typical (10.7 - 15V range). MOSFETs used are IPA60R120P7XKSA1. Their acceptable Vgs is +-20V, with Vgs threshold 3.5V typical (3-5V range). Should this mean that the MOSFETs can be driven directly from the GDA and GDB? 

  • 0
    TI__Mastermind 44220 points

    Hi D R,

    I would have to check with our product design services team but looking at the FETs, they may have chosen a stronger gate driver due to the higher gate charge of the Infineon FETs. These show a typical 36nC whereas the FETs used on the EVM have a maximum of 18nC and here no external gate drivers are used.

    I hope this answers your question.

  • +1
    TI__Mastermind 29350 points

    Hello D R,

    Thank you for your query regarding the UCC28064A gate-drive capability. 

    In some high power designs where very large MOSFETs or multiple MOSFETs are driven in parallel, the drive capability of the UCC28064A GDx outputs may be insufficient to handle the total gate charge with reasonable speed. In such cases an external gate-drive IC with higher drive power is warranted. 

    In the case of the TIDA-010015, the PFC power level is relatively low and the MOSFETs are relatively small with low gate charge, so I think the UCC28064A can easily drive these MOSFETs directly as you suggest.  In my opinion, the external gate-drivers (although good devices in their own right) provide no significant benefit to the design, and can be deleted (along with their input R-C filters and VDD caps).
    The TIDA designer may have included them to reduce turn-off loss if he thought that the 4A peak drive would discharge the 36nC gate charge of the MOSFETs in ~9ns compared to ~24ns by the controller drive.  However, the turn-off delay from Coss of these MOSFETs is typically longer than this time so the faster gate discharge has little to no effect. 

    Regards,
    Ulrich