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UCC5350-Q1: Is Miller Clamp Required for MOSFET 3 phase Motor Driver

Egemen Aksoy
Intellectual 975 points
Part Number: UCC5350-Q1
Other Parts Discussed in Thread: UCC21551,

Hello,

In our project, we will use 8 MOSFETs in parallel for both the low side and the high side of a 3-phase motor driver — a total of 16 MOSFETs per phase and 48 in total for all three phases.
The MOSFET ordering codes are IPTC014N10NM5ATMA1 and IPTC034N15NM6ATMA1.
Do we need to use a gate driver with Miller clamp to drive these MOSFET gates, or can we use a product like UCC21551 instead?

Best regards,

  • 0
    TI__Intellectual 2705 points

    Hi Egemen,

    UCC5350MC includes a miller clamp pin as a protection feature to prevent false turn-on of the MOSFETs due to miller current. I highly recommend to read up on this Application Brief if you are not familiar with Miller clamp circuitry [Link]. However, if your system does not require a gate driver with a miller clamp pin and you would rather use a dual-channel gate driver instead, then the UCC21551 is a great option from that portfolio that I would recommend to look into first.

    Best regards,

    Will

  • 0 in reply to Will Appelt
    Intellectual 975 points

    Hello,

    Thank you for your reply,

    Actually I have read application brief before.

    Our system is unipolar supply which shall be supplied with 24V to 96V vehicle batteries.

    According to the application brief, it is recommended of course but I think it is more crucial for bipolar supply systems.

    Could you please share your thoughts about does our system needs miller clamp?

    Best regards,

  • 0 in reply to Egemen Aksoy
    Intellectual 975 points

    Hello,

    Additionally for the last question, if we decide to use miller clamp do you recommend internal (which the case directly using UCC5350-Q1) or external miller clamp?

    Best regards,

  • 0 in reply to Egemen Aksoy
    TI__Intellectual 2705 points

    Hi Egemen,

    For unipolar supplies, having a miller clamp is more crucial than a bipolar system, since the voltage spike needed to generate a false-turn on would be smaller on a unipolar system due to the VEE voltage being 0V instead of -8V for example.

    As for internal vs external miller clamp, the Application Brief has a section that covers this topic titled "Purpose of the Miller Clamp and Internal Versus External Implementation". The general recommendation is to use an external miller clamp implementation if you are driving parallel FETs, which seems to be the case for your system.

    Best regards,

    Will

  • 0 in reply to Will Appelt
    Intellectual 975 points

    Hello Will,

    We shall operate gate drivers with 15V. And system shall be isolated system.

    In our system gate drivers shall be close to the MOSFETs, since this is the case still we need external miller clamp?

    If you strictly recommend external miller clamp, should we use BJT or FET? What should be the BJT or FET specs for the miller clamp? (Current rating, voltage etc.). Could you recommend some parts for that purpose?

    Best regards,

  • 0 in reply to Egemen Aksoy
    TI__Intellectual 2705 points

    Hi Egemen,

    If the trace distance from the MOSFETs to the gate driver is not very long, then internal miller clamp would probably be fine.

    If you choose to use an external miller clamp, it is generally recommended to use FETs for the external clamp. The specs of these FETs depends on your system needs. Voltage rating, threshold voltage, drive strength, etc. are all examples of specs to consider, but will largely depend on what is needed in order to clamp the miller current in your system.

    Best regards,

    Will