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UCC21755-Q1: UCC21755-Q1

Naveen Devarakonda
Prodigy 10 points
Part Number: UCC21755-Q1
Other Parts Discussed in Thread: SN6501,

Hi TI,

Happy New Year. I'm using UCC21755 gate driver to drive SiC Mosfet (NTH4L020N120SC1) to control 3-Ph BLDC Motor. I'm in a early stage of designing the Inverter circuit. I have only positive 15V available to Power up gate driver. It means, I do not have -ve bias voltage to VEE pin. Could you please guide how to make connections towards High side of Mosfet? Please let me know if you have any questions. 

Details: 

Working voltage: 270V

Working current: 35Amps. 

Isolated voltage: 15VDC 

  • 0
    TI__Genius 15286 points

    Hi Naveen,

    Thank you for your question, you are in the right place!

    The power supply for the high-side gate driver is the most difficult to understand when getting started with half bridge drivers. This primer is a must-read: https://www.ti.com/lit/ml/slua618a/slua618a.pdf  Most people start with a non-isolated gate driver and a bootstrap supply, as this describes.

    But for higher voltages (>120V), you have to switch to an "isolated" gate driver like the UCC21755-Q1. It can survive much higher switch node voltages and ringing. These also require using an isolated supply, such as the SN6501 and a small transformer. You can use a isolated single supply with a bootstrap circuit on the isolated side, or you can use two isolated supplies, one for the high-side and one for the low-side. 

    In general, a bootstrap circuit works by charging a capacitor to ~15V through a high voltage diode when the low-side switch is closed. When the low side switch opens, this capacitor is allowed to float on top of the switch node (open switch). This gives you a power source that is 15V above the switch node. You can power the high-side gate driver with this capacitor.

    Here is a reference design I made while in HSAMPS that you might find helpful as well: https://www.ti.com/lit/ug/tidueh2c/tidueh2c.pdf It has some helpful links to InstaSPIN and the DRV8301-69M kit that I found to be very helpful when designing my first motor inverter.

    Best regards,

    Sean

  • 0
    TI__Expert 4460 points

    Hi Naveen, 

    Welcome to E2E! If you are not designing the gate driver circuit with a negative bias, you can simply tie the VEE pin on the gate driver to the COM pin. The COM pin is then tied to the source of the MOSFET you're trying to drive. 

    If you're not using negative bias, I highly recommend using CLMPI pin on UCC21755 to prevent false turn-on caused by the Miller capacitance. You can connect the CLMPI pin to the gate of the MOSFET with a short trace. 

    Please don't hesitate to reach out if you have any other questions. 

    Thanks! 

    Vivian