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UCC27533: Three Phase Inverter Driver Circuit using ISO7710 and UCC27533

Part Number: UCC27533

Hi,

I am referring to Application Report SLUA669A.

I have a three phase inverter using a setup similar to the application note. The PWM inputs go through a ISO7710f isolator and then power MOSFET's through a UCC27533 driver, unlike figure 3 I am using an isolated supply to power the driver and isolator like in figure 4. I want to make sure that this setup is valid, I see in figure 3, that there is a resistor on the VDD line of each isolator, is there a purpose to this resistor, will not having it cause reliability concerns? Are there any specific recommendations for this setup in regards to driving SiC MOSFET's, for example which setup is best suited or will any problems arise from these figures?

Regards,

Ryan Fernandes

  • Hello Ryan,

    Thanks for reaching out.

    The resistor in Figure 3 are just current limiting resistors to limit the slew rate on the VDD supply and Cboot supply. They act as additional protection against potential surges on the supply. These are generally optional but highly recommended.

    The setup depends on your application: Figure 4 uses an isolated driver (taking care of the isolation and the gate drive portion at the same time) on the high-side therefore you only one ISO77xx and the floating transformer bias. Copied is an example reference design.

    Figure 3 uses a low-side driver on both high-side and low-side where you need isolators acting as a level-shifter and the driver taking care of the gate drive portion.

    Regards,

    -Mamadou 

  • Hi,

    Can you reference an application note or guideline on how to size these resistors if they are indeed recommended?

    Regards,

    Ryan Fernandes

  • Hi,

    We do not currently have a dedicated app note discussing this topic but we have commonly used Rdd resistors anywhere between 2 to 5-Ohms with our drivers as shown on the copied EVM

    Again optional but good idea to at least have a placeholder that you can short if your application do not expect surges.

    Regards,

    -Mamadou