UCC21710-Q1: Gate resistor selection

Arun Kumar

Part Number: UCC21710-Q1
Other Parts Discussed in Thread: UCC21710

Hello Experts,

We are using the UCC21710 as our main gate driver.

Is there any application notes/Theory available to suggest how do we calculate the optimum gate resistor values.

In our custom motor drive inverter board, we had origenally kept a value of 2 Ohm(OUTH and OUTL), we observed a lot of dv/dt unstability at higher loads,

Later we changed the OUTH resistor to 10 ohms are the dv/dt related unstability significantly reduced. I know this is also dependent on the MOSFET that is used and its gate charge and the load on the MOSFET itself, but i dont have a full understanding of this.

Could you please help me understand how do we calculate the ideal gate resistors.

Thanks

over 2 years ago

+1 Pratik Adibatla over 2 years ago

TI__Expert 8578 points

Hi AK,

Thanks for the interesting question. You're correct that the external gate resistor affects the turn-on time, turn-off time, switching loss, transient voltage (dv/dt) and transient current (di/dt) of the device. For power devices, rise time, fall time and delays between turn on and turn off are usually different, and thus require separate consideration. For example, the di/dt at turn off can result in a large voltage overshoot, so it is beneficial to reduce the switching speed. However, during turn on, it is better to switch fast to reduce switching losses. In addition, having lower gate resistance at turn off is beneficial for SiC MOSFETs to prevent false turn on caused by fast switching and miller current. Therefore, highly depends on the type of switch and its characteristics as well.

Please refer to the below app note for more details:

https://www.ti.com/lit/an/slla385a/slla385a.pdf?ts=1693240200994&ref_url=https%253A%252F%252Fwww.google.com%252F

https://www.ti.com/lit/an/slla387a/slla387a.pdf?ts=1611333491703&ref_url=https%253A%252F%252Fwww.google.com%252F

Best,

Pratik

0 Arun Kumar over 2 years ago in reply to Pratik Adibatla

Expert 1030 points

Thanks Pratik. The application note was usefull

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UCC21710-Q1: Gate resistor selection