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how to understand the peak sink/source current for gate driver

Aki Li
Genius 9785 points
Other Parts Discussed in Thread: UCC27524, UCC21520

We defined the peak sink and source current for every gate driver, like 5A/5A for UCC27524. If we used a small gate driving resistor and the calculated peak current is larger the defined max value, how would the actual peak gate driver current during the turn on and off? For example, the calculated peak source current can reach up to 6A, is there any scheme for clamp the actual peak source current at 5A? 

In the UCC21520 datasheet, when estimating the gate driver power loss, it assumed the source and sink current is constant at peak values during the turn on and off transient, if the source/sink current is saturated.

  • 0
    TI__Mastermind 23155 points

    Hello Aki,

    The only way to realistically limit the gate driver current to a specific value would be by sizing the resistance to achieve the given peak current based on the VDD to the driver. You would need to include the resistance of the internal driver device and the internal Rg of the FET. For example if your VDD is 15V and the target is 5A the external resistance would be 15V/5A - Rg(FET - Rdriver. 

    Regards,

  • 0 in reply to Richard Herring
    TI__Genius 9785 points

    Hi Richard,

    In some actual applications, like SR FETs in LLC, customer used very small gate resistor and expect to maximize the peak current capability. In such case, the calculated gate driver current( considering the resistance of the internal driver device and the internal Rg of the FET) is larger than 5A, does it make sense? Will it be a risk for gate driver to work in this way, if the thermal performance is acceptable?

  • 0 in reply to Aki Li
    TI__Mastermind 23155 points

    Hello Aki,

    I agree that in many applications the gate resistance can actually be 0 ohms to achieve the fastest possible Vgs rise and fall time. This is not a concern for the driver to operate in this condition. As long as the temperature rise and junction temperature is within the datasheet recommended range, and also the average current is within the average current ratings.The driver average current is just the Qg x fsw for each driver channel.

    Regards,

  • 0 in reply to Richard Herring
    TI__Genius 9785 points

    Richard,

    Thank you for the detailed explanation!