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UCC2808-2: Gate drive resistor values vs absolute maximum ratings?

Part Number: UCC2808-2

Hello,

Your data sheets for all UCCx808x products describe a max rating of -0.5A (source) and 1.0A (sink) on the OUTA and OUTB pins. Yet, in all the data sheets for these products, I see reference designs that have low sibgle-digit ohm ratings for the resistors between the OUTs and the FET gates, which would seem to be contradictory. If I was looking to run any of these parts at 14V, it seems to me I'd have to have a resistor above 28 ohms to prevent burning out the device. Is there something I'm missing here? Is it that the peak value of current driving the FET gates is so brief as to ignore the max rating?

In short, I'm having trouble driving gates to said 14V with resistors large enough to prevent exceeding absolute maximum ratings, but the one time I attempted a smaller resistance  (in this case 10 ohms) I ended up cooking the part.

Thanks!

  • Hello Brian,

    The -0.5A and 1.0A limits are continuous current limits and if you use the UCC2808-2 to drive a pair of FETs the current is pulsed due to the capacitive nature of the gate to source connection. This means the average drive current is very low, well within the device limits.
    The data sheet uses a 2.2 Ohm gate resistor and the TIDA-00821 reference design uses a direct connection between the outputs and the gates.

    Please check your OUTA and OUTB connection to GND.

    You should be able to use 10 Ohms between these nodes and the gates of your FETs

    Regards

    John

  • John,

    Thank you for getting back to me. That is the answer I was hoping for. Just so you know, the datasheet for the "sister" UCCx808x devices identifies this as a peak current, as opposed to a continuous average.

    I'll take a closer look at what else might have done damage.

    Thanks again!