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Gate Drive Comparison - TPS40304 and TPS40170

Bill Drumheller
Prodigy 135 points
Other Parts Discussed in Thread: TPS40304, TPS40170

Hello,

I am curious what the gate drive performance of two similar PWM synchronous buck controllers are.  I currently have a design using the TPS40304 that has the following gate drive characteristics:

Voltage rail - 6.5 V

High side turn-on resistance - 1.5 ohms

High side turn-off resistance - 1.0 ohms

Low side turn-on resistance - 1.5 ohms

Low side turn-off resistance - 0.6 ohms

I want to convert this design to a TPS40170 (with the same switching frequency and same MOSFETs) but I want to be sure that it will drive the FETs properly and maintain a similar efficiency.  I can see from the TPS40170 data sheet that the voltage rail is higher than the TPS40304 (8.0 V) but the resistances are higher across the board.  Is there a way to analyze this to determine drive capabilities?  Can I setup something in TINA to check this or is there someway to compare the two drivers using the data sheet?

Thanks,

Bill

  • 0
    TI__Mastermind 35115 points

    With higher pull-down and pull-up resistance the turn-off and turn-on speeds should be a little bit slower with the TPS40170 increasing the switching losses in the high-side FET some. Calculating the switching losses isn't very straight forward, but a reasonable estimation of the relative switching losses could be done using the equations on page 9 in the document below. As this document mentions, a lot of parisitics are ignored that can be found in the real system.

    http://www.ti.com/lit/ml/slup169/slup169.pdf

    The higher voltage rail will also increase the TPS40170 driver switching loss slightly as the FET gate will be charged up to a higher voltage increasing the gate charge. This loss is estimated by VIN*Qg*fsw. I expect this to be small in comparison to the increase in the FET switching loss.

    Hope this helps.

    Best Regards,
    Anthony