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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
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