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CSD17578Q3A: How to estimate the max switching frequency

Dong Shen
Prodigy 400 points
Part Number: CSD17578Q3A

Hi, Team

We know that A MOSFET is a switch, the switching frequency is determined by the device or circuit driving the MOSFET. But in many time, we need to estimate the max switching frequency of MOSFET. Whether we can use Switching Times of mosfet to estimate it?

For example, td(on), tr, td(off) and tf can be got from datasheet. The minimum time of a switching period under the test condition of datasheet is: T= td(on)+tr+td(off) + tf=2+6+13+1=22ns. Then the maximum switching frequency under the test condition of datasheet is : f = 1/T = 45MHz.

In this way, we can estimate the max switching frequency. Is it correct?


  • 0
    TI__Mastermind 18200 points

    Dong, 

    While you are correct in theory, the reality is a bit more complicated. 

    For one, rise times and fall times in MOSFET datasheets are historically unreliable and pretty useless parameters. I wrote a blog about this here:

    Secondly, when you approach the MHz frequency range, keep in mind your switching losses are going to be very severe. You are  most likely going to be thermally limited by your switching losses long before you ever get near 45MHz, unless  you are using an RF FET or something along those lines.