Input Impedance of High Side Buck (MP173A)

DC-DC Power Converters
1

Hello,

We are building a high side buck solution using the MP173A. We would like to place an LC filter at the input, like this:

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Based on this application note from TI (https://www.ti.com/lit/an/snva538/snva538.pdf), we understand it is important for stability that the output impedance of the LC filter is smaller than the input impedance of the switching converter. That same app note provides an analytical expression for the input impedance of a traditional buck converter on page 13.

My question is, what is the analytical expression for the input impedance of a high-side buck converter using MP173A? Is it the same as the traditional buck? Is the input impedance different if operating in DCM versus CCM mode?

Thanks,
Dustin

2

This is a buck, so same equations apply. The controlled switch is from Vin to the inductor