TPS54160A: Ripple noise countermeasures

Hello Ishwata,

Placing a resistor in series with the Cboot can help slow the rise time of the internal high-side FET, which can reduce the fast turn-on ringing and output noise. 

The negative of including the series R is that it will dissipate power during switching the FET. Increasing the R value will reduce efficiency by increase the switching loss. If the R is too large, it may affect the gate drive by tripping the internal gate drive UVLO. 

100Ω may be larger than recommended. Typically a value of up to 20Ω or 30Ω might be recommended. You might want to look at the PH node waveforms to make sure that the device is switching properly. You may also want to measure efficiency with and without the series R.

If you are trying to reduce output ripple and noise, you can also try adding some ceramic output caps or additional filtering to meet your ripple and noise requirements instead of adding the series Rboot which affects efficiency.