TPS56C215: Cff change

Brian Chan 

Amod is out of the office today in observance of the US holiday.  He will get back to you once he is back in the office.

Hi Brian,

Please refer to table 8-2 in the datasheet for recommended Cff value. for 0.9V and 1.2V no need to populate Cff.

Thanks,

Nancy

Hi Nancy

I have check it on datasheet. and customer would like to know about the side effect part.

thx for your reply

BRs

Brian

Hello Nancy,

Sorry to push but customer need an explanation tomorrow morning. Do you have the side effect on those >=10nF Cff? If no side effect, please provide your description for it. Thanks a lot!

Best regards,

Ann Lien

Hi Ann, Brian,

Generally Cff provides a low impedance path for the high frequency signal from Vout to FB. With larger Cff value, the impedance for this path at high frequency range is smaller. That means the output voltage variation can be transmitted to FB pin more quickly. From the view of stability, the larger Cff could help to increase bandwidth and boost phase margin. It benefits the load transient performance. Usually recommend use at higher output voltage. However, this cap pushes bandwidth to high and may cause instability. Please refer to below application note and datasheet recommendation for Cff value.

We recommend add Cff as placeholder and install it if needs for improvement of load transient.

https://www.ti.com/lit/an/slva289b/slva289b.pdf?ts=1688561342289&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fen-us%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253DSLVA289B%2526nr%253D39

Hope this helps.

Thanks,

Nancy

Hello Nancy,

Thanks for your reply. If customer has passed their system's test and there is no double pulse on the ripple or unstability on transient waveform, could we say it is okay for use? Thanks!

Best regards,

Ann Lien

Hi Ann,

That is ok. No issue.

Thanks,

Nancy