UCC28951: Output capacitor selection

Hi Ahmed,

Thank you for the query on UCC28951.

The output capacitor value would be calculated based on load transient, output holdup and ripple voltage as explained in the application note

. The same  would go for a battery application as well as per the equations below.

For charging a battery you might need to implement a CC-CV loop in the method described in the following link:

/cfs-file/__key/communityserver-discussions-components-files/196/5751.CI_5F00_CV.docx

We recommend using the values as per the calculations rated to habdle the required ripple current and provide adequete transient response.

Regards,

Harish

Hi Harish,

Thank you for your reply. 

Referring to my second question. I have a ripple current of 11 A at a frequency of 200 kHz. So, if I decide to go for electrolytic capacitors, I will need to use many to handle this ripple current.

I am asking if using MLCCs only is ok. MLCCs have a low ESR as well. Will that cause stability problems in my design?

Thanks

Hi Ahmed,

I think 10 10uF MLCC will be less for your application.

You would typically require much more than that considering your power level and load currents. Hence we would suggest using combination of Electrolytic capacitors and ceramic capacitors. Please refer to this app note for choice of capacitor.

https://www.ti.com/lit/an/slyt639/slyt639.pdf?ts=1667842984350&ref_url=https%253A%252F%252Fwww.google.com%252F

https://training.ti.com/capacitor-selection-overview

Thank you

Regards,

Harish

Hi Harish,

Thank you for your reply.

Just to clear things for me. If I am just going to use an electronic load (constant current), no load transient requirements, will I need anything more than these few MLCCs? will their very low ESR values cause any problems for me?

Kind regards

Ahmed