TPS54260-Q1: Minimum input capacitance required

Hello Vishwad

Vishwas H R said:

Due to design constraint I have only two MLCC 2.2uF 100V and after considering derating factor effective is only 1.1uF (including both).

Yes, you would need to keep 3uF effective capacitance. It is required to keep slew rate at Vin pin below desired level. Additionally, ripple at that pin should below small enough for device to function properly.

At 8V input, 100V cap is experiencing 75% deratings which looks bit high. Could you please share part no. of capacitor  

Thank you

Regards

Onkar Bhakare

Hello Onkar,

How much small the ripple voltage should be?

If I use this formula, ripple voltage is around 250mV for 1.1uF. This is still a concern?

Sorry, the 75% derating I mentioned is for 48V input and for 8V effective is around 2.9uF.

Nominal input voltage is 28V.

Thank you,

Hello Vishwas

I would recommend keeping it below 1% of nominal input voltage while maintaining minimum of 3uF. This is required for reliable operation of the internal circuitry of the device. As IC uses analog circuits inside, clean input is required for their proper operation

Thank you

Regards

Onkar Bhakare 

Hello Onkar,

Ok, understood. Can we connect offline to discuss few points? as I have some design contraints also to be considered

Thank you,

Hello Onkar,

As discussed, I will check possible combination to use cermaic and tantalum.

Thanks for your time and inputs.