TPS552882: Output capacitor selection

Hi Ganesh,

Yes, if you want to achieve 10mV voltage ripple, you have to select Cout higher than 113uF.

But if you could accept bigger output ripple like 50mV, you could use smaller Cout.

Don't remember to add some ceramic capacitors in parallel with aluminum electrolytic capacitor at output side.

Zack Liu,

Thanks you for your support.

To reduce the output capacitance am changing Fsw as 1.2Mhz then my Cout will be 38.7 uF. Can we use this to achieve 10mV output ripple.

Also we need provide output not more than 2% regulation, 

In order to achieve that Feedback resistor tolerance am considering 0.1%,

Could you please suggest any other thing to be consider to achieve the better output regulation.   

Hi Genesh,

Yes, increase the  Fsw is a good method to reduce the output capacitance. But it means the switching loss would be higher so efficiency is lower than 400kHz. It's a trade-off.

There is no other suggestion for the load regulation. You need to use smaller tolerance feedback resistor.

Hi,

Thanks for your support,

I have bit confusion here,

In webench design it is showing the output capacitor around 100uF x 3 Nos, for 1.2Mhz

But according to my calculation it is showing 38.7 uF for 1.2Mhz.

Could you please explain what is difference, and what value we have to consider,

Here is the our specification 

Also, Please clarify the Rlim resistor calculation 

Is it (10.6 x Vout)x330000/Iavg_limit)  ?

Thanks 

Ganesh V

I understand the Rilim calculation.

Please ignore that alone.

Hi Ganesh,

You could use the equation to calculate the needed output capacitance. But please note that the ceramic capacitor has derating effect under DC bias. For example, the effective capacitance is only 40-50% of its nominal value. You need to check the capacitor datasheet carefully and leave some margin. Normally a capacitance value has +-20% tolerance.

Hi Zack,

Thanks four your support, I understand that.

Also, please provide the Pin no 1 and pin no 2 maximum voltage and minimum voltage range worst case.

Thanks,

Ganesh V