TPS40305: Ripple to large

Hi

   I have attached an excel calculator to help you calculate the impedance of the output ripple. Please use this to check if it matches your design. After that the next thing to consider would be the layout

Regards,

Gerold

Impedance of a Mixed Capacitor.xlsx

Hi

Thanks for the quick replay and excel sheet, When I enter data the with ESR of 2E-3 I get a ripple of 2.6mVpp but when I change ESR to higher which you can find in the market (2ohm)it goes to 744mVpp.

Do I am putting data not correctly or I need go find Capacitor with very low mohm ESR.

Thank you

Hi Amir,

Do you have polygon pours for some nodes like GND and VOUT that are not shown in the layout snipped that you shared?

What are the output caps you are using (part number)?

Kris

Hi kris,

Thanks for the reply, Yes I have polygon pour on my GNDand Vout as seen in the below image.   Also, FSS is disabled by connecting to  3.3nF then to GND 

The output capacitor is two 22uF part number GRM21BR61E226ME44K.

Please let me know if you have any questions. 

Hi

   The capacitor is derated by 50% at 5V Vout. Irrespective of that, the output current is only 100mA. So, I think that the capacitance should be ok.

Can you please let us know how you are measuring the Vout ripple? You need to be measuring Vout directly across the Cout capacitor with as minimum ground leads as possible.

Here is an article that talks about the best way to do it.

https://e2e.ti.com/blogs_/b/powerhouse/archive/2016/07/27/how-you-measure-your-ripple-can-make-you-or-break-you

Regards,

Gerold

Hi

Thanks for replay gain. I will measure the ripple on output capacitor on Monday since I am out of office. Regarding output current just want let you know my output current is around 1A not 100mA.

Thank you

Thanks