Hi,
I'm having trouble with TPS54231. It fails at CISPR22 class B conducted emissions. I can see a huge peak around 570KHz (switching frequency). It was tested with a custom board and also with TPS54231 evaluation module which is even worse.
This power supply is used directly on a 12V input and conducted emissions are directly measured on the 12V.
Do I have to systematically use an input filer (LC filter, common mode choke) ? I don't see any parameter I could change to improve it, since it's not an external mosfet that is used for switching.
Thanks in advance for your help!
Yes, teh TPS54231 will have a significant switching frequency ripple component on the input voltage. You will need to filter it. The filter requirements wil depend a lot on the rest of your system.
John Tucker
Consumer DC/DC Applications
Thanks for this quick reply. Is this specific to TPS54231 or is it more of a common issue with buck converters? I tested an older system of our using TPS54225 and also found a way too big peak at switching frequency.
Yes it is common to switching power supplies, not just buck converters. For buck converters, during the high side ON time, current is drawn from the input and during the off time, the current is supplied from energy stored in the inductor. This causes ripple on teh input at the switching frequency