we have trouble with the TPS564201 and the UCC3813D-2 in EMC immunity tests for the standart EN61000-4-3. We use the TPS564201 to generate our logic voltage of 3.3V from 12V input.
There are 3 PCBs using this converter. Some of these PCB are built into a fridge, so they are surrounded by a metal housing connected to PE.
Within the first test the PCBs were not mounted into the fridge and supplied by a 12V battery. In this setup (on a table) we had no problems with the immunity test, everything worked fine fine over all frequencies (30MHz-1GHz).
The test is done with an influence with a field strength of 10V/m.
Mounted to the fridge the power supply of 12V is done by our own designed Mainboard including a AC/DC Flyback converter with UCC3813D-2.
Our first "little" problem is, that we can see that the power supply breaks down to ~8V for ~1s for some frequencies (150MHz, 200MHz...) over the whole range.
It looks like the UCC3813D-2 shortly stops regulating the voltage sometimes. It is not a big problem because we use a backup battery, that holds the 12V directly if the power supply breaks down.
What i want to ask is, whether there are some known problems with this IC on immunity tests or some solutions to prevent these problems.
Out big problem is the TPS564201. At influence frequencies of 300-320MHz this IC creates a short circuit and breaks down directly. When the power supply breaks down in the same moment,
and the battery supplies the circuit, the IC makes a short circuit to the battery and burns down directly with enormerous currents.
This problem occurs simultaneously on the mainboard and the other PCB that is not mounted into the fridge (TPS564201 in both cases). This second PCB is a Human Machine Interface and placed in front of the fridge door.
All logic parts behind the TPS564201 are unaffected and the boards work again after replacing the TPS564201, so it looks like a short circuit inside the IC.
Here i have the same question. Are there any recommendations for such problems? Do some sensitive pins of the ICs need a special filtering with RC, LC or CLC filers? Or can you see possible other reasons for this behavour?
It would be nice if someone has an idea.