TPS564201: Short circuit on EMC immunity tests

Friedrich Ermert9

Part Number: TPS564201

Hello,

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.

Thanks.

Best regards
Friedrich Ermert

over 5 years ago

0 Vental Mao over 5 years ago

TI__Expert 5745 points

Hi，
In your words, you use 3 TPS564201 in your design. One is out of the fridge, powered by battery. The second and the third one is power by AC-DC and Backup(battery).For the two parts ,one is in the fridge and another is in front of the fridge door. Right?

Please upload the schematic and the layout. And see the waveform of the SW at influence frequencies of 300-320MHz with a low field strength.

Try add a metal mask to shield the TPS564201 to see the result.

0 Friedrich Ermert9 over 5 years ago in reply to Vental Mao

Prodigy 40 points

Hello,
thanks for that fast Response.
Sorry i expressed myself unclear.

It was just the first test we did without the AC/DC and without mounting the parts into the fridge. Here the boards were placed on a table and were only powerd by the battery. In this case we did not use the Mainboard, but a smaller version without AC/DC converter and the HMI.
This test was fine and we had no Problems.

In the fridge we have only 2 boards at the same time. Both of them use the same power supply. Thats the AC/DC Output of 12V + backup battery. The first of them is the Mainboard inside the fridge, the other one is the HMI in the frontside of the door.

Tomorrow is our next date for measurements in the EMC lab. Then i will plot some waveforms and try to shield the IC. Thanks for the hints.

In case that SW is the problem and/or shielding fixes the problem, can u see other ways but shielding to fix it? Or do you have some more hints we can test tomorrow?

Hier the schematrics and the layout