Circuit input for EMC two capacitores 90 degree

Anyone knows why some input circuit use two series capacitors in 90 degrees between input and GND?

Hi,

I assume you mean 90° mechanical orientation. This has nothing to do with electrical function.

--> show us the schematic. This tells the electrical function.

Klaus

Hi Klaus, yes 90 degrees mechanical. I have found two circuits in last week that use this arrangement, in one the person said that it was necessary to EMC tests pass. The second is a Texas Instruments application note without details about this configuration.

TI application: http://www.ti.com/lit/ug/tiduc41/tiduc41.pdf look schematic at page 16 and PCB at pag 1.

The second circuit is:

An FAE told me that the redundant capacitor series circuit is required by automotive standards to reduce the risk of supply shorts. The 90° placement might be chosen to avoid simultaneous damage of both capacitors by board flexure.

That is the correct explanation for ceramic surface-mount capacitors. It is common for them to fail to short when they ***** because of mechanical stress.
It is even safer to remove the capacitor(s), but then expect the design to fail in EMC testing.