0
\$\begingroup\$

I trying to make tps54202 switch regulator for esp32-wroom which would pass EMC test. https://www.ti.com/tool/TIDA-00948 By reading guidelines of designing they say that to pass EMC test you need to add small filter L+C of 5uH and 10uF. However they dont provide this filter layout, schematic or BOM. I can figure out schematics and pcb layout, but not BOM for input filter, as there are many complicated formulas to calculate esr value, resistance, etc... Anyone could reccomend me BOM for input filter?

\$\endgroup\$

1 Answer 1

1
\$\begingroup\$

Choose a ceramic capacitor with an X7R temperature coefficient and a voltage rating of at least 25 volts, and an inductor with at least a 1 amp rating at 125 Celsius. The schematic is

schematic

simulate this circuit – Schematic created using CircuitLab

Keep the traces as short and wide as possible, and run the ground trace from C7-ground directly to the ground of input capacitors C5 and C2 (also short as possible). Run the Trace from L2 directly to the high side of input capacitors C5 and C2.

Good Luck!

\$\endgroup\$
3
  • \$\begingroup\$ Should L2 be ferrite based? And what aprox esr resistance C7 should be? \$\endgroup\$
    – TheAfrizzz
    Jan 24, 2020 at 21:05
  • \$\begingroup\$ L2 should be a shielded power inductor and will have a ferrite core, and any multilayer ceramic cap with an X7R rating will have a low enough ESR. There won't be too much current in the cap anyway; this circuit is just to filter the switching noise from getting back onto the line input. \$\endgroup\$ Jan 24, 2020 at 23:34
  • \$\begingroup\$ How can you know that this will make OPs circuit pass "EMC test"? We don't know anything about the layout, how the circuit is encapsulated, where it is supposed to be used/installed (which is relevant for the tests both wrt emission and immunity, be it conducted or radiated) \$\endgroup\$
    – MrGerber
    Feb 14 at 16:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.