Input/output filter of DCDC module needs replacing?

[zenerbjt]

Dear Engineers,

I have been shown a schematic and PCB for a DCDC module power supply which has a vin of a 48V battery (14S LiPO) . Vout is 5V and 5.5W.

I believe the input and output filter is very sub-optimal, and will cause problems with EMC and connector sparking and subsequent degradation.

I attach schematics of the current setup, and the proposed setup. Would you agree that the proposed setup is better from an EMC point of view? (and connector lifetime point of view?)
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The nearest output cap to the DCDC module is some 3.5cm from the module and is a 47uF, 16v, X6S, 1210. You can see switching spikes on the Vout at the output terminals of the DCDC module which comprise 50MHz ringing, up to 5.5V. This appears to be due to the ESL of the 47u and the PCB trace inductance, ringing with the 47uF cap. I believe it needs a 100n,0603 right at the DCDC module output terminals to mitigate this.

Also, there is an 82uF input capacitor, which will mean high inrush from the battery when connected, and high sparking at the connector (it will get connected/disconnected once per day). Thus I proposed an inrush limiter and smaller input capacitor value.

Also, the capacitor at the input to the DCDC module is a alum poly A759KK225M2EAAE685 (2u2, 250V) with 0.685R of ESR. This to me , is more like an RC damper at the DCDC module’s input. From Middleman’s theorem, we know that at the input to a DCDC converter we need a very low impedance, (looking back from the DCDC’s input, to the input filter), so we need some ceramic capacitance there. As such, I am proposing a 100n ceramic and a 1u ceramic in parallel at the DCDC module’s input, as well as a 10uF film capacitor.

I appreciate that the DCDC module works OK as it is now…and successfully supplies the load which is some 5.5W (might go up to 10W in future). However, I believe for EMC reasons, when this product finally goes for approvals testing, I believe the proposed input/output filter is preferable…would you agree?

The DCDC module used is Traco “THN 20-4811WI”.
https://www.tracopower.com/int/model/thn-20-4811wi-a1

(the DCDC module footprint is “doubled up” as sometimes the Battery will be 24S, and a higher voltage DCDC module will then be placed)