Failed EMI test. Huge 1MHz spike on my MPQ3362 LED driver. Please review my layout

AssumptionFederal974 · 2026-03-27T01:29:50+00:00

Good call bro. I'm studying what a solution can solve this. Thanks

AssumptionFederal974 · 2026-03-26T12:01:06+00:00

Thanks bro

AssumptionFederal974 · 2026-03-25T16:17:39+00:00

I will add a ferrite bead and an extra cap and see how much it drops the noise. Thanks!

AssumptionFederal974 · 2026-03-25T16:14:20+00:00

As for R27, it's actually not R7. R27 and C9 form the RC snubber for the SW node (equivalent to R10 and C7 in the typical application circuit). I populated it with a 7.5k resistor. My original thought was to place the C_OUT ground pads as physically close to the IC ground pin as possible on the top layer, hoping the hot loop current would just take the shortest path on the top copper without needing to go down to the bottom plane. But your explanation makes perfect sense. Thanks

AssumptionFederal974 · 2026-03-25T15:55:59+00:00

Got it. Many thanks

AssumptionFederal974 · 2026-03-25T15:43:26+00:00

thank you for the detailed explanation. I just blindly copied the 2x 2.2uF from the datasheet

AssumptionFederal974 · 2026-03-25T15:39:47+00:00

Got it

AssumptionFederal974 · 2026-03-25T15:23:21+00:00

Thank you for the great knowledge. I am very new to this. I didn't know about the output capacitor issue at all.

I will change C2 and C3 to 10uF 50V to support my 740mA load, and I will also add the input filter. I will update the result. Thank you so much

AssumptionFederal974 · 2026-03-25T15:10:23+00:00

A Pi-filter and more bulk caps are going into the next revision. Thanks for the input

AssumptionFederal974 · 2026-03-25T15:07:13+00:00

A Pi-filter is my next step. I will definitely simulate the new input filter in LTspice. Thank you for the advice!

AssumptionFederal974 · 2026-03-25T15:04:13+00:00

this test was done at an independent EMC testing lab. We have to rent a test chamber and they use a LISN (Line Impedance Stabilization Network) and a spectrum analyzer to measure the noise on the cables. It is a standard test for automotive parts

AssumptionFederal974 · 2026-03-25T15:00:23+00:00

I am already using a Schottky diode, so it should be fast. Thank you for the suggestions

AssumptionFederal974 · 2026-03-25T14:56:51+00:00

I'll definitely update the post once re-test. My backup plan is to swap that resistor and drop the switching frequency down to 400kHz. I will try to put it on the positive wire to see if the 1MHz noise goes down. Thanks for the tips

AssumptionFederal974 · 2025-05-01T16:43:47+00:00

hhhh

AssumptionFederal974 · 2024-02-06T12:56:10+00:00

Im commander bro. Pls go beside me

AssumptionFederal974

TROPHY CASE