MP2459 EMI Issue


Have problem at around 470kHz, any recommends to fix this problem?

Regards,
Jay

Regards,
Jay

Hi Jay,

Typically the best solution is in regards to the circuit layout. Of course, barring any external metal shielding that you can mount around the circuit components, which also will be a large help with reducing emissions.

A large unbroken ground plane underneath the buck converter is the best way to mitigate radiated emissions. Unbroken, meaning no large cuts created by vias placed too close together, which can increase the length of the return path of the current, which further increases the inductance of the current loop.

Along with this, a multi-layer board will have superior EMI performance to a single or 2-layer stackup. This is because the GND plane will be closer to radiation culprits, and will be much more effective at reducing the emissions. Aim for at least 4 layers if possible.

Speaking of which, minimizing the length of all critical loops (the SW loop and input capacitance especially on a buck converter) is also essential to good EMI performance.

You can post the layout here if it is not sensitive and we can review.

1 Like

Hi Jay,

I think your Inductor/BST/Diode placement looks fine, and you have a nice wide GND plane on top.

However, your input capacitors are kind of far away from your regulator, and the input capacitors on a buck converter are the biggest culprits for EMI in my experience. Please shuffle some components around so you can bring them closer.

Another couple of PCB layers would also help, or external shielding, but these will of course increase production cost.

There is a trace that’s being routed under the regulator, is it possible to keep the GND layer underneath unbroken?

Hi Jay,
I think your issue is L6. It is ferrite bead which starts to attenuate around 10MHz. Your conducted emission issue is related to MP2459 switching frequency, which is not attenuated by input filter. Please add proper inductor and calculate low pass filter cut-off frequency to about 50kHz (10 times lower than actual switching frequency of SMS). This shall help to resolve your issue.