LM5176: LM5176 EMI radiation issue

Hi Hsu,
expert supporting this device is out of office now. he will reply you after the weekend.

Hi Hsu,

Thank you for using the LM5176, and for offering the sch and layout. However the layout is not clear about your MOSFET orientation, although I can guess. Do you have a picture of the solder mask openings, so I can easily align the part connections and review the circuit? I would like to see the inner layer artworks.

Please also show the switch node voltages (SW1 and SW2).

Initial assessment is that both the switch nodes and the ac current loops are large, prone to radiation. There is also a possibility of slight shoot through between the high side and low side MOSFETs, because your gate resistor is 4.7Ohm, appear to be large for the LM5176. What MOSFET do you use? Can you reduce the gate resistor to 1 Ohm, or even 0 Ohm to see if this 40 MHz radiation still there?

Thanks,
Youhao Xi, Applications Engineering

The customer asks, can the IC be placed directly below the MOSFET to reduce the loop path? Thanks.

My customer changed the gate resistance to 0 ohms, but the IC, MOSFET and Fuse both died when the load was turned on. 

Does the LM5176 have similar similar files for reference?

https://www.analog.com/media/en/dsp-documentation/evaluation-kit-manuals/dc2457af.pdf

 

Hi Hsu,

The LM5176 has a series of blogs that covers layout tips. These should help with the layout of the circuit.

The AC loop is between the MOSFETs and input capacitor (buck leg) and the MOSFETs and the output capacitors (boost leg). These are the loops that should be minimized.

Thanks,

Garrett