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LMZ21701: radiated EMI test in the datasheet

Jason Cuadra35
Intellectual 260 points
Part Number: LMZ21701

Hi,

I'm looking at Figure 10 on page 8 of the datasheet, which is the radiated EMI scan. 
I'd like to know the test setup - i.e. cabling, and is it a 2-layer PCB with a ground plane?

Also, if I needed to reduce the radiated EMI by 20 dB in the 700-900 MHz range (I need < 10 dBuV/m) , how would I do it?

Right now I can meet EMI with my current buck converter designs (12V->5V and 3V3) either by adding an RC snubber to the switching node or adding a small resistor in series with the bootstrap (hi side driver) capacitor to slow down the upper FET turn-on.  

The LMZ21071 is attractive due to the PCB footrpint area savings.

TIA

  • 0
    TI__Guru 50120 points

    Hi Jason,

    To get a better understanding of the device, I'd recommend looking at the User's Guide for the EVM. This way you will know what components are used and how the PCB is laid out. The EVM is made of 4-layer PCB with Mid Layer 1 and Bottom Layer being ground plane. When laying out your board, I'd recommend "sandwiching" the signals between two ground plane like what you see done in Mid Layer 2. This will greatly help with EMI mitigation. 

    Additionally for more EMI filtering, you might be interested in this application note. Using an input pi-filter can greatly help with conducted and radiated EMI. 

    Regards,

    Jimmy