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IWR6843AOP: IWR6843AOP: IWR6843ARQGALPR, LP87524JRNFRQ1, TPS62130ARGTR

Bryan Chan
Prodigy 10 points
Part Number: IWR6843AOP

Tool/software:

We designed a people presence, and vital monitoring device using the IWR6843ARQGALPR mmWave Radar. The radar is powered by a PMIC LP87524JRNFRQ1 and voltage regulator TPS62130ARGTR.

During the EMI scan, we experience a high emission at 400Mhz from the antenna and PMIC. We aren't able to isolate the noise as both ICs are next to each other. 

These are my questions:

1. According to TI's reference design, the input voltage to the PMIC is 3.3V. If the voltage is greater then 4V, a snubber components are needed at the output nodes to reduce EMI. Is there any reason we have to drive the PMIC at 5V?

2. TI recommended X7R type capacitors for both input and out. What is we go wIth X5R capacitors?

3. We power the PMIC using 5V, but without snubbers installed. Does this cause the 400MHz emission?

Best Regards,

Bryan

  • 0
    TI__Expert 4360 points

    Bryan, 

    1. I don't think it is possible to run the PMIC at 3.3V if you are using the 3.3V output of the PMIC. This is becuase the efficiency of the PMIC is not 100%. It seems to be at worst case around 70%. As long as you can ensure that there is enough overhead, I don't see a problem. The safest bet would be to power at 5V. 

    2. X7R are to ensure that the value of the capacitor doesn't derate across temperature. Capcitor derating could increase noise on the line and lead to emissions or poor performance on the radar. 

    3. Not using the snubbers, or having unideal layout design (long ground return paths or long current paths) can result in an increase in noise on the power inputs to the radar. Increased noise or even tones can result in EMI or poor radar performance. I'm not sure if the 400 MHz could be caused directly by the PMIC itself. It would be the 100th harmonic of the switching frequency when the PMIC is not in spread spectrum mode. Concurrently, I haven't seen the radar emit a 400 MHz spur either. 

    I would recomend reviewing the layout and design guide for the radar and comparing it against your design. Specific decaps are used on the radar side to ensure that the power supply is at a low enough noise and ripple to not result in spurrious emitions. https://www.ti.com/lit/zip/swrr161 

    I hope this helps with your design!

    Let me know if you have more questions! 

    Blake