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Original question:

BQ24250: BQ24250RGET creates 300MHz EMC noise

BQ24250: BQ24250RGET 300MHz EMI

Brad Buike
Prodigy 110 points
Part Number: BQ24250

Hi,

We are looking at ways to reduce the 300MHz EMI being generated when charging.

There was a suggestion in a previous related ticket to add a resistor in series with the capacitor between the SW output and the BOOT pin. The suggestion was  to add a 1-10 ohm resistor in series with C1 to slow down the SW rise time. Does anyone know how to calculate the value?

 

  • 0
    TI__Mastermind 24465 points

    Hi Brad, 

    All suggestions from the related ticket you linked remain valid methods to reduce the 300MHz EMI you are observing. 

    I do not have a formula to provide to determine the appropriate value for your system. The general principle is as you increase the resistance value between SW and BOOT pin the switching slew rate will become slower. We do not recommend using a resistor larger than 10 ohms because a significantly slower slew rate will adversely affect converter efficiency. 

    My best recommendation is to perform the EMI test with a couple different resistor values in the 1 ohm to 10 ohm range and compare the results. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 110 points

    Hi Garrett, we tried 1R, 2R, 5R1 and 10R) between C805 and SW and none them helped. We will investigation to reduce the 300MHz EMI. Please close this ticket.

    Brad.

  • 0 in reply to Brad Buike
    TI__Mastermind 24465 points

    Hi Brad, 

    Understood, I will close this thread. I recommend trying to use one of the other suggestions mentioned in the linked thread or a combination of multiple suggestions to help reduce the EMI observed. 

    Best Regards,

    Garrett