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LM74700-Q1: EMI issue

PYTsai
Genius 11565 points
Part Number: LM74700-Q1

Hi 

We got EMI issue as below would you help review our schematics how to solve it? 

Below is our schematics, the issue disappear if remove LM74700 and bypass Q1

  • 0
    TI__Guru 57737 points

    Hi,

    This is probably due to the internal charge pump Frequency of Lm74700-Q1. Let me check the value of internal charge pump frequency and get back to you. 

  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi,

    The internal Charge pump Frequency of LM74700 is around 25 MHz. 

    The major EMI contributor should be Anode pin as this pin acts as a supply pin and also sees peak current demand from internal charge pump. For the gate can also couple some of the CP noise based on it’s mode of operation. We expect gate pin to induce more noise in full conduction mode compared to regulation mode because of the fact that we connect VCAP voltage to VGATE when in full conduction mode.

     Can you check the EMI performance with following,

    • Increase Anode capacitor, may be 220 nF or higher. This will reduce the current peak amplitude compared to 100nF capacitor.
    • Add a resistance (10 ohms) in series on the Gate signal