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AMC3311: EMC Issue

Francis Jiang
Expert 4340 points

Part Number: AMC3311

Hi Team,

Customer used AMC3311 with EMC issue due to long sensing cable on the input(6/7 pin, up to 12m).

image.png

Currently, they would like to put divider in the middle of the series, instead of connecting it directly to GND.

image.png

Will this work? Could you please help provide your proessional advise here? Thanks a lot.

BRs,

Francis

  • +1
    TI__Guru 59532 points

    Hi Francis, 

    Moving to the middle of the resistor divider will certainly help. What frequency range are they having issues with? I assume 30MHz or 60MHz, but there is no limit on the provided plot to specify. 

    Depending on frequency range of interest, it would be good to check the common-mode choke part number and impedance over frequency curve. 

    We can also look at the layout to check for near-field coupling issues that could allow the noise to bypass the common-mode choke. 

  • 0 in reply to Alexander Smith
    TI__Expert 4340 points

    Hi Alexander,

    Thanks a lot, it‘s working!

    Customer further asking why it can help, could you please help kindly answer? Thanks.

    Alexander Smith said:
    Moving to the middle of the resistor divider will certainly help.

    BRs,

    Francis

  • +1 in reply to Francis Jiang
    TI__Guru 59532 points

    Hi Francis, 

    Thanks for confirming! Who is the customer? 

    If placed in the middle of the resistor divider, the resistors in the resistor divider can help to attenuate the emissions coming out of the device, similar to how the resistor divider helps to attenuate the input voltage to the device. Granted, the resistor divider itself will have capacitance and therefor the impedance of the resistor divider will decrease as frequency increases.

    If placed on the bottom of the resistor divider, the emissions coming out of the device ground are not attenuated at all and directly pass to DC- or neutral for example.