adp2323 emi and snubber design

I am using the ADP2323 for one of our designs and i can see low amplitude spikes (10mVpp) at the switching frequency on some board outputs (on clock signals ). I was wondering if an RC snubber circuit at the output MOSFET could help reduce these spikes leaking into sensitive sections of the board.

I see that the ADP2323 evaluation board has provision for RC snubber (R6, C11 and R20, C14) but is not populated. Is there any reference for optimal RC values that can be calculated for APD2323 ? I would appreciate any inputs.

Thanks.

AB

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    •  Analog Employees 
    on Oct 18, 2014 5:03 AM

    AB,

    if I understand correctly you see the 10mV noise on the output of the clock generator correct? How are you measuring this noise? I want to make sure it is not just picked up by the scope probe rather than actually being in the signal. Do you see that noise on the high level only of the clock or also on the low level?

    Can you post a picture of the scope measurement and maybe even a picture of your set-up while measuring?

    Is it a differential clock signal or single ended?

    We need to differentiate between conducted noise versus radiated noise. Conducted noise is handled through filtering between the power supply and the clock circuit.

    Radiated noise (actual EMI) would need to be addressed through layout or shielding. If your layout is not optimal then it's possible that there is some coupling between the circuits. But 10mV on a clock signal seem high for radiated coupling.

    The snubber would not improve conducted noise much and may only improve radiated noise if the layout is already well done.

    LucaV

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  • 0
    •  Analog Employees 
    on Oct 18, 2014 5:03 AM

    AB,

    if I understand correctly you see the 10mV noise on the output of the clock generator correct? How are you measuring this noise? I want to make sure it is not just picked up by the scope probe rather than actually being in the signal. Do you see that noise on the high level only of the clock or also on the low level?

    Can you post a picture of the scope measurement and maybe even a picture of your set-up while measuring?

    Is it a differential clock signal or single ended?

    We need to differentiate between conducted noise versus radiated noise. Conducted noise is handled through filtering between the power supply and the clock circuit.

    Radiated noise (actual EMI) would need to be addressed through layout or shielding. If your layout is not optimal then it's possible that there is some coupling between the circuits. But 10mV on a clock signal seem high for radiated coupling.

    The snubber would not improve conducted noise much and may only improve radiated noise if the layout is already well done.

    LucaV

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