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AMC1336-Q1: DOUT/CLIKIN pin RC filter connection

Sherry Liang
Genius 10255 points

Part Number: AMC1336-Q1
Other Parts Discussed in Thread: AMC1336EVM

Dear team,

Can we add RC pulldown at the DOUT/CLKIN pins. If it is ok, do we have any requirements for the RC? Do we have the maximum limit for the RC value?

Thanks & Best Regards,

Sherry

  • 0
    TI__Mastermind 22950 points

    Hi Sherry,

    I don't think a pull-down will hurt but I don't see it to be necessary. The CLK is driven so the host controller should be driving that clock signal. If the customer is worried that the CLK may not be properly driven then I can see where a pull-down might be needed. In any case, leaving the footprint for the pull-down there wouldn't hurt. 

    As for the RC values, 20ohm and 10pF is a good choice. The AMC1336EVM uses 100ohms and 33pF but I personally think the 100ohms is a bit too large. I would keep the series resistor between 20-33ohms. That being said, we don't necessarily have a min/max value for the filter. You obviously don't want the cutoff frequency of the filter to be less than or near the CLK frequency. 


    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Genius 10255 points

    Hi Aaron,

    Thanks for your reply!

    I notice the CLKIN pin has a internal pull down resistor (typical value: 1 MΩ). If the customer add one external pull down resistor 10kohm, this will decrease the equivalent resistance. Is there any bad impact for this pin? This external pulldown resistor is used for the capacitor of RC discharging.

    For the RC value, the only limit is cutoff frequency, no other limit, right? This RC is used for passing EMC test successfully. The larger RC value, the better EMC performance, so they want to know the largest value of RC that we can accept.

    Thanks & Best Regards,

    Sherry

  • 0 in reply to Sherry Liang
    TI__Mastermind 22950 points

    Hi Sherry,

    Let me discuss the 10kohm pull-down resistor with the team. I will get back to you tomorrow. As for the RC values, I recommend to keep them as the values I mentioned above. The larger the RC values, the more it can affect the slew rate. The part may be fine but it is hard to say with certainty what the max values of the filter can be before any unexpected behavior occurs. 

    Regards,

    Aaron Estrada

  • 0 in reply to Aaron Estrada
    TI__Mastermind 22950 points

    Hi Sherry,

    I spoke with some team members and we really don't think the pull-down resistor is necessary but we also don't believe it will affect the operational behavior of the device. 

    Regards,
    Aaron