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SDI Drier: Routing and component placement for unused output

Madhu Sharma
Expert 2915 points
Other Parts Discussed in Thread: LMH0302, LMH1218, LMH1218EVM

Hi,

For SDI drier IC LMH0302, the layout example explains the placement when both SDO and SDO# outputs are used. In one of my earlier queries, it was suggested to terminate the unused SDO# using R-L network, 4.7uF and a 75 ohm resistor to GND. Please let me know if there is any reference design/ routing guidelines available for this case.

Regards

Madhu

  • 0
    TI__Mastermind 29655 points

    Hi Madhu,

    Yes, please recommend the unused SDO# output after the RL network and 4.7 uF to GND in order to provide proper load termination for both signal output polarities. While we don't have an example of this in the SD3GDA, I recommend taking a look at the LMH1218EVM as a reference. This device has the unused 75-ohm output terminated by connected a via to the GND layer. Please note that since the RL network is integrated into the package of the LMH1218, it is not shown in this layout. However, this should serve as a reference for what it looks like:

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Expert 2915 points

    Hi Michael,

    Whether the traces of SDO and SDO# must be of equal lengths?

    Also, how the capacitors ( C7 and C8 in above fig) must be placed? is it fine if i keep near the IC? because i am routing traces on the top, it is not possible to keep it under the connector as shown in above fig.

    Regards

    Madhu

  • 0 in reply to Madhu Sharma
    Expert 2915 points

    Hi Michael,

    For maintaining symmetry, we have done the connection as shown in below figure. 

    It is routed such that total trace length ( SDO pin to R-L network + R-L to capacitor + capacitot to Resistor ) of both SDO and SDO# are equal.

    Is it okay if it is done like that shown below?

    Regards

    Madhu

  • 0 in reply to Madhu Sharma
    TI__Mastermind 29655 points
    Hi Madhu,

    There is no issue with routing the traces and caps the way you have done so in the attachment. I do not think it's necessary for you to use the snake-pattern on the unused 75-ohm trace so that the polarities match exactly, but there is no harm in doing this.

    Regards,

    Michael