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ADC1xDxxxx(RF)RB: Termination Resistors

Richard Katz
Intellectual 290 points
Other Parts Discussed in Thread: ADC12D1600, ADC10D1500

Hi,

I have the ADC1xDxxxx(RF)RB board configured for the ADC12D1600 (our target part for our design).

The schematic shows that on each of the 4 output data buses, there are two sets of three resistors each, going from V_ADC to ground. It's not clear what they hook up to but based on the table, they appear to be LVDS signal terminations in case a 10-bit device is used.  For 12-bit devices, the table specifies "NA".

But looking at the board, it looks like the resistors are populated.  Was that an oops?  Or is there something that we need to consider in our board design since, based on the data sheet, it looks like all of the drivers are the same.

Thanks,

rich :-)

  • 0
    TI__Genius 13335 points

    Hello Richard,

    It looks like there is a mistake. The BOM shows those resistors as DNI but it looks like they are installed. The resistors should be there for the 10 bit device only. They are meant to terminate the RSV pins as called out in the schematic and ADC10D1500 datasheet on page 63.

     For the 12 bit devices those pins are the 2 LSBs of the data buses which do not need any special termination. If the receiver is a 100Ω LVDS receiver then you do not need any additional termination or biasing in the path. It is appears as though there is not enough signal loss to cause a problem on the 12 bit boards, but the resistors should not be populated. Thank you for pointing this out and we'll have this corrected moving forward.

    Thanks,
    Luke LaPointe
    High Speed Data Converters