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LMX2572: I have a few questions

Part Number: LMX2572
Other Parts Discussed in Thread: LMX2594, , LMX2582

Hello,

The datasheet says in section 8.3 that there is not a need to pull up the output lines.  However, in the evaluation board, there is still a population option to pull up the output through an inductor.  Which is correct?

Secondly, if the SYNC, SysRefReq, RAMPCLK, and RAMPDIR pins are not used, do they need any special termination or are there appropriate terminations internal to the chip?

Regards,

David

  • David,

    The LMX2594/95, LMX2582/92, and LMX2572 are all pinout compatible. 

    Although the LMX2572 does not need these pull-ups, the other devices do.

    So from a logistical standpoint, it is easier for us to make one PCB that supports all options, which is what we have done.

    In summary, you don't need to accomodate these pull-up components, however, you might consider this if you think that there is ever a possibility of you re-using this designs using some of these other pinout-compatible parts  that do require a pull-up.

    As for the SYNC, SysRefReq, RAMPCLK, and RAMPDIR pins, these features are completely shut off if you power them down in software; there is no special termination.   As you don't need these features, I would just try to simplify things so you don't put a lot of unnecessary vias that compromise routing for other things, like the high frequency outputs.  In other words, you can float them or ground them to the DAP.

    Regards,

    Dean