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Original question:

ADS42JB46EVM: ADC not outputting CGS and ILA sequences

ADS42JB46EVM: Inverted SYNC~ Polarity?

Sharon Tseng
Prodigy 60 points
Part Number: ADS42JB46EVM
Other Parts Discussed in Thread: ADS42JB49, ADS42JB46, ADS42JB49EVM

I see in this post: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/687965/ads42jb46evm-adc-not-outputting-cgs-and-ila-sequences that the ADS42JB46EVM is using a SYNC polarity inverted from the JESD standard. Using the ADS42JB46EVM, I see that it only works if I invert the SYNC polarity. If I use ADS42JB49 in a design, will I also need to invert the polarity? I don't see anything in the ADS42JBx9 datasheet indicating an inversion of SYNC polarity and the table in the datasheet below seems to indicate that the SYNC polarity follows the JESD standard.

Thanks,

Sharon

  • 0
    TI__Intellectual 1180 points

    Hi Sharon,

    Thanks for reaching out! The datasheet for the ADS42JB46 has an identical table to the one you have pulled from that for the -49, so that may not tell you everything. Looking a little further, both datasheets are near identical within the sections concerning the JESD204B standard, that is to say they both seem to claim they respect it.

    I will see if I can track down an ADS42JB49EVM in the lab to test on. Jim S. is still with the group and I would ask him directly, but he is currently on leave. I will try to give you an update tomorrow.

    Thanks,

    Drew

  • 0 in reply to Drew Pierpont
    TI__Intellectual 1180 points

    Hi Sharon, thanks for your continued patience.

    Ok, it looks like they do follow the same inverted scheme. Reference Figures 4 and 5 from the ADS42JB46 datasheet and compare them to correspondingly identical Figures 74 and 75 in the ADS42JB49 datasheet. The patterns for CGS and ILA match in both devices.

    -JB46:

    -JB49:

    You will need to invert the polarity for it to work properly. Hope this helps!

    - Drew

  • 0 in reply to Drew Pierpont
    Prodigy 60 points

    Hi Drew,

    Thanks for the response. These diagrams match the JESD standard of a SYNC~ that is active low. However, what the post I linked indicates, and what I have observed in my EVM is that the EVM SYNC is actually active high, so the opposite of what all of the diagrams in the 46 and 49 datasheets indicate. 

    Thanks, Sharon

  • +1 in reply to Sharon Tseng
    TI__Mastermind 19415 points

    Sharon, 

    I'm not sure who worked on this datasheet, however it's highly likely that these figures were copy/pasted from a previous datasheet and this was not updated.. The previous post's answer (that the device SYNC is active high) will apply to this device since it's in the same device family.

    Regards, Chase