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ADS4249: ads4249 doesn't work on second channel if an signal on first

Massimo Malatesta
Prodigy 10 points
Part Number: ADS4249


We have some conversion board with some ads4249 adc and we have seen that on some of those ads4249 after some time of work the second channel of one of those adc stop to work, or bad work, if there is a  simultaneous  signal on the first.

Why?

Are those chip with problem?

Thanks in advance.

Massimo

  • 0
    TI__Mastermind 23880 points

    Hi Massimo,

    Are you overdriving the ADC input level beyond what is acceptable? This device works with both channels active with a -1dBFS differential fullscale signal. Is this happening on multiple boards or a single board?

    Regards, Chase

  • 0 in reply to Chase W
    Prodigy 10 points

    Hi,
    the adc input are on the acceptable range.
    The problem is on multiple boards always on the second channel, usually on a single chip .

    I have seen that there is a ver. E of the datasheet.Is there some important difference from first release of this?.
    The adc input circuit in board should be or must be like the circuit in the datasheet ?
    These boards have at least 10 years.

    Thanks, Massimo

  • 0 in reply to Massimo Malatesta
    TI__Mastermind 23880 points

    Hi Massimo,

    The input circuit in the datasheet between Figure 74 and Figure 76 are examples of matching networks to achieve certain bandwidths using 1:1 transformers. It is not required, but this matching network counteracts the internal ADC parasitics of the device and allows for higher or flatter frequency response of the ADC. Can you share a portion of the schematics which show the full input connections to the ADC?

    There would not be any major difference from the previous datasheet releases. The revision history section describes the changes between each version of the datasheet if you are curious, it is mostly correcting text mistakes or adding more information to confusing sections to make it easier to understand.

    Just to confirm, there was not any issue with this same design for 10 years and now the issue is showing for the first time in 10 years? 

    Regards, Chase

  • 0 in reply to Chase W
    Prodigy 10 points

    Hi Chase,

    I gave you a wrong info. The time is not 10 years but 5 . I confirm the issue after some years.

    There is not decoupling from analog signal to input adc but there is an pedestal setting to set the right continuous input level(offset).

    The offset must be identical to vcm or it's range have to be the same value positive for inp and the same value negative for inm?

    The last one is just a my doubt.I'm not the designer but the debugger.

    Regards, Massimo

  • 0 in reply to Massimo Malatesta
    TI__Mastermind 23880 points

    Hi Massimo,

    Correct, the offset should match the ADC input common mode VCM or the adc will overrange and clip. Can you share images or csv data of the channels? Please share both channels with the inputs off and also share both channels with the channel A input enabled.

    Regards, Chase