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ADS122U04EVM: Gerber Files/Altium Design Files and Shielding Question

Frank Roberts
Intellectual 355 points
Part Number: ADS122U04EVM
Other Parts Discussed in Thread: ADS122U04

Hello,

  I am finalizing a PCB design with the ADS122U04.  It would be very helpful if I could receive the Gerber files for the EVM.  I in particular want to review the Ground partitions.  I am debating between a single Ground Pour on a 4layers board or having 2 Ground pours AGND and DGND.  I have a BLE device also on the PCB and on our first prototype when we increased the output power of the BLE device we could clearly see the 2.4GHz noise on the output of the ADS122xxx when viewing the data through a FFT.  

  I am putting a grounded shield over the ADC circuitry to help alleviate this on this 2nd version and I have moved the BLE module to the other side of the PCB.

A general question I would have about the shield is whether I should attempt to create a shield that would also cover the terminal block where the 4 wires from the bridge come into the unit.  I am using a low profile SMT terminal block that is only 5mm high.  It would seem like it would be ideal to shield the wires as much as possible upon where the cable shielding has been pulled away to bring the individual wires into the system...

Thoughts/Opinions??

Regards,

Frank

  • 0
    TI__Guru** 112765 points

    Hi Frank,

    Included with the EVM GUI device package are the PCB gerbers.  The general information is contained in this post:

    https://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/694249

    You would just substitute the mentions of the 'C04' with 'U04'.  Actually the same PCB is used for both EVMs.

    The first thing to do is to determine the how the 2.4GHz is getting into the measurement.  It is certainly possible that an unstable ground can be an issue, but the radiated energy is more likely the source.  This can get into any wiring for the supply or input.  I don't know your sensor, but in many load cell applications (which is also a bridge sensor) the issue is the cabling.  This should be a shielded cable properly terminated.  Where I have seen the most issues is with termination.  Once the wires are outside of the shield they become exposed, so make sure all exposed wiring is as limited as possible when connecting to the terminal block.  If some of the wiring acts as an antenna, then it will get worse with gain.  So you will want to make sure you have adequate filtering to the analog inputs.  Ferrites can be beneficial, but you must make sure you use ferrites that filter in the high frequency range (1GHz or more).  These ferrites can be added in series with normal RC filtering at the analog inputs.

    I also mentioned proper termination.  Generally you would like to have your shield wire isolated to a ground ring around your normal PCB ground.  This topic can be pretty extensive, so I would suggest reviewing material by Henry Ott.  One Ott book I use as a reference is Electromagnetic Compatibility Engineering. 

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 355 points

    Thanks Bob for the response that is what I was looking for.  The gerbers were available for the U04 package also I just didn't know where they were at.

    Thanks again

    Regards,

    Frank