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ADS114S08B: ADS114S08BIPBSR chipset getting hang due to Noise

Hitesh Barot
Prodigy 10 points
Part Number: ADS114S08B


Hi There,

Hope you guys are doing well.

We are facing an issue with ADS114S08BIPBSR chipset, in our design we have 2 chipsets of ADS114S08BIPBSR, each chipset is getting analog input from 9 different CTs ( current transformer) so having total 18 CTs with 2 chipsets.

All CTs are providing continuous input voltage to chipset is 0 -333 mV.

City_Cabinet_TOP_V2.1_TI.pdf 

In the same design, we are having relays which are operating power contactors now at the operation of contactor switching, both the chipset got hangs.

I am expecting it is due to switching noise from the contactor.

Attaching the schematic for the reference.

 

Let me know if you have any more details.

Kindly help to solve this issue.

Looking forward to hearing from you as soon as possible.

 

Thanking You,

Regards,

Hitesh

  • 0
    Prodigy 10 points

    During the debugging, I have some more findings.

    I had probed +5VDC (AVDD) , 3.3VDC (DVDD) and +1VDC (REFP0) and fond that during the switching of power contactors , all 3 voltage rails got huge noises.

     Kindly find the attached images, also for the reference below are the legends.

    Yello :- +1VDC

    Purple:- 3.3VDC

    Blue:- 5VDC line.

     Thanking You,

    Regards,

    Hitesh

  • 0 in reply to Hitesh Barot
    TI__Mastermind 48680 points

    Hello Hitesh,

    Thank you for the additional information.  With that much noise, I am surprised the ADC continues to work without a full reset.


    Regarding the attached schematic, the use of an inductor (or ferrite) between the AVSS and DGND pins may be an issue.  Although this may not help, I suggest replacing this with a very low impedance shunt (wire).  If this inductor is not physically next to the ADC, then adding a local short between AVSS and DGND may also help.  The idea is to reduce impedance between AVSS and DGND to reduce the magnitude of noise.

    Adding TVS or Zener diodes to the 5V and 3.3V supplies may also help with the voltage overshoots.  Additional capacitance on the 5V and 3.3V lines will help with both overshoot and undershoot on the supplies.

    Although separate ground planes can help with moderate noise, when the noise magnitude is large enough to exceed the ABS max specs between AVSS and DGND, it can make things worse.

    Other than the ferrite suggestion, you may need to look at the power supplies (do they need better filtering?) or the source of the noise.  You mention a relay and contactor.  Do you have a flyback diode in parallel with the relay and contactor coils to reduce any voltage overshoot?

    You may also need some type damping circuit across the switch contacts of the relay and/or contactor to reduce the noise generated when these make/break the electrical circuit.

    I would focus first on trying to reduce the source of noise, and then add additional filtering/voltage clamps on the power supplies to help with any remaining noise.

    If you can provide additional schematics for the power supplies and the relay/contactor driver, I would be happy to review.

    Regards,
    Keith Nicholas
    Precision ADC Applications