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Digital MSB is toggling in ADS4125/22 even though Analog input is absent

Prashant Unch
Prodigy 170 points
Other Parts Discussed in Thread: ADS4122

Hi,

I am using ADS4122 in my card and I am surprisingly observing that MSB is toggling even though ADC has no analog input.

The differential input at ADC shows 0V on oscilloscope.

I thought there might be something wrong with my card, but the same thing also observed with evaluation board ADS4125EVM.

The power supply has no noise in Analog & Digital VCC and GND and this is observed in all configurations like Offset Binary LVCMOS/LVDS and 2's complement LVCMOS/LVDS.


I am looking for your valuable suggestion to find out what is going wrong.

Thanks

Prashant

  • TI__Genius 12965 points
    We will get back with you shortly. Do you have any FFT plots or captures of the data? This would help us understand if the signal is just toggling around mid scale.

    Ken.
  • TI__Guru* 91947 points

    Prashant,

    Is this still an issue? If so, can you send the portion of your board design showing the analog input stage to the ADC? You mention there is 0V at the input. Since the device has a differential input, both cannot be 0V. What are you reading on each input? We are guessing the ADC is at mid-scale, thus the reason for the MSB toggling.

    Regards,

    Jim