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TMDSCNCD28379D: ADC B1 input resistance

Zhou Dong
Prodigy 100 points

Part Number: TMDSCNCD28379D

Hello,

I'm using the ADC modules of the TMDSCNCD28379D controlcard. I found that the input resistance of ADC B1 pin is only 100kohm while others are all around 2.8Mohm. This seriously influenced my sampling results since I didn't use any voltage follower between the voltage divider and ADC input pin.

Is there any way to change the input resistance? I think it should due to some circuits in the controlcard.

Thanks!

  • 0
    TI__Guru 60865 points

    Hi Zhou,

    This is due to the muxing with the buffered DAC on this pin:

    Not sure exactly how you are using the input impedance measurement, but generally the ADC inputs are not high impedance.  Instead, you want to treat them like a switched capacitor circuit when the ADC is sampling the voltage: