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TLA2024: ADC result is randomly a large number, though the corresponding input pin is empty

QM Hou
Prodigy 150 points
Part Number: TLA2024

Hello,

Now I met a stranger problem that the ADC result is randomly a larger number, while the corresponding input pin is empty. 

My hardware connected 4 sensors, which is DC output, to TLA2024 4 inputs pins which are configured as single-end input mode, with 100ohm series resistor and 0.47uF parallel capacitor to GND as analog input filter, TLA2024 VCC=+5V,   data rate = 1600 SPS, FSR set at ±6.144 V or ±4.096 V which depends on input level. Firmware control external sensors power on/off and TLA2024 to sample each channel one by one at single-shot mode.

When there is actual signal inputted, almost no problem, just start qualification now, but if there is no input, the actual case is the input port is empty by no connection for these corresponding ADC input ports, there is low chance that the ADC readout is a large number. Can somebody help to figure out what the problem of my design?

Thanks in advance!

Best Regards!

QM

 

  • 0
    TI__Guru* 98025 points

    QM,


    In many ADCs, if the inputs are floating, the output data may be undetermined. The input may float high or low depending on the input current of the ADC.

    Generally, the input current for the TLA2024, would have a little higher input current, and I would have expected the ADC data to stay near 0, with a floating input. However, it could give much larger input if there are other connections to the input (intentional or parasitic).

    Again, with the inputs floating, the output value could float to anywhere in the input range. If you need the ADC readout to go to near 0V with the input floating, I would insert some sort of pull-down resistor on the input.

    I'll close this post, but if you have other questions or if I didn't address your concern post back and we'll be able to continue this thread.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 150 points

    Ho Josepy,

    Thanks for your explain.

    Regards!

    QM