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ADS124S08: Current when floating analog input

Leonardo Santiago17
Prodigy 10 points
Part Number: ADS124S08

Hello,

I'm using the ADS124S08 to measure 12 single ended inputs. I'm using the internal 2.5V as references, and because of my signal, I have to use a voltage divider (2 resistors of 10Kohm).

When the analogue pins are floating the ADC measures something, with an oscilloscope I can see that there are 1.5V in the ANX pins, how is that possible if the IDACx are disabled?

If I connect the AN0 to GND to tests, it should measure 0V but that does not happen either beacuse of the current comming out of the ANX pins.

Regards.

  • 0
    TI__Guru** 112885 points

    Hi Leonardo,

    Welcome to the forum! It is possible that the inputs will float to some value when left floating. When connected to a voltage source the input should follow the source.  You may see a conversion result other than 0 when you ground the input if you do not have the PGA bypassed as the PGA output cannot drive all the way to ground.  This setting is in the Gain register (0x03) and is the default value.

    How have you determined that current is coming out of the inputs?  Even if the IDACs are not turned on, maybe the VBIAS or the burn-out current sources are on.

    Can you share your schematic and all register settings being used?

    Best regards,

    Bob B