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ADS124S08: ADS124S08 Schematic Review

alikaan
Expert 2325 points
Part Number: ADS124S08


Hi,

Could you please review the schematic ? I would like to use PT100 sensor for my application.

Thanks

.910.36.ET.01.KT.100004.AB.pdf

  • 0
    TI__Guru** 113765 points

    Hi alikaan,

    I take it you will be using 2-wire RTDs?  Basically the circuit appears to be ok, but I think you have a cut and past error as you have the ADC_REFOUT portion for the ratiometric reference placed 2 times in the schematic.  Also, the input resistors that are 0Ω are going to create an error if any other value other than 0 is used.  So you could just remove them.  I'm not sure why the 1kΩ resistors are used on the ADC_REFOUT net.  These resistors will just add an additional voltage drop and limit your IDAC compliance range.

    The input filters for RTD3 and RTD4 should also match that of RTD1 and 2.

    I also see that you have ferrites on the supply pins.  Some customers have had issues using ferrites on the supplies as the inductance can limit sharp current demands that are required from time to time by the ADC.  This is especially true on the AVDD supply.  You can leave them in for now, but if you have issues you may want to replace with a 0Ω resistor in place of the ferrite.

    For additional information and circuits I recommend that you take a look at A Basic Guide to RTD Measurements.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2325 points

    Hi Bob,

    Thank you for your reply. Please check the revised schematic. RTD_Measurement.pdf

  • 0 in reply to alikaan
    TI__Guru** 113765 points

    Hi alikaan,

    This version appears to cover the issues I saw previously.  The only suggestion I will make is to remove the filter resistor connected to REFN0.  As REFN0 is at ground potential you will not be able to use the reference buffer, so any bias current through the filter resistor will result in a voltage drop across the resistor creating an error in the reference voltage input.

    Best regards,

    Bob B