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ADS1220: About ADS1220EVM

user4967788
Prodigy 70 points
Part Number: ADS1220
Other Parts Discussed in Thread: ADCPRO,

I have a board of ADS1220evm, and I want to measure the temperature using 4-wire RTD when studying this development board. Because is a beginner, I don't understand, so encountered difficulties in connection, and, when using ADCPro, I according to clew input values, but the output data, I don't quite understand, read how to use the data to calculate RRTD on both ends of the resistance, which can draw the corresponding resistance, I in the development board R31 welding resistance value is 3.24 K ohm resistance, the R30 welding resistance of the resistance value of 0. and RTD has a resistance of 110 ohms,The development board is the one that just got it, there is a program, so there is no change in the program.The following is my connection mode, and the data read by ADCPro. What went wrong, please give a detailed explanation. I need your help very much. Looking forward to your letter, thank you.

  • 0
    TI__Guru** 113765 points

    Hi user4967788,

    I would appear that the basic connections are correct, but have you actually measured externally the voltages to make sure that current is actually flowing through the RTD and through resistor R3?  You should see a voltage drop across R3 that is about 1/2 of AVDD.  However, as you are using 3.24k bias/reference resistor and with R30 installed and IDAX current routed out AIN3 you are actually trying to drive 1mA total through R3.  This will force the IDAC out of compliance.  So either remove R30 or turn off the IDAC current for AIN3.

    If current is flowing properly and you have verified the RTD connections, then you should see a data result other than 0.  At some point you may also want to change the reference from internal to REFP0/REFN0 so the measurement is ratiometric.  I would suggest reviewing the datasheet application shown on page 55 of the ADS1220 datasheet.  Note that it is not necessary to route IDAC current out AIN3 as this connection is for 3-wire RTDs only.  Remove R30 as this will affect the measurement (or turn the current off).  For 4-wire RTDs, you only need one current source and there is no need to consider the effects of lead resistance as the connection is Kelvin to the ADS1220 inputs.

    Best regards,

    Bob B