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ADS1220: the IDAC of ADS1220connected to REFP1，Can REFP1 be used as a reference source simultaneously?

cong li
Prodigy 20 points
Part Number: ADS1220

Tool/software:

When using ADS1220 for bridge measurement, I use the built-in IDAC for bridge excitation, connected to AIN0/REFP1, and the other end of the bridge connected to AIN3/REFN1.

When converting, AIN3/REFN1 is connected to VSS, and the reference voltage source is built-in 2.048V.

However, I hope to reduce common mode interference and want to change the reference voltage source from the built-in voltage source to REFP1 and REFN1. I wanna to ask if IDAC can be used simultaneously to connect to REFP1 and input REFP1 as the reference source?

  • 0
    TI__Guru 52496 points

    Hi ? ?

    Yes the IDAC output can be used simultaneously with the REFP1 pin input. Can you provide a board schematic so we can review to make sure combining these functions on a single pin is the best option for your system

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 20 points

    bridgeADChere is it, thank you for review.

  • 0 in reply to cong li
    TI__Guru 52496 points

    Hi cong li,

    I don't think you need so much capacitance on the inputs and VREF. Typically you want to use ceramic (C0G) capacitors on the inputs for best performance, and you will have difficulty finding capacitors >=1uF in C0G. I recommend scaling those caps by a factor of 10x at least, and do the same with the common-mode capacitors e.g. C22

    What is the point of connecting to REFP1 and REFN1 if you are using the internal VREF anyway?

    I also recommend against holding the CS pin low. Any glitch on the SCLK pin could either be interpreted as an additional SCLK period or a missed SCLK period, throwing off the entire communication. Yes it is possible to tie CS to ground, but again, not recommended because you must be very careful with the communication

    Please follow the guidelines for unused inputs (REFN0 and REFP0) from the datasheet

    -Bryan