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ADS795x - ADS7952 Rsource

CedricP
Prodigy 40 points

Hi,

What is happening if you have the buffered ainp/MXO configuration and you have a 1 Mohms voltage divider as an input  (see DS 9.2.2)?

Why the voltage follower doesn't act as a buffer for the ADC in this configuration? Is it the MUX that requires a low impedance input? 

What am I missing?

Cedric

 

  • 0
    TI__Genius 9165 points
    Hello Cedric,

    The device expects source impedance to be less than 1kohm when you have buffered MXO to Ainp configuration. With higher source impedance you will start observing errors.

    Datasheet www.ti.com/.../ads7952.pdf page 40 has reference towards this number.

    Also, the TYP characteristics graph show the variation in performance with various input impedance.

    Thanks & Regards,
    Shridhar.
  • 0 in reply to Shridhar%20More
    Prodigy 40 points

    Why the voltage follower doesn't act as a buffer for the ADC in this configuration? Is it the MUX that requires a low impedance input? 

    What am I missing?

  • 0 in reply to CedricP
    TI__Genius 9165 points
    Hello Cedric,

    Apologies for delay. I somehow missed your last communication.

    I would like to know more about "voltage follower doesn't act as buffer".

    I think you have placed voltage follower between MXO & AINP pins. Please share a schematic around this portion. If you can also measure the voltage on the MXO pin & AINP pin when the ADC is converting it will help.

    Thanks & Regards,
    Shridhar.