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ADS7864 can not work

rihui xin
Prodigy 30 points
Other Parts Discussed in Thread: ADS7864

HI! when I use the ADS7864 at the first time, I forget that its input voltage range  is between -2.5V and 2.5V and I input 5V  .So the output data is all the same wheter i input 5V or 0V .However, I can see the BUSY pin falling  when I give  a pulse to HOLDA . i am not sure wheter the chip has been broken down? or just my programme is bad .  please help me

  • 0
    TI__Guru**** 182301 points

    Hi Rihui,

    The input voltage range to the ADS7864 is actually 0-5V.  The input span is +/-2.5 at a +2.5V common mode level.  Can you share your schematic and let us know what the output code you are seeing is?

  • 0 in reply to Tom Hendrick
    Prodigy 30 points

    Thank you ! The referernce voltage  is the internal reference voltage which is 2.5V and I use 8M OSC for the clock input .I input 5V to the CHA0+ and 0V to the CHA0-. I give a high level to the BYTE pin because the IO of the MCU is less.The output code is always  0100 0000.If I change the input chanel ,the output code may change but always the same  whatever the voltage that I input .

  • 0 in reply to rihui xin
    TI__Guru**** 182301 points

    Hi Rihui,

    With the input voltage you describe above, the output should show full scale positive output code (0x7FF) along with the 'valid data' indication at DB15.  A schematic showing the area around the ADS7864 and some timing diagrams would be a big help in trying to determine where the issue might be.  Does this happen on multiple boards or are you working with a single prototype?

  • 0 in reply to Tom Hendrick
    Prodigy 30 points

    Thank you for your timely help! I have given different voltages to the chip by a DA and I found that the output pins change ragularly. Next I will make the STM32 to read these data. Sincere thanks !