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ADS1232: Single Ended input

Hector
Intellectual 526 points
Part Number: ADS1232

Hello ; 

I know ADS1232 is not designed to used in single ended input ; but I beleive we still can use it in still ended in case gain =1 or 2 . 

I am trying to read 4-20Ma and  an analog voltage from  a POT ; my shematics is down ; please could you check and suggest any think to impoove? 

My questions : 

1. Do I still need to the common mode filter on IN-  in case of single ended ? or I can just connect to ground ? 

2. Can I sync  2 ADS1232 using  PWDN ? 

press_2023.PDF

Thank you in advanced 

Regards 

Hector 

  • 0
    TI__Mastermind 40950 points

    Hello Hector,

    Your schematic is missing the bypass caps for the supplies and does not show the connections to the processor, but what you have included, looks like it should work well regarding the analog input.  For single ended, you can simply connect AINN to ground without the filter network, but including it may help with external noise getting into the inputs, as the differential input will reject any common mode noise on your board.  If you have room for the 2 additional parts, then I would recommend keeping the full differential filter.  Since you have the reference connected to +5V, the singled ended input range will be 0V to +2.5V.

    I noticed there are no connection dots for your input differential filter; you should check these to make sure all points are actually connected in your schematic.

    Also, as I mentioned, the power supply pins and reference pins should include bypass capacitors.  You can follow Figure 11-1 for the recommended components and layout.

    Yes, you can resynchronize the 2 ADC's by using the /PWDN pin, but the parts will not stay synchronized if using the internal oscillator, since there is a +/-3% tolerance from part to part.  If you want to keep the ADC's synchronized after /PWDN, then you will need to use an external oscillator.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Intellectual 526 points

    Hi Keith ; 

    Thank you for the answer. 

    For sync  2 or 3  ADS1232  what is the best connetion ?   Is it connect the all PWDN together , all SCLK together , and  all CLKin together ?  

    Thank you 

    Regards 

    Hector

  • 0 in reply to Hector
    TI__Mastermind 40950 points

    Hello Hector,

    Yes, use a common external clock oscillator and connect the CLK pins together to this external oscillator.  Connect the /PWDN pins together and toggle so that all ADC's are synchronized to each other.  The SCLK pins can also be shared, but this is not a requirement for synchronization.

    The DOUT pins cannot be connected together as these pins are always driven high or low; there is no chip select to force DOUT into hi-z.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    Intellectual 526 points

    Thank  you Kieth; 

    I am using differential input s for analog inputs and reference inputs ; but the values not same for  analog inputs I use    1K resistor with 100nF diff. capacitor and 10nF common mode capacitor  

    while for reference input I use 100R with 2u2F diff and 100nF common mode capacitor . 

    should be they same  ? or its not an issue 

    Thank  you 

    Regards 

    Hector 

  • 0 in reply to Hector
    TI__Mastermind 40950 points

    Hello Hector,

    If you are measuring a bridge sensor, typical for a weigh scale application, then keeping the same filter for both analog input and reference input is helpful for ratiometric configurations (refer to for A Basic Guide to Bridge Measurements more details).  In your case, you are using the ADS1232 in a single-ended configuration, and having different filters will not be an issue.

    Regards,
    Keith