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LMP91200: LMP91200 config for ADC internal of MCU module

Alone173
Expert 1325 points
Part Number: LMP91200


Hi everyone
Im trying to config for PH measurement with LMP91200 IC
While ADC input of MCU is 0-1.8V
So, i have more unclear point about Vout and Vref when design schematic with this IC
Can Tier help me to solve this problem?

Thanks

  • 0
    TI__Expert 5695 points
    Hi Alone173,
    Please try the Webench Designer tool for LMP91200 located in the product page of the IC. This tool will guide you on the design approach based on the characteristics of your pH sensor. If your part is not listed there you can manually enter the key parameters of the one you are using.
    webench.ti.com/.../

    For recommended design techniques I recommend to look at the following TI design:
    www.ti.com/.../tida-00561
  • 0
    TI__Intellectual 1960 points

     Hi Alone173

    Your schematic seems ok.

    The VCC_1.8 is divided by 2 internally and 0.9V is the VCM value.

    VCM=0.9V

    pH sensor output signal is usually 0V at pH=7 and pH sensor has a sensitivity of 59.16 mV/pH

    The signal from the pH sensor range ranges from (-414.12mV+VCM) and (414.12+VCM).

    In your case:

    pH=0 --> VOUT= 485mV

    pH=14 --> VOUT = 1314.12mV

    In your schematic seems that you are going to use a single ended ADC. In this case the fluctuation on VREF becomes input signal to the ADC. Usually this is not a big issue if the VREF is well filtered.

    Using a differential ADC is possible to use the VOCM signal to remove the VREF influence. VOCM is the VREF signal buffered to drive the external ADC.

    Regards

    Massimo