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CC3220SF-LAUNCHXL: ADC measures wrong digital value

Varunkumar Uthayakumaran
Prodigy 110 points
Part Number: CC3220SF-LAUNCHXL
Other Parts Discussed in Thread: CC3220SF

Hi, I'm currently working with CC3220sf LaunchXL. The ADC digital value is exactly half of what its supposed to be when I use the adcsinglechannel project from the resources. First I thought

the ADC was damaged but then it seems to linearly increase and decrease as per the input. The digital value is half of the correct value. According to my understanding the input range for the ADC 

is from 0- 1.5V and it is a 12 bit adc which means it has 4096 digital values. 

Example:

If input signal is 1.1V then the digital value read is 1400 but the correct value is 2800

The same thing happens when I tested it with another cc3220sf Launchxl.

I would really appreciate if anyone can help me with this?

Thank you.

Kind regards

Varunkumar 

  • 0
    TI__Mastermind 28285 points

    Varunkumar,

    On the front end of the ADC pin, we have have a voltage divider and then a op amp in a buffer configuration. The reason for this is to protect our device from getting over the voltage tolerance of the pin.

    The resistor values are 576k and 422k, so with alittle math you should be able to add this to your code to get the expected value.

    Best Regards,

    Vince 

  • 0 in reply to Vincent Rodriguez
    Prodigy 110 points

    Thank you so much that helped me to fix the ratio. Appreciate it!

  • 0 in reply to Vincent Rodriguez
    Prodigy 10 points

    Hi Vincent,

    What is the VCC_OPAMP value in this circuit?

    I went through the datasheet of this board and couldn't seem to find this circuit. I followed the demo provided in the SDK. I read the readme file of the demo and didn't see any mentions of this circuit. The datasheet says the maximum voltage for the pin is 1.5V. The demo suggests connecting the input pin to 3V3 pin of the board. Even if you do that, the reading is based on 1.46V. It seems very inconsistent. Don't you think it is a little inconvenient for the users to have inconsistent material coming from the actual web page of the product?

  • 0 in reply to Arman Pouraghily
    TI__Mastermind 28285 points

    VCC_OPAMP is 3v3 from the board. I'm unsure what is inconsistent in our documenation, but if you can send me links and tell me where i can report it and get them updated.

    BR,

    Vince