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MSP430G2432: ADC issue

Part Number: MSP430G2432

Team,

My customer is experiencing problems with MSP430G2432 ADC:

I’m experiencing a critical issue with the ADC on the MCU I’m using.  I had a product that I sent to the customer. It worked great for around 5 hours of testing.  When the customer tried to use it, it wasn't behaving as it should.  I got the unit back and found that the analog pin that reads the voltage across the sensor is not reading correctly.  I measured the voltage at the pin and it was ~3.3V, but the ADC was reading ~850 counts.  What could cause that pin to suddenly start reading the voltage incorrectly?  

Thank you

Viktorija

  • HI Viktorija,

    What would be the expected value?
    How is the ADC configured, do you use the internal or external reference?
    If external, have you checked the voltage on the external ref pin?
    What is your VCC?
    What is meant with "when customer tried to use it" exactly? (waking up from lpm, power cycle, reset...)
    What happens if you replace the micro with a new one?
    Is the micro soldered to the board?

    Regards
    Lukas
  • Hi Lukas,

    I am the customer having issues. Thank you for the fast response! The responses to your questions follow.

    What would be the expected value?
    Approximately 1028 (I'm using the 10-bit ADC)

    How is the ADC configured, do you use the internal or external reference?
    I'm using VCC as the reference

    What is your VCC?
    3.3V

    What is meant with "when customer tried to use it" exactly? (waking up from lpm, power cycle, reset...)
    I'll need to provide a little more information here. The product is a light that senses ambient light. The customer that was referred to here is our company's customer. The light was working correctly while I tested it for several hours. When that person tried to use it, the light never sensed darkness. When I got it back, I debugged the code in Code Composer Studio and found that the pin that reads voltage across the phototransistor to detect darkness was reading 850 counts even though I measured the voltage at close to 3.3V.

    What happens if you replace the micro with a new one?
    I'm getting ready to try that now. I'll let you know shortly.

    Is the micro soldered to the board?
    Yes. It is in a TSSOP package.

    Thanks,
    John
  • Hi Lukas,

    One of my colleagues figured out my issue for me. It turns out that I was sampling the ADC too quickly. Once I increased the sample and hold time and decreased the ADC clock frequency, it started working correctly. What's weird is that it ever worked to begin with, but since it is fixed, I won't worry about that too much :)

    Thanks,
    John
  • Ok, thanks for the information.

    I will close this case.

    Lukas