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MSP430FR5969: Occasional 14-bit number from 12-bit ADC

Steven Hunter
Intellectual 420 points
Part Number: MSP430FR5969


Our processor is in a pulse power system and we occasionally get bad ADC data, like a 14-bit number even though the ADC is only 12-bit. Naturally, we have filtering on the ADC inputs, but the EMI environment is severe. The ADC is set up to scan the inputs and we read the block of data when the scan is complete.

  • 0
    TI__Mastermind 39775 points

    I don't understand why you can read 14-bit data from ADC. It seems only can output 12 bit.

    Can you tell me what you want us help? To avoid read out 14 bit data or help you read the right data. You information is too less for us to give further support.

  • 0 in reply to Eason Zhou
    Intellectual 420 points

    I don't understand how it can return a 14-bit number either, that is the question.

  • 0 in reply to Steven Hunter
    Guru 42145 points

    Since you have to read 2 bytes, I guess a few of the normal zeros in the top 4 bits are getting flipped by the noise.

  • 0
    Guru 24915 points

    EMI can find paths that you didn't think of.

    You say you have filtering on the ADC inputs but what about the rest of the system? Does the MCU get clean power?

    One devious detail is that your typical voltage regulator, that one you are using for 3.3V for the MCU, is series pass. Which means they can source current but not sink it. Not normally a problem but if you have diodes to clamp inputs to Vcc they can inject enough current into the Vcc rail to raise the voltage. All you have to do is inject more current than is being drawn by the system.

    A real problem with a low power device like a MSP430.

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