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MSP430I2030: SD24 ADC offset voltage

Part Number: MSP430I2030
Other Parts Discussed in Thread: MSP430F423

Hi,

does anybody has a software routine to calculate and eliminate the offset voltage from the SD24V ADCs of the MSP430i2030?

I use them with an OSR=64, LSBACC=0 and gain=2. The offset voltage is up to +-0x80h if I short circuit the ADC input pins.

Regards

Wolfgang

  • Hello Wolfgang,

    Thank you for your post. For eliminating offset, you'll just want to subtract the offset (positive or negative) from the ADC value in SD24MEMx for each channel before applying any type of scaling factor.

    Assuming decimal values, subtracting the offset takes care of both positive and negative offsets for positive and negative ADC values. See example calculations in table below.

    ADC Value Before Offset Offset After Offset
    Max Positive +505

    +5

    +505 - (+5) = +500
    Max Negative -495 +5 -495 - (+5) = -500
    Max Positive +490 -10 +490 - (-10) = +500
    Max Negative -510 -10 -510 - (-10) = -500

    If your output format is Offset Binary (SD24DF = 0), subtracting the offset will work fine. However, if your output format is Twos Complement (SD24DF = 1), you'll need to account for converting to/from two's complement when subtracting. You define different offsets per channel too.

    I hope this helps!

    Regards,

    James

    MSP Customer Applications

  • Hello Wolfgang,

    As a follow-up, I’m happy to inform you that the official software release for the new Energy Measurement Design Center (EMDC) and Software Library is available on TI.com. It includes documentation and Design Center examples for the supported EVMs.

    EMDC Product Page

    EMDC Software Download Page

    EMDC Technology Guide

    EMDC API Guide

    Regards,

    James

    MSP Customer Applications

  • Hello James,

    thank you, but I would like to know, how I can measure the offset value of the ADC24.

    The MSP430F423 has the opportunity to short circuit the ADC input pins internally. After this I can measure the offset voltage.

    The i2030 dosen't have this opportunity.

    At your example 5 and 10.

    Regards

    Wolfgang

  • Hello Wolfgang,

    Wolfgang Meid said:
    The offset voltage is up to +-0x80h if I short circuit the ADC input pins.

    I'm sorry if I misunderstood your question. In your initial post, you mentioned that you needed to calculate and eliminate the offset and that you were shorting the ADC channel input pins (which is the correct way to measure offset on the i20xx devices). Unfortunately, the i20xx devices do not feature an internal short for the ADC channels, so this must be done externally.

    Regards,

    James

    MSP Customer Applications

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