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ADS1258-EP: ADS1258MRTCTEP

Johnathan Williams
Prodigy 40 points
Part Number: ADS1258-EP
Other Parts Discussed in Thread: ADS1258

One more thing, I understand the datasheet states that the ADS1258MRTCTEP, outputs data in the SPI interface that reports the gain error of the device (.5% max) and the reference reading error (1% ==> 3%) when it is sampling input signals. I'm assuming this means that software/firmware can read those errors in the datastream, which would allow those measurement errors in particular to be factored/canceled out of the measurement reading? For instance if a differential analog signal of 100uV is fed into the ADC, it is possible for software/firmware to look at the gain errors and reference reading errors during that measurement, cancel out those error factors and calculate the exact actual value of 100uV seen directly at the input?

  • 0
    TI__Genius 14540 points

    Hi,

    I am researching your inquiry and hope to get back with a response within a day.

    Thanks

    Christian

  • 0 in reply to Christian Yots
    TI__Genius 14540 points

    Hi Johnathan,

    I got the following information from the team that developed this device.

    "It sounds like Johnathan is asking about calibrating the ADS1258, which is possible but it must be done in the customer’s MCU/firmware since the ADS1258 does not have any calibration registers/math blocks to perform the calibration internally. Therefore, the MCU will need to store offset errors and gain errors for every channel that the customer wants to calibrate, and then perform the math operation: (OUTPUT_CODE – MEASURED_OFFSET_CODE) / (MEASURED_GAIN_ERROR)

     He can first measure and calibrate the offset with the ADC inputs shorted, and then measure and calibrate the gain error (in that order). However, for gain error calibration to be effective, the calibration signal must have and accuracy better than 0.5% (otherwise calibration will only be making the gain error worse). If this criteria cannot be met, then it is best to only measure and calibrate the ADC offset and live with the ADC’s uncalibrated gain error."

    Thanks

    Christian

  • 0 in reply to Christian Yots
    Prodigy 40 points

    Also just to confirm, when output data is being sent out from the ADC during the sampling/measuring period, among the data being provided is the reference reading error (+/- 1% ===> +/- 3%) for each individual channel that is currently being sampled? So there are methods to cancel out any measurement errors due ADC reference mis-readings?

  • 0 in reply to Johnathan Williams
    TI__Mastermind 44680 points

    Hi Johnathan,

    Take a look at Figure 36 in the datasheet... The internal gain monitor can help you calibration for internal ADC gain errors, but it does not account for gain errors associated with each channel since the input MUX (and all external circuitry) is bypassed.

    You can use the internal gain monitor to account for the ADC's internal gain error, but to get a more accurate gain error calibration for each channel, you would need to provide a calibration signal to each input channel (or measure your sensors in a controlled environment, such that you know what you can expect for he input voltages) and then measure the voltage on each channel and compare it to the expected value.