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ADS114S06B: ADS114S06B calibration

wfink
Prodigy 40 points
Part Number: ADS114S06B

Hello support team,

I have a question regarding offset and gain calibration of ADS114S06B.

Which commands and in which order must be perfirm to calibrate ADS114S06B?

Best regards,

W. Fink

  • 0
    TI__Guru** 113765 points

    Hi W. Fink,

    Welcome to the E2E forum!  Offset calibration should always be done before gain calibration.  ADS114S06B offset calibration can be accomplished in two different ways.  The first method uses the SFOCAL command (self offset calibration) which is done to remove the offset inherent to the ADS114S06B.  It is always a good idea to issue this command after device power up (unless you use the SYOCAL, the system offset calibration).  The second offset calibration is the SYOCAL which takes into account any sensor, op amp or other factor that may introduce an offset.  In this case, you would set the inputs to what should be a '0' and then issue the SYOCAL command. 

    The gain calibration may not be necessary. The device is trimmed such that the Electrical Characteristics for gain error are maintained as specified for the device. If this is good enough for the application, then gain calibration for the ADS114S06B is not necessary.  However, if you wish to issue a gain calibration (SYGCAL command) for the ADS114S06B, then you would need to externally apply a full-scale voltage to the analog inputs and then issue the command.

    This device calibration commands only calibrates the ADS114S06B and does not take into account any sensor error specifically.  If you are using a bridge sensor, RTD, thermistor, etc., you may want to skip the device calibration commands and include the sensor in the calibration.  In this case you would need to do at least a 2 point calibration of the sensor while connected to determine offset and gain and adjust the output code accordingly.  This method of calibration is done in firmware/software.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 40 points

    Hi Bob,

    thanks for the answer.

    I'd like to specify my question: must I send the SFOCAL command after START command and than wait for DRDY output goes low? Are the conversion data than valid?

    What is with calibration by converting in continuous conversion mode? May I send SFOCAL command any time or first restart the conversion and than send the SFOCAL command?

    Best regards,

    Vladimir

  • 0 in reply to wfink
    TI__Guru** 113765 points
    Hi Vladimir,

    Let me start with the second question first. The calibration commands will not be acted upon unless the the ADS114S06B is in the conversion state. Take a look at Figure 67 on page 42 of the datasheet. The Operating Flow Chart shows the various states of the device. If the calibration command is issued while in Standby or Power-down Modes, the command will not be recognized as the command requires that the device be converting. Another way to state this is the device cannot calibrate if it is asleep because it must be actively converting to collect the information for calibration.

    If the START pin is high, then the ADC will be converting and the SFOCAL can be sent at any time.

    If the START pin is being held low and the device is currently in the Standby Mode, then the START command must be issued first (to move from the Standby Mode to Conversion Mode) followed by issuing the SFOCAL command. As long as the ADC has not completed the conversion following the START command, then the SFOCAL command can be issued. Another way to say this is if the device is in an active state of conversion, then the SFOCAL can be issued.

    As long as the ADS114S06B has started a conversion or is in the process of conversion, then the SFOCAL can be issued and the calibration will take place by interrupting the current conversion. When DRDY transitions from high to low, this is the signal that the calibration has completed, a new 'normal' conversion has started and the data are valid for the configured input.

    Best regards,
    Bob B