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ADS124S08: SYOCAL result

Taketo Sato
Genius 10565 points

Part Number: ADS124S08

Hello team,

My customer tried to calibrate ADS124S08 offset by SYOCAL command with SYS_MON[2:0]=001 which is setting for "PGA inputs shorted to (AVDD + AVSS) / 2 and disconnected from AINx and the multiplexer; gain set by user".

With above trial, customer found OFC registers get 0x7fffff.

SFOCAL command is enough for this calibration case, but I would like to understand why OFC register value gets such value with SYOCAL command because I think above customer condition is similar to SFOCAL condition. Could you please let me know possible reason?

Can SYOCAL command cancel the setting of  SYS_MON[2:0]=001 so that ADS124S08 can calibrate system level offset calibration?

Best regards,

  • 0
    TI__Guru** 113765 points

    Hi Sato-san,

    If just the ADC offset is to be removed the proper command is the SFOCAL as this will automatically apply the internal short and does not required extra register writes.  The SYOCAL is the system offset calibration command and is expecting an externally applied 0V input (at the device ADC input pins) to remove any offset including sensor imbalance.

    It the OFC registers are showing full-scale it would appear that perhaps no valid reference voltage is selected.  I tested this same procedure on the EVM  and was able to get similar results when using the SFOCAL and the SYOCAL with the SYS register configuration to the internal short.

    There are a couple of considerations with the calibration commands.  The first is the ADS124S08 must be in conversion mode (as opposed to idle) when the command is issued.  the second consideration is a valid reference must be selected.  For example, if the internal reference is selected but the reference is powered down the offset calibration result may be 0x7FFFFF.  I was able to duplicate this in both SFOCAL and SYOCAL if the reference was not valid.

    Best regards,

    Bob B