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ADS1258-EP: ADS1258-EP

Sonia Vargas
Prodigy 95 points
Part Number: ADS1258-EP

There is some doubt regarding the datasheet line: "Note that the AINCOM input and the internal system registers cannot be referenced in this mode."

If it is wanted to used the channels in single-ended using AINCOM as common input, the ADC can be used both in fixed mode and scan mode, or only in scan mode?

or only means that you can not measure AINCOM, or read internal readings of VCC, GAIN, REF, TEMP, OFFSET in fixed mode?

 

  • 0
    TI__Guru 52296 points

    Hi Sonia,

    AINCOM cannot be selected as an analog input, nor can the internal readings be used, in Fixed-Channel Mode. The section on Converting Modes in the ADS1258-EP datasheet mentions this. Moreover, you can see from register MUXSCH (02h) that the selection for AINP and AINN are only 4 bits each, allowing for only 16 options (AIN0 to AIN15).

    If you would like to measure 16 single-ended inputs that are all referenced to AINCOM, please use Auto-Scan Mode. Or, if you want to be able to use the internal diagnostic features on the ADS1258-EP, you will need to use Auto-Scan mode as well. You can see in Table 13 in the ADS1258-EP datasheet that the Status Byte is not used in either operating mode when Fixed-Channel mode is selected.

    Regards,

    Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 95 points

    If I like to measure 16 single-ended inputs that are referenced to AINCOM (ADC ground), is it not possible to use fixed mode and change the channel via commands?

    If it is not possible, could you please give an explanation of such limitations?  

  • 0 in reply to Sonia Vargas
    TI__Guru 52296 points

    Hi Sonia,

    If you need to measure all 16 inputs relative to AINCOM, then you will need to use Auto-Scan Mode. Fixed Channel Mode does not support this configuration natively.

    In Fixed Channel Mode, you measure between two inputs selected from AIN0 to AIN15. AINCOM cannot be selected in Fixed Channel Mode. See the image below regarding the Fixed Channel Mode channel selection register. You can see there are 4 bits per input (AINP and AINN), so there are only 16 channel options (AIN0:AIN15).