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Original question:

ADS124S06: Differential measurement and ADC counts output

ADS124S06: How to use different ADC channels sequentially.

Surya Mohan
Prodigy 160 points
Part Number: ADS124S06
Other Parts Discussed in Thread: ADS124S08

Hello,

We are using 4 analog channels to measure 2 differential signals as:

AIN0, AIN1 for one differential signal measurement and AIN4, AIN5 for second differential signal measurement. Global chop mode is ON in both the cases.

What will be the programming flow diagram for sequential measurements of above two signals. Also, let us know the time delay (if any) required while switching the value of INPMUX register.

Regards

Surya Mohan

  • 0
    TI__Guru 55342 points

    Hi Surya,

    Please see sections 9.3.1 Multiplexer, 9.3.6.5 Global Chop Mode, and 9.4.4.3 Programmable Conversion Delay in the datasheet.

    Select any of the six (ADS124S06) or 12 (ADS124S08) analog inputs as the positive or negative input for the PGA using the MUX_P[3:0] and MUX_N[3:0] bits in the input multiplexer register (02h).

    In global chop mode, sequences are similar to taking consecutive single-shot conversions and swapping the input on each conversion. Output data are averaged using the last two data read operations by the ADC with the inputs swapped. Figure 74 shows the time sequence for the ADC using global chop mode.

    The programmable conversion delay is intended to accommodate the analog settling time on the inputs (for example, when changing a multiplexer channel). Use the DELAY[2:0] bits in the gain setting register (03h) to program a delay time ranging from 1 · tMOD to 4096 · tMOD (where tMOD = 16 · tCLK). The default programmable conversion delay setting is 14 · tMOD.

    Additionally, try searching "Configuration Measurement Settings" within this document, it provides several example code flows for different types of measurements: www.ti.com/.../sbaa275.pdf

    I have adapted one of the example code flows below for you:

    Configuration Measurement Settings

    For the first measurement, set the register values:
    • Select multiplexer settings for AINP and AINN to perform the first measurement
    • Enable the PGA, set gain to desired value
    • Select data rate and digital filter settings
    • Select reference settings
    • Take measurement

    For the second measurement, set the register values:
    • Select multiplexer settings for AINP and AINN to perform the second measurement
    • Take measurement

  • 0 in reply to Alexander Smith
    Prodigy 160 points

    In our application, we have bypassed the PGA and the datasheet recommends to set the delay to 14.tMod in this case. So, can we still change this delay according to our need or any other alternative? 

  • 0 in reply to Surya Mohan
    TI__Guru 55342 points
    Hi Surya,

    Yes, the delay is set by a register and 14*tMod is the default value. Please see page 76 of the datasheet to see the possible delay times. Based on your external circuitry, you may need a longer delay in order for the signal to properly settle after switching.