Version 23

    WIP

     

    This blog documents the characteristics of the DAC/ADC BoosterPack of the electronic load that peteroakes, jc2048 and jancumps are designing.

    We have the same DAC/ADC BoosterPacks so we can compare the measurements of each ADC and DAC channel. Check the main document for anything related to hardware and firmware.

     

    Test Setup

     

    Peter has created a GUI that we can use to shoot SCPI commands. We can control the DACs and read the ADCs.

    Measurements are performed with and without the power driver BoosterPack installed. We'll use 5V to power the DACs and ADCs in both situations.

     

    P1 and P2 on the bottom of the DAC/ADC BoosterPack have to be open. Else you'll inject 5V onto the LaunchPad 3V3 rail and you'll damage components.

     

    It's not critical if you switch on the power supply before or after you connect the LaunchPad to your computer. The circuits are isolated.

    All measurements use P3.10 as GND reference and P3.1 as reference voltage.

     

    schematics

     

    Setup without the power driver BoosterPack:

    Mount the DAC/ADC BoosterPack on the LaunchPad.

    Use a +5V power supply. It should be a decent one, current is approximately 5 mA.

    Connect with DAC/ADC BoosterPack P4.2  and with P4.1.

     

    Setup with the power driver BoosterPack:

    Mount the DAC/ADC BoosterPack on the LaunchPad and the Power Driver BoosterPack on top of that.

    On the Power Driver BoosterPack, bridge pins P2.4, P2.5 and P2.6 to tie both opamp inputs of opamp 3D to ground.

    Use a +12V power supply. It should be a decent one, current is approximately 50 mA.

    Connect   with Power Driver BoosterPack P1.1   and with P1.2.

     

     

    Measurements

     

    In the table, the first column shows what we're measuring, the second column the SCPI command to execute with Peter's GUI.

    The next columns are the measurements for Peter, Jon or Jan with and without the Power Driver BoosterPack.

    The last column is for comments. We can indicate odds, errors, learnings.

     

    JonPeterJan
    Data PointSCPIWithoutWithWithoutWithWithoutWithMeasurement method
    SupplyN/A4.989 V11.88 VDMM
    DAC/ADC V+N/A4.989 V5.035 VDMM
    VREFN/A2.046 V2.046 VDMM
    ADC A GNDDEVE:ADC1?2SCPI output
    ADC A VREFDEVE:ADC1?10918SCPI output
    ADC ADEVE:ADC1?1138SCPI output
    ADC B GNDDEVE:ADC2?12SCPI output
    ADC B VREFDEVE:ADC2?10920SCPI output
    ADC BDEVE:ADC2?1
    SCPI output
    ADC C GNDDEVE:ADC3?22SCPI output
    ADC C VREFDEVE:ADC3?1092010919SCPI output
    ADC CDEVE:ADC3?26868SCPI output
    ADC D GNDDEVE:ADC4?83SCPI output
    ADC D VREFDEVE:ADC4?1091910919SCPI output
    DAC A 0DEVE:DAC1 00.000 V0.001 VDMM
    DAC A maxDEVE:DAC1 655352.040 V2.040 VDMM
    DAC B 0DEVE:DAC2 00.005 V0.005 VDMM
    DAC B maxDEVE:DAC2 655352.046 V2.046 VDMM
    DAC C 0DEVE:DAC3 00.000 V0.000 VDMM
    DAC C maxDEVE:DAC3 655352.039 V V2.039 VDMM
    DAC D 0DEVE:DAC4 00.000 V0.000 VDMM
    DAC D maxDEVE:DAC4 655352.039 V2.039 VDMM

     

     

    To resolve

    With the power driver installed, ADC C and D act strange (probably also A and B, but I didn't inject a voltage in them because they are connected to opamp pins).

    In particular strange for ADC D, because that one isn't routed. Strange.

    I will try to decrease the frequency of the sample speed and the i²c speed to see if it's related to that ...

     

    Follow up: the cause is that OPAMP 3C injects -0.8V into ADC A. All measurements are off when that happens. As soon as I force ADC A positive (by tying it to ground or a positive voltage) all measurements are correct.

     

     

    We have a separate document to analyse the summing node at zero.