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LAUNCHXL-F280049C: Protection of the ADC Input Pin

Andreas Jedek
Prodigy 60 points
Part Number: LAUNCHXL-F280049C
Other Parts Discussed in Thread: BOOSTXL-BUCKCONV, TIDM-DC-DC-BUCK, SYSCONFIG, C2000WARE

Do I have any chance to avoid that the 9VDC supply do not destroy the ADC input, except switching off the 9V supply and than the switching off of LAUNCHXL-F280049C?

  • +1
    TI__Guru 62975 points

    Andreas,

    ADC damage relating to the 9VDC supply on the BOOSTXL-BUCKCONV is unlikely because of the voltage-divider and series resistance in the ADC path.  There is also a small possibility that external voltages may create a latchup condition in the device, which would lead to functional faults.  This faulty state can be cleared by removing the external voltage source and power-cycling the device.

    The notes in the TIDM-DC-DC-BUCK user guide are primarily there to make users aware that there is a non-zero risk and to encourage precautions when designing custom boards.

    -Tommy

  • 0 in reply to tlee
    Prodigy 60 points

    Tommy

    the ADC is not demaged. I have a new board and the behavior is the same.

    BUCK_vInSensed_Volts=0.43 I expect 0.02 or 9V

    -Andreas

  • 0 in reply to Andreas Jedek
    TI__Guru 62975 points

    Andreas,

    Can you help to clarify the nature of the issue that you are investigating?  For example, is this a minor issue where the buck converter works, but you just want to understand the source of error, or is this a major issue where the converter is not working and this is the first clue?

    I would recommend measuring the voltage on VinFB (H2[8]) directly using a multimeter or oscilloscope to see if it's close to what the ADC is converting.  If you have a programmable bench supply, it would also be good to see if the conversions track with changes in voltage.

    -Tommy

  • 0 in reply to tlee
    Prodigy 60 points

    Hi Tommy,

    this is a major problem. I got a second board but the behavior is the same.

    I did a measurement with multimeter and I have around~2 Volt when I switch on the 9V. But the The BUCK_vInSensed_Volts value in the Expressions windows shows me always the same value. Independent of the supply voltage.

    -Andreas

  • 0 in reply to Andreas Jedek
    TI__Guru 62975 points
    Andreas Jedek said:
    I got a second board but the behavior is the same.

    Which boards have you swapped?  Both the LAUNCHXL-F280049C and BOOSTXL-BUCKCONV?

    Andreas Jedek said:
    I did a measurement with multimeter and I have around~2 Volt when I switch on the 9V.

    The VinFB voltage divider gain is about 0.25, so 9V input should appear as ~2.25V on H2[8]. Your multimeter reading looks reasonable. I would focus more on the LAUNCHXL-F280049C or software configuration.

    Andreas Jedek said:
    But the The BUCK_vInSensed_Volts value in the Expressions windows shows me always the same value. Independent of the supply voltage.

    Are you using the standard SysConfig-based walkthrough instructions from TIDM-DC-DC-BUCK?

    Can you confirm that the Site # selection in SysConfig (or software) is matching the LAUNCHXL-F280049C J# headers that are being used?

    If everything above checks out, I would recommend modifying the adc_ex1_soc_software example from C2000Ware to convert C0 and C5 to see if the simpler program is able to track with the input voltage: ~C2000Ware_XXXX\driverlib\f28004x\examples\adc

  • 0 in reply to tlee
    Prodigy 60 points

    Hi Tommy,

    thanks for the hint. The LaunchPad Site was the wrong.  It is Site 2 in my case before it was Site 1. 

    With your new E2E I cannot add pictures like before.

    Now it is working like I expect.

    -Andreas

  • 0 in reply to Andreas Jedek
    TI__Guru 62975 points

    Andreas,

    I'm happy to hear that it's working for you now.

    -Tommy