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MSP430FR2676: CAPx,y pin self test

Koichiro Tashiro
Mastermind 22945 points

Part Number: MSP430FR2676
Other Parts Discussed in Thread: CAPTIVATE-FR2676

Hi,

My customer is evaluating their own sensor connected to CAPTIVATE-FR2676 board.
There are a few mutual buttons on customer sensor.

They want to check if each mutual button is properly connected by self-test.
For example, checking capacitance on each CAPx,y signal.
Is this possible? If so, how?

Customer found below description in technology guide, but it is not clear how to use these Reference Capacitors in self-test.
http://software-dl.ti.com/msp430/msp430_public_sw/mcu/msp430/CapTIvate_Design_Center/latest/exports/docs/users_guide/html/CapTIvate_Technology_Guide_html/markdown/ch_technology.html?highlight=calibration#reference-capacitors


Do you have more document or sample code for self-test using Reference Capacitors?

Thanks and regards,
Koichiro Tashiro

  • 0
    TI__Mastermind 22945 points

    Hi,

    I have additional question.
    The customer is using CapTIvate Design Center GUI and tuning their sensors.
    When they click “Force_Recalibration” in Tuning window (see below), sometimes LTA value gets strange values.




    I guess usually LTA value is around “Conversion Count” value.
    In customer case, “Conversion Count” is 1500 and “Conversion Gain” is 100.
    But LTA sometimes gets ~1000 or ~3000 when “Force_Recalibration” is clicked.

    What is potential cause of this behavior? What should be checked?

    Thanks and regards,
    Koichiro Tashiro

  • 0 in reply to Koichiro Tashiro
    TI__Mastermind 30426 points

    Hi Koichiro,

    Looks strange, and I also find your count too big, 1500?

    And if there are any other errors occur in GUI?
    Did you touch with your hand when you run forced calibration?

    Thanks!

    Best Regards

    Johnson

  • 0 in reply to Johnson He
    TI__Mastermind 22945 points

    Hi Johnson,

    Sorry for late reply.
    Here are feedback from the customer.

    Johnson He said:
    Looks strange, and I also find your count too big, 1500?


    The count value 1500 is selected because of their system requirements.
    (proximity sensing with small capacitance change)
    Customer refers Figure 10 or 12 to select 1500.
    https://www.ti.com/lit/an/slaa843a/slaa843a.pdf

    Johnson He said:
    And if there are any other errors occur in GUI?
    Did you touch with your hand when you run forced calibration?

    Customer does not found any other errors in GUI.
    And the sensor is not touched during forced calibration period.

    Could you also answer to the 1st question about self-test?

    Thanks and regards,
    Koichiro Tashiro

  • 0 in reply to Koichiro Tashiro
    TI__Mastermind 30426 points

    Hi Koichiro,

    For 1st question, you would like to calculate the capacitance for each pin?

    If yes, I think we have some method can help you, I will check those data and update here.

    Thanks!

    Best Regards

    Johnson

  • 0 in reply to Johnson He
    TI__Mastermind 30426 points

    Hi Koichiro,

    I think maybe I am misunderstand your means for Q1? could you share some details about this?

    Thanks!

    Best Regards

    Johnson

  • 0 in reply to Johnson He
    TI__Mastermind 22945 points

    Hi Johnson,

    Sorry for my late reply. Here is background of Q1.
    The customer is planning to connect a number of sensors (buttons) to MPS430.
    He wants to check whether each button is properly connected to each pin in self-test.
    If user can measure capacitance of each pin and check if these values agree to the default button capacitance,
    it can be used as self-test. This is what customer wants to know.

    Thanks and regards,
    Koichiro Tashiro

  • 0 in reply to Koichiro Tashiro
    TI__Mastermind 22945 points

    Hi Johnson,

    Regarding Q1, is this possible to detect by software whether CAPx.y is left open or not?

    Thanks and regards,
    Koichiro Tashiro

  • 0 in reply to Koichiro Tashiro
    TI__Mastermind 30426 points

    Hi Koichiro,

    Understood your customer needs, update my comments here:

    I think if you would like to chech if CAPx.y is normal or open, the best method is function test.

    And if you would like to use software to detect those pin, I think is not easy, bucause our CapTIvate IP will do some calibration for each channel, here are some ideals maybe used for you:

    • Calculate the capacitance for each pin.
    • Check the value of "Coarse Gain Ration" and "Fine Gain Ratio"

    Actually, CapTIvate IP will adjust  "Coarse Gain Ration" and "Fine Gain Ratio" automatically to match your setting(LTA and Gain), thus this value will influence by pin capacitance and reference capacitance(internal MCU), if CAP Pin is left open, the pin capacitance value will be small, so the  "Coarse Gain Ration" and "Fine Gain Ratio"  value will be different.
    But the reference capacitance of each device is also different, so the different of "Coarse Gain Ration" and "Fine Gain Ratio" may be caused by devices reference capacitance, here maybe need to do more test, but I think it should be more difficult.

    So I recommend you should do function test to check CAPx.y is left open or not.

    Thanks!

    Best Regards

    Johnson

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