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Original question:

MSP430FR2633: MSP430FR2633: RST pin and SBWTDIO pin

MSP430FR2633: MSP430FR2633: C onnecting Resistors or Capicator along CapTIvate channel

Himani Bhatt
Intellectual 390 points
Part Number: MSP430FR2633
Other Parts Discussed in Thread: CAPTIVATE-FR2633, TIDM-CAPTIVATE-64-BUTTON

Hi, I am designing capacitive touch keypad using MSP430FR2633.

I wanted to inquire if I have to connect resistors of 470k at processor side along capacitive channel as shown in pdf document CAPTIVATE-FR2633_REV_C_Schematic or will it do without resistors?

Also is it necessary to connect capacitors of 33pF at processor side along capacitive channel as shown in ALTIUM schematic file TIDM-CAPTIVATE-64-BUTTON?

I am confused if to connect capacitor or resistor as both document differ slightly.

Thank you.

  • 0
    TI__Intellectual 2315 points

    Thank you for your question,

    An assigned MSP member will assist you shortly with this issue.

    Please expect a response in the next couple of days.

  • 0 in reply to Christopher Vendette
    TI__Intellectual 2885 points

    Hallo

    Thanks for the question.

    sorry for the confusion and thanks for informing us about that. We will try to solve that in the documentation.

    The implementation of the R and C depends on your design and applications as well as what kind of electrodes are you planing to implement, (Self or Mutual).

    It basically helps improving noise and EMC robustness of the system.

    For designs which do not require high EMC robustness, the resistor and Capacitance are not required.

    For an EMC robust design we recommend to implement them in your design.

    The resistor works with the I/O capacitance to form a low-pass filter, limiting the effect of high-frequency noise on the electrode.

    The capacitor provides a path for noise currents and stabilizes the sensitive receive electrode. (for mutual electrodes only)

    Some additional info can be found under:

    in section 4.2.8.

    Please let me know if that helps and answers your questions. Please feel free to come back if you have additional questions.

    Best regards

    Kostas

  • 0 in reply to Kostas Aslanidis
    Intellectual 390 points

    Thank you for your response, I'll try to implement the way you suggested.

    Regards

    Himani

  • 0 in reply to Himani Bhatt
    TI__Intellectual 2885 points

    Hi Himani,

    happy to hear that this helps.

    I will set the thread to "TI thinks Resolved" status. If you think it's resolved, please close this thread from your side.

    You can start any time a new conversation if you have additional questions.

    Regards

    Kostas

  • 0 in reply to Kostas Aslanidis
    Intellectual 390 points

    Ok sure.

    Thanks and regards,

    Himani

  • 0 in reply to Himani Bhatt
    Intellectual 390 points

    Hi,

    What should be the minimum distance between the two consecutive buttons for Mutual Capacitance for Captivate phone keypad?

  • 0 in reply to Himani Bhatt
    TI__Intellectual 2885 points

    Hi Himani,

    if you are referring to the PHONE board, please find all the documentation and the design files under

    In general the distance between the mutual buttons depends on different parameters like overlay thickness, dimensions of the electrode, touch area etc.

    The advantage of mutual vs self electrodes is that with mutual you can design smaller buttons and tight packed. 

    I would recommend also to read following document which I think is a very good start for our technology.

    Another good reference design for mutual is also

    Please let me know if that answers your question.

    Best regards

    Kostas

  • 0 in reply to Kostas Aslanidis
    Intellectual 390 points

    Hi Kostas,

    Thank you for documents but I have already refered these documents, in that distance between two electrodes is defined but distance between two buttons is not suggested.

    Also I would like to know if it is necessary to introduce hatch ground pour between two buttons in top layer?

  • 0 in reply to Himani Bhatt
    TI__Intellectual 2885 points

    Hi Himani,

    it's difficult to give an exact recommendation here as this depends on the way of touching, overlay dimensions total size of the panel and the number of electrodes.

    I would suggest for example, for a 10x10mm mutual electrode to keep minimum 5 mm distance. This will give a good separation between the two buttons. It will also work with smaller distance.

    The ground pour on top is normally not necessary. It would give you some additional protection and increase the noise immunity. This depends also from the space available between the buttons. For a mutual key pad, we normally use the guard around the electrodes (see also BOOSTXL design).

    It would be easier to answer the questions, if you could share some additional information on design.

    Best regards

    Kostas

  • 0 in reply to Kostas Aslanidis
    Intellectual 390 points

    Hi Kostas,

    Thank you for information it will help alot.

    Right now the things are going good as per the solution you suggest.

    Thank you for support.

    Regards,

    Himani

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