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MSP430FR2676: Difference in resolution between Gen1 and Gen2

O.H
Mastermind 6340 points
Part Number: MSP430FR2676

Hi experts,

Q:Does the Gen2 device have higher resolution than the Gen1 device when used as a simple button (e.g. using a single electrode with self-capacitance method)?

Currently, I need a more detailed response when I put my finger close to a single electrode. I understand that this can be adjusted by parameters, but what I would like to know is the difference in resolution as a device.

In the "Device Family" section of the Technology Guide, the resolution when used with the slider and wheel is mentioned, but the resolution for a single electrode is not.
: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_device.html#id3

If the resolution is higher with Gen2, it would be helpful to know why.

Best regards,
O.H

  • +1
    TI__Guru 70996 points

    Hi O.H-san,

    Well, you are certainly busy helping support Captivate customers - thank you.

    This is actually a very good question.  Both device families have about the same sensitivity or resolution (being able to detect the smallest possible change).  You can think of it as the LSB for an ADC. The performance differences between these two families is the GEN1 devices have a slightly higher 'internal' noise level compared to the GEN2 devices.  This noise level was reduced in GEN2 devices as part of the redesign. So what this means is if you set a sensitivity of 1000 target conversion counts on both GEN1 and GEN2 device, and set the same touch or prox threshold, it is much more likely that the GEN1 device will cause a 'false' detect due to the higher internal noise level compared to the GEN2 device. Since the GEN2 noise level is lower, the touch/prox threshold can be set lower without risk of false detect due to noise, which is effectively increasing the sensitivity or resolution.  Does this make sense?

    This is all explained nicely in the Sensitivity, SNR, and design margin document for captivate, https://www.ti.com/lit/an/slaa843a/slaa843a.pdf. If you haven't already reviewed this document, I would highly recommend that you do.  It will help you understand the importance of the SNR and more importantly how to properly set the sensitivity and touch thresholds for the best performance.

    So for your button sensitivity question, I don't know if you are using GEN1 or GEN2, but in either case, start with a conversion gain value = 100.  Then, if the problem is you are not seeing a large enough 'delta' measurement, try increasing the target conversion count.  If you do have plenty of delta, but the finger is not reliably triggering a 'touch' detect, try lowering the touch/prox threshold.  Again, refer to the SNR guide for guidance.

    If that doesn't help and you are using a GEN1 device, consider switching to a GEN2 device.  Also, take a look at the PCB layout.  Do you have a lot of ground or ground pours around the electrode or directly behind the electrode on another layer?  If so, this will increase the electrode's parasitic capacitance, thus reducing the sensitivity.

    Let me know if this is not clear or you still need help.

  • 0 in reply to Dennis Lehman
    Mastermind 6340 points

    Hi Dennis-san,

    Thank you for your detail answer. I have checked the Application Report. I understood that the theoretical resolution of the device remains the same, but the sensitivity/resolution to touch increases because the noise immunity changes. I will proceed with the evaluation based on the adjustment method and information you provided. I will contact you again when I find something unclear.

    Best regards,
    O.H

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