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LDC1614: Spike noise in Low resonant frequency operation

Takashi Onawa
Genius 13200 points
Part Number: LDC1614

Hi Team,

My customer is just facing a spike noise issue now. They are evaluating LDC1614 under following condition but measurement result sometimes jumped due to spike noise(See measurement result : here)

- Resonant Frequency rage : less than 50kHz
- Distance from the sensor to the measured object : 0mm (When sensor is attached to object)
- MUX_CONFIG : C20D(Deglitch Filter:10MHz)

Then, They are looking for workaround of this though, have you seen such the issue before?
If you have any advice about their measurement conditions, we would appreciate your comments, like "resonant frequency is too low" and so on.

Regards,

Takashi Onawa

  • 0
    TI__Genius 10080 points

    Hi Onawa-san,

    Please ensure that the input deglitch filter is set correctly. This value must be set to the smallest frequency above the oscillation frequency. Further details can be found in section 8.1.7 – Input Deglitch Filter. 

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Genius 13200 points

    Hi Nicole-san,

    Sorry for my slow response on this.

    They are just trying to change some registers like IDRIVE setting and the input deglitch filtering now and let me update the result when their evaluation will be done.

    Then, I got some question regarding layout and influence of external noise on measurement results
    Let me ask some questions to answer their questions.

    1. Is there a possibility of noise in the measurement results due to crosstalk when 4 channels are activated simultaneously?
    2. If an IC such as DCDC is placed nearby, is there a possibility that it will affect the measurement results?
    3．If the above point is Yes, what measures should be taken to reduce the effects of disturbance noise and crosstalk?


    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Genius 10080 points

    Hi Onawa-san,

    Regarding the spikes that are being seen, please refer to this Inductive Sensing FAQ that covers proper deglitch settings.

    Takashi Onawa said:

    1. Is there a possibility of noise in the measurement results due to crosstalk when 4 channels are activated simultaneously?

    I don't think that there would be an issue when activating all 4 channels simultaneously. In multi-channel mode the LDC sequentially samples the selected channels, and only one channel is active at a time while the others are held in an inactive state.

    Takashi Onawa said:

    2. If an IC such as DCDC is placed nearby, is there a possibility that it will affect the measurement results?

    I do not believe that this placement will affect measurement results. The Layout Guidelines in section 10.1 provide more information on how to optimize sensor layout.

    Takashi Onawa said:

    3．If the above point is Yes, what measures should be taken to reduce the effects of disturbance noise and crosstalk?

    For minimum noise it is recommended to perform the sensor measurement after the amplitude has stabilized. You can adjust the sensor startup timing per channel by using the SETTLECOUNTx register. More information on Sensor Startup and Glitch Configuration can be found in section 7.3.3 of the datasheet.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Genius 13200 points

    Hi Nicole-san,

    I think I can close No2 and No3. Sorry, I should have told my customer's situation as background.

    I understand that ch2ch crosstalk is not a problem when operating with a single device, but if multiple devices are running on the board, could they be affected by crosstalk?

    They are considering running more than 10 LDC1614s in their system.
    Should they avoid using devices at the same time in order to minimize the noise effects caused by crosstalk?

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Genius 10080 points

    Hi Onawa-san,

    There is a large chance that two or more coils could end up being driven at the same time if there are 10 devices in the system, causing interactions between LDCs. This situation has not really been tested, but the following E2E thread discusses LDC1614 applications with more than 4 coils:

    Best regards,

    Nicole