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LDC1312: About the coil of the LDC1312

Masami Michino
Genius 5070 points
Part Number: LDC1312

Dear, All

The customer has a question about the pattern coil used for the LDC1312.
They use two LDC1312 and use four pattern coils side by side.
Measurement is carried out using two coils at the same time, but it is always considered not to use adjacent coils at the same time.
The diameter of the coil is assumed to be 8 mm. In this case, how much should the distance between the coils be so that adjacent coils do not influence the measurement?
Please tell me if you have recommendations.
Also, please tell us the possibility of how the adjacent coils created will affect.

Thanks, Masami M.

  • 0
    TI__Genius 17440 points
    Hi Masami,

    In general we recommend that you separate coils that may be used simultaneously by about 50% of the coil diameter, in this case 4mm. Because you are not using adjacent coils at the same time, this separation shouldn't be a problem. We also recommend keeping the simultaneously operating sensor frequencies about 10% apart.

    If you do have adjacent coils operating that violate these recommended conditions, the coils can magnetically couple and uncouple. This will show up as EMI based noise in your measurements.

    Regards,
  • 0 in reply to Kristin Jones93
    Genius 5070 points

    Hi Kristin-san,

    Thank you for your reply.
    I am sorry that the reply was delayed by Japanese Long vacation.

    I explained it to the customer.
    They understood the conditions, but we found that LDC 1312 uses more than 5 and that more than 5 coils are used at the same time.
    Therefore, they want to check whether only adjacent coils are enough to operate the sensor frequency 10% apart.
    For example, if they use 1 to 10 coils and only operate on odd coils, they can set the same sensor frequencies for 1, 5 and 9 coils and set the 3 and 7 coils to about 10% apart frequency Could it be?

    Thanks, Masami M.

  • 0 in reply to Masami Michino
    TI__Genius 17440 points

    Hi Masami-san,

    The LDC1312 shorts the inactive coil to ground while it stimulates the active coil. If your coils are arranged so that all of the active coils have an inactive coil in between them, this should satisfy the spacing recommendation. For example, if coils 1-10 are arranged in a line and even coils are always inactive when odd coils are active, this spacing would prevent the coils from coupling. In addition, you may prevent the magnetic coupling through either the spacing recommendation or the frequency shift recommendation; you do not need to satisfy both recommendations, though doing so would create a more robust design. If the odd coils you described are adjacent, then setting the frequency of coils 3 and 7 about 10% apart from coils 1,5, and 9 should satisfy the frequency shift requirement. As long as coils 1,5, and 9 are spaced at least 50% of the coil diameter apart, they should not couple, even if they are operating at the same resonant frequency. 

    Regards,

  • 0 in reply to Kristin Jones93
    Genius 5070 points

    Hi Kristin-san,

    Thank you for your answer.
    I understand.
    I will respond to customers.

    Thanks, Masami M.