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LDC1101: LDC1101 / Sensor frequency goes high when sensor cap is decreased

S.Satoshi
Guru 21675 points
Part Number: LDC1101

Hi,

Now my customer has evaluated LDC1101EVM and measure the sensor frequency with various sensor cap. Then they can see the unexpected behavior when sensor cap is decreased as below.

[GUI setting]

LDC1101EVM GUI Ver.1.0.0.6

LHR mode

L only

[Coil]

Ls ： 6.93 uH ， Rs：5.90 Ohm

[Sensor cap]

330pF : 3,353,000 count ，2.398 MHz

1,000pF : 2,316,000 count ，1.656 MHz

3,300pF : 14,093,000 count ，10.079 MHz ---> 900kHz was expected but show 10MHz

Can you give your opinion why the 10MHz can be seen with 3300pF? Please let me know if you need more information for other setting.

Best Regards,

Satoshi / Japan Disty

  • 0
    TI__Intellectual 2725 points

    Hi Satoshi,

    A bigger capacitor requires more current to to resonate or in other words the Rp of the resonating circuit is too low. The Rp range for supported sensors is between 1.25 KOHM to 90 KOHM. You can use the LDC_DesignTools spreadsheet to calculate the Rp of a sensor and ensure it is within the LDC1101 design space.

    Regards,

    Varn.