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FDC2214; the role of Idrive

Takao Yamamoto
Genius 4135 points

Dear all,

What does 'Idrive' show? What is the mean of 'Idrive'?

You said about the appropriate value, but what is this mean?

How did you calculate this value?

Best regards,

  • 0
    TI__Expert 8050 points
    Hello Yamamoto-san,

    Idrive sets the drive current for the LC tank. The best way to visualize it is to measure the oscillation amplitude of the LC tank with an oscilloscope.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Genius 4135 points
    Dear Yibo,

    Thank you or your reply.
    And I am sorry for my confusing question.

    I know that Idrive is used for LC tank to oscillate.
    However, I do not understand that how to set this value appropriately.
    Especially, I do not understand the relationship between Idrive and sensor oscillation amplitude.

    Could you teach me the way to set and the relationship?

    Best regards,
  • 0 in reply to Takao Yamamoto
    TI__Expert 8050 points
    Dear Yamamoto-san,

    Given the L and C values of the LC tank, you can analyze the relationship using the parallel resonant impedance model. However, this only gives you an approximate value because it does not take into account the sensor capacitance and parasitics.

    Probing with an oscilloscope using your sensor configuration is the best way to measure the exact oscillation amplitude at various current drives.

    In terms of sensitivity, the optimal amplitude varies for different sensors. For a particular sensor configuration, it's best to sweep Idrive and test the sensitivity at each Idrive in order to find the optimal setting for that sensor.

    Regards,
    Yibo
  • 0 in reply to Yibo Yu
    Genius 4135 points
    Dear Yibo,

    Thank you for your reply, but I could not understand 'you can analyze the relationship using the parallel resonant impedance model'.

    How can I know the relationship of Idrive and amplitude by the parallel resonant impedance model?

    Best regards,
  • 0 in reply to Takao Yamamoto
    TI__Genius 9300 points
    Yamamoto-san,

    Oscillation voltage is proportional to driving current. IDRIVE setting control amount of driving current.
    Depending on Rp (equivalent parallel resistance of the LC tank) you choose IDRIVE setting, according to Figure 14 of the DS.
    If Rp value is not known, the simplest way to set IDRIVE is to disable auto-amplitude correction, set RP override=1 and use a scope on INA pin. Change IDRIVE setting until oscillation amplitude is between 1.2 and 1.8V