• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 29 subscribers
  • Views 447 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

FDC2214: Detection principle of FDC2214.

Wenhan He
Prodigy 230 points
Part Number: FDC2214
Other Parts Discussed in Thread: FDC1004

In the datasheet, it is indicated that IDRIVE is to be configured and the amplitude of the detection voltage is within 1.2V to 1.8V. What is the relationship between IDRIVE and VSENSOR?

Whether the LC tank is driven by IDRIVE and the output voltage is detected. If so, what is the frequency of the IDRIVE?

If not, how can this chip detect the resonant frequency? 

  • 0
    TI__Expert 3435 points

    Hi

    The CHx_IDRIVE field should be programmed such that the sensor oscillates at an amplitude between 1.2Vpk (VSENSORMIN) and 1.8Vpk (VSENSORMAX). An IDRIVE value of 00000 corresponds to 16 µA, and IDRIVE = b11111 corresponds to 1563 µA.

    As you increase the IDRIVE, the sensor amplitude increases, so the proper IDRIVE should be selected for the senor amplitude to be between 1.2V to 1.8V. The frequency is based on the LC values that the device detects and reports its digital equivalent.

    Regards

    sharath.

  • 0 in reply to Sharath Vallamkonda
    Prodigy 230 points

    Thank you for your answer.

    DC IDrive can't make LC resonant. Only when IDrive frequency reaches LC resonance frequency can the amplitude of output voltage be the highest.

    Therefore, how to adjust IDrive frequency to reach LC resonant frequency?

    Wenhan

  • 0 in reply to Wenhan He
    TI__Expert 3435 points

    Hi Wenhan,

    LC with Idrive current creates oscillations, where the frequency depends on the inductance & capacitance and the amplitude of the signal depends on the strength of the current. The IDRIVE value should be selected in such a way that the amplitude of the signal is between 1.2V to 1.8V.

    Regards

    Sharath.

  • 0 in reply to Sharath Vallamkonda
    Prodigy 230 points

    Your answer is too rough. What you describe is the working principle of FDC surface. I want to know how FDC works inside.

    How to measure the resonant frequency accurately. What is the internal iDrive signal (half sine wave or square wave or others?)

    I have EVM on hand now. How can I test to see the voltage of vsensor?

  • 0 in reply to Wenhan He
    TI__Expert 3435 points

    Hi Wenhan,

    As explained in the other E2E, I strongly recommend reading all the technical documents related to FDC2214 and FDC1004. The operating principle will be clear to you once you finish reading all the documents. 

    "DC IDrive can't make LC resonant. Only when IDrive frequency reaches LC resonance frequency can the amplitude of output voltage be the highest"


    This is not how the FDC2214/FDC1004 works. What is the source of your statement? 

    The frequency is constant for a constant L and C. But, when C or L changes, the frequency changes. The FDC2214 converts this frequency to digital code accessible through I2C communication. But, for the device to work properly, the amplitude of this frequency should be between 1.2V to 1.8V. This can be adjusted by measuring it with a scope and change the IDRIVE current to meet this requirement. 

    How to measure the resonant frequency accurately. What is the internal iDrive signal (half sine wave or square wave or others?)

    Please use an oscilloscope to measure this amplitude and adjust the IDRIVE setting accordingly.

    Regards

    Sharath.

  • 0 in reply to Sharath Vallamkonda
    Prodigy 230 points

    Thank you very much.