• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 29 subscribers
  • Views 455 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.

FDC1004: The principle of FDC1004

Wenhan He
Prodigy 230 points
Part Number: FDC1004
Other Parts Discussed in Thread: TIDA-00317

1.The datasheet said that the detection range of fdc1004 is ± 15pF. Can the chip also measure negative capacitance? How to understand?

2, How to set bias capacitance for this chip?

3.The chip has two special functions, Shield drivers and out of phase technology.

Shield dirves is to eliminate the interference that may be introduced in the test line from the chip to the capacitance detection board, and configure the active drive signal and CIN in the same voltage excitation, so as to shield the external interference.

4. The OOP is to configure the shield and CIN  into opposite phase signals, ao as to Suppress the common mode signal interference.

Is my understanding correct? Thank you for your time.

  • 0
    TI__Expert 3435 points

    Hi,

    Please find answers below

    1. FDC1004 can have a max offset of 100pf. The device is not suitable for measuring the absolute capacitance but can be used for relative capacitance measurement. Let's say you measure 50pf when the liquid is half full in a container and the offset is set at 50pf. This will measure it as 0pf at the half-full condition. When the liquid level is reduced, then the capacitance decreases results in -ve capacitance reading. 

    2. There is no need to set bias capacitance with FDC1004 devices

    3. Yes, your understanding is correct regarding the shield drivers

    4. Exactly, your understanding regarding OOP technique is correct. Please refer to Out-of-Phase Liquid Level Technique application note (SNOA925) and the Capacitive-Based Liquid Level Sensing Sensor Reference Design (TIDA-00317)

    Regards

    sharath.