FDC2144‘s questions

user6129715

Other Parts Discussed in Thread: FDC2114, FDC1004

Ladies and gentlemen:

I would like to ask what is the meaning of the dotted line of the differential connection method in the fdc2114 specification book, and does it mean that one more plate is needed between the two plates?

over 4 years ago

0 Nicole Khoury over 4 years ago

TI__Genius 10080 points

Hello,

Thank you for posting.

The dotted line in Figure 54 and Figure 55 is to represent that there are 2 options for ground in these configurations. There can be a virtual ground, where the target object is floating, or an earth ground, where the target object is grounded.

Best regards,

Nicole

0 user6129715 over 4 years ago

Prodigy 10 points

Mr Nicole:

Thank you for your answer

If you want to ask the following question, as you said below, does it mean that we only need to connect the two plates of fdc2114 to the A and B pins of FDC chip to carry out accurate differential test without grounding and other operations.

I also want to know that we plan to use the chip for paper detection. I feel that sometimes the value will fluctuate. I want to know how to connect it more accurately

Best regards

0 Nicole Khoury over 4 years ago in reply to user6129715

TI__Genius 10080 points

Hello,

That is correct, the target object can be left floating and unconnected to ground.

Please refer to the Ground Shifting in Capacitive Sensing application note for further information on system designs that are best suited for your application. Additionally, the FDC2x1x Capacitive Sensing FAQ is a great resource for additional application notes and design guides.

Best regards,
Nicole

0 user6129715 over 4 years ago in reply to Nicole Khoury

Prodigy 10 points

Mr Nicole:

Thank you for your answer

I understand what you said, There is another point that we want to ask. Now when we use fdc2114 to measure, we find that under the same environment, the capacitance value will decrease with time. I don't know why. I hope you can answer it.

Best regards

0 Nicole Khoury over 4 years ago in reply to user6129715

TI__Genius 10080 points

Hello,

It is possible that system parasitics could be causing a shift in capacitance due to changing L and C parameters. Please see the following E2E thread for more information: https://e2e.ti.com/support/sensors/f/sensors-forum/948440/fdc2114-parasitic-resistance?tisearch=e2e-sitesearch&keymatch=fdc2114%252520capacitance%252520decreasing

The FDC1004 is recommended to reduce system noise and improve accuracy because it has integrated shield drivers.

Best regards,

Nicole

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