FDC2114 datasheet(39/61 Pages) TI1

39 / 61 page

FDC211x / FDC221x

IN0A

IN0B

18 H

33 pF

Sensor plate (1)

Target object

Sensor plate (2)

Target object

Virtual GND (target floating)

Earth GND (target grounded)

FDC211x / FDC221x

IN0A

IN0B

18 H

33 pF

Sensor plate

Target object

Virtual GND (target floating)

Earth GND (target grounded)

FDC2212, FDC2214, FDC2112, FDC2114

www.ti.com

SNOSCZ5A – JUNE 2015 – REVISED JUNE 2015

10 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

10.1 Application Information

10.1.1 Sensor Configuration

The FDC supports two sensor configurations. Both configurations use an LC tank to set the frequency of

oscillation. A typical choice is an 18

μH shielded SMD inductor in parallel with a 33 pF capacitor, which result in a

6.5 MHz oscillation frequency. In the single-ended configuration in Figure 54, a conductive plate is connected

IN0A. Together with a target object, the conductive plate forms a variable capacitor.

Figure 54. Single-ended Sensor Configuration

In the differential sensor configuration in Figure 55, one conductive plate is connected to IN0A, and a second

conductive plate is connected to IN0B. Together, they form a variable capacitor. When using an single-ended

sensor configuration, set CHx_FIN_SEL to b10 (divide by 2).

Figure 55. Differential Sensor Configuration

The single-ended configuration allows higher sensing range than the differential configuration for a given total

sensor plate area. In applications in which high sensitivity at close proximity is desired, the differential

configuration performs better than the single-ended configuration.

10.1.2 Shield

in order to minimize interference from external objects, some applications require an additional plate which acts

as a shield. The shield can either be:

•

actively driven shield: The shield is a buffered signal of the INxA pin. The signal is buffered by an external

amplifier with a gain of 1.

•

passive shield: The shield is connected to GND. Adding a passive shield decreases sensitivity of the sensor,

but is dependent on the distance between the distance between the sensing plate and the shield. The

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