FDC2114RGHT datasheet(41/60 Pages) TI1

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ENVIRONMENTAL

SENSOR

LIQUID

SENSOR

LEVEL

SENSOR

IN0A

IN0B

IN1A

IN1B

FDC2114 / FDC2214

VDD

GND

SCL

SDA

Int. Osc.

ADDR

INTB

GND

MCU

VDD

3.3 V

GPIO

0.1 F 1 F

Core

Resonant

circuit driver

Resonant

circuit driver

peripheral

3.3 V

CLKIN

40 MHz

Cap

Sensor 0

Cap

Sensor 1

IN2A

IN2B

IN3A

IN3B

Resonant

circuit driver

Resonant

circuit driver

Cap

Sensor 2

FDC2212, FDC2214, FDC2112, FDC2114

www.ti.com

SNOSCZ5A – JUNE 2015 – REVISED JUNE 2015

Typical Application (continued)

10.2.1 Schematic

Figure 56. FDC (Liquid Level Measurement)

10.2.2 Design Requirements

The liquid level measurement should be independent of the liquid, which can be achieved using the 3-electrode

design described above. Moreover, the sensor should be isolated from environmental interferers such as a

human body, other objects, or EMI.

10.2.3 Detailed Design Procedure

In capacitive sensing systems, the design of the sensor plays an important role in determining system

performance and capabilities. In most cases the sensor is simply a metal plate that can be designed on the PCB.

The sensor used in this example is implemented with a two-layer PCB. On the top layer, which faces the tank,

there are the 3 electrodes (Reference Environmental, Reference Liquid, and Level) with a ground plane

surrounding the electrodes.

Depending on the shape of the container, the FDC can be located on the sensor PCB to minimize the length of

the traces between the input channels and the sensors. In case the shape of the container or other mechanical

constraints do not allow having the sensors and the FDC on the same PCB, the traces which connect the

channels to the sensor need to be shielded with the appropriate shield.

10.2.3.1 Application Performance Plot

A liquid level sensor with 3 electrodes like the one shown in the schematic was connected to the EVM. The plot

shows the capacitance measured by Level sensor at different levels of liquid in the tank. The capacitance of the

Reference Liquid and Reference Environmental sensors have a steady value because they experience

consistent exposure to liquid and air, while the capacitance of the level sensor (Level) increases linearly with the

height of the liquid in the tank.

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FDC2114RGHT Datasheet(PDF) 41 Page - Texas Instruments

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