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Distance between Sensor and Target (mm)
Sensor Indu
ctance (
H)
μ
Sensor Fre
que
ncy
(MH
z)
0
1
2
3
4
5
6
7
8
9
10
3
3
3.5
3.25
4
3.5
4.5
3.75
5
4
5.5
4.25
6
4.5
6.5
4.75
7
5
D010
Sensor Inductance (μH)
Sensor Frequency (MHz)
Figure 8-2. Sensor Inductance and Frequency vs. Target Distance. Sensor Diameter = 14 mm
The output DATA
n
registers (Addresses 0x02 through 0x09) of the LDC3114 contain the processed values of the
changes in sensor frequencies.
8.1.2 Designing Sensor Parameters
shows that each inductive touch button uses an LC resonator sensor, where L is the inductor, C is the
capacitor, and R
S
is the AC series resistance of the sensor at the frequency of operation. The key parameters
of the LC sensor include frequency, effective parallel resistance R
P
, and quality factor Q. These parameters
must be within the ranges as specified in the
Sensor
section of the
table. Note that the
effective R
P
and Q changes when the conductive target is in place.
L
R
S
C
Figure 8-3. LC Resonator
The LC sensor frequency defined in
must be between 1 MHz and 30 MHz. For optimal performance,
configure the sensor frequency to be greater than 3 MHz.
f
SENSOR
1
2
LC
S
(3)
The sensor quality factor defined in
must be between 5 and 30.
SENSOR
S
1
L
Q
R
C
(4)
The series resistance defined in
can be represented as an equivalent parallel resistance, R
P
.
P
S
L
R
R C
(5)
SNOSDD0 – DECEMBER 2021
38
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