Touch sensing controller (TSC) RM0367
416/1043 RM0367 Rev 7
Figure 80. Surface charge transfer analog I/O group structure
Note: Gx_IOy where x is the analog I/O group number and y the GPIO number within the selected
group.
The surface charge transfer acquisition principle consists of charging an electrode
capacitance (C
X
) and transferring a part of the accumulated charge into a sampling
capacitor (C
S
). This sequence is repeated until the voltage across C
S
reaches a given
threshold (V
IH
in our case). The number of charge transfers required to reach the threshold
is a direct representation of the size of the electrode capacitance.
Table 81 details the charge transfer acquisition sequence of the capacitive sensing channel
1. States 3 to 7 are repeated until the voltage across C
S
reaches the given threshold. The
same sequence applies to the acquisition of the other channels. The electrode serial
resistor R
S
improves the ESD immunity of the solution.
MSv30930V2
C
X1
Gx_IO1
R
S1
C
X2
Gx_IO3
R
S2
C
X3
Gx_IO4
R
S3
Gx_IO2
C
S
Analog
I/O group
Electrode 1
Electrode 2
Electrode 3
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