Nuvoton NuMicro ML51 Series, Technical Reference Manual, Page: 670 / 719

ML51/ML54/ML56
Sep. 01, 2020 Page 670 of 719 Rev 2.00
ML
51
/ML
54
/ML
5
6 S
E
RI
E
S
TECHNI
CA
L
RE
F
E
R
E
NC
E
M
A
NU
A
L
ML51/M
L54
/M
L56
Series
Tec
hnical Reference
Manual
+
_
CB CCB
CMPX_IN
CMPX_IP
Complement
Capacitor Bank
for Touch Key
Capacitor Bank
for Reference
C
R
No Finger Touch
Finger Touch
Reference Pad
Touch Key
CMP
Capacitor Bank
Polarity Select
counter
C
F
+
_
CB CCB
C
R
Reference Pad
Touch Key
CMP
Capacitor Bank
Polarity Select
C
T
C
P
C
P
CMPX_IP ( C
R
)
CMPX_IN ( C
P
)
Touch Key Scan
Enabled Cycle
Capacitor Bank
Polarity
AV
SS
Time
Voltage
CMPX_IN ( C
T
)
CMPX_IP ( C
R
)
Capacitor Bank
Polarity
AV
SS
Time
Voltag
e
Complement
Capacitor Bank for
Touch Key
Capacitor Bank
for Reference
counter
Touch Key Scan
Enabled Cycle
CMPX_IN
CMPX_IP
Figure 6.19-2 Touch Key Sensing Method
After touch key calibration, C
P
and C
R
are balanced with C
B
and C
CB
. A finger touches presents on
sensing touch key results in C
T
(C
T
= C
P
+ C
F
), makes negative input terminal voltage of the
comparator is lower than positive side and comparator output is “high”. This means C
T
and C
R
are not
balanced, and the touch key controller will increase C
CB
to C
CB
’ to make C
T
and C
R
are balanced
again. A finger touch can be detected by checking the difference of C
CB
and C
CB
’, please refer to
Figure 6.19-3.