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7
SCD Pin Touch Key Status Request
Sensitivity Adjustment
·
The sensitivity of the switch is a very important consider-
ation in most applications whose requirements will vary
according to the user application. The user should
therefore be aware of the factors which will affect the
overall sensitivity of their touch key application. Factors
to take into consideration include the electrode size and
the capacitance of the connection lines from the elec-
trode to the BS80xC device. Therefore the sensitivity
will vary according to the actual PCB layout and design.
An external capacitor, Cs, connected to the Cref pin, is
used to set the overall sensitivity of all pins. Some of the
most important factors affecting sensitivity are the fol-
lowing:
Touch key pad size
Larger touch key sizes will increase sensitivity and of
course vice-versa, small electrode sizes will decrease
sensitivity.
·
·
Touch key pad insulating panel thickness
A thinner panel will result in higher sensitivity and of
course thicker panels will result in a lower sensitivities.
Touch key pad insulating panel material
The choice of the dielectric material for the panel will in-
fluence the sensitivity. Materials with higher dielectric
constants will result in higher sensitivities and lower di-
electric constants will result in lower sensitivities.
Touch
Key
·
Cref capacitor value - Cs
Key
The purpose of the Cs capacitor is to allow for adjust-
ment of touch key sensitivity and power noise rejec-
tion. The optimal choice of sensitivity and power noise
rejection will be obtained when the value of the Cs ca-
pacitor is equivalent to the touch pad capacitance,
however the value can still be changed to obtain the
required sensitivity value. Higher Cs values will result
in higher levels of sensitivity. Recommended values
for Cs are between 0pF and 10pF.
Cs
Cref
0pF~
10pF
Rev. 1.00
8
December 2, 2009
HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
