QTouch Schematic and Layout Checklist [APPLICATION NOTE]
Atmel-42094C-QTouch-Schematic-and-Layout-Checklist-ApplicationNote_072014
8
•
Do not use AIN1 pin for PWM generation
QMatrix method uses Analog comparator for touch measurement and the AIN1 pin is connected to negative
terminal of Analog comparator. So, the switching signals in AIN1 pin would affect touch measurement.
•
Using same Port for YA/YB Lines
Prefer using different Port for YA and YB lines, in case of designs that does not have pin count constraints.
•
Multiplexing sense lines with Programming lines
X lines can be multiplexed with ISP lines. It is preferable to not share Y lines (both YA and YB) with programming
lines.
For lesser pin count devices which mandate multiplexing, Y lines can be used with shorter trace length possible.
Do not share same channel Y lines (YA and YB) with programming lines.
•
Slider/Wheel uses four to eight channels
A QMatrix Slider/Wheel always uses a minimum of four channels. This can be increased up to eight channels for
a bigger Slider/Wheel. It is important to use channels with similar sensitivity. Using mismatched channels with
significantly different sensitivities will lead to an unbalanced Slider/Wheel.
•
Slider/Wheel resistive interpolation resistors are in range
Total resistance between channels is 2kΩ to 10kΩ. The resistance between segments will depend on the
number of segments used.
There are no end resistors or split channels for a QMatrix Slider.
Figure 2-6.
Resistive Interpolated QMatrix Slider and Wheel