QT60248C-ASG Atmel, QT60248C-ASG Datasheet - Page 22

• Manufacturer Part Number: QT60248C-ASG
• Description: IC TOUCH SENSOR 24KEY 32TQFP
• Manufacturer: Atmel
• Series: QMatrix™, QProx™r
• Type: Capacitiver

Specifications of QT60248C-ASG

• Number Of Inputs/keys: 24 Key
• Resolution (bits): 9, 11 b
• Data Interface: Serial, SPI™
• Voltage - Supply: 3 V ~ 5 V
• Current - Supply: 25mA
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFP, 32-VQFP
• Output Type: *
• Interface: *
• Input Type: *
• For Use With: 427-1087 - BOARD EVAL QT60248-AS QMATRIX
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

10620D–AT42–04/09
Self-capacitance Zero-dimensional Sensors
3.2.2
3-2
Electrode Shapes
An electrode is simply the patch of conductive material on the substrate that forms the sensor. Common
shapes are filled discs, squares and rectangles (see
Figure 3-2.
It is also possible to use a hatched pattern (such as a 50 percent mesh fill) for the electrode, if desired
(see
area interacting with the touch, and so there is some drop in sensitivity.
Figure 3-3.
It is a common mistake to assume that the electrode shape and the graphic key symbol on the panel
should be the same. In fact, it is often better to make the electrodes larger than the graphic especially
with small key sizes since key sensitivity falls off at the edges; an oversize electrode not only
compensates for this but also allows for off-center touch with good response. Generally, it is a good idea
to make the electrode shape extend 2–3 mm beyond the graphic symbol. Of course, this is not always
possible, for example on a densely spaced panel. As a rule, the electrode shape should have a minimum
dimension of at least 4 times the panel thickness for reliable operation.
Electrodes that are implemented by interdigitating the sensor electrode with ground
be considered a “waste” of capacitance and degrade SNR; plain and simple electrodes are almost
always better.
Figure 3-4.
Remember that with self-capacitance sensors, the sensitivity comes from the area of the electrode that
is interacting with the touching object, and nowhere else. Therefore, electrodes with exotic shapes are
not recommended (for example, long, thin electrodes or electrodes with complex “pointy” boundaries).
1. A mesh pattern may have some advantages for aesthetic or optical reasons.
Figure
3-3). This tends to reduce the natural capacitance of the key, but also equally reduces the
Common Electrode Shapes
Electrodes with 50 Percent Mesh Fills
Interdigitating Electrodes Result in a Poor SNR
Sensor
Trace
Figure
3-2).
Ground
Trace
Touch Sensors Design Guide
(Figure
3-4) can also
(1)