AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 48

• Manufacturer Part Number: AT42QT1040-MMH
• Description: IC TOUCH SENSOR 4KEY 20-VQFN
• Manufacturer: Atmel
• Series: QTouch™r
• Type: Resistiver

Specifications of AT42QT1040-MMH

• Touch Panel Interface: 4, 2-Wire
• Number Of Inputs/keys: 4 Key
• Data Interface: I²C, Serial
• Data Rate/sampling Rate (sps, Bps): 200k
• Voltage Reference: Internal
• Voltage - Supply: 1.8 V ~ 5.5 V
• Current - Supply: 10mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-VQFN Exposed Pad, 20-HVQFN, 20-SQFN, 20-DHVQFN
• Output Type: Logic
• Input Type: Logic
• Supply Voltage: 1.8 V to 5.5 V
• Dimensions: 3 mm L x 3 mm W x 0.8 mm H
• Output Voltage: 0.7 V to 0.8 V
• Temperature Range: - 40 C to + 85 C
• Termination Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: AT42QT1040-MMH; AT42QT1040-MMHTR

10620D–AT42–04/09
Self-capacitance One-dimensional Sensors
5.2.3
5.2.4
5.2.5
5-2
Hand Shadow Effect
Floating Conductive Items
Conductive Paints
When a sensor is particularly large in proportion to a hand, it is possible for a false touch to be detected
from the hand as it is held over the sensor, rather than from the user’s finger. This is known as the hand
shadow effect (see
Figure 5-1.
This effect presents a particular problem for large sliders or wheels that use the self-capacitance style of
electrode. These electrodes are generally scanned so that all the channels are measured at the same
time, which makes all the channels equally touch sensitive.
The considerations for the use of floating conductive items described in
Conductive Items” on page 3-6
The considerations for the use of conductive paints described in
page 3-7
Note that wheels and sliders, in particular, can be badly affected by conductive paints and finishes. The
reason for this is that the calculation of the touch position relies on the difference in signal between the
various channels, and the conductive paint has a tendency to make the channels cross-couple together.
The result is a considerable degradation of the resolution of the sensor.
If this is not possible, and the connecting traces have to be routed on the same layer as the electrodes
themselves, always escape the traces as quickly as possible out of the touch area; then regroup the
three traces for their path to the sensor chip. It can be useful in some cases to run a thin ground trace
alongside these escaping traces to desensitize them to touch. Note that some experimentation is
usually necessary.
apply.
Hand Shadow Effect
Touch here
Figure
5-1).
apply.
Sensor
Section 3.2.7 “Conductive Paints” on
Influence here despite
no panel contact
Touch Sensors Design Guide
Section 3.2.6 “Floating