AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 26

• 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 Zero-dimensional Sensors
3.2.6
3-6
Floating Conductive Items
Figure 3-7.
Another common method of backlighting is to use a light spreader sheet with side illumination and
controlled light leakage areas above the keys (see
illuminated structures.
Electroluminescent lamps have also been successfully used with Atmel’s capacitive sensors, but this is a
much more complex topic and is beyond the scope of this document.
Figure 3-8.
Regions of floating metal, or any other conductor, that are in close proximity to sensors of this type (that
is, nearer than 10 mm edge to edge) can tend to re-radiate the sensor's electric field and so become
touch-sensitive themselves. Usually this is undesirable, as it can cause strange behavior in key
detection, depending on what the metal is contacting. Touching such nearby floating metal can also
cause false key detection.
Always ground nearby conductive regions. This can be accomplished by a direct wire connection to
power supply common, or by means of a 47 nF capacitor back to supply common.
Backlighting Using an LED
Backlighting Using Side Illumination and Light Spreader Sheet
Sidefire LED
Surface Treated
To Cause Total
Internal Reflection
Sensor
Sensor
Hole
To Cause Diffraction
Backfire LED
Surface Treated
Figure 3-8 on page
Optically Clear Adhesive
Light Spreader
Optically Clear
Adhesive
3-6). This can yield very thin
Touch Sensors Design Guide