AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 37

• 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

4.2.2.9
Touch Sensors Design Guide
Merging X Regions
Figure 4-4.
Due to the key size and panel thickness, the resulting key is far from ideal and has a lack of
interdigitation – there is only one X finger! Such a low degree of interdigitation leads to very low key Cx
and a lack of sensitivity. It also tends to render the design more susceptible to Cp on the Y line
small keys with relatively long interconnections and thick panels are a bad combination.
As can be seen from this example, designs with smaller keys and thicker panels make effective
interdigitation very hard when following the guidelines. In such cases, it is better to break the guidelines
by closing the gaps slightly (0.75 x T/2 minimum) and thinning down the X regions.
See also
For keys that share the same X line, the X regions can be merged, as shown in
Figure 4-5.
1. The ratio of Cx to Cpy is important as the maximum QMatrix terminal voltage that can be accumulated is directly
proportional to this ratio. If the ratio is too small, it may be impossible to achieve acceptable key performance.
Section 3.2.3 “Ground Loading” on page 3-3
Example Resulting In Low Interdigitation
Merged X Regions
1.5 mm
1.6 mm
(Lines Merged)
X Electrode
8 mm
0.75 mm
Mutual-capacitance Zero-dimensional Sensors
for suggested compromises.
2.02 mm
Y Electrode
8 mm
Figure
4-5.
10620D–AT42–04/09
(1)
. Hence
4-5