AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 44

• 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
Mutual-capacitance Zero-dimensional Sensors
4.3.3
4-12
Spring Method
A useful method for transferring the touch-sensitive region of a mutual-capacitance sensor, is to use a
conductive spring or hollow conductive tube to act as an X emitter, with the Y electrode placed centrally
on the substrate below the panel inside the X electrode (see
The spring should have an inner diameter of 8 to 10 mm. The Y electrode should be a circular pad with a
diameter of half the spring’s inner diameter.
The compressed length of the spring, and hence the distance from the inside of the panel to the front of
the PCB, should be less than 1 spring inner diameter. The pitch of the coils of the spring is not vitally
important, but generally try to have the gaps approximately the same size as the diameter of the spring
wire when the spring is compressed to its final position.
Figure 4-11. Using a Spring In a Mutual-capacitance Type Sensor
Neighboring coils can be arranged next to each other, ideally with a minimum center-to-center distance
of 1.5 x spring outer diameter
Note that the spring is not intended to compress when touched; it is always maintained in a compressed
state. The spring forms a static electrode that bridges the gap between the touch panel and the
component PCB. The change happens because the field inside the spring is redistributed during a touch
(see Figure 4-12).
Figure 4-12. Effect of a Touch With a Spring
1. This helps to keep cross-coupling between keys to a manageable level. Using continuous tube type X electrodes
will relax this requirement.
Y (Centre Pad
Half Diameter
Of Spring)
Control PCB
Panel
(1)
Field distributed
inside spring
.
No Touch
Field
Some of field diverted
Touch (Cx Reduced)
towards finger
Figure
4-11).
Touch Sensors Design Guide
X Emitter
(Conductive Spring,
Rubber, Foam or
Plastic Tube)
Control PCB
Front Panel