AT42QT1040-MMH Atmel, AT42QT1040-MMH Datasheet - Page 29

• 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

Touch Sensors Design Guide
Figure 3-11. Philipp Spring Products
Using a conventional spring may also work, but it tends to result in low sensitivity keys and a poor SNR,
due to the low surface area of the top of the spring.
Figure 3-12. Compressing a Philipp Spring Product
Make sure that when the spring is placed under compression that it still contacts properly on the PCB
contact pad. It has been known for a spring to spread out and overlap a nearby track or ground region,
causing loss of sensitivity or an intermittent fault. In addition, remember that the pad is just as much part
of the electrode structure as the spring itself. You should therefore minimize the area of the contact pad
to avoid building up Cx that is not touchable, and keep ground planes away from this pad to reduce the
parasitic capacitance (Cp).

Spring Before Compression
Through-hole PCB Mounting

Spring After Compression
The collapsible region flattens
to form an electrode disc.
Self-capacitance Zero-dimensional Sensors
Over-LED
Mounting
Collapsible
Region
Compliant
Bridge
Compressed Spring Viewed
Through a Clear Front Panel
The channel in the middle can
be used for an LED.
10620D–AT42–04/09
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