AT42QT1070-MMH Atmel, AT42QT1070-MMH Datasheet - Page 39

• Manufacturer Part Number: AT42QT1070-MMH
• Description: IC TOUCH SENSOR 7KEY 20-VQFN
• Manufacturer: Atmel
• Type: Capacitiver

Specifications of AT42QT1070-MMH

• Number Of Inputs/keys: 7 Key (Comms), 5 Key (Standalone)
• Data Interface: I²C
• Voltage Reference: Internal
• Voltage - Supply: 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-VFQFN Exposed Pad
• Supply Voltage: 1.8 V to 5.5 V
• Dimensions: 3 mm L x 3 mm W x 0.8 mm H
• Temperature Range: - 40 C to + 85 C
• Termination Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Resolution (bits): -
• Touch Panel Interface: -
• Data Rate/sampling Rate (sps, Bps): -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

4.2.4
4.2.4.1
4.2.4.2
Touch Sensors Design Guide
Interconnection
X Routing
Y Routing
X routing is fairly trivial as long as RC time constant rules are observed. Nearby foreign signals that have
large kHz frequency
the charge transfer. Examples of circuits to consider include D-class amplifier signals, LCD or LED drive
signals.
X routing is not touch sensitive, and so X traces can be routed with ease on any layer of a PCB, including
the side nearest to touch. However, X routing must also take the Y routing into account.
Y routing must be more carefully considered, due to Cp build-up and the need to avoid an effect called
false key detection. Y routing is only very weakly touch sensitive, so it is good practice to run Y traces on
a layer that is far from touch.
The first factor, Cp build-up, is easily dealt with by avoiding routing Y traces over or close to ground
planes (or other power planes).
The second factor, false key detection, can occur wherever there is an interaction of the Y traces with the
X traces. Remember that anywhere where X and Y get close (less than 10 mm), and the field between
them is allowed to be influenced by touch, you have a potential key or at least a touch sensitive zone that
you do not expect (see
Figure 4-8.
1. High kHz to hundreds of kHz in particular.
Potential False Key
(1)
Potential False
Key Detection
switching transients should be routed well away from X traces as they can disturb
Figure
X Trace
4-8).
Y Trace
Mutual-capacitance Zero-dimensional Sensors
Overlying Panel
10620D–AT42–04/09
4-7