AT42QT1012-MAH Atmel, AT42QT1012-MAH Datasheet - Page 6

• Manufacturer Part Number: AT42QT1012-MAH
• Description: IC SENSR TOUCH/PROX 1CH SOT23-8
• Manufacturer: Atmel
• Series: QTouch™r
• Type: Capacitiver

Specifications of AT42QT1012-MAH

• Touch Panel Interface: 1, 2-Wire
• Number Of Inputs/keys: 1 Key
• Resolution (bits): 9, 14 b
• Data Interface: Serial
• Voltage Reference: Internal
• Voltage - Supply: 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-UFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

2.4
2.4.1
2.4.2
2.4.3
6
Sensitivity
AT42QT1012
Introduction
Increasing Sensitivity
Decreasing Sensitivity
A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress
electrostatic discharge (ESD) and electromagnetic compatibility (EMC) effects.
Figure 2-1.
The sensitivity on the QT1012 is a function of things like the value of Cs, electrode size and
capacitance, electrode shape and orientation, the composition and aspect of the object to be
sensed, the thickness and composition of any overlaying panel material, and the degree of
ground coupling of both sensor and object.
In some cases it may be desirable to increase sensitivity; for example, when using the sensor
with very thick panels having a low dielectric constant, or when the device is used as a proximity
sensor. Sensitivity can often be increased by using a larger electrode or reducing panel
thickness. Increasing electrode size can have diminishing returns, as high values of Cx will
reduce sensor gain.
The value of Cs also has a dramatic effect on sensitivity, and this can be increased in value with
the trade-off of a slower response time and more power. Increasing the electrode's surface area
will not substantially increase touch sensitivity if its diameter is already much larger in surface
area than the object being detected. Panel material can also be changed to one having a higher
dielectric constant, which will better help to propagate the field.
Ground planes around and under the electrode and its SNSK trace will cause high Cx loading
and destroy gain. The possible signal-to-noise ratio benefits of ground area are more than
negated by the decreased gain from the circuit, and so ground areas around electrodes are
discouraged. Metal areas near the electrode will reduce the field strength and increase Cx
loading and should be avoided, if possible. Keep ground away from the electrodes and traces.
In some cases the QT1012 may be too sensitive. In this case gain can be easily lowered further
by decreasing Cs.
Sense Connections
ELECTRODE
SENSE
Cx
RS
CS
3
4
SNS
SNSK
VDD
VDD
VSS
5
2
TIME
OUT
6
1
Cby
9543D–AT42–08/10