E102 Atmel, E102 Datasheet - Page 7

• Manufacturer Part Number: E102
• Description: KIT EVAL/DEV USING QT102-ISG
• Manufacturer: Atmel
• Series: Quantum, QTouch™r

Specifications of E102

• Sensor Type: Touch, Capacitive
• Sensing Range: 1 Button/Key
• Interface: Logic Level
• Voltage - Supply: 3V
• Embedded: No
• Utilized Ic / Part: QT102
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -

3 Operation
3.1 Acquisition Modes
3.1.1 Introduction
The OUT pin of the QT102 can be configured to be active
high or active low (see Section 3.3).
The acquisition mode depends on the state of the OUT pin
(on or off) and whether a touch is detected. In the following
text ‘on’ is when the output is in its active state.
3.1.2 OUT Pin ‘On’ (Fast Mode)
The QT102 runs in Fast mode when the OUT pin is on. In this
mode the device runs at maximum speed at the expense of
increased current consumption. The delay between bursts in
Fast mode is approximately 2.6ms, as shown in Figure 3.1.
3.1.3 OUT Pin ‘Off’ (Low Power Mode)
The QT102 runs in Low Power (LP) mode if the OUT pin is off.
In this mode it sleeps for approximately 85ms at the end of
each burst, saving power but slowing response. On detecting
a possible key touch, it temporarily switches to Fast mode
until either the key touch is confirmed or found to be spurious
(via the detect integration process). If the touch is confirmed
the QT102 will switch to Fast mode as shown in Figure 3.2. If
a touch is denied the device will revert to normal LP mode
operation automatically.
3.2 Signal Processing
3.2.1 Detect Integrator
It is desirable to suppress detections generated by electrical
noise or from quick brushes with an object. To accomplish
this, the QT102 incorporates a ‘detect integration’ (DI) counter
that increments with each detection until a limit is reached,
after which the output is activated. If no detection is sensed
prior to the final count, the counter is reset immediately to
zero. In the QT102, the required count is four.
lQ
QT102
SNSK
OUT
•
•
QT102
SNSK
If active high then
If active low then
Figure 3.2 Low Power Mode/Touch Detection
‘on’ is high
‘off’ is low
‘on’ is low
‘off’ is high
Figure 3.1 Fast Mode Bursts
~85ms
sleep
(Output in On condition)
~2.6ms
sleep
fast detect
integrator
7
The DI can also be viewed as a 'consensus' filter, that
requires four successive detections to create an output.
3.2.2 Detect Threshold
The device detects a touch when the signal has crossed a
threshold level. The threshold level is fixed at 10 counts.
3.3 Output Polarity Selection
The output (OUT pin) of the QT102 can be configured to have
an active high or active low output by means of the output
configuration resistor Rop. The resistor is connected between
the output and either Vss or V
Table 3.1). A typical value for Rop is 100k .
Note that some devices such as Digital Transistors have an
internal biasing network that will naturally pull the OUT pin to
its inactive state. If these are being used then the resistor Rop
Figure 3.4 Output Connected to Digital Transistor
is not required (see Figure 3.4).
ELECTRODE
ELECTRODE
SENSE
SENSE
Table 3.1 Output Configuration
RS
CS
Rm
RS
CS
Rm
Figure 3.3 Output Polarity
3
4
3
4
Name
(Vop)
SNSK
SNS
Vss
V
SNSK
SNS
DD
VDD
VDD
VDD
VDD
VSS
VSS
5
2
5
2
(Output polarity)
DD
TIME
TIME
Active high
Function
OUT
Active low
OUT
(see Figure 3.3 and
QT102_2R3.05_1007
1
1
6
6
Rop
Load
Vop