E100S Atmel, E100S Datasheet - Page 5

• Manufacturer Part Number: E100S
• Description: KIT EVAL FOR QT100
• Manufacturer: Atmel
• Series: Quantum, QTouch™r

Specifications of E100S

• Sensor Type: Touch, Capacitive
• Sensing Range: 1 Button/Key
• Interface: Logic Level
• Voltage - Supply: 3V
• Embedded: No
• Utilized Ic / Part: QT100
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: QT100-ISG
• Other names: 427-1128

2.5 Forced Sensor Recalibration
The QT100 has no recalibration pin; a forced
recalibration is accomplished when the device is
powered up or after the recalibration timeout.
However, supply drain is low so it is a simple
matter to treat the entire IC as a controllable load;
driving the QT100's V
logic gate or a microcontroller port will serve as
both power and 'forced recal'. The source
resistance of most CMOS gates and
microcontrollers are low enough to provide direct
power without problem.
2.6 Drift Compensation
Signal drift can occur because of changes in Cx
and Cs over time. It is crucial that drift be
compensated for, otherwise false detections,
nondetections, and sensitivity shifts will follow.
Drift compensation (Figure 2.5). is performed by making the
reference level track the raw signal at a slow rate, but only
while there is no detection in effect. The rate of adjustment
must be performed slowly, otherwise legitimate detections
could be ignored. The QT100 drift compensates using a
slew-rate limited change to the reference level; the threshold
and hysteresis values are slaved to this reference.
Once an object is sensed, the drift compensation mechanism
ceases since the signal is legitimately high, and therefore
should not cause the reference level to change.
The QT100's drift compensation is 'asymmetric'; the reference
level drift-compensates in one direction faster than it does in
the other. Specifically, it compensates faster for decreasing
signals than for increasing signals. Increasing signals should
not be compensated for quickly, since an approaching finger
could be compensated for partially or entirely before even
approaching the sense electrode. However, an obstruction
over the sense pad, for which the sensor has already made
full allowance, could suddenly be removed leaving the sensor
with an artificially elevated reference level and thus become
insensitive to touch. In this latter case, the sensor will
compensate for the object's removal very quickly, usually in
only a few seconds.
With large values of Cs and small values of Cx, drift
compensation will appear to operate more slowly than with the
converse. Note that the positive and negative drift
compensation rates are different.
lQ
Getting HeartBeat pulses with a pull-up resistor
HeartBeat™ Pulses
Ro
Figure 2.6
DD
pin directly from another
1
OUT
VDD
SYNC/MODE
5
2
VDD
VSS
SNSK
SNS
3
4
6
Threshold
Output
Microcontroller
5
2.7 Response Time
The QT100's response time is highly dependent on run mode
and burst length, which in turn is dependent on Cs and Cx.
With increasing Cs, response time slows, while increasing
levels of Cx reduce response time. The response time will
also be a lot slower in LP or SYNC mode due to a longer time
between burst measurements.
2.8 Spread Spectrum
The QT100 modulates its internal oscillator by ±7.5 percent
during the measurement burst. This spreads the generated
noise over a wider band reducing emission levels. This also
reduces susceptibility since there is no longer a single
fundamental burst frequency.
2.9 Output Features
2.9.1 Output
The output of the QT100 is active-high upon detection. The
output will remain active-high for the duration of the detection,
or until the Max On-duration expires, whichever occurs first. If
a Max On-duration timeout occurs first, the sensor performs a
full recalibration and the output becomes inactive (low) until
the next detection.
Using a micro to obtain HeartBeat pulses in either output state
Figure 2.5 Drift Compensation
P ORT_M.x
P ORT_M.y
Signal
R eference
R
o
Figure 2.7
1
QT100_3R0.09_0707
OU T
H ysteresis
S Y N C /MOD E
S N S K
S N S
3
4
6