QT113A-ISG Atmel, QT113A-ISG Datasheet - Page 4

• Manufacturer Part Number: QT113A-ISG
• Description: IC SENSOR TOUCH/PROX 1CHAN 8SOIC
• Manufacturer: Atmel
• Series: QProx™r
• Type: Capacitiver

Specifications of QT113A-ISG

• 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: 2 V ~ 5.25 V
• Current - Supply: 600µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Type: Logic
• Input Type: Logic
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -
• Other names: 427-1138-2

2 - QT113 SPECIFICS
2.1 SIGNAL PROCESSING
The QT113 processes all signals using 16 bit math, using a
number of algorithms pioneered by Quantum. The algorithms
are specifically designed to provide for high 'survivability' in
the face of numerous adverse environmental changes.
2.1.1 D
Signal drift can occur because of changes in Cx and Cs over
time. It is crucial that drift be compensated for, otherwise
false detections, non-detections, and sensitivity shifts will
follow.
Drift compensation (Figure 2-1) 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 QT113 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 QT113'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 for, could
suddenly be removed leaving the sensor with an
artificially elevated reference level and thus
lQ
Sense
wire
Figure 1-4 Shielding Against Fringe Fields
RIFT
U ns hielded
Electrode
C
OMPENSATION
A
LGORITHM
Sense
wire
E lectrode
S hielded
T hre sh old
Ou tpu t
4
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.
2.1.2 T
The internal threshold level is fixed at one of two setting as
determined by Table 1-1. These settings are fixed with
respect to the internal reference level, which in turn will move
in accordance with the drift compensation mechanism.
The QT113 employs a hysteresis dropout below the
threshold level of 17% of the delta between the reference and
threshold levels.
2.1.3 M
If an object or material obstructs the sense pad the signal
may rise enough to create a detection, preventing further
operation. To prevent this, the sensor includes a timer which
monitors detections. If a detection exceeds the timer setting,
the timer causes the sensor to perform a full recalibration
(when not set to infinite). This is known as the Max
On-Duration feature.
After the Max On-Duration interval, the sensor will once again
function normally to the best of its ability given electrode
conditions. There are two finite timeout durations available
via strap option: 10 and 60 seconds (Table 2-1).
2.1.4 D
It is desirable to suppress detections generated by electrical
noise or from quick brushes with an object. To accomplish
this, the QT113 incorporates a detect integration 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 QT113, the required count is 3.
The Detection Integrator can also be viewed as a 'consensus'
filter, that requires three successive detections to create an
output.
Table 1-1 Gain Setting Strap Options
Figure 2-1 Drift Compensation
HRESHOLD
ETECTION
AX
O
Low - 12 counts
S ig na l
High - 6 counts
N
-D
Gain
URATION
I
R efer ence
C
NTEGRATOR
ALCULATION
H ys te res is
Tie Pin 5 to:
Vss (Gnd)
Vdd
R1.05/0405