QT110-IS Atmel, QT110-IS Datasheet - Page 5

• Manufacturer Part Number: QT110-IS
• Description: SENSOR IC TOUCH/PROXMTY 1CH8SOIC
• Manufacturer: Atmel
• Series: QTouch™r
• Type: Capacitiver

Specifications of QT110-IS

• Rohs Status: RoHS non-compliant
• Touch Panel Interface: 1, 2-Wire
• Number Of Inputs/keys: 1 Key
• Resolution (bits): 14 b
• Data Interface: Serial
• Voltage Reference: Internal
• Voltage - Supply: 2.5V, 3.3V, 5V
• Current - Supply: 20µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Type: Logic
• Interface: 2-Wire
• Input Type: Logic
• Other names: 427-1002

number of strategies: making the electrode smaller,
connecting a very small capacitor in series with the sense
lead, or making the electrode into a sparse mesh using a
high space-to-conductor ratio (Figure 1-4). A deliberately
added Cx capacitor can also be used to reduce sensitivity
according to the gain curves (see Section 4).
Intermediate levels of gain (e.g. between 'medium' and 'low'
can be obtained by a combination of jumper settings with
one or more of the above strategies.
2 - QT110 SPECIFICS
2.1 SIGNAL PROCESSING
The QT110 processes all signals using 16 bit math, using a
number
algorithms are specifically designed to provide for high
'survivability'
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 QT110 drift compensates using a
slew-rate limited change to the reference level; the threshold
and hysteresis values are slaved to this reference.
Once an
mechanism ceases since the signal is legitimately high, and
therefore should not cause the reference level to change.
The QT110'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 touching the sense pad. 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 become insensitive to touch. In this latter case, the
Figure 2-2 Powering From a CMOS Port Pin
m icro controller
RIFT
C MO S
of
C
object
OMPENSATION
algorithms
in
the
is
P O RT X .m
P O RT X .n
face
sensed,
pioneered
A
LGORITHM
of
O U T
the drift
all
by
kinds
Q T11 0
V d d
V s s
Quantum.
compensation
of
0 . 0 1 µ F
adverse
The
- 5 -
sensor will compensate for the object's removal very quickly,
usually in only a few seconds.
2.1.2 T
Sensitivity is dependent on the threshold level as well as
ADC gain; threshold in turn is based on the internal signal
reference level plus a small differential value. The threshold
value is established as a percentage of the absolute signal
level. Thus, sensitivity remains constant even if Cs is altered
dramatically, so long as electrode coupling to the user
remains constant. Furthermore, as Cx and Cs drift, the
threshold level is automatically recomputed in real time so
that it is never in error.
The QT110 employs a hysteresis dropout below the
threshold level of 50% 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.
This is known as the Max On-Duration feature.
After the Max On-Duration interval, the sensor will once
again function normally, even if partially or fully obstructed,
to the best of its ability given electrode conditions. There are
two timeout durations available via strap option: 10 and 60
seconds.
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 QT110 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 QT110, the required count is 4.
The Detection Integrator can also be viewed as a
'consensus' filter, that requires four detections in four
successive bursts to create an output. As the basic burst
spacing is 75ms, if this spacing was maintained throughout
all 4 counts the sensor would react very slowly. In the
QT110, after an initial detection is sensed, the remaining
three bursts are spaced about 18ms apart, so that the
slowest reaction time possible is 75+18+18+18 or 129ms
and the fastest possible is 54ms, depending on where in the
initial burst interval the contact first occurred. The response
time will thus average 92ms.
Table 2-1 Output Mode Strap Options
DC Out
DC Out
Toggle
HRESHOLD
ETECTION
AX
Pulse
O
N
-D
URATION
I
C
Pin 3 to:
NTEGRATOR
ALCULATION
Gnd
Gnd
Vdd
Vdd
Tie
Pin 4 to:
Gnd
Gnd
Vdd
Vdd
Tie
Duration
Max On-
10s
60s
10s
10s