qt160 Quantum Research Group, qt160 Datasheet - Page 5

• Manufacturer Part Number: qt160
• Description: 6 Key Charge-transfer Qtouch? Sensor Ic
• Manufacturer: Quantum Research Group

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
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.
2.1.2 T
The internal threshold level is fixed at 6 counts for all
channels. These IC's employ a fixed hysteresis of 2 counts
below the threshold (33%).
2.1.3 M
If an object or material contacts a sense pad the signal may
rise enough to trigger an output, preventing further normal
operation. To prevent this ‘stuck key’ condition, the sensor
includes a timer on each channel to 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 channel will
once again function normally, even if partially or fully
obstructed, to the best of its ability given electrode
conditions. There are three timeout durations available via
strap option: 10s, 60s, and infinite (disabled) (Table 2-1).
Max On-Duration works independently per channel; a
timeout on one channel has no effect on another channel
except when the AKS feature is impacted on an adjacent
key. Note also that the timings in Table 2-1 are dependent
on the oscillator frequency: Doubling the recommended
frequency will halve the timeouts.
Infinite timeout is useful in applications where a prolonged
detection can occur and where the output must reflect the
detection no matter how long. In infinite timeout mode, the
designer should take care to be sure that drift in Cs, Cx, and
Vdd do not cause the device to ‘stick on’ inadvertently even
when the target object is removed from the sense field.
The delay timings for max on-duration will increase if the
total duration of all bursts is greater than 33ms, i.e. an
average of 5.5ms per channel.
2.1.4 D
It is desirable to suppress detections generated by electrical
noise or from quick brushes with an object. To accomplish
lQ
Threshold
Output
HRESHOLD
ETECTION
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URATION
Figure 2-1 Drift Compensation
I
C
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Signal
R eference
H ysteresis
5
Pin 28 can also be controlled by logic or a microcontroller to
force the chip to recalibrate, by toggling it low for 5µs then
raising it high again.
The option pins are read by the IC once each acquisition
cycle and can be changed during operation.
2.1.6 R
Response time is fixed at 99ms at a 10MHz clock. Response
time can be altered by changing the clock frequency.
Doubling the recommended clock frequency to 20MHz will
halve the response time to 49ms.
Response time will become slower if the total duration of all
bursts is greater than 33ms, i.e. an average of 5.5ms per
channel.
2.2 OUTPUT FEATURES
The ICs are designed for maximum flexibility and can
accommodate most popular sensing requirements. These
are selectable using strap options on pins OPT1 and OPT2.
All options are shown in Table 2-1.
2.2.1 DC M
The outputs of these ICs can respond in a DC mode, where
they are active upon detection. The output will remain active
for the duration of the detection, or until the Max On-Duration
expires (if not infinite), whichever occurs first. If a max
on-duration timeout occurs first, the sensor performs a full
recalibration and the output becomes inactive until the next
detection.
2.2.2 T
This makes the sensor respond in an on/off mode like a flip
flop. It is most useful for controlling power loads, for example
in kitchen appliances, power tools, light switches, etc.
Max On-Duration in Toggle mode is fixed at 10 seconds.
When a timeout occurs, the sensor recalibrates but leaves
the output state unchanged.
2.2.3 O
The outputs are active-high and can source 1mA and sink
5mA of non-inductive current. If inductive loads are used,
such as small relays, the inductances should be diode
clamped to prevent damage. When set to operate in a
proximity mode (at high gain) Out currents should be limited
to 1mA to prevent gain shifting side effects from occurring,
which happens when the load current creates voltage drops
on the die and bonding wires; these small shifts can
materially influence the signal level to cause detection
instability as described below.
UTPUT
OGGLE
ESPONSE
this, the IC's incorporate 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
QT160/161, the required count is 3.
The Detection Integrator can also be viewed as a
'consensus' filter, that requires three detections in
three successive bursts to create an output.
2.1.5 F
Pin 28 is a Reset pin, active-low, which in cases
where power is clean can be simply tied to Vdd. On
power-up, the device will automatically recalibrate
all 6 channels of sensing.
ODE
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UTPUT
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QT160/161 1.07/0904
ECALIBRATION