QT110-IS Atmel, QT110-IS Datasheet - Page 7

• 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

2.2.5 P
A piezo drive signal is generated for use with a bare piezo
sounder immediately after a detection is made; the tone lasts
for a nominal 75ms to create a reassuring ‘tactile feedback’
sound.
The sensor will drive most common bare piezo ‘beepers’
directly using an H-bridge drive configuration for the highest
possible sound level at all supply voltages; H-bridge drive
effectively doubles the supply voltage across the piezo. The
piezo is connected across pins SNS1 and SNS2. This drive
operates at a nominal 4kHz frequency, a common resonance
point for enclosed piezo sounders. Other frequencies can be
obtained upon special request.
If desired a bare piezo sounder can be directly adhered to
the rear of a control panel, provided that an acoustically
resonant cavity is also incorporated to give the desired
sound level.
Since piezo sounders are merely high-K ceramic capacitors,
the sounder will double as the Cs capacitor, and the piezo's
metal disc will act as the sensing electrode. Piezo transducer
capacitances typically range from 6nF to 30nF (0.006µF to
0.03µF) in value; at the lower end of this range an additional
capacitor should be added to bring the total Cs across SNS1
and SNS2 to at least 10nF, or more if Cx is large.
The burst acquisition process induces a small but audible
voltage step across the piezo resonator, which occurs when
SNS1 and SNS2 rapidly discharge residual voltage stored on
the resonator. The resulting slight clicking sound can be
used to provide an audible confirmation of functionality if
desired, or, it can be suppressed by placing a non-critical 1M
to 2M ohm bleed resistor in parallel with the resonator. The
resistor acts to slowly discharge the resonator, preempting
the occurrence of the harmonic-rich step (Figure 2-6).
With the resistor in place, an almost inaudible clicking sound
may still be heard, which is caused by the small charge
buildup across the piezo device during each burst.
2.2.6 O
The QT110’s `output is active low (QT110) or active high
(QT110H) and can source 1mA or sink 5mA of non-inductive
current. If an inductive load is used, such as a small relay,
the load should be diode clamped to prevent damage.
Care should be taken when the IC and the load are both
powered from the same supply, and the supply is minimally
regulated. The device derives its internal references from the
power supply, and sensitivity shifts can occur with changes
IEZO
UTPUT
C M O S
MIC RO INPU T
Figure 2-5 Eliminating HB Pulses
G ATE OR
A
COUSTIC
D
100p F
RIVE
C
D
o
RIVE
2
3
4
O UT
O PT1
O PT2
SN S 2
GA IN
SN S 1
7
5
6
- 7 -
in Vdd, as happens when loads are switched on. This can
induce detection ‘cycling’, whereby an object is detected, the
load is turned on, the supply sags, the detection is no longer
sensed, the load is turned off, the supply rises and the object
is reacquired, ad infinitum. To prevent this occurrence, the
output should only be lightly loaded if the device is operated
from an unregulated supply, e.g. batteries. Detection
‘stiction’, the opposite effect, can occur if a load is shed
when Out is active.
QT110: The output of the QT110 can directly drive a
resistively limited LED. The LED should be connected with
its cathode to the output and its anode towards Vcc, so that
it lights when the sensor is active-low. If desired the LED can
be connected from Out to ground, and driven on when the
sensor is inactive, but only with less drive current (1mA).
QT110H: This part is active-high, so it works in reverse to
that described above.
3 - CIRCUIT GUIDELINES
3.1 SAMPLE CAPACITOR
Charge sampler Cs can be virtually any plastic film or high-K
ceramic capacitor. Since the acceptable Cs range is
anywhere from 10nF to 30nF, the tolerance of Cs can be the
lowest grade obtainable so long as its value is guaranteed to
remain in the acceptable range under expected temperature
conditions. Only if very fast, radical temperature swings are
expected will a higher quality capacitor be required, for
example polycarbonate, PPS film, or NPO/C0G ceramic.
3.2 PIEZO SOUNDER
The use of a piezo sounder in place of Cs is described in the
previous
uncharacterized thermal coefficients and should not be used
if fast temperature swings are anticipated.
3.3 OPTION STRAPPING
The option pins Opt1 and Opt2 should never be left floating.
If they are floated, the device will draw excess power and the
options will not be properly read on powerup. Intentionally,
Figure 2-6 Damping Piezo Clicks with R
2
3
4
section.
OU T
OP T1
OP T2
+ 2.5 to 5
1
8
V dd
V ss
Piezo
S N S1
G A IN
S N S2
7
5
6
sounders
have
R x
E LEC TRO DE
S ENSING
very
x
C x
high,