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PDF QT401 Data sheet ( Hoja de datos )
| Número de pieza | QT401 | |
| Descripción | QSLIDE TOUCH SLIDER IC | |
| Fabricantes | QUANTUM | |
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lQ
QT401
QSLIDE™ TOUCH SLIDER IC
z 1-dimensional finger-touch slider
z Extremely simple circuit - no external active components
z Completely passive sensing strip: no moving parts
z Compatible with clear ITO over LCD construction
z SPI slave-mode interface
z Self-calibration and drift compensation modes
z Proximity mode for wake up of a product
z Spread-spectrum operation for optimal EMC compliance
z 2.5 - 5.5V single supply operation; very low power
z 14-pin SOIC, TSSOP lead-free packages
z Inexpensive, simple 1-sided PCB construction possible
z E401 reference design board available
VDD
SDO
/SS
SCLK
SDI
SNS1A
SNS1B
1 14
2 13
3 QT401 12
4 11
5 10
69
78
GND
DRDY
DETECT
PROX
N/A
SNS2A
SNS2B
APPLICATIONS
y Lighting controls
y Appliance controls
y Touch-screens
y Automotive controls
The QT401 QSlide™ IC is a 1-dimensional position sensor IC designed for human interfaces. This unique IC allows designers
to create speed or volume controls, menu bars, and other more exotic forms of human interface on the panel of an appliance
or over an LCD display.
The device uses a simple, inexpensive resistive sensing strip between two connection end points. The strip element can be an
arc or a semicircle or simply linear. The strip can also be used as a proximity sensor out to several centimeters, to wake up an
appliance or display from a sleep mode in a dramatic fashion.
The QT401 can report a single rapid touch anywhere along the slider element, or, it can track a finger moving laterally along
the slider strip in real time. The device self-calibrates under command from a host controller in one of two modes.
The QT401 is a new type of capacitive sensor based on Quantum’s patented charge-transfer methods. This device uses two
channels of simultaneous sensing across a resistive element to determine finger position, using mathematical analysis. The
accuracy of QSlide™ is theoretically the same as a conventional potentiometer. A positional accuracy of 5% (or better) is
relatively easy to achieve.
The acquisitions are performed in a burst mode which uses proprietary spread-spectrum modulation for superior noise
immunity and low emissions.
The output of the QT401 can also be used to create discrete controls on a strip, by interpreting sets of number ranges as
buttons. For example, the number range 0..19 can be button A, 30..49 button B, 60..79 button C etc. Continuous slider action
and discrete controls can be mixed on a single strip, or, the strip can be reinterpreted differently at different times, for example
when used below or on top of an LCD to act as a menu input device that dynamically changes function in context. In this
fashion the QT401 can be used to create ultra-simple, extremely inexpensive ‘touch screens’. The device is compatible with
ITO (Indium Tin Oxide) overlays on top of various displays.
TA
-400C ~ +850C
LQ
AVAILABLE OPTIONS
SO-14
QT401-ISG
TSSOP-14
QT401-ISSG
Copyright © 2004 QRG Ltd
QT401 R10.04/0505
1 page  
values 0 and 127 can be easily achieved by both large and
small fingers at the ends.
Increasing the Rs values will move the reported ends
‘outwards’. If they are too large, the values 0 and/or 127 will
not be reportable. The Rs resistors can have differing values.
Having well-defined ends is important in most applications, so
that the user can select the absolute minimum and maximum
values (ie OFF, MAX etc) reliably. If the numerical ends
cannot be achieved the user can have difficulty in controlling
the product.
The end zones should be defined to be physically large
enough so that over a wide range of values of Cs, Rslider etc
a usable set of ends are always preserved.
End zone tolerances can be affected by Cs1 / Cs2
capacitance matching and the values of Rs1 and Rs2 if fixed
end-cal is used. See also Section 2.2.
2.4 Power Supply
The usual power supply considerations with QT parts applies
also to the QT401. The power should be very clean and come
from a separate regulator if possible. This is particularly
critical with the QT401 which reports continuous position as
opposed to just an on/off output.
A ceramic 0.1uF bypass capacitor should be placed very
close to the power pins of the IC.
Regulator stability: Most low power LDO regulators have
very poor transient stability, especially when the load
transitions from zero current to full operating current in a few
microseconds. With the QT401 this happens when the device
comes out of sleep mode. The regulator output can suffer
from hundreds of microseconds of instability at this time,
which will have a deleterious effect on acquisition accuracy.
To assist with this problem, the QT401 waits 500µs after
coming out of sleep mode before acquiring to allow power to
fully stabilize. This delay is not present before an acquisition
burst if there is no preceding sleep state.
Use an oscilloscope to verify that Vdd has stabilized to within
5mV or better of final settled voltage before a burst begins.
2.5 PCB Layout and Mounting
The E401 PCB layout (Figure 1-3) should be followed if
possible. This is a 1-sided, 144 x 20 x 0.6mm board; the
blank side is simply adhered to the inside of a 2mm thick (or
less) control panel. Thicker panels can be tolerated with
additional positional error due to capacitive ‘hand shadow’
effects and will also have poorer EMC performance.
This layout uses 18 copper pads connected with 17
intervening series resistors in a chain. The end pads are
larger to ensure a more robust reading of 0 (left) and 127
(right). The finger interpolates between the copper pads (if
the pads are narrow enough) to make a smooth, 0..127 step
output with no apparent stair-casing. A wide ground border
helps to suppress the sense field outside of the strip area,
which would otherwise affect position accuracy.
The small electrodes of this PCB measure about 12.5 x
5.2mm. The lateral (eg 5.2mm) dimension of these electrodes
should be no wider than the expected smallest diameter of
finger touch, to prevent stair-casing of the position response.
Other geometries are possible, for example arcs and
semicircles over a small scale (50mm radius max
recommended semicircle, or any radius as a shallow arc).
The strip can be made longer or shorter and with a different
width. The electrode strip should be about 10mm wide or
more, as a rule. Other features of the PCB layout are:
The components are oriented perpendicular to the strip
length so that they do not fracture easily when the PCB is
flexed during bonding to the panel.
The slider end connections should have a symmetrical
layout; note the dummy end trace connected to Rs1 just
below the slider element, to replicate the upper end trace
connected to Rs2. Without this the slider will be
unbalanced and will tend to skew its result to one side.
The ground ring around the slider measures 2mm thick
and is spaced 1mm from the long end traces. The end
traces should be placed as close as possible to the slider
element and be of the thinnest possible trace thickness.
0-ohm 0805 jumpers are used to connect the ground ring
back to circuit ground. These bridge over the two end
traces.
Additional ground area or a ground plane on the PCB’s
rear will compromise signal strength and is to be avoided.
The slider should normally be used in a substantially
horizontal orientation to reduce tracking accuracy
problems due to capacitive ‘hand shadow’ effects. Thinner
panels and an electrode strip on the back of the PCB (so
it has less material to penetrate) will reduce these effects.
‘Handshadow’ effects: With thicker or wider panels an effect
known as ‘handshadow’ can become noticeable. If the
capacitive coupling from finger to electrode strip is weak, for
example due to a narrow electrode strip or a thick, low
dielectric constant panel, the remaining portion of the human
hand can contribute a significant portion of the total
detectable capacitive load. This will induce an offset error,
which will depend on the proximity and orientation of the hand
to the remainder of the strip. Thinner panels will reduce this
effect since the finger contact surface will strongly domina te
the total signal and the remaining handshadow capacitance
will not contribute significantly to create an error offset.
Slider strips placed in a vertical position are more prone to
handshadow problems than those that are horizontal.
PCB Cleanliness: All capacitive sensors should be treated
as highly sensitive circuits which can be influenced by stray
conductive leakage paths. QT devices have a basic
resolution in the femtofarad range; in this region, there is no
such thing as ‘no clean flux’. Flux absorbs moisture and
becomes conductive between solder joints, causing signal
drift and resultant false detections or temporary loss of
sensitivity. Conformal coatings will trap in existing amounts of
moisture which will then become highly temperature
sensitive.
The designer should specify ultrasonic cleaning as part of the
manufacturing process, and in extreme cases, the use of
conformal coatings after cleaning.
2.6 ESD Protection
Since the electrode is always placed behind a dielectric
panel, the IC will be protected from direct static discharge.
However even with a panel transients can still flow into the
lQ
5
QT401 R10.04/0505
5 Page 
4.6 Typical Position Response - Raw Cal (0x01) Only
120
100
80
60
40
20
0
10 20 30 40 50 60 70 80 90 100
DISTANCE FROM END (mm)
4.7 Typical Position Response - After Auto End Cal (0x01 + 0x02)
120
100
80
60
40
20
0
10 20 30 40 50 60 70 80 90 100
DISTANCE FROM END (mm)
lQ
11
QT401 R10.04/0505
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet QT401.PDF ] | |
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