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PDF QT320 Data sheet ( Hoja de datos )

Número de pieza QT320
Descripción 2 CHANNEL PROGAMMABLE ADVANCED SENSOR IC
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No Preview Available ! QT320 Hoja de datos, Descripción, Manual

LQ
QPROXQT320
2-CHANNEL PROGAMMABLE ADVANCED SENSOR IC
Two channel digital advanced capacitive sensor IC
Projects two ‘touch buttons’ through any dielectric
Cloning for user-defined sensing behavior
100% autocal - no adjustments required
Only one external capacitor per channel
User-defined drift compensation, threshold levels
Variable gain via Cs capacitor change
Selectable output polarities
Toggle mode / normal mode outputs
HeartBeat™ health indicator on outputs (can be disabled)
1.8 ~ 5V supply, 60µA
APPLICATIONS
Light switches
Industrial panels
Appliance control
Security systems
Access systems
Pointing devices
Computer peripherals
Entertainment devices
The QT320 charge-transfer (“QT’”) touch sensor chip is a self-contained digital IC capable of detecting near-proximity or
touch on two sensing channels. It will project sense fields through almost any dielectric, like glass, plastic, stone, ceramic,
and most kinds of wood. It can also turn small metal-bearing objects into intrinsic sensors, making them respond to proximity
or touch. This capability coupled with its ability to self calibrate continuously can lead to entirely new product concepts.
It is designed specifically for human interfaces, like control panels, appliances, security systems, lighting controls, or
anywhere a mechanical switch or button may be found; it may also be used for some material sensing and control
applications provided that the presence duration of objects does not exceed the recalibration time-out interval.
The IC requires only a common inexpensive capacitor per channel in order to function.
Power consumption and speed can be traded off depending on the application; drain can be as low as 60µA, allowing
operation from batteries.
The IC’s RISC core employs signal processing techniques pioneered by Quantum; these are specifically designed to make
the device survive real-world challenges, such as ‘stuck sensor’ conditions and signal drift. Even sensitivity is digitally
determined. All key operating parameters can be set by the designer via the onboard eeprom which can be configured to alter
sensitivity, drift compensation rate, max on-duration, output polarity, and toggle mode independently on each channel.
No external switches, opamps, or other analog components aside from Cs are usually required.
The Quantum-pioneered HeartBeat™ signal is also included, allowing a host controller to monitor the health of the QT320
continuously if desired; this feature can be disabled via the cloning process.
By using the charge transfer principle, the IC delivers a level of performance clearly superior to older technologies in a highly
cost-effective package.
AVAILABLE OPTIONS
TA
00C to +700C
-400C to +850C
SOIC
-
QT320-IS
8-PIN DIP
QT320-D
-
LQ
Copyright © 2002 QRG Ltd
QT320/R1.03 08/02

1 page




QT320 pdf
Figure 1-7 Burst lengths without Csx installed
(observed using a 750K resistor in series with probe)
Figure 1-8 Burst lengths with Csx installed
(observed using a 750K resistor in series with probe)
strength, even if the fiber density is too low to make the
plastic electrically conductive.
1.4.2 DECREASING SENSITIVITY
In some cases the circuit may be too sensitive, even with high
signal threshold values. In this case gain can be lowered by
making the electrode smaller, using sparse mesh with a high
space-to-conductor ratio (Figure 1-3), and most importantly by
decreasing Cs. Adding Cx capacitance will also decrease
sensitivity.
It is also possible to reduce sensitivity by making a capacitive
divider with Cx by adding a low-value capacitor in series with
the electrode wire.
1.4.3 HYSTERESIS
Hysteresis is required to prevent chattering of the output lines
with weak, noisy, or slow-moving signals.
The hysteresis can be set independently per channel.
Hysteresis is a reference-based number; thus, a threshold of
10 with a hysteresis of 2 will yield 2 counts of hysteresis
(20%); the channel will become active when the signal equals
or exceeds a count of 10, and go inactive when the count falls
to 7 or lower.
Hysteresis can also be set to zero (0), in which case the
sensor will go inactive when the count falls to 9 or lower in the
above example.
Threshold levels of under 4 counts are hard to deal with as
the hysteresis level is difficult to set properly.
1.4.4 CHANNEL BALANCE
Channel 1 has less internal Cx than Channel 2, which makes
it more sensitive than Channel 2 given equal Cx loads and Cs
capacitors. This can be useful in some designs where one
more sensitive channel is desired, but if equal sensitivity is
required a few basic rules should be followed:
1. Use a symmetrical PCB layout for both channels: Place
the IC half way between the two electrodes to match Cx
loading. Avoid routing ground plane (or other traces) close
to either sense line or the electrodes; allow 4-5 mm
clearance from any ground or other signal line to the
electrodes or their wiring. Where ground plane is required
(for example, under and around the QT320 itself) the
sense wires should have minimized adjacency to ground.
2. Connect a small capacitor (~5pF) between S1a or S1b
(either Channel 1 pin) and circuit ground (Csx in Figure
1-6), this will increase the load capacitance of Channel 1,
thus balancing the sensitivity of the two channels (see
Figures 1-7, 1-8).
3. Adjust Cs and/or the internal threshold of the two channels
until the sensitivities of the two channels are
indistinguishable from each other.
Since the actual burst length is proportional to sensitivity, you
can use an oscilloscope to balance the two channels with
more accuracy than by empirical methods (See Figures 1-7
and 1-8). Connect one scope probe to Channel 1 and the
other to Channel 2, via large resistors (750K ohms) to avoid
disturbing the measurement too much, or, use a low-C FET
probe. The Csx balance capacitor should be adjusted so that
the burst lengths of Channels 1 and 2 look nearly the same.
With some diligence the PCB can also be designed to include
some ground plane nearer to Channel 1 traces to induce
about 5pF of Csx load without requiring an actual discrete
capacitor.
lQ
5
QT320/R1.03 08/02

5 Page





QT320 arduino
3.4 ESD ISSUES
In cases where the electrode is placed behind a dielectric
panel, the device will usually be well protected from static
discharge. However, even with a plastic or glass panel,
transients can still flow into the electrode via induction, or in
extreme cases, via dielectric breakdown. Porous materials
may allow a spark to tunnel right through the material;
partially conducting materials like 'pink poly' static dissipative
plastics will conduct the ESD right to the electrode. Panel
seams can permit discharges through edges or cracks.
Testing is required to reveal any problems. The QT320 has
internal diode protection which can absorb and protect the
device from most induced discharges, up to 20mA; the
usefulness of the internal clamping will depend on the
dielectric properties, panel thickness, and rise time of the
ESD transients.
ESD protection can be enhanced with an added resistor as
shown in Figure 3-1. Because the charge and transfer times
of the QT320 are 1us in duration, the circuit can tolerate
values of Re which result in an RC timeconstant of about
200ns. The Cof the RC is the Cx load on the distant side
from the QT320. Thus, for a Cx load of 20pF, the maximum
Re should be 10K ohms. Larger amounts of Re will result in
an increasingly noticeable loss of sensitivity.
3.5 EMC ISSUES
Electromagnetic and electrostatic susceptibility are often a
problem with capacitive sensors. QT320 behavior under these
conditions can be improved by adding the series-R shown in
Figure 3-1, exactly as shown for ESD protection. The resistor
should be placed next to the chip.
This works because the inbound RC network formed by Re
and Cs has a very low cutoff frequency which can be
computed by the formula:
Fc
=
1
2Re Cs
If Re = 10K and Cs = 10nF, then Fc = 1.6kHz.
This leads to very strong suppression of external fields.
Nevertheless, it is always wise to reduce lead lengths by
placing the QT320 as close to the electrodes as possible.
Likewise, RF emissions are sharply curtailed by the use of
Re, which bandwidth limits RF emissions based on the value
of Re and Cx, the electrode capacitance.
Line conducted EMI can be reduced by making sure the
power supply is properly bypassed to chassis ground. The
OUT lines can also be paths for conducted EMI, and these
can be bypassed to circuit ground with an RC filter network.
4 PARAMETER CLONING
The cloning process allows user-defined settings to be loaded
into internal eeprom, or read back out, for development and
production purposes.
The QTM300CA cloning board in conjunction with QT3View
software simplifies the cloning process greatly. The E3B eval
OUT1
Vdd
8
VDD
S1A 3
1 OUT1
S1B 5
CS1
SENSOR 1
OUT2
7 OUT2
S2A 6
S2B 2
VSS
4
CS2
SENSOR 2
Figure 4-1 Clone interface wiring
board has been designed with a connector to facilitate direct
connection with the QTM300CA. The QTM300CA in turn
connects to any PC with a serial port which can run QT3View
software (included with the QTM300CA and available on
Quantums web site).
The connections required for cloning are shown in Figure 4-1.
Further information on the cloning process can be found in
the QTM300CA instruction guide. Section 3.3.2 discusses
wiring issues associated with cloning.
The parameters which can be altered are shown in Table 4-1
(next page).
Parameters that can be altered for each channel
independently are:
Threshold
Hysteresis
Detect Integrator A
Detect Integrator B
Max On-Duration
Output Mode
Parameters that are common to the entire part are:
Detect Integrator Speed
Negative Drift Compensation
Positive Drift Compensation
Sleep Cycles
It is possible for an on-board host controller to read and
change the internal settings via the interface, but doing so will
inevitably disturb the sensing process even when data
transfers are not occuring. The additional capacitive loading
of the interface pins will contribute to Cx; also, noise on the
interface lines can cause erratic operation.
The internal eeprom has a life expectancy of 100,000
erase/write cycles.
A serial interface specification for the device can be obtained
by contacting Quantum.
lQ
11
QT320/R1.03 08/02

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