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PDF QT240 Data sheet ( Hoja de datos )
| Número de pieza | QT240 | |
| Descripción | 4 KEY QTOUCH SENSOR IC | |
| Fabricantes | QUANTUM | |
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lQ
QT240
4 KEY QTOUCH™ SENSOR IC
z Four independent charge-transfer (‘QT’) touch keys
z Individual outputs per channel - active high
z Projects prox fields through any dielectric
z Sensitivity easily adjusted on a per-channel basis
z 100% autocal for life - no adjustments required
z 3.9V ~ 5.5V single supply operation
z 10s, 60s, infinite auto-recal timeout (strap options)
z Sync pin for line sync to suppress noise
z Spread spectrum operation
z Pin options for auto recalibration timings
z Extremely low cost per key
z 20-SSOP Pb-free package
SNS2
SNS2K
SNS1
SNS1K
OUT1
OUT2
OUT3
VSS
SS/SYNC
n.c.
1 20
2 19
3 18
4 17
QT240
5 16
20-SSOP
6 15
7 14
8 13
9 12
10 11
SNS3K
SNS3
SNS4K
SNS4
n.c.
OSC
VDD
/RES
OUT4
n.c.
APPLICATIONS
PC Peripherals
Backlighted buttons
Appliance controls
Security systems
Access systems
Pointing devices
Instrument panels
Gaming machines
The QT240 charge-transfer (“QT’”) QTouch IC is a self-contained digital sensor IC capable of detecting near-proximity or touch
on 4 electrodes. It allows electrodes to project independent sense fields through any dielectric like glass, plastic, stone,
ceramic, and wood. It can also turn metal-bearing objects into intrinsic sensors, making them responsive to proximity or touch.
This capability coupled with its continuous self-calibration feature can lead to entirely new product concepts , adding high value
to product designs.
Each of the channels operate s independently of the others, and each can be tuned for a unique sensitivity level by simply
changing its sample capacitor value. Two speeds are supported, one of which consumes on ly 90µA of typical current at 4V.
Unique among capacitance sensors, the device incorporates spread spectrum modulation for unsurpassed EMC compliance.
The devices are designed specifically for human interfaces, like control panels, appliances, gaming devices, lighting controls,
or anywhere a mechanical switch or button may be found; they may also be used for some material sensing and control
applications.
These devices feature a SYNC pin which allows for synchronization with additional similar parts and/or to an external source to
suppress interference. This pin doubles as a drive pin for spread-spectrum modulation. Option pins are provided which allow
different timing and feature settings.
The RISC core of these devices use signal processing techniques pioneered by Quantum which are designed to survive
numerous real-world challenges, such as ‘stuck sensor’ conditions, component ageing, moisture films, and signal drift.
By using the charge transfer principle, these devices deliver a level of performance clearly superior to older technologies yet
are highly cost-effective.
AVAILABLE OPTIONS
TA
-400C to +850C
SSOP-20
QT240-ISS-G
LQ
Copyright © 2003 QRG Ltd
QT240R R1.10/0905
1 page  
TABLE 2-1 S1 SPEED / SYNC OPTIONS - SNS1K PIN 4
Fast / Spread Spectrum
Vss
Slow / Sync
Vdd
TABLE 2-2 OPT OPTIONS
S2 S3
SNS3K pin 20 SNS4K pin 18 Max On-Duration
DC Out
Vss
Vdd
10s
DC Out
Vdd
Vss
60s
Toggle
Vdd
Vdd
10s
DC Out
Vss
Vss
infinite
Timings assume 100 kHz operation
Response time can also be modified by changing the
oscillator frequency (Section 3.3).
Recalibration / toggle select (S2, S3): See Table 2-2.
There are 3 recalibration timing options (‘Max On-Duration’;
see Section 2.1.3) and one toggle mode option. The
recalibration options control how long it takes for a
continuous detection to trigger a recalibration on a key.
When such an event occurs, only the ‘stuck’ key is
recalibrated. S2 / S3 should be connected as shown in Table
2-2 to achieve the desired Max On-Duration of either 10s,
60s, or infinite.
Toggle option: One option is toggle mode, which allows all
four keys to behave with flip-flop action. In this mode, each
key’s corresponding OUT pin will toggle High / Low with
successive touches on the key. The underlying Max
On-Duration is 10s in this mode. If a timeout occurs in
Toggle mode, the toggle state is not affected. Toggle state
flips only when the corresponding Out pin goes High.
This is useful for controlling power loads, for example in
kitchen appliances, power tools, light switches, etc . or
wherever a ‘touch-on / touch-off’ effect is required.
2.3 SYNCHRONIZATION
Sync capability is only present in Slow mode (Section 2.2). If
SYNC is not desired, SYNC/SS should be connected to Vss.
Adjacent capacitive sensors that operate independently can
cross-interfere with each other in ways that will create
sensitivity shifts and spurious detections. Since Quantum’s
QT devices operate in burst mode, the opportunity exists to
solve this problem by time-sequencing sensing channels so
that physically adjacent keys do not sense at the same time.
Within the QT240 the four channels operate synchronously,
so it is not possible for these channels to cross interfere.
However 2 or more adjacent chips will cross-interfere if they
are not synchronized to each other. The same is true of the
effects of unsynchronized external noise sources.
External noise sources can also be heavily suppressed by
synchronizing the QT240 to the noise source period. External
noise creates an ‘aliasing’ or ‘beat’ frequency effect between
the sampling rate of the QT part and the external noise
frequency. This shows up as a random noise component on
the internal signals, which in turn can lead to false activation.
Mains frequency is one common source of interference. A
simple AC zero-crossing detector feeding the SYNC pin is
enough to suppress this kind of periodic noise. Multiple
devices tied to SYNC can be synchronized to the mains
frequency in this fashion.
If two physically adjacent devices are to be synchronized to
each other, they should be connected via the SYNC pin to a
clock source that is slower than the burst rate of either
device. For example, a 50Hz clock can synchronize two
QT240’s running with burst spacings of up to 10ms each.
The two QT240’s should be synchronized on opposite
phases of the clock source, ie the clock source should feed
one part and its inverted phase, the other part.
A sync pulse on SYNC/SS in slow mode acts to break the
QT240 out of its sleep state between bursts, and to do
another burst. The device will then go back to sleep again
and await a new SYNC pulse. If a Sync pulse does not arrive
within about 90ms, it will wake again and run normally.
External sync pulses can be used to accelerate response
time (at the expense of power) in Slow mode. Sync pulses
running at 25Hz for example will improve response time by a
factor of 2. Sync cannot be used to slow down the device.
Sync Mode Effects on Timings: In the absence of a Sync
signal, the Max On-Duration timings and drift compensation
rates in Slow mode are nominally correct. It should be
understood that the Max On-Duration timings and drift
compensation rates are slaved to the burst interval in Slow
mode, and that changing the burst interval will have direct
effects on these parameters.
Since the most common use of Sync is to synchronize the
device to Mains frequency (50 or 60Hz) the device makes an
assumption that the presence of a Sync signal is at 55Hz,
and the timings are made to be correct at this frequency.
Should the Sync pulses vary from this frequency, the Max
On-Duration timings and drift compensation rates will vary
proportionately. Thus, if the Sync pulses are 25Hz, the
10-second Max On-Duration timing will become 10*55/25 =
22 seconds nominal. Only at Sync=55Hz will the 10s timeout
be 10s (the same as if there were no Sync signal, or the
device was in Fast mode).
3 - CIRCUIT GUIDELINES
3.1 CS SAMPLE CAPACITOR
Charge sampler caps Cs can be virtually any plastic film or
low to medium-K ceramic capacitor. The ‘normal’ Cs range is
4.7nF to 47nF depending on the sensitivity required; larger
values of Cs require higher stability to ensure reliable
sensing. Acceptable capacitor types for most uses include
plastic film (especially PPS film and polypropylene film) and
X7R ceramic. Lower grades than X7R are not advised;
higher-K ceramics have nonlinear dielectrics which induce
instabilities.
3.2 POWER SUPPLY, PCB LAYOUT
The power supply can range from 3.9 to 5. 5 volts. If this
fluctuates slowly with temperature, the device will track and
compensate for these changes automatically with only minor
changes in sensitivity. If the supply voltage drifts or shift
quickly, the drift compensation mechanism will not be able to
keep up, causing sensitivity anomalies or false detections.
lQ
5
QT240R R1.10/0905
5 Page 
NOTES
lQ
11
QT240R R1.10/0905
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet QT240.PDF ] | |
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