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PDF QST108 Data sheet ( Hoja de datos )
| Número de pieza | QST108 | |
| Descripción | Capacitive touch sensor device 8 keys | |
| Fabricantes | STMicroelectronics | |
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QST108
Capacitive touch sensor device
8 keys with individual key state outputs or I2C interface
Not For New Design
Features
■ Patented charge-transfer design
■ Up to 8 independent QTouch™ keys supported
■ Individual key state outputs or I2C interface
■ Fully “debounced” results
■ Patented AKS™ Adjacent Key Suppression
■ Self-calibration and auto drift compensation
■ Spread-spectrum bursts to reduce EMI
■ Up to 5 general-purpose outputs
■ ECOPACK® (RoHS compliant) package
Applications
This device specifically targets human interfaces
and front panels for a wide range of applications
such as PC peripherals, home entertainment
systems, gaming devices, lighting and appliance
controls, remote controls, etc.
QST devices are designed to replace mechanical
switching/control devices and the reduced
number of moving parts in the end product
provides the following advantages:
■ Lower customer service costs
■ Reduced manufacturing costs
■ Increased product lifetime
LQFP32 (7x7 mm)
Description
The QST108 is the ideal solution for the design of
capacitive touch sensing user interfaces.
Touch-sensitive controls are increasingly
replacing electromechanical switches in home
appliances, consumer and mobile electronics,
and in computers and peripherals. Capacitive
touch controls allow designers to create stylish,
functional, and economical designs which are
highly valued by consumers, often at lower cost
than the electromechanical solutions they
replace.
The QST108 QTouch™ sensor IC is a pure digital
solution based on Quantum's patented charge-
transfer (QProx™) capacitive technology.
QTouch™ and QProx™ are trademarks of the
Quantum Research Group.
Table 1. Device summary
Feature
Operating supply voltage
Supported interfaces
Operating temperature
Package
Order codes
QST108KT6
2.4 to 5.5 V
Individual key state outputs or I2C Interface
-40° to +85° C
LQFP32 (7x7 mm)
July 2008
Rev 5
This is information on a product still in production but not recommended for new designs.
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QST108
1 Device overview
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The QST108 capacitive touch sensor IC is a pure digital solution based on Quantum's
patented charge-transfer (QProx™) capacitive technology.
This technology allows users to create simple touch panel sensing electrode interfaces for
conventional or flexible printed circuit boards (PCB/FPCB). Sensing electrodes are part of
the PCB layout (copper pattern or printed conductive ink) and may be used in various
shapes (circle, rectangular, etc.).
By implementing the QProx™ charge-transfer algorithm, the QST108 detects finger
presence (human touch) near electrodes behind a dielectric (glass, plastic, wood, etc.). Only
one external sampling capacitor by channel is used in the measuring circuitry to control the
detection.
QST technology also incorporates advanced processing techniques such as drift
compensation, auto-calibration, noise filtering, and Quantum's patented Adjacent Key
Suppression™ (AKS™) to ensure maximum usability and control integrity.
In order to meet environmental requirements, ST offers this device in ECOPACK®
packages. These packages have a lead-free second level interconnect. The category of
second level interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97.
The maximum ratings related to soldering conditions are also marked on the inner box label.
ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
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QST108
QST touch sewnswiwn.gDatetacShhneeotl4oUg.cyom
3.9 Max On-Duration
The device can time out and automatically recalibrate each key independently after a fixed
duration of continuous touch detection. This prevents the keys from becoming ‘stuck on’ due
to foreign objects or other sudden influences. This is known as the Max On-Duration feature.
After recalibration, the key will continue to operate normally, even if partially or fully
obstructed. Max On-Duration works independently per channel: a timeout on one channel
has no effect on another channel.
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 ensure that drift in CS, CX, and VDD do not cause the device to
remain “stuck on” inadvertently even when the touching object is removed from the sense
field. Timeout durations are not accurate and can vary substantially depending on VDD and
temperature values, and should not be relied upon for critical functions.
3.10
Caution:
Drift compensation
Signal drift can occur because of changes in CX, CS, and VDD over time. Depending on the
CS type and quality, the signal may vary substantially with temperature and veiling. If keys
are subject to extremes of temperature or humidity, the signal can also drift. It is crucial that
drift be compensated, otherwise false detections, non detections, and sensitivity shifts will
follow.
Drift compensation slowly corrects the reference level of each key while no detection is in
effect. The rate of reference adjustment must be performed slowly or else legitimate
detections can also be ignored. The device compensates drift on each channel
independently using a maximum compensation rate to the reference level.
Once a touch is sensed, the drift compensation mechanism ceases since the signal is
legitimately high, and therefore should not cause the reference level to change.
The signal drift compensation is “asymmetric”: the reference level compensates drift in one
direction faster than it does in the other. Specifically, it compensates faster for increasing
signals than for decreasing signals. Decreasing signals should not be compensated for
quickly, since an approaching finger could be compensated for partially or entirely while
approaching the sense electrode. However, an obstruction over the sense pad, for which the
sensor has already made full allowance, 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.
When only one key is enabled or if keys are very close together, the common drift
compensation must be disabled or its rate must be reduced to ensure correct device
operation.
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet QST108.PDF ] | |
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