QST108
Capacitive touch sensor device
8 keys with individual key state outputs or I2C interface
Not For New Design
Features
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■
■
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Patented charge-transfer design
Up to 8 independent QTouch™ keys supported
Individual key state outputs or I
2
C 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
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.
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:
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Lower customer service costs
Reduced manufacturing costs
Increased product lifetime
Device summary
Table 1.
Order codes
Feature
QST108KT6
Operating supply voltage
Supported interfaces
Operating temperature
Package
2.4 to 5.5 V
Individual key state outputs or I
2
C Interface
-40° to +85° C
LQFP32 (7x7 mm)
July 2008
Rev 5
1/51
www.st.com
1
This is information on a product still in production but not recommended for new designs.
Contents
QST108
Contents
1
2
3
Device overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
QST touch sensing technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Spread-spectrum operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Faulty and unused keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Detection threshold levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Detection integrator filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Self-calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Fast positive recalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Forced key recalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Max On-Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Drift compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Adjacent key suppression (AKS™) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4
Device operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1
4.2
4.3
4.4
4.5
Reset and power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Burst operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Low power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Mode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Stand-alone mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5.1
4.5.2
4.5.3
Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
KOUT outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Option descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
General-purpose outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
IRQ pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Communication packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
I2C address selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.6
I2C mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.6.1
4.6.2
4.6.3
4.6.4
4.6.5
4.7
Supported commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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QST108
Contents
5
Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1
5.2
C
S
sense capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Sensitivity tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2.1
5.2.2
5.2.3
Increasing sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Decreasing sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Key balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3
5.4
5.5
5.6
Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
ESD protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Crosstalk precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
PCB layout and construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1
Parameter conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
Minimum and maximum values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Typical values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Typical curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Loading capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Pin input voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.2
6.3
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
EMC characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.3.1
6.3.2
6.3.3
Functional EMS (electro magnetic susceptibility) . . . . . . . . . . . . . . . . . 32
Electro magnetic interference (EMI) . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Absolute maximum ratings (electrical sensitivity) . . . . . . . . . . . . . . . . . 33
6.4
6.5
6.6
6.7
Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Supply current characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Capacitive sensing characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
KOUTn/OPTn/GPOn pin characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.7.1
6.7.2
General characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Output pin characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.8
6.9
RESET pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
I2C control interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.1
Soldering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8
9
Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Device revision information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3/51
Contents
QST108
9.1
9.2
Device revision identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Device revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
9.2.1
9.2.2
Revision 2.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Revision 2.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
10
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
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QST108
Device overview
1
Device overview
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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