QST108
Capacitive touch sensor device 8 keys with individual key state outputs or I2C interface
Features
Patented charge-transfer design Up to 8 independent QTouchTM keys supported Individual key state outputs or I2C interface Fully "debounced" results Patented AKSTM 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 QTouchTM sensor IC is a pure digital solution based on Quantum's patented chargetransfer (QProxTM) capacitive technology. QTouchTM and QProxTM are trademarks of the Quantum Research Group. Table 1. Device summary
Order code Feature QST108KT6 Operating supply voltage 2.4 to 5.5 V Suppor ted interfaces Operating temperature Package Individual key state outputs or I2C Interface -40 to +85 C LQFP32 (7x7 mm)
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
November 2007
Rev 4
1/47
www.st.com 1
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Fast positive recalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Forced key recalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Max On-Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Drift compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Adjacent key suppression (AKSTM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4
Device operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1 4.2 4.3 4.4 4.5 Reset and power-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Burst operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Low power mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Mode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Stand-alone mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5.1 4.5.2 4.5.3 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 KOUT outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Option descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Main features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 General-purpose outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 IRQ pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Communication packet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 I2C address selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.6
I2C mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.6.1 4.6.2 4.6.3 4.6.4 4.6.5
4.7
Suppor ted commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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QST108
Contents
5
Design guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1 5.2 CS 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.2 6.3 6.4 6.5 6.6
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Supply current characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Capacitive sensing characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 KOUTn/OPTn/GPOn pin characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.6.1 6.6.2 General characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Output pin characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.7 6.8
RESET pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 I2C control interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7 8 9
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Part numbering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Device revision information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1 9.2 Device revision identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Device revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.2.1 9.2.2 Revision 2.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Revision 2.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
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Contents
QST108
10
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
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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 (QProxTM) 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 QProxTM 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 SuppressionTM (AKSTM) 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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Pin description
QST108
2
Pin description
Figure 1. 32-pin package pinout
GPO4/KOUT4/OPT4 (HS) GPO5/KOUT5/OPT5 (HS) IRQ/KOUT6/OPT6 (HS) I2C_SDA/KOUT71) (HS) I2C_SCL/KOUT81) (HS) RESET NC VDD_1
1 2 3 4 5 6 7 8
32 3 1 30 29 2 8 27 26 2 5 24 23 22 21 QST108KT6 20 19 18 17 9 10 11 12 13 1 4 15 16
GPO3/OPT3/KOUT3 (HS) GPO2/OPT2/KOUT2 (HS) GPO1/OPT1/KOUT1 (HS) SNSK_SCK8 SNS_SCK8 SNSK_SCK7 SNS_SCK7 SNSK_SCK6 SNS_SCK6 SNSK_SCK5 SNS_SCK5 SNSK_SCK4 SNS_SCK4 SNSK_SCK3 SNS_SCK3 SNSK_SCK2
(HS) 20 mA high sink capability (on N-buffer only)
1. An external pull-up is required on these pins.
Table 2.
Pin 1
Device pin description
Pin name Type (1) PP (HS) Stand-alone mode function Key 4 output / BCD output 4 and MOD_0 option resistor Key 5 output and MOD_1 option resistor Key 6 output and OM_0 option resistor Key 7 output Key 8 output I2C mode function If unused
GPO4/OPT4/KOUT4 (2)
2
GPO5/OPT5/KOUT5 (2)
PP (HS)
VSS_1 VSS_2 VSS_3 VSS_4 VDD_2 SNS_SCK1 SNSK_SCK1 SNS_SCK2 General purpose output 4 Option and I²C address bit 2 resistor option resistor Open or General purpose output 5 option resistor Interrupt line (active low) Open or option resistor Open Open I2C serial data I2C serial clock
3
OPT6/KOUT6/IRQ (2)
PP/OD (HS) TOD (HS) TOD (HS)
4 5
KOUT7/I2C_SDA(3) KOUT8/I2C_SCL(3)
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QST108 Table 2.
Pin 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Pin description Device pin description (continued)
Pin name Type (1) BD Stand-alone mode function Reset (active low) Not connected S S S S S S SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS SNS PP (HS) Supply voltage Ground voltage Ground voltage Ground voltage Ground voltage Supply voltage Key 1 sense pin to Cs Key 1 sense pin to Cs/Rs Key 2 sense pin to Cs Key 2 sense pin to Cs/Rs Key 3 sense pin to Cs Key 3 sense pin to Cs/Rs Key 4 sense pin to Cs Key 4 sense pin to Cs/Rs Key 5 sense pin to Cs Key 5 sense pin to Cs/Rs Key 6 sense pin to Cs Key 6 sense pin to Cs/Rs Key 7 sense pin to Cs Key 7 sense pin to Cs/Rs Key 8 sense pin to Cs Key 8 sense pin to Cs/Rs Key 1 output / BCD output 1 and MODE option resistor Key 2 output / BCD output 2 and AKS option resistor Key 3 output / BCD output 3 and LP option resistor Open Open Open Open Open Open Open Open Open Open Open Open Open Open Open Open General purpose output 1 Option and MODE option resistor resistor General purpose output 2 Option and I2C address bit 0 resistor option resistor General purpose output 3 Option and I2C address bit 1 resistor option resistor I2C mode function If unused 10nF capacitor to ground
RESET NC VDD_1 VSS_1 VSS_2 VSS_3 VSS_4 VDD_2 SNS_SCK1 SNSK_SCK1 SNS_SCK2 SNSK_SCK2 SNS_SCK3 SNSK_SCK3 SNS_SCK4 SNSK_SCK4 SNS_SCK5 SNSK_SCK5 SNS_SCK6 SNSK_SCK6 SNS_SCK7 SNSK_SCK7 SNS_SCK8 SNSK_SCK8 GPO1/OPT1/KOUT1 (2)
31
GPO2/OPT2/KOUT2 (2)
PP (HS)
32
GPO3/OPT3/KOUT3 (2)
PP (HS)
1. S: supply pin, BD: bidirectional pin, SNS: capacitive sensing pin, PP: Output push-pull, OD: Output open-drain, TOD: Output true open-drain and HS: 20mA high sink (on N-buffer only) 2. During the reset phase, these pins are floating and the state depends on the option resistor. 3. An external pull-up is required on these pins.
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QST touch sensing technology
QST108
3
3.1
QST touch sensing technology
Functional description
QST devices employ bursts of charge-transfer cycles to acquire signals. Burst mode permits low power operation, dramatically reduces RF emissions, lowers susceptibility to RF fields, and yet permits excellent speed. Signals are processed using algorithms pioneered by Quantum which are specifically designed to provide reliable, trouble-free operation over the life of the product. The QST switches and charge measurement hardware functions are all internal to the device. An external CS capacitor accumulates the charge from sense-plate CX, which is then measured. Larger values of CX cause the charge transferred into CS to rise more rapidly, reducing available resolution. As a minimum resolution is required for proper operation, this can result in dramatically reduced gain. Larger values of CS reduce the rise of differential voltage across it, increasing available resolution by permitting longer QST bursts. The value of CS can thus be increased to allow larger values of CX to be tolerated. The device is responsive to both CX and CS, and changes in either can result in substantial changes in sensor gain. Figure 2. QTouchTM measuring circuitry
CT (~5 pF)
SNSK_SCKn Sense capacitor CS (a few nF)
Ear th
SNS_SCKn
Cx (~20 pF)
Ai12569
3.2
Spread-spectrum operation
The bursts operate over a spread of frequencies, so that external fields will have minimal effect on key operation and emissions are very weak. Spread-spectrum operation works with the Detection Integrator mechanism (DI) to dramatically reduce the probability of false detection due to noise.
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QST108
QST touch sensing technology
3.3
Faulty and unused keys
Any sensing channel that does not have its sense capacitor (CS) fitted is assumed to be either faulty or unused. This channel takes no further part in operation unless a Mastercommanded recalibration operation shows it to have an in-range burst count again. Faulty, unused or disabled keys are still bursted but not processed to avoid modifying the sensitivity of active keys. This is important for sensing channels that have an open or short circuit fault across CS. Such channels would otherwise cause very long acquire bursts, and in consequence would slow the operation of the entire QST device. To optimize touch response time and device power consumption, if some keys are not used, we recommend to try suppressing the ones which belong to the same burst. Bursts which do not have any keys implemented will then not be processed.
3.4
Detection threshold levels
The key capacitance change induced by the presence of a finger is sensed by the variation in the number of charge transfer pulses to load the capacitor. The difference in the pulse count number is compared to a threshold in order to detect the key as pressed or not. Two different thresholds, one for detection and one for the end of detection, create an hysteresis in order to prevent erratic behavior. The default threshold levels and hysteresis values are described in Section 6.5: Capacitive sensing characteristics on page 34.
3.5
Detection integrator filter
Detect Integrator (DI) filter mechanism works together with spread spectrum operation to dramatically reduce the effects of noise on key states. The DI mechanism requires a specified number of measurements that qualify as detections (and these must occur in a row) or the detection will not be reported. In a similar manner, the end of a touch (loss of signal) also has to be confirmed over several measurements. This process acts as a type of "debounce" mechanism against noise. The default DI value for confirming start of touch and end of touch is described in Section 6.5: Capacitive sensing characteristics on page 34.
3.6
Self-calibration
On power-up, all keys are self-calibrated to provide reliable operation under almost any conditions. The calibration phase is used to compute a reference value per key which is then used by the process determining if a key is touched or not. The reference is an average of 8 single acquisitions. As a result, the calibration time of the system can be simply calculated using the following formula: tCAL = 8 * Burst_Period. The methodology used to measure the burst period is described in application note AN2547. For a maximum calibration duration (tCAL), please refer to Section 6.5: Capacitive sensing characteristics on page 34.
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QST touch sensing technology
QST108
3.7
Fast positive recalibration
The device autorecalibrates a key when its signal reflects a decrease in capacitance higher than a fixed threshold (PosRecalTh) for a defined number of acquisitions (PoseRecalI).
3.8
Forced key recalibration
A recalibration of the device may be issued at any time by sending to the QST device the appropriate I2C command or by tying the RESET pin to ground. It is possible to recalibrate independently any individual key using an I2C command.
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
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.
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QST108 Caution:
QST touch sensing technology 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.
3.11
Adjacent key suppression (AKSTM)
Adjacent key suppression (AKSTM) is a Quantum-patented feature which prevents multiple keys from responding to a single touch. This can happen with closely spaced keys, or a scroll wheel that has buttons very near it. The QST108 supports two AKS modes: Locking AKS Once a key is considered as "touched", all other keys are locked in an untouched state. To unlock these keys, the touched key must return to an untouched state. Then, the key having the lowest key ID number is declared as the "touched" one.
Unlocking AKS On each acquisition, the signal strengths from each key are compared and the key with the highest signal level is declared as the "touched" one.
In I2C mode, up to 8 AKS groups can be specified. Note: All keys belonging to the same AKS group must have the same AKS mode.
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Device operating modes
QST108
4
4.1
Device operating modes
Reset and power-up
At power-up, the device configures itself according to the pull-up or pull-down option resistors present on pins OPT1 to OPT6. The device start-up and configuration may take up to tSetup. When the power is established, it is possible to force a new device configuration by applying a negative pulse on the RESET pin. The RESET pin is a bidirectional pin with an internal pull-up. The line is forced low when the device resets itself (through an I²C command, for example). A 10nF capacitor is recommended on the RESET pin to ensure reliable start-up and noise immunity.
4.2
Burst operation
The device operates in "Burst" mode. Each key touch is acquired using a burst of chargetransfer sensing pulses whose count varies depending on the value of the sense capacitor CS and the load capacitance CX. Key touches are acquired using two successive bursts of pulses:
Burst A: Keys 1, 2, 3, and 4 Burst B: Keys 5, 6, 7, and 8
Bursts always operate in an A-B sequence. If Keys 5 to 8 are not implemented, the QST device will not perform the Burst B to improve the response time and reduce the power consumption when in Low Power (LP) mode. In Low Power mode, the device sleeps in an ultra-low current state between bursts to conserve power.
4.3
Low power mode
In order to reduce the device power consumption, the QST family include scalable low power modes.
Standard low power mode When the device is in standard low power mode, a window with very low power consumption is inserted between the acquisition of the last active key and the following acquisition of the first active key. This window duration is programmable as the 'sleep duration time'. Note that the sleep window insertion is cancelled in the following conditions: If a change is detected on a key, in order to speed up the DI process, the sleep window insertion is skipped until the end of the DI process. In I2C mode, when a key change is actually detected and reported with a negative pulse on the IRQ pin. In this case, the low power mode is disabled until a command is received from the host. Inside an I2C command, between the Write and the Read I2C frames, the sleep period is skipped.
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QST108
Device operating modes Free run in detect The behavior in this mode is the same as in the standard low power mode except that the sleep window insertion is always skipped if any of the active keys is detected as touched. This is useful to improve the wheel response time.
Deep Sleep mode In Deep Sleep mode, the device enters a very low power mode indefinitely. The device resumes its operations after receiving an I2C frame with any address or a reset.
Caution:
If an I2C frame is received while in Sleep or Deep Sleep mode, the device wakes up but does not acknowledge the frame (even if it has an I2C frame with the device address). The host must therefore send again the frame until it is taken in account and acknowledged.
4.4
Mode selection
The device options are configured by connecting pull-up or pull-down resistors on OPTn pins. The device operating mode is selected using option pin 1 (OPT1) while the device settings are configured using option pins OPT2 to OPT6 (Table 3). Option pins are sampled at power-up and after a reset. To fit most applications, the QST108 device offers two different operating modes: Stand-alone mode This mode allows the user to simply replace existing mechanical switches with a capacitive sensing solution. It is designed for maximum flexibility and can accommodate most popular sensing requirements via option resistors (AKS, Low power, Max On-Duration and output modes). In this mode, the 8 output pins reflect the status of the 8 sensing channels. I2C mode In this mode, which is the most open one, the device is driven using the I2C interface. To avoid polling, the QST device features an output interrupt pin (IRQ). The IRQ line reports all key changes to the Master device. The QST (Slave) device can drive up to five general-purpose outputs. Table 3. Operating modes
Option resistor function OPT1: Mode selection OPT2 Pin OPT1 is high at start-up Stand-alone mode Pin OPT1 is low at start-up I2C mode AKS ADD0 OPT3 LP ADD1 OPT4 OPT5 OPT6 OM MOD_0 MOD_1 ADD2
Unused Unused
4.5
Stand-alone mode
This mode allows the user to simply replace existing mechanical switch interface with a capacitive sensing solution. It is designed for maximum flexibility and can accommodate most popular sensing requirements via option resistors (see Figure 3).
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Device operating modes
QST108
4.5.1
Main features
Pins KOUT1 to KOUT8 directly reflect the state of keys Selectable global adjacent key suppression (AKSTM) Selectable sleep duration Selectable Max On-Duration values Selectable BCD mode
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QST108 Figure 3. Stand-alone mode typical schematic
VDD VUNREG
4.7F 2.4~5.5V Volt. Reg. 4.7F 100nF 100nF
Device operating modes
8
13
Keep these parts close to IC RS8 Key8
10k
29
VDD_1
VDD_2 RESET
6
SNSK_SCK8 SNS_SCK8 SNSK_SCK7 SNS_SCK7 SNSK_SCK6 SNS_SCK6 SNSK_SCK5 SNS_SCK5 SNSK_SCK4 SNS_SCK4 SNSK_SCK3 SNS_SCK3 SNSK_SCK2 SNS_SCK2
To Host
10nF
CS8
28
RS7 Key7
10k
27
VDD VDD
CS7
26
RS6 Key6
10k
10k
10k
25
CS6
24
KOUT8 KOUT7 OM/KOUT6
5
KOUT8 KOUT7 KOUT6 VDD VSS KOUT5 VDD VSS KOUT4 VDD BinaryVSS coded KOUT3 Output Mode VDD VSS KOUT2 VDD VSS KOUT1 VDD
RS5 Key5
10k
23
4
CS5
22
3
RS4 Key4
10k
21
1M
CS4
20
MOD_1/KOUT5
2
RS3 Key3
10k
19
1M
CS3
MOD_0/KOUT4
1
18
1M
RS2 Key2
10k
17
LP/KOUT3
32
CS2
16
1M
RS1 Key1
10k
AKS/KOUT2
15
31
SNSK_SCK1 SNS_SCK1 VSS_1
9
1M
CS1
14
MODE/KOUT1 VSS_3
11
30
VSS_2
10
VSS_4
12
1M
Ai12560
4.5.2
KOUT outputs
KOUTn outputs directly reflect the state of keys. These pins are push-pull outputs except for pins KOUT7 and KOUT8 which are true open-drain outputs. Under RESET, these pins are floating and their state depends on the option resistors. Pins KOUTn are active high meaning that when a key is "touched", the corresponding KOUT pin outputs a `1'.
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Device operating modes
QST108
4.5.3
Option descriptions
Adjacent key suppression (AKSTM)
The QST108 features an adjacent key suppression (AKSTM) function. This function is enabled using the AKS option resistor (OPT2) in standard output mode as described in Table 4. In BCD output mode, the AKS function is always enabled, regardless of the option resistor configuration. Table 4. AKS truth table
Description Disabled Global locking AKS on all available keys
OPT2/AKS VSS VDD
Low Power mode option
This option resistor (OPT3) selects whether the device is always sensing the keys or if a low power consumption phase is introduced between bursts as described in Table 5. In Low Power mode, a very low consumption (sleep) phase of 100ms is inserted between the Group B burst and the Group A burst. This significantly reduces the overall consumption of the device. Sleep duration is not accurate and can vary substantially depending on VDD and temperature values. Note: In Low Power mode, the response time is increased. Table 5. Low power (LP) mode truth table
Description Free running mode 100ms sleep duration
OPT3/LP VSS VDD
Max On-Duration
There are four recalibration timing options ("Max On-Duration"). The recalibration option resistors (OPT4 and OPT5) control how long it takes for a continuous detection to trigger a recalibration on a key as described in Table 6. When such an event occurs, only the "stuck" key is recalibrated. Table 6. Max On-Duration (MOD) truth table
Description Infinite 60s 20s 10s
OPT4/MOD_0 OPT5/MOD_1 VSS VSS VDD VDD VSS VDD VSS VDD
16/47
QST108
Device operating modes
Output mode option
The QST108 offers several outputs mode to fit any existing application. Table 7.
OPT6/OM VSS VDD
Output mode (OM) truth table
Description Individual key state output mode: One output per sensing channel BCD output mode: Binary-coded touched key number (see Table 8)(1)
1. In BCD mode, the AKS function is always active.
Table 8.
Binary code truth table
Description All released Key 1 pressed Key 2 pressed Key 3 pressed Key 4 pressed Key 5 pressed Key 6 pressed Key 7 pressed Key 8 pressed Not used
KOUT4 KOUT3 KOUT2 KOUT1 0 0 0 0 0 0 0 0 1 0 0 0 0 1 1 1 1 0 Other 0 0 1 1 0 0 1 1 0 0 1 0 1 0 1 0 1 0
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Device operating modes
QST108
4.6
I2C mode
The I2C mode offers the largest configurability and functionality of the QST108.
4.6.1
Main features
5 general-purpose outputs Configuration of up to 8 AKS groups Additional low power modes Accessible internal capacitive sensing parameters Continuous range of Max On-Duration I2C mode typical schematic
VDD VUNREG
2.4~5.5V Volt. Reg. 100nF 4.7F 4.7F 100nF
Figure 4.
8
13
VDD
VDD_1
Keep these parts close to IC
VDD_2
RS8
Key8
10k
2.7k
CS8
28 27
RS7
Key7
10k
SNS_SCK8 SNSK_SCK7 SNS_SCK7 SNSK_SCK6 SNS_SCK6 SNSK_SCK5 SNS_SCK5 SNSK_SCK4 SNS_SCK4 SNSK_SCK3 SNS_SCK3 SNSK_SCK2 SNS_SCK2 SNSK_SCK1 SNS_SCK1 MODE/GPO1 VSS_1
9
CS7
26 25
RS6
Key6
10k
I2C_SCL I2C_SDA IRQ RESET
5 4 3 6
2.7k
29
10k
SNSK_SCK8
To Host MCU
To Host
10nF
CS6
24 23
RS5
Key5
10k
CS5
22 21
RS4
Key4
10k
GPO5
2
GPO5
CS4
20 19
RS3
Key3
10k
ADD2/GPO4
1
CS3
18 17
1M
GPO4 VDD VSS GPO3 VDD VSS GPO2 VDD VSS GPO1 VSS
RS2
Key2
10k
ADD1/GPO3
32
CS2
16 15
1M
RS1
Key1
10k
ADD0/GPO2
31
CS1
14
1M
30
VSS_2
10
VSS_3
11
VSS_4
12
1M
Ai12559
18/47
QST108
Device operating modes
4.6.2
General-purpose outputs
I2C mode allows to drive up to 5 general-purpose outputs. These output pins are configured in output push pull mode 0 by default. Their state can be changed using the SET_GPIO_STATE I2C command. Figure 5. Optional LED schematic
VUNREG
R
GPOn
C (10 nF)
Ai12570
4.6.3
IRQ pin
The IRQ pin is an open drain output with an internal pull-up. It can be used to inform the Master device about any change in the key status. The IRQ line is pulled low every time the state of any of the enabled keys changes. This includes any change in the touch state of the key, a faulty key or a new calibration of one or more keys. The reported changes may then be accessed by the Master device by using the GET_KEY_STATE command. To improve communication response time, this signal suspends Low Power mode until the Master device has issued a communication with the QST device.
4.6.4
Communication packet
The communication between the Master device and the QST108 (Slave) consists of two standard I2C frames. The first frame is sent by the Master device using the QST108 device address with the write bit set. The data bytes consist of the command byte which is eventually followed by the parameters and a checksum byte. The second one is sent by the Master device using the QST108 device address with the write bit reset. The QST108 completes the frame with data according to the command previously sent by the Master device. The device finishes the frame by sending a checksum byte for communication integrity verification. If the read frame is omitted, the command may not be taken into account. To initiate the communicate with the QST108, the Master device must send the GET_DEVICE_INFO command in order to unlock access to all the other commands.
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Device operating modes
QST108
4.6.5
I2C address selection
The QST108 slave address is programmable using the option resistors mapped on pins OPT2 to OPT4 (see Table 9). Table 9. I²C address versus option resistor
I2C Address ADD[6:3] ADD2 0 0 0 0 0101 1 1 1 1 0 0 1 1 0 1 0 1 0x2C 0x2D 0x2E 0x2F ADD1 0 0 1 1 ADD0 0 1 0 1 Hex value 0x28 0x29 0x2A 0x2B
Option configuration OPT4 VSS VSS VSS VSS VDD VDD VDD VDD OPT3 VSS VSS VDD VDD VSS VSS VDD VDD OPT2 VSS VDD VSS VDD VSS VDD VSS VDD
4.7
Note:
Supported commands
Table 10 lists the supported I²C commands and available arguments. For more information on the supported commands and I2C protocol, please refer to the QST standard communication protocol reference manual. Table 10. Supported commands
I2C commands CALIBRATE_KEY (All keys) Write Read 0x98 ErrCode Forces the recalibration of all keys. ErrCode: Standard Error code (see Table 11) Description
CALIBRATE_KEY (Single key) Write Read 0x9B KeyID Checksum ErrCode Forces the recalibration of a single key. KeyId: Binary-coded key number (see Table 14) ErrCode: Standard Error code (see Table 11)
GET_DEBUG_INFO Write 0xF7 KeyID Checksum 0x0B KeyDbgState RefMSB RefLSB BCMSB BCLSB Checksum Returns the debug info of the single KeyID channel. KeyDbgState: Current Key Debug state (see Table 19) RefMSB: Reference Count MSB RefLSB: Reference Count LSB BCMSB: Burst Count MSB BCLSB: Burst Count LSB
Read
20/47
QST108 Table 10. Supported commands (continued)
I2C commands GET_DEVICE_INFO Write
Device operating modes
Description
Read
Returns the QST108 device version and ASCII-coded device name. This command must be sent first to enable the communication flow. 0x15 MainVers SubVers MainVers: Device main version NbSCkey NbMCkey SubVer: Device sub-version `Q' 'S' `T' `1' `0' `8' NbSCkey: 0x08 single-channel keys Checksum NbMCkey: 0x00 multi-channel keys Q S T 1 0 8: ASCII-coded device name
0x85
GET_KEY_ERROR Write Read 0xC4 0x11 KeyError1 KeyError2 ... KeyError8 CheckSum Returns the error information on each key. KeyErrorN: KeyError byte description (see Table 12)
GET_KEY_STATE Write Read 0xC1 0x03 AllKeyState KeyError Checksum Returns the state of all keys. AllKeyState: Touched/untouched state for all 8 keys. Refer to Table 13: AllKeyState. KeyError : Refer to Table 12: KeyError byte description
GET_PROTOCOL_VERSION Write Read 0x80 0x07 MainVers SubVer I2CSpeed Checksum Returns the QST108 protocol version. MainVers: Protocol main version SubVer: Protocol sub-version I2CSpeed: 0x00 (100 kHz maximum)
RESET_DEVICE Write Read 0xFD ErrCode Restar ts the device (options Read and Calibration) after reading the ErrCode (see Table 11).
SET_DETECT_INTEGRATORS Write 0x03 0x04 0x00 DI EDI PosRecaII CheckSum Sets the detection, End Of Detection and Positive Recalibration Integrators for all keys. DI: Detection Integrator 1) 3) EDI: End of Detection Integrator 1) 3) PosRecaII: Positive Recalibration Integrator 1) 3) ErrCode: Standard Error code (see Table 11)
Read
ErrCode
SET_GPIO_STATE Write Read 0x08 0x01 GPOState Checksum ErrCode Controls the state of the general-purpose outputs. GPOState: State of general-purpose outputs (see Table 16) ErrCode: Standard Error code (see Table 11)
21/47
Device operating modes Table 10. Supported commands (continued)
I2C commands SET_KEY_ACTIVATION (see Note 4) Write Read 0x97 KeyActivation Checksum ErrCode Description
QST108
Enables or disables a single key. KeyActivation: Byte containing the key number selection and requested state. ErrCode: Standard Error code (see Table 11)
SET_KEY_GROUP 0x00 0x09 AKSGrpMode Key1Grp Key2Grp ...Key8Grp CheckSum ErrCode Defines the AKS groups for each key. AKSGr pMode: AKS mode selection of each group (see Table 17) KeynGrp: AKS group selection for key n (see Table 18) ErrCode: Standard Error code (see Table 11)
Write
Read
SET_LOW_POWER_MODE Write Read 0x92 LowPowerMode Checksum ErrCode Selects standard or Low Power mode. LowPowerMode: Configure Low Power mode (see Table 15) ErrCode: Standard Error code (see Table 11)
SET_MAX_ON_DURATION Write Read 0x8A MaxOnDuration Checksum ErrCode Sets the maximum detected ON time before triggering an automatic recalibration. MaxOnDuration: Time, in second (0 for infinite) ErrCode: Standard Error code (see Table 11)
SET_SCKEY_PARAMETERS Write 0x01 0x04 0x00 DeTh EofDeTh PosRecalTh Checksum ErrCode Sets the Detection, End Of Detection and Positive Recalibration Thresholds for a single key. DeTh: Detection Threshold 1) 2) EofDeTh: End of Detection Threshold 1) 2) PosRecalTh: Positive Recalibration Threshold 1) 2) ErrCode: Standard Error code (see Table 11)
Read
Note:
1 2 3 4
See Section 6.5: Capacitive sensing characteristics on page 34 for default values. The value is a signed character (0x80...0x7F <=> -128 ... +128). The value is an unsigned number (0x00..0xFF <=> 0 ... 255). Enabling or disabling keys triggers a new calibration of all enabled keys.
22/47
QST108
Device operating modes
Error codes
Table 11 lists the I2C error codes. Table 11.
ErrCode 0x01 0x83 0x85 0xA1 0xA3 0xE0 No Error Command not supported Parameter not supported Parity Error Checksum Error Initialization process (GET_FIRMWARE_INFO command not received)
ErrCode
Description
KeyError byte description
Table 12.
Bit 7 Key State
KeyError byte description
Bit 6 0 Bit 5 0 Bit 4 0 Bit 3 0 Bit 2 Bit 1 Key error codes Bit 0
Key state (Bit 7) When set to `1', the corresponding key is touched. This bit is always cleared for the GET_KEY_STATE command. Key error codes (Bits 2:0) When answering the GET_KEY_STATE command, the key error code corresponds to the error codes of all the keys ORed toghether. When answering the GET_KEY_ERROR command, each key error code describes the errors of one defined key. Bit 0: When set to `1', calibration in progress Bit 1: When set to `1', maximum count reached Bit 2: When set to `1', minimum count not reached
All key state description
Table 13.
Bit 7
AllKeyState
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Key 8 State Key 7 State Key 6 State Key 5 State Key 4 State Key 3 State Key 2 State Key 1 State
Key n state When set to `1', the corresponding key is touched.
23/47
Device operating modes
QST108
Key activation description
Table 14.
Bit 7 Key Activation
KeyActivation
Bit 6 0 Bit 5 0 Bit 4 0 Bit 3 Bit 2 Bit 1 Bit 0
Key ID (binary coded)
Key activation (Bit 7) 0: Key enabled 1: Key disabled Key identifier (Bits 3:0) 0000: All keys 0001: Key 1 0010: Key 2 0011: Key 3 0100: Key 4 0101: Key 5 0110: Key 6 0111: Key 7 1000: Key 8
Low power mode description
Table 15.
Bit 7 0
SetLowPower
Bit 6 Free Run in Detect Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Sleep Duration Factor
Free Run in Detect (Bit 6) 0: Low Power mode is always enabled, whatever the state of the keys. 1: Low Power mode is automatically suspended when any key is in Detect state. Low Power mode is automatically resumed when no key is in Detect state. Sleep Duration Factor (Bits 5 to 0) 0x00 or 0x20 to 0x3E: Low power mode is disabled. 0x01 to 0x19: Low Power mode. The sleep duration is `Sleep Duration Factor' x 20 milliseconds (20 ms to 500 ms) 0x3F: Deep Sleep mode is entered immediately. Only a reset or an I2C frame with the correct device address allows exiting Deep Sleep mode. Note: 1 2 When the device is in Sleep or Deep Sleep, any I2C bus activity will wake-up the device. The I2C QST device address is not acknowledged but forces the QST device to exit from Low Power mode. The Master device will have to repeat the command to ensure that it is taken in account.
24/47
QST108
Device operating modes
GPO state description
Table 16.
Bit 7 0
GPOState
Bit 6 0 Bit 5 0 Bit 4 GPO 5 state Bit 3 GPO 4 state Bit 2 GPO 3 state Bit 1 GPO 2 state Bit 0 GPO 1 state
GPOState Defines the state of the selected general-purpose output pin. For more information, see Section 4.6.2: General-purpose outputs on page 19. 0: GPO state is `0' 1: GPO state is `1'
AKS group mode description
Table 17.
Bit 7 AKSGr p8 Mode
AKSGrpnMode
Bit 6 AKSGrp7 Mode Bit 5 AKSGr p6 Mode Bit 4 AKSGrp5 Mode Bit 3 AKSGr p4 Mode Bit 2 AKSGrp3 Mode Bit 1 AKSGrp2 Mode Bit 0 AKSGr p1 Mode
AKSGrpnMode Defines the type of AKS for the Group n: 0: Locking AKS First key pressed within the group locks out all other keys. 1: Unlocking AKS Most heavily pressed key (highest signal level) is selected over all other keys in the group.
AKS group selection description
Table 18.
Bit 7 Gr p8
KeynGrp
Bit 6 Grp7 Bit 5 Gr p6 Bit 4 Grp5 Bit 3 Grp4 Bit 2 Gr p3 Bit 1 Grp2 Bit 0 Gr p1
Grpx The selected key is a member of AKS Group x.
25/47
Device operating modes
QST108
Key debug state description
Table 19. KeyDbgState
Description On-going calibration Key released Key touched Key in error Key calibration filter triggered (PosRecalI) Key detection filter triggered (DI) Key end of detection filter triggered (EDI)
Value 0x01 0x02 0x04 0x08 0x11 0x14 0x24
26/47
QST108
Design guidelines
5
5.1
Design guidelines
CS sense capacitor
The CS sense capacitors accumulate the charge from the key electrodes and determine sensitivity. Higher values of CS make the corresponding sensing channel more sensitive. The values of CS can differ for each channel, permitting differences in sensitivity from key to key or to balance unequal sensitivities. Unequal sensitivities can occur due to key size and placement differences and stray wiring capacitances. More stray capacitance on a sense trace will desensitize the corresponding key. Increasing the CS for that key will compensate for the loss of sensitivity. The CS capacitors can be virtually any plastic film or low- to medium-K ceramic capacitor. The normal CS range is 1nF to 50nF depending on the sensitivity required: larger values of CS require better quality to ensure reliable sensing. In certain circumstances the normal CS range may be exceeded. Acceptable capacitor types for most uses include PPS film, polypropylene film, and NP0 and X5R / X7R ceramics. Lower grades than X5R or X7R are not recommended.
5.2
Sensitivity tuning
Sensitivity can be altered to suit various applications and situations on a channel-bychannel basis. The easiest and most direct way to impact sensitivity is to alter the value of each CS: more CS yields higher sensitivity. Each channel has its own CS value and can therefore be independently adjusted.
5.2.1
Increasing sensitivity
Sensitivity can also be increased by using larger electrode areas, reducing panel thickness, or using a panel material with a higher dielectric constant.
5.2.2
Decreasing sensitivity
In some cases the circuit may be too sensitive. Gain can be lowered further by a number of strategies:
making the electrode smaller making the electrode into a sparse mesh using a high space-to-conductor ratio decreasing the CS capacitors
5.2.3
Key balance
A number of factors can cause sensitivity imbalances. Notably, SNS wiring to electrodes can have differing stray amounts of capacitance to ground. Increasing load capacitance will cause a decrease in gain. Key size differences, and proximity to other metal surfaces can also impact gain. The keys may thus require "balancing" to achieve similar sensitivity levels. This can be best accomplished by trimming the values of the CS capacitors to achieve equilibrium. The RS resistors have no effect on sensitivity and should not be altered. Load capacitances to ground can also be added to overly sensitive channels to reduce their gain. These should be in the order of a few picofarads.
27/47
Design guidelines
QST108
5.3
Power supply
If the power supply fluctuates slowly with temperature, the QST device compensates automatically for these changes with only minor changes in sensitivity. However, if the supply voltage drifts or shifts quickly, the drift compensation mechanism is not able to keep up, causing sensitivity anomalies or false detections. The power supply should be locally regulated, using a three-terminal regulator. If the supply is shared with another electronic system, care should be taken to ensure that the supply is free of digital spikes, sags and surges which can cause adverse effects. It is not recommended to include a series inductor in the power supply to the QST device. For proper operation, a 0.1 F or greater bypass capacitor must be used between VDD and VSS. The bypass capacitor should be routed with very short tracks to the device's VDD and VSS pins. The PCB should, if possible, include a copper pour under and around the device, but not extensively under the SNS lines.
5.4
ESD protection
In normal environmental conditions, only one series resistor is required for ESD suppression. A 10 kOhm RS resistor in series with the sense trace is sufficient in most cases. The dielectric panel (glass or plastic) usually provides a high degree of isolation to prevent ESD discharge from reaching the circuit. RS should be placed close to the chip. If the CX load is high, RS can prevent total charge and transfer and as a result gain can deteriorate. If a reduction in RS increases gain noticeably, the lower value should be used. Conversely, increasing the RS can result in added ESD and EMC benefits, provided that the increase does not decrease sensitivity.
5.5
Crosstalk precautions
Adjacent sense traces might require intervening ground traces in order to reduce capacitive cross bleed if high sensitivity is required or high values of delta-CX are anticipated (for example, from direct human touch to an electrode connection). In normal touch applications behind plastic panels, this is rarely a problem regardless of how the electrodes are wired. Higher values of RS will make crosstalk problems worse; try to keep RS to 22 kOhm or less if possible. In general try to keep the QST device close to the electrodes and reduce the adjacency of the sense wiring to ground planes and other signal traces; this will reduce the Cx load, reduce interference effects, and increase signal gain. The one and only valid reason to run ground near SNS traces is to provide crosstalk isolation between traces, and then only on an as-needed basis.
5.6
PCB layout and construction
The PCB traces, wiring, and any components associated with or in contact with either SNS pin will become touch sensitive and should be treated with caution to limit the touch area to the desired location. Multiple touch electrodes connected to any sensing channel can be used, for example, to create control surfaces on both sides of an object.
28/47
QST108
Design guidelines It is important to limit the amount of stray capacitance on the SNS terminals, for example by minimizing trace lengths and widths to allow for higher gain without requiring higher values of CS. Under heavy delta-CX loading of one key, cross coupling to another key's trace can cause the other key to trigger. Therefore, electrode traces from adjacent keys should not be run close to each other over long runs in order to minimize cross-coupling if large values of delta-CX are expected, for example when an electrode is directly touched. This is not a problem when the electrodes are working through a plastic panel with normal touch sensitivity. For additional information on PCB layout and construction, please contact your local ST Sales Office for a list of available application notes.
29/47
Electrical characteristics
QST108
6
6.1
Electrical characteristics
Parameter conditions
Unless otherwise specified, all voltages are referred to VSS.
6.1.1
Minimum and maximum values
Unless otherwise specified the minimum and maximum values are guaranteed in the worst conditions of ambient temperature, supply voltage and frequencies by tests in production on 100% of the devices with an ambient temperature at TA = 25C and TA = TAmax (given by the selected temperature range). Data based on characterization results, design simulation and/or technology characteristics are indicated in the table footnotes and are not tested in production. Based on characterization, the minimum and maximum values refer to sample tests and represent the mean value plus or minus three times the standard deviation (mean3).
6.1.2
Typical values
Unless otherwise specified, typical data are based on TA = 25 C, VDD = 5 V (for the 4.5V VDD 5.5 V voltage range) and VDD = 3.3 V (for the 3.0 V VDD 3.6 V voltage range). They are given only as design guidelines and are not tested.
6.1.3
Typical curves
Unless otherwise specified, all typical curves are given only as design guidelines and are not tested.
6.1.4
Loading capacitor
The loading conditions used for pin parameter measurement are shown in Figure 6. Figure 6. Pin loading conditions
Output pin
30/47
QST108
Electrical characteristics
6.1.5
Pin input voltage
The input voltage measurement on a pin of the device is described in Figure 7. Figure 7. Pin input voltage
Input pin
VIN
6.2
Absolute maximum ratings
Stresses above those listed as "absolute maximum ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device under these conditions is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. Table 20.
Symbol TSTG TJ
Thermal characteristics
Ratings Storage temperature range Maximum junction temperature Value -65 to +150 Unit C
Table 21.
Symbol
Voltage characteristics
Ratings Maximum value 7.0
(1)(2)
Unit
VDD - VSS Supply voltage VIN Input voltage on any pin
VSS-0.3 to VDD+0.3 2000 500
V
VESD(HBM) Electrostatic discharge voltage (Human Body Model) VESD(CDM) Electrostatic discharge voltage (Charge Device Model)
1. Directly connecting the RESET and I/O pins to VDD or VSS could damage the device if an unintentional internal reset is generated or an unexpected change of the I/O configuration occurs (for example, due to a corrupted program counter). To guarantee safe operation, this connection has to be done through a pull-up or pull-down resistor (typical: 4.7k for RESET, 10k for I/Os). 2. IINJ(PIN) must never be exceeded. This is implicitly insured if VIN maximum is respected. If VIN maximum cannot be respected, the injection current must be limited externally to the IINJ(PIN) value. A positive injection is induced by VIN>VDD while a negative injection is induced by VIN
31/47
Electrical characteristics Table 22.
Symbol I VDD IVSS
QST108
Current characteristics
Ratings Total current into VDD power lines (source)(1) Total current out of VSS ground lines (sink) Output current sunk by RESET pin
(1)
Maximum value 75 150 20 40 - 25 5 5 20
Unit
II O
Output current sunk by output pin Output current source by output pin
mA
IINJ(PIN)(2)
(3)
Injected current on RESET pin Injected current output pin
IINJ(PIN)(2) Total injected current (sum of all I/O and control pins)
1. All power (VDD) and ground (VSS) lines must always be connected to the external supply. 2. IINJ(PIN) must never be exceeded. This is implicitly ensured if VIN maximum is respected. If VIN maximum cannot be respected, the injection current must be limited externally to the IINJ(PIN) value. A positive injection is induced by VIN>VDD while a negative injection is induced by VIN
6.3
Operating conditions
Table 23.
Symbol VDD TA Operating supply voltage Operating temperature
Operating conditions
Feature Value 2.4 to 5.5 -40 to +85 Unit V C
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QST108
Electrical characteristics
6.4
Supply current characteristics
Table 24.
Symbol
Supply current characteristics
Parameter Conditions VDD = 2.4 V Min. Typ. (1) 1.71 2.17 3.35 276 389 637 108 144 246 1 A A A mA Max. Unit
Average suppy current IDD (FR) Free Run mode
VDD = 3.3 V VDD = 5 V
IDD Average suppy current (Sleep 100ms Sleep mode 100ms) IDD Average suppy current (Sleep 500ms Sleep mode 500ms) IDD Halt Average suppy current Halt mode
VDD = 2.4 V VDD = 3.3 V VDD = 5 V VDD = 2.4 V VDD = 3.3 V VDD = 5 V
1. The results are based on CS = 2.7nF and CX = 12.5pF
Figure 8.
IDD Sleep mode current characteristics
33/47
Electrical characteristics
QST108
6.5
Capacitive sensing characteristics
Table 25.
Symbol CS CX CT RS Sense capacitor Equivalent electrode capacitor Equivalent touch capacitor Serial resistance 5 10 22
External sensing components
Parameter Min. Typ. Max. 100 100 Unit nF pF pF kOhm
Table 26.
Symbol tCAL tSetup DI DeTh EDI EofDeTh PosRecalI
Capacitive sensing parameters
Parameter Calibration duration Setup duration Detection integrator Detection threshold End of detection integrator End of detection threshold Positive recalibration integrator Positive recalibration threshold 0 -128 0 -128 0 1 1 0.1 0.1 0.1 0.1 0 0 0 0 20 100 2 -10 2 -8 2 6 Infinite 1 1 0.2 0.2 10 10 10 2 255 -1 255 -1 255 128 255 25.5 25.5 25.5 25.5 255 255 255 255 2000 Counts Min. Default Max. TBD Unit ms ms Counts Counts Counts Counts Counts Counts s s/level s/level s/level s/level
PosRecalTh
MaxOnDuration Max on-duration delay PosDiffDrift NegDiffDrift PosComDrift NegComDrift PosDriftI NegDriftI ComFact DiffFact BurstCount Positive differential drift compensation rate Negative differential drift compensation rate Positive common drift compensation rate Negative common drift compensation rate Positive drift integrator Negative drift integrator Common time step factor Differential time step factor Burst length
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QST108
Electrical characteristics
6.6
6.6.1
KOUTn/OPTn/GPOn pin characteristics
General characteristics
Subject to general operating conditions for VDD and TA unless otherwise specified. Table 27.
Symbol VIL VIH VHys IL CIO tf(IO)out tr(IO)out
General characteristics
Parameter Input low level voltage (1) Input high level voltage (1) Schmitt trigger voltage hysteresis(2) Input leakage current I/O pin capacitance Output high to low level fall time (2) Output low to high level rise time (2) CL = 50 pF Between 10% and 90% VSS VIN VDD 5 25 ns 25 Conditions Min. VSS -0.3 0.7x VDD 400 1 Typ. Ma x . 0.3x VDD VDD + 0.3 V Unit
mV A pF
1. Not tested in production, guaranteed by characterization. 2. Data based on validation/design results.
6.6.2
Output pin characteristics
Subject to general operating conditions for VDD, fCPU, and TA unless otherwise specified. Table 28.
Symbol VOL
(1)
Output pin current
Parameter Output low level voltage for a high sink I/O pin when 4 pins are sunk at same time (see Figure 14) Output high level voltage for an I/O pin when 4 pins are sourced at same time (see Figure 19) Output low level voltage for a high sink I/O pin when 4 pins are sunk at same time Output high level voltage for an I/O pin when 4 pins are sourced at same time (Figure 17) Output low level voltage for a high sink I/O pin when 4 pins are sunk at same time Output high level voltage for an I/O pin when 4 pins are sourced at same time Conditions IIO = +20mA IIO = +8mA IIO = -5mA IIO = -2mA VDD = 2.4V VDD = 3.3V IIO = +8mA IIO = -2mA IIO = +8mA IIO = -2mA VDD-0.9 VDD-0.8 0.6 VDD-1.5 VDD-0.8 0.5 V Min. Max. 1.3 0.75 Unit
VOH(2) VOL(1)(3) VOH(2)(3) VOL(1)(3) VOH(2)(3)
1. The IIO current sunk must always respect the absolute maximum rating specified in Table 22 and the sum of IIO (I/O ports and control pins) must not exceed IVSS. 2. The IIO current sourced must always respect the absolute maximum rating specified in Table 22 and the sum of IIO (output and RESET pins) must not exceed IVDD.. 3. Not tested in production, based on characterization results.
VDD = 5V
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Electrical characteristics
QST108
Figure 9.
Typical VOL at VDD = 2.4 V
VOL vs Iload @ VDD = 2.4 V HS pins
Figure 10.
Typical VOL vs VDD at Iload = 2 mA
V OLvs VDD @Iload=2 mA HS Pins
120
1 2 00 1 0 00 8 00 -4 0 C 2 5 C 1 2 5C
V OL[m V]
- 40C 25C 85C 125C
110 100 90 80 70 60 50 40 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8
8 5 C
VOL [V]
6 00 4 00 2 00 0 0 2 4 6 8 10 12 14 16
4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
VDD [V]
I l oad [mA]
Figure 11.
Typical VOL at VDD = 3 V
VOLvs Iload @ VDD = 3 V HS pins
Figure 12.
Typical VOL vs VDD at Iload = 8 mA
VOL vs VDD@Iloa d = 8 mA HS Pins
1 6 00 1 4 00 1 2 00
-4 0 C 2 5 C 8 5 C 1 2 5C
VOL [mV]
540 490 440 390 340 290 240 190 140 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8
- 40C 25C 85C 125C
VOL [V]
1 0 00 8 00 6 00 4 00 2 00 0 0 2 4 6 8 10 12 14 16 18 20
4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
VD D [V]
I l oad [mA]
Figure 13.
Typical VOL at VDD = 5 V
VOL vs Iload @ VDD = 5 V HS pins
Figure 14.
Typical VOL vs VDD at Iload = 12 mA
VOL vs VDD @Iloa d = 12 mA HS Pins
900 800 700 600
-4 0 C 2 5 C 8 5 C 1 2 5 C
VOL [mV]
1040 940 840 740 640 540 440 340 240 140
- 40C 25C 85C 125C
VOL [V]
500 400 300 200 100 0 0 2 4 6 8 10 12 14 16 18 20
2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6
VD D [V]
I l oad [mA]
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QST108
Figure 15. Typical VDD-VOH vs. Iload at VDD = 2.4 V
VDD-VOH vs Iload @ VDD = 2.4 V HS Pins
Electrical characteristics
Figure 16. Typical VDD-VOH vs. VDD at Iload = 2 mA
VDD-VOH vs VDD @Iload = 2 mA HS Pins
800
-40C 25C 85C 125C
800 700 600 VD D -VOH [mV] 500 400 300 200 100 0
700 600 VD D -VOH [mV] 500 400 300 200 100 0
-40C 25C 85C 125C
2. 8
3. 6
4
4. 4
5. 2
2. 4
3. 2
4. 8
2
Il o ad [m A]
4
VD D [V]
Figure 17.
Typical VDD-VOH vs. Iload at VDD = 3 V
VDD-VOH vs Iload @ VDD = 3 V HS Pins
Figure 18.
Typical VDD-VOH vs. VDD at Iload = 4 mA
VDD-VOH vs VDD @Iload = 4 mA HS Pins
1800 1600 1400 -40C 25C 85C 125C
1800 1600 1400 VDD-VOH [mV] 1200 1000 800 600 400 200 0
-40C 25C 125C 85C
VD D -VOH [mV]
1200 1000 800 600 400 200 0
3 2. 6 3. 4 3. 8 4. 2 4. 6 5
0
2
Iload[m A]
4
6
VD D [V]
Figure 19.
Typical VDD-VOH vs. Iload at VDD = 5 V
V DD- V OH vs Iload @ V DD = 5 V HS Pins
4500 4000 3500 VDD-VOH [mV] 3000 2500 2000 1500 1000 500 0
-40C 25C 85C 125C
0
2
4
6
8
10
12
14
Iload[mA]
5. 4
5. 6
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Electrical characteristics
QST108
6.7
RESET pin
TA = -40C to 125C, unless otherwise specified. Table 29.
Symbol VIL VIH Vhys VOL RON tw(RSTL)out th(RSTL)in tg(RSTL)in
RESET pin characteristics
Parameter Input low level voltage Input high level voltage Schmitt trigger voltage hysteresis(1) Output low level voltage(2) Pull-up equivalent resistor(3) Generated reset pulse duration External reset pulse hold time(4) Filtered glitch duration VDD = 5V VIN = VSS IIO = +2mA VDD = 5V VDD = 3V 30 Conditions Min. VSS - 0.3 0.7 x VDD 2 200 50 90(1) 90(1) 20 200 70 Typ. Max. 0.3x VDD VDD + 0.3 V mV k s s ns Unit V
Internal reset sources
1. Data based on characterization results, not tested in production. 2. The IIO current sunk must always respect the absolute maximum rating specified in Table 22: Current characteristics on page 32 and the sum of IIO (I/O ports and control pins) must not exceed IVSS. 3. The RON pull-up equivalent resistor is based on a resistive transistor. Specified for voltages on RESET pin between VILmax and VDD. 4. To guarantee the reset of the device, a minimum pulse has to be applied to the RESET pin. All short pulses applied on RESET pin with a duration below th(RSTL)in can be ignored.
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QST108
Electrical characteristics
6.8
I2C control interface
Subject to general operating conditions for VDD, and TA unless otherwise specified. The QST108 I2C interface meets the requirements of the Standard I2C communication protocol described in the following table with the restriction mentioned below: Refer to I/O port characteristics for more details on the input/output alternate function characteristics (SDA and SCL). Table 30.
Symbol tw(SCLL) tw(SCLH) tsu(SDA) th(SDA) tr(SDA) tr(SCL) tf(SDA) tf(SCL) th(STA) tsu(STA) tsu(STO) Cb SCL clock low time SCL clock high time SDA setup time SDA data hold time SDA and SCL rise time SDA and SCL fall time START condition hold time Repeated START condition setup time STOP condition setup time Capacitive load for each bus line 4.0 4.7 4.0 4.7 400
I²C characteristics
100 kHz speed Parameter Min. (1) 4.7 4.0 250 0 (2) 1000 ns 300 s s s pF Max. (1) Unit
s ns
tw(STO:STA) STOP to START condition time (bus free)
1. Data based on standard I2C protocol requirement, not tested in production.
2. The maximum hold time of the START condition has only to be met if the interface does not stretch the low period of the SCL signal.
Table 31.
Symbol tW(IRQ) RIRQ
IRQ specific pin characteristics (1)
Parameter IRQ pulse width IRQ internal pull-up (2) VDD = 5V VDD = 3V Conditions Min. 10 100 120 300 Typ. Ma x . 15 140 Unit s k
1. For additional pin parameters, please use the pin description in Section 6.6: KOUTn/OPTn/GPOn pin characteristics on page 35. 2. The IRQ pull-up equivalent resistor is based on a resistive transistor.
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Electrical characteristics Figure 20. Typical application with I2C bus and timing diagram
VDD 4.7k I
2C
QST108
VDD 4.7k 100 100 SDA SCL
BUS
QST device
REPEATED START START
tsu(STA)
SDA
tw(STO:STA)
START
tf(SDA)
SCL
tr(SDA)
t su(SD A )
th(SDA)
STOP
th(STA)
tw(SCKH)
tw(SCKL)
tr(SCK)
tf(SCK)
tsu(STO)
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QST108
Package mechanical data
7
Package mechanical data
Figure 21. 32-pin low profile quad flat package (7x7) outline
Seating plane C A A2 A1 ccc C D D1 D3 24 17 16 A1 L L1 K c 0.25 mm Gage plane
b
25
E3
E1
E
32 Pin 1 identification
9
1
8 e
5V_ME
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Package mechanical data Table 32.
Dim. Min. A A1 A2 b c D D1 D3 E E1 E3 e L L1 K ccc 0.0 0.450 8.800 6.800 0.050 1.350 0.300 0.090 8.800 6.800 9.000 7.000 5.600 9.000 7.000 5.600 0.800 0.600 1.000 3.5 Tolerance (mm) 0.10 7.0 0.0 0.750 0.0177 9.200 7.200 0.3465 0.2677 1.400 0.370 Typ. Max. 1.600 0.150 1.450 0.450 0.200 9.200 7.200 0.0020 0.0531 0.0118 0.0035 0.3465 0.2677 0.3543 0.2756 0.2205 0.3543 0.2756 0.2205 0.0315 0.0236 0.0394 3.5 Tolerance (inches) 0.0039 0.0551 0.0146 Min. Typ.
QST108
32-pin low profile quad flat package mechanical data
mm inches(1) Max. 0.0630 0.0059 0.0571 0.0177 0.0079 0.3622 0.2835 0.3622 0.2835
0.0295 7.0
1. Values in inches are converted from mm and rounded to 4 decimal digits.
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QST108
Part numbering
8
Part numbering
Table 33.
Example: Device type QST = Capacitive touch sensor Device sub-family 1: 5: 6: 11: 15: 16: QTouch (3 to 5 V) QMatrix (3 to 5 V) QSlide/QWheel (3 to 5 V) QTouch (1.8 to 3.6 V) QMatrix (1.8 to 3.6 V) QSlide/QWheel (1.8 to 3.6 V)
Ordering information scheme
QST 1 08 K T 6
Channel count Number of channels Pin count A: Y: K: 8 pins 16 pins 32 pins S: 44 pins C: 48 pins M: 80 pins
Package B: H: M: N: T: U: DIP (dual in-line) BGA (ball grid array) SO (small outline) TSSOP (thin-shrink small outline package) LQFP (thin quad flat) QFN (dual quad flat no lead)
Temperature range 0: 1: 5: +25C 0 to +70C 10C to +85C 6: 40C to +85C 7: 40C to +105C 9: 40C to + 125C
For a list of available options (speed, package, etc.) or for further information on any aspect of this device, please contact your nearest ST Sales Office. 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.
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Device revision information
QST108
9
9.1
Device revision information
Device revision identification
The marking on the right side of the second line (Line B) of the package top face identifies the device revision. Figure 22. Device revision identification (TQFP package)
A
QST108 QRG
D
B
F01
E
C
F
G
H
a
J
I
K
Table 34.
Device revision identification
Marking F00 F01 Device revision V 2.1 V 2.3
The device revision can also be obtained using the GET_DEVICE_INFO I2C command. For more information, refer to Section 4.9: Supported commands on page 16.
9.2
Device revision history
This section identifies the device deviations from the present specification for each device revision.
9.2.1
Revision 2.1
Engineering samples. For more information regarding this revision, please contact your local ST sales office.
9.2.2
Revision 2.3
When the device enters low power mode, an additional sleep time is inserted after each burst, instead of once after every complete burst cycle. As a result, if only one burst is required, the sleep duration during low power mode is doubled. And if two bursts are required, the sleep duration is tripled.
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QST108
Device revision information In standalone mode, the 100ms sleep duration low power becomes either a 200ms or 300ms sleep duration depending on the number of bursts required. In I2C mode, it is required to program a sleep duration for one half or a third of the desired sleep duration depending on the number of bursts required. GET_PROTOCOL_VERSION returns 0x01 as I2CSpeed byte while it should return 0x00 (maximum speed is 100 kHz).
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Revision history
QST108
10
Revision history
Table 35.
Date 8-Jun-2007 15-Jun-2007
Document revision history
Revision 1 2 Initial release. Datasheet status changed to Preliminary Data. Removed Beeper function. Changed LED output pins to GPO pins. Updated pin names and functions in Section 2: Pin description on page 5. Added Figure 2: QTouchTM measuring circuitry on page 7. Changed order of chapters in Section 3 for better comprehension. Removed Simplified independent output mode from Section 4: Device operating modes on page 11. Independent output mode renamed Stand-alone mode. Added Section 4.2: Reset and power-up on page 11. Removed Power supply option chapter from Section 4.4.2: Option descriptions on page 14. Updated Table 6: Max On-Duration (MOD) truth table on page 14 and Table 7: Output mode (OM) truth table on page 15. Updated Figure 3: Stand-alone mode typical schematic on page 13 and Figure 4: I2C mode typical schematic on page 16. Updated Table 9: I²C address versus option resistor on page 18. Added Figure 5: Optional LED schematic on page 17. Updated Section 4.5: I2C mode on page 15. Added Section 5.2.3: Key balance on page 25. Updated Section 6.4: Supply current characteristics on page 31. Added Section 6.5: Capacitive sensing characteristics on page 32. and Section 6.7: RESET pin on page 36. Updated Table 30: I²C characteristics on page 37. Document status promoted from Preliminary Data to Datasheet. Added ECOPACK information. Updated CX value in Figure 2: QTouchTM measuring circuitry on page 7. Added Caution note in Section 3.10: Drift compensation on page 11. Added Section 4.3: Low power mode on page 13. Updated hex values in Table 9: I²C address versus option resistor on page 20. Updated Table 24: Supply current characteristics on page 33, Table 26: Capacitive sensing parameters on page 34 and added Figure 8: IDD Sleep mode current characteristics on page 33. Added Table 31: IRQ specific pin characteristics on page 39. Added Section 9: Device revision information on page 44. Changes
26-Sep-2007
3
22-Nov-2007
4
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QST108
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