QT100-ISG

QT100 CHARGE-TRANSFER QTOUCH™ IC LQ This datasheet is applicable to all revision 3 chips The QT100 charge-transfer (‘QT’) touch sensor is a self-contained digital IC capable of detecting near-proximity or touch. It will project a touch or proximity field through any dielectric like glass, plastic, stone, ceramic, and even most kinds of wood. It can also turn small metal-bearing objects into intrinsic sensors, making them responsive to proximity or touch. This capability, coupled with its ability to self-calibrate, can lead to entirely new product concepts. It is designed specifically for human interfaces, like control panels, appliances, toys, lighting controls, or anywhere a mechanical switch or button may be found. OUT 1 6 SYNC/MODE VSS 2 5 VDD SNSK 3 4 SNS AT A GLANCE Number of keys: One Technology: Patented spread-spectrum charge-transfer (direct mode) Key outline sizes: 6mm x 6mm or larger (panel thickness dependent); widely different sizes and shapes possible Electrode design: Solid or ring electrode shapes Layers required: One Electrode materials: Etched copper, silver, carbon, Indium Tin Oxide (ITO), Orgacon† ink Electrode Substrates: PCB, FPCB, plastic films, glass Panel materials: Plastic, glass, composites, painted surfaces (low particle density metallic paints possible) Panel thickness: Up to 50mm glass, 20mm plastic (electrode size dependent) Key sensitivity: Settable via capacitor Interface: Digital output, active high Moisture tolerance: Good Power: 2V ~ 5V Package: 6-pin SOT23-6 RoHS compliant Signal processing: Self-calibration, auto drift compensation, noise filtering Applications: Control panels, consumer appliances, toys, lighting controls, mechanical switch or button Patents: QTouch™ (patented Charge-transfer method) HeartBeat™ (monitors health of device) † Orgacon is a registered trademark of Agfa-Gevaert N.V AVAILABLE OPTIONS TA SOT23-6 -40ºC to +85ºC LQ QT100-ISG CCopyright © 2006-2007 QRG Ltd QT100_3R0.09_0707 Contents 2.9 Output Features 1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Basic Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Electrode Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4.2 Increasing Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.4.3 Decreasing Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Operation Specifics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1 Run Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.2 Fast Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.3 Low Power Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.4 SYNC Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2 Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3 Max On-duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4 Detect Integrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.5 Forced Sensor Recalibration . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.6 Drift Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.7 Response Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.8 Spread Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 lQ .................................... 5 ........................................ 5 2.9.2 HeartBeat™ Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.9.3 Output Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Circuit Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 Application Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2 Sample Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 Power Supply, PCB Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4 Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1 Absolute Maximum Specifications . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2 Recommended Operating Conditions . . . . . . . . . . . . . . . . . . . . . 7 4.3 AC Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.4 Signal Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.5 DC Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.6 Mechanical Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 4.7 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.8 Moisture Sensitivity Level (MSL) . . . . . . . . . . . . . . . . . . . . . . . . . 9 5 Datasheet Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1 Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.2 Numbering Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.9.1 Output 2 QT100_3R0.09_0707 1 Overview Figure 1.1 Basic Circuit Configuration VDD 1.1 Introduction SENSE ELECTRODE 5 The QT100 is a digital burst mode charge-transfer (QT) sensor designed specifically for touch controls; it includes all hardware and signal processing functions necessary to provide stable sensing under a wide variety of changing conditions. Only a single low cost, noncritical capacitor is required for operation. VDD 1 OUT SNSK Rs 3 Cs SNS Figure 1.1 shows a basic circuit using the device. 4 SYNC/MODE 6 VSS 1.2 Basic Operation Cx 2 The QT100 employs bursts of charge-transfer cycles to acquire its signal. Burst mode permits power consumption in the microamp range, dramatically reduces RF emissions, lowers susceptibility to EMI, and yet permits excellent response time. Internally the signals are digitally processed to reject impulse noise, using a 'consensus' filter which requires four consecutive confirmations of a detection before the output is activated. Note: A bypass capacitor should be tightly wired between Vdd and Vss and kept close to QT100 pin 5. The value of Cs also has a dramatic effect on sensitivity, and this can be increased in value with the trade-off of slower response time and more power. Increasing the electrode's surface area will not substantially increase touch sensitivity if its diameter is already much larger in surface area than the object being detected. Panel material can also be changed to one having a higher dielectric constant, which will better help to propagate the field. The QT switches and charge measurement hardware functions are all internal to the QT100. 1.3 Electrode Drive For optimum noise immunity, the electrode should only be connected to SNSK. Ground planes around and under the electrode and its SNSK trace will cause high Cx loading and destroy gain. The possible signal-to-noise ratio benefits of ground area are more than negated by the decreased gain from the circuit, and so ground areas around electrodes are discouraged. Metal areas near the electrode will reduce the field strength and increase Cx loading and should be avoided, if possible. Keep ground away from the electrodes and traces. In all cases the rule Cs >> Cx must be observed for proper operation; a typical load capacitance (Cx) ranges from 5-20pF while Cs is usually about 2-50nF. Increasing amounts of Cx destroy gain, therefore it is important to limit the amount of stray capacitance on both SNS terminals. This can be done, for example, by minimizing trace lengths and widths and keeping these traces away from power or ground traces or copper pours. 1.4.3 Decreasing Sensitivity In some cases the QT100 may be too sensitive. In this case gain can be easily lowered further by decreasing Cs. The traces and any components associated with SNS and SNSK will become touch sensitive and should be treated with caution to limit the touch area to the desired location. 2 Operation Specifics A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress ESD and EMC effects. 2.1 Run Modes 1.4 Sensitivity 2.1.1 Introduction 1.4.1 Introduction The QT100 has three running modes which depend on the state of SYNC, pin 6 (high or low). The sensitivity on the QT100 is a function of things like the value of Cs, electrode size and capacitance, electrode shape and orientation, the composition and aspect of the object to be sensed, the thickness and composition of any overlaying panel material, and the degree of ground coupling of both sensor and object. 2.1.2 Fast Mode The QT100 runs in Fast mode if the SYNC pin is permanently high. In this mode the QT100 runs at maximum speed at the expense of increased current consumption. Fast mode is useful when speed of response is the prime design requirement. The delay between bursts in Fast mode is approximately 1ms, as shown in Figure 2.2. 1.4.2 Increasing Sensitivity In some cases it may be desirable to increase sensitivity; for example, when using the sensor with very thick panels having a low dielectric constant. Sensitivity can often be increased by using a larger electrode or reducing panel thickness. Increasing electrode size can have diminishing returns, as high values of Cx will reduce sensor gain. lQ 2.1.3 Low Power Mode The QT100 runs in Low Power (LP) mode if the SYNC line is held low. In this mode it sleeps for approximately 85ms at the end of each burst, saving power but slowing response. On detecting a possible key touch, it temporarily switches to Fast mode until either the key touch is confirmed or found to be spurious (via the detect integration process). It then returns to LP mode after the key touch is resolved as shown in Figure 2.1. 3 QT100_3R0.09_0707 The SYNC pin is sampled at the end of each burst. If the device is in Fast mode and the SYNC pin is sampled high, then the device continues to operate in Fast mode (Figure 2.2). If SYNC is sampled low, then the device goes to sleep. From then on, it will operate in SYNC mode (Figure 2.1). Therefore, to guarantee entry into SYNC mode the low period of the SYNC signal should be longer than the burst length (Figure 2.3). Key touch Figure 2.1 Low Power Mode (SYNC held low) ~85ms sleep SNSK QT100 fast detect integrator sleep sleep However, once SYNC mode has been entered, if the SYNC signal consists of a series of short pulses (>10µs) then a burst will only occur on the leading edge of each pulse (Figure 2.4) instead of on each change of SYNC signal, as normal (Figure 2.3). SYNC OUT In SYNC mode, the device will sleep after each measurement burst (just as in LP mode) but will be awakened by a change in the SYNC signal in either direction, resulting in a new measurement burst. If SYNC remains unchanged for a period longer than the LP mode sleep period (about 85ms), the device will resume operation in either Fast or LP mode depending on the level of the SYNC pin (Figure 2.3). Figure 2.2 Fast Mode Bursts (SYNC held high) SNSK QT100 There is no DI in SYNC mode (each touch is a detection) but the Max On-duration will depend on the time between SYNC pulses; see Sections 2.3 and 2.4. Recalibration timeout is a fixed number of measurements so will vary with the SYNC period. ~1ms SYNC Figure 2.3 SYNC Mode (triggered by SYNC edges) 2.2 Threshold SNSK QT100 sleep sleep SYNC sleep The internal signal threshold level is fixed at 10 counts of change with respect to the internal reference level, which in turn adjusts itself slowly in accordance with the drift compensation mechanism. Revert to Fast Mode slow mode sleep period SNSK QT100 sleep sleep sleep The QT100 employs a hysteresis dropout of two counts of the delta between the reference and threshold levels. Revert to Slow Mode SYNC Figure 2.4 SYNC Mode (Short Pulses) SNSK QT100 >10us >10us 2.3 Max On-duration If an object or material obstructs the sense pad the signal may rise enough to create a detection, preventing further operation. To prevent this, the sensor includes a timer which monitors detections. If a detection exceeds the timer setting the sensor performs a full recalibration. This is known as the Max On-duration feature and is set to ~80s (at 3V). This will vary slightly with Cs and if SYNC mode is used. As the internal timebase for Max On-duration is determined by the burst rate, the use of SYNC can cause dramatic changes in this parameter depending on the SYNC pulse spacing. slow mode sleep period >10us 2.4 Detect Integrator SYNC It is desirable to suppress detections generated by electrical noise or from quick brushes with an object. To accomplish this, the QT100 incorporates a ‘detect integration’ (DI) counter that increments with each detection until a limit is reached, after which the output is activated. If no detection is sensed prior to the final count, the counter is reset immediately to zero. In the QT100, the required count is four. In LP mode the device will switch to Fast mode temporarily in order to resolve the detection more quickly; after a touch is either confirmed or denied the device will revert back to normal LP mode operation automatically. 2.1.4 SYNC Mode It is possible to synchronize the device to an external clock source by placing an appropriate waveform on the SYNC pin. SYNC mode can synchronize multiple QT100 devices to each other to prevent cross-interference, or it can be used to enhance noise immunity from low frequency sources such as 50Hz or 60Hz mains signals. The DI can also be viewed as a 'consensus' filter, that requires four successive detections to create an output. lQ 4 QT100_3R0.09_0707 2.5 Forced Sensor Recalibration The QT100 has no recalibration pin; a forced recalibration is accomplished when the device is powered up or after the recalibration timeout. However, supply drain is low so it is a simple matter to treat the entire IC as a controllable load; driving the QT100's VDD pin directly from another logic gate or a microcontroller port will serve as both power and 'forced recal'. The source resistance of most CMOS gates and microcontrollers are low enough to provide direct power without problem. 2.6 Drift Compensation Figure 2.5 Drift Compensation Signal H ysteresis Threshold R eference Output Signal drift can occur because of changes in Cx and Cs over time. It is crucial that drift be compensated for, otherwise false detections, nondetections, and sensitivity shifts will follow. 2.7 Response Time The QT100's response time is highly dependent on run mode and burst length, which in turn is dependent on Cs and Cx. With increasing Cs, response time slows, while increasing levels of Cx reduce response time. The response time will also be a lot slower in LP or SYNC mode due to a longer time between burst measurements. Drift compensation (Figure 2.5). is performed by making the reference level track the raw signal at a slow rate, but only while there is no detection in effect. The rate of adjustment must be performed slowly, otherwise legitimate detections could be ignored. The QT100 drift compensates using a slew-rate limited change to the reference level; the threshold and hysteresis values are slaved to this reference. 2.8 Spread Spectrum Once an object is sensed, the drift compensation mechanism ceases since the signal is legitimately high, and therefore should not cause the reference level to change. The QT100 modulates its internal oscillator by ±7.5 percent during the measurement burst. This spreads the generated noise over a wider band reducing emission levels. This also reduces susceptibility since there is no longer a single fundamental burst frequency. The QT100's drift compensation is 'asymmetric'; the reference level drift-compensates in one direction faster than it does in the other. Specifically, it compensates faster for decreasing signals than for increasing signals. Increasing signals should not be compensated for quickly, since an approaching finger could be compensated for partially or entirely before even 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. 2.9 Output Features 2.9.1 Output The output of the QT100 is active-high upon detection. The output will remain active-high for the duration of the detection, or until the Max On-duration expires, whichever occurs first. If a Max On-duration timeout occurs first, the sensor performs a full recalibration and the output becomes inactive (low) until the next detection. With large values of Cs and small values of Cx, drift compensation will appear to operate more slowly than with the converse. Note that the positive and negative drift compensation rates are different. Figure 2.6 Figure 2.7 Getting HeartBeat pulses with a pull-up resistor Using a micro to obtain HeartBeat pulses in either output state VDD HeartBeat™ Pulses 5 Ro 1 VDD OUT SNSK 3 1 P ORT_M.x OU T SNSK 3 Ro SNS SYNC/MODE VSS 4 Microcontroller 6 SNS P ORT_M.y S Y N C /MOD E 4 6 2 lQ 5 QT100_3R0.09_0707 The Cs capacitor should be a stable type, such as X7R ceramic or PPS film. For more consistent sensing from unit to unit, 5 percent tolerance capacitors are recommended. X7R ceramic types can be obtained in 5 percent tolerance at little or no extra cost. In applications where high sensitivity (long burst length) is required the use of PPS capacitors is recommended. 2.9.2 HeartBeat™ Output The QT100 output has a HeartBeat™ ‘health’ indicator superimposed on it in both LP and SYNC modes. This operates by taking the output pin into a three-state mode for 15µs once before every QT burst. This output state can be used to determine that the sensor is operating properly, or it can be ignored, using one of several simple methods. The HeartBeat indicator can be sampled by using a pull-up resistor on the OUT pin, and feeding the resulting positive-going pulse into a counter, flip flop, one-shot, or other circuit. The pulses will only be visible when the chip is not detecting a touch. 3.3 Power Supply, PCB Layout The power supply can range between 2.0V and 5.5V. At 3V current drain averages less than 500µA in Fast mode. If the power 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 adversely affect the QT100. The QT100 will track slow changes in VDD, but it can be badly affected by rapid voltage fluctuations. It is highly recommended that a separate voltage regulator be used just for the QT100 to isolate it from power supply shifts caused by other components. If the sensor is wired to a microcontroller as shown in Figure 2.7, the microcontroller can reconfigure the load resistor to either VSS or VDD depending on the output state of the QT100, so that the pulses are evident in either state. Electromechanical devices like relays will usually ignore the short Heartbeat pulse. The pulse also has too low a duty cycle to visibly affect LEDs. It can be filtered completely if desired, by adding an RC filter to the output, or if interfacing directly and only to a high-impedance CMOS input, by doing nothing or at most adding a small noncritical capacitor from OUT to VSS. If desired, the supply can be regulated using a Low Dropout (LDO) regulator, although such regulators often have poor transient line and load stability. See Application Note AN-KD02 (see Section 3.1) for further information on power supply considerations. 2.9.3 Output Drive Parts placement: The chip should be placed to minimize the SNSK trace length to reduce low frequency pickup, and to reduce stray Cx which degrades gain. The Cs and Rs resistors (see Figure 1.1) should be placed as close to the body of the chip as possible so that the trace between Rs and the SNSK pin is very short, thereby reducing the antenna-like ability of this trace to pick up high frequency signals and feed them directly into the chip. A ground plane can be used under the chip and the associated discretes, but the trace from the Rs resistor and the electrode should not run near ground to reduce loading. The OUT pin is active high and can sink or source up to 2mA. When a large value of Cs (>20nF) is used the OUT current should be limited to