AT42QT1012-TSHR

AT42QT1012 AT42QT1012 Data Sheet Introduction The AT42QT1012 (QT1012) is a single key device featuring a touch on/touch off (toggle) output with a programmable auto switch-off capability. The device is One-channel Toggle-mode QTouch® Touch Sensor IC with Power Management Functions. The QT1012 features a digital burst mode charge-transfer sensor designed specifically for touch controls and a unique “green” feature - the timeout function, which can turn off power after a time delay. Features • • • • • • • • • • • • • Number of Keys: – One, toggle mode (touch-on / touch-off), plus programmable auto-off delay and external cancel – Configurable as either a single key or a proximity sensor Technology: – Patented spread-s 6 mm x 6 mm or larger (panel thickness dependent); widely different sizes and shapes possible Electrode design: – Solid or ring electrode shapes PCB Layers required: – One Electrode materials: – Etched copper, silver, carbon, Indium Tin Oxide (ITO) Electrode substrates: – PCB, FPCB, plastic films, glass Panel materials: – Plastic, glass, composites, painted surfaces (low particle density metallic paints possible) Panel thickness: – Up to 12 mm glass, 6 mm plastic (electrode size and Cs dependent) Key sensitivity: Settable via external capacitor (Cs) Interface: – Digital output, active high or active low (hardware configurable) Moisture tolerance: – Increased moisture tolerance based on hardware design and firmware tuning Power: © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 1 AT42QT1012 • • – 1.8 V – 5.5 V; 32 µA at 1.8 V Package: – 6-pin SOT23-6 (3 x 3 mm) RoHS compliant – 8-pin UDFN/USON (2 x 2 mm) RoHS compliant Signal processing: – Self-calibration, auto drift compensation, noise filtering © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 2 Table of Contents Introduction......................................................................................................................1 Features.......................................................................................................................... 1 1. Pinout and Schematic................................................................................................5 1.1. 1.2. 1.3. Pinout Configurations................................................................................................................... 5 Pin Descriptions........................................................................................................................... 5 Schematics...................................................................................................................................6 2. Overview of the AT42QT1012................................................................................... 7 2.1. 2.2. 2.3. 2.4. 2.5. Introduction...................................................................................................................................7 Basic Operation............................................................................................................................7 Electrode Drive.............................................................................................................................7 Sensitivity..................................................................................................................................... 8 Moisture Tolerance....................................................................................................................... 8 3. Operation Specifics................................................................................................. 10 3.1. 3.2. 3.3. 3.4. 3.5. 3.6. 3.7. 3.8. 3.9. 3.10. 3.11. 3.12. Acquisition Modes...................................................................................................................... 10 Detect Threshold........................................................................................................................ 10 Detect Integrator.........................................................................................................................11 Recalibration Timeout.................................................................................................................11 Forced Sensor Recalibration...................................................................................................... 11 Drift Compensation.....................................................................................................................11 Response Time.......................................................................................................................... 12 Spread Spectrum....................................................................................................................... 12 Output Polarity Selection............................................................................................................12 Output Drive............................................................................................................................... 13 Auto-Off Delay............................................................................................................................13 Examples of Typical Applications............................................................................................... 21 4. Circuit Guidelines.................................................................................................... 22 4.1. 4.2. 4.3. 4.4. More Information........................................................................................................................ 22 Sample Capacitor.......................................................................................................................22 Rs Resistor.................................................................................................................................22 Power Supply and PCB Layout.................................................................................................. 22 4.5. Power On................................................................................................................................... 23 5. Specifications.......................................................................................................... 24 5.1. 5.2. 5.3. 5.4. 5.5. 5.6. 5.7. Absolute Maximum Specifications..............................................................................................24 Recommended Operating Conditions........................................................................................ 24 AC Specifications....................................................................................................................... 24 Signal Processing.......................................................................................................................25 DC Specifications....................................................................................................................... 25 Mechanical Dimensions............................................................................................................. 26 Part Marking............................................................................................................................... 28 © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 3 AT42QT1012 5.8. 5.9. Part Number............................................................................................................................... 28 Moisture Sensitivity Level (MSL)................................................................................................ 29 6. Associated Documents............................................................................................30 7. Revision History.......................................................................................................31 The Microchip Web Site................................................................................................ 32 Customer Change Notification Service..........................................................................32 Customer Support......................................................................................................... 32 Microchip Devices Code Protection Feature................................................................. 32 Legal Notice...................................................................................................................33 Trademarks................................................................................................................... 33 Quality Management System Certified by DNV.............................................................34 Worldwide Sales and Service........................................................................................35 © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 4 1. Pinout and Schematic 1.1 Pinout Configurations 1.1.1 6-pin SOT23-6 1.1.2 OUT 1 VSS 2 SNSK 3 QT1012 AT42QT1012 6 TIME 5 VDD 4 SNS 8-pin UDFN/USON Pin 1 ID 1.2 8 SNS 7 VDD 3 6 TIME 4 5 OUT SNSK 1 N/C 2 N/C VSS QT1012 Pin Descriptions Table 1-1. Pin Listing 6-Pin 8-Pin Name Type Description If Unused, Connect To... 1 5 OUT O(1) Output state. To switched circuit and output polarity selection resistor (Rop) 2 4 VSS P Ground 3 1 SNSK I/O Sense pin. To Cs capacitor and to sense electrode Cs + key 4 8 SNS I/O Sense pin. To Cs capacitor and multiplier configuration resistor (Rm). Rm must be fitted and connected to either VSS or VDD. See Section 3.11.4 for details. Cs 5 7 VDD P Power 6 6 TIME I Timeout configuration pin. Must be connected to either VSS, VDD, OUT or an RC network. See Section 3.11 for details. — 2 N/C — Not connected Do not connect — 3 N/C — Not connected Do not connect © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 5 AT42QT1012 (1) I/O briefly on power-up I Input only O Output only, push-pull I/O Input/output P Ground or power 1.3 Schematics 1.3.1 6-pin SOT23-6 Figure 1-1. Basic Circuit Configuration (active high output, toggle on/off, no auto switch off) Note: bypass capacitor to be tightly wired between VDD and VSS and kept close to pin 5. VDD SENSE ELECTRODE Cby Rs 5 3 VDD SNSK OUT 1 Cs 4 SNS Rop Rm TIME 6 VSS 2 1.3.2 8-pin UDFN/USON Figure 1-2. Basic Circuit Configuration (active high output, toggle on/off, no auto switch off) SENSE ELECTRODE Note: bypass capacitor to be tightly wired between VDD and VSS and kept close to pin 7. VDD Cby Rs 7 1 VDD SNSK OUT 5 Cs 8 SNS Rop 2 Rm 3 N/C N/C TIME 6 VSS 4 For component values in Figure 1-1 and Figure 1-2, check the following sections: • • • • • • Cs capacitor (Cs) – see Section 4.2 on page 20 Sample resistor (Rs) – see Section 4.3 on page 20 Voltage levels – see Section 4.4 on page 20 Output polarity selection resistor (Rop) – see Section 3.9 on page 10 Rm resistor – see Section 3.11.2 on page 11 Bypass capacitor (Cby) – see page 20 © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 6 AT42QT1012 2. Overview of the AT42QT1012 2.1 Introduction The AT42QT1012 (QT1012) is a single key device featuring a touch on/touch off (toggle) output with a programmable auto switch-off capability. The QT1012 is a digital burst mode charge-transfer 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 low cost, noncritical components are required for operation. With its tiny low-cost packages, this device can suit almost any product needing a power switch or other togglemode controlled function, especially power control of small appliances and battery-operated products. A unique “green” feature of the QT1012 is the timeout function, which can turn off power after a time delay. ® Like all QTouch devices, the QT1012 features automatic self-calibration, drift compensation, and spreadspectrum burst modulation in order to provide for the most reliable touch sensing possible. 2.2 Basic Operation Figure 1-1 and Figure 1-2 show basic circuits for the 6-pin and 8-pin devices. The QT1012 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. The QT switches and charge measurement hardware functions are all internal to the QT1012. 2.3 Electrode Drive Figure 2-1 shows the sense electrode connections (SNS, SNSK) for the QT1012. For optimum noise immunity, the electrode should only be connected to the SNSK pin. In all cases the sample capacitor Cs should be much larger than the load capacitance (Cx). Typical values for Cx are 5 – 20 pF while Cs is usually 2.2 – 50 nF. Note: Cx is not a physical discrete component on the PCB, it is the capacitance of the touch electrode and wiring. It is show in Figure 2-1 to aid understanding of the equivalent circuit. Increasing amounts of Cx decrease gain, therefore it is important to limit the amount of load 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. 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. To endure that the correct output mode is selected at power-up, the OUT trace should also be carefully routed. A series resistor, Rs, should be placed in line with SNSK to the electrode to suppress electrostatic discharge (ESD) and electromagnetic compatibility (EMC) effects. © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 7 AT42QT1012 Figure 2-1. Sense Connections VDD SENSE ELECTRODE Cby 5 Rs 3 VDD SNSK OUT 1 Cs 4 SNS Cx TIME 6 VSS 2 2.4 Sensitivity 2.4.1 Introduction The sensitivity on the QT1012 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. 2.4.2 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, or when the device is used as a proximity sensor. 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. The value of Cs also has a dramatic effect on sensitivity, and this can be increased in value with the trade-off of a 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. Ground planes around and under the electrode and its SNSK trace will cause high Cx loading and decrease 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. 2.4.3 Decreasing Sensitivity In some cases the QT1012 may be too sensitive. In this case gain can easily be lowered further by decreasing Cs. 2.5 Moisture Tolerance The presence of water (condensation, sweat, spilt water, and so on) on a sensor can alter the signal values measured and thereby affect the performance of any capacitive device. The moisture tolerance of QTouch devices can be improved by designing the hardware and fine-tuning the firmware following the © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 8 AT42QT1012 recommendations in the application note Atmel AVR3002: Moisture Tolerant QTouch Design (downloadable from www.microchip.com). © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 9 AT42QT1012 3. Operation Specifics 3.1 Acquisition Modes 3.1.1 Introduction The OUT pin of the QT1012 can be configured to be active high or active low. • • 3.1.2 If active high then: – “on” is high – “off” is low If active low then: – “on” is low – “off” is high OUT Pin The QT1012 runs in Low Power (LP) mode. In this mode it sleeps for approximately 80 ms 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). • • If the touch is confirmed, the OUT pin is toggled and the QT1012 returns to LP mode (see figure "Low Power Mode: Touch Confirmed" below). If the touch is not valid then the chip returns to LP mode but the OUT pin remains unchanged (see figure "Low Power Mode: Touch Denied" below). ~80 ms SNSK sleep Key touch Figure 3-1. Low Power Mode: Touch Confirmed (Output in Off Condition) fast detect integrator sleep OUT SNSK ~80 ms Key touch Figure 3-2. Low Power Mode: Touch Denied (Output in Off Condition) Sleep Sleep Fast detect integrator Sleep Sleep OUT 3.2 Detect Threshold The device detects a touch when the signal has crossed a threshold level. The threshold level is fixed at 10 counts. © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 10 AT42QT1012 3.3 Detect Integrator It is desirable to suppress detections generated by electrical noise or from quick brushes with an object. To accomplish this, the QT1012 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 QT1012, the required count is four. The DI can also be viewed as a “consensus filter” that requires four successive detections to create an output. 3.4 Recalibration Timeout If an object or material obstructs the sense electrode the signal may rise enough to create a detection, preventing further operation. To stop this, the sensor includes a timer which monitors detections. If a detection exceeds the timer setting, the sensor performs a full recalibration. This does not toggle the output state but ensures that the QT1012 will detect a new touch correctly. The timer is set to activate this feature after ~60 s. This will vary slightly with Cs. 3.5 Forced Sensor Recalibration The QT1012 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 QT1012 VDD pin directly from another logic gate or a microcontroller port will serve as both power and “forced recalibration”. The source resistance of most CMOS gates and microcontrollers is low enough to provide direct power without a problem. 3.6 Drift Compensation 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. Drift compensation (Figure 3-3) 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 QT1012 drift compensates using a slew-rate limited change to the reference level; the threshold and hysteresis values are slaved to this reference. 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. Figure 3-3. Drift Compensation Signal Hysteresis Threshold Reference Output The QT1012 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 © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 11 AT42QT1012 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. 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. 3.7 Response Time The QT1012 response time is highly dependent on the 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. 3.8 Spread Spectrum The QT1012 modulates its internal oscillator by ±7.5% 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. 3.9 Output Polarity Selection The output (OUT pin) of the QT1012 can be configured to have an active high or active low output by means of the output configuration resistor Rop. The resistor is connected between the output and either Vss or Vdd (see Figure 3-4 and Table 3-1). A typical value for Rop is 100 kΩ. Figure 3-4. Output Polarity (6-pin SOT23) SENSE ELECTRODE VDD Cby 100 nF 5 Rs VDD Rop 3 SNSK Vop Cs 4 SNS OUT Rm 1 TIME 6 VSS 2 © 2017 Microchip Technology Inc. Datasheet DS40001948A-page 12 AT42QT1012 Table 3-1. Output Configuration Name (Vop) Function (Output Polarity) Vss Active high Vdd Active low Note: Some devices, such as Digital Transistors, have an internal biasing network that will naturally pull the OUT pin to its inactive state. If these are being used then the resistor Rop is not required (see Figure 3-5). Figure 3-5. Output Connected to Digital Transistor (6-pin SOT23) SENSE ELECTRODE VDD Cby 100 nF 5 Rs VDD Load 3 SNSK Cs 4 SNS OUT 1 TIME 6 Rm VSS 2 3.10 Output Drive The OUT pin can sink or source up to 2 mA. When a large value of Cs (>20 nF) is used the OUT current should be limited to