AT42QT1040

Features • Number of Keys: – Up to 4 • Discrete Outputs: – 4 discrete outputs indicating individual key touch • Technology: – Patented spread-spectrum charge-transfer (direct mode) • Electrode Design: – Simple self-capacitance style (refer to the Touch Sensors Design Guide) • 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 10 mm glass, 5 mm plastic (electrode size dependent) Key Sensitivity: – Fixed key threshold, sensitivity adjusted via sample capacitor value Adjacent Key Suppression™ – Patented Adjacent Key Suppression™ (AKS™) technology to enable accurate key detection Interface: – Pin-per-key outputs, plus debug mode to observe sensor signals Moisture Tolerance: – Good Power: – 1.8V ~ 5.5V Package: – 20-pin 3 x 3 mm VQFN RoHS compliant Signal Processing: – Self-calibration, auto drift compensation, noise filtering, Adjacent Key Suppression technology Applications: – Mobile, consumer, white goods, toys, kiosks, POS, and so on QTouch™ 4-key Sensor IC AT42QT1040 • • • • • • • • • 9524B–AT42–04/09 1. Pinout and Schematic 1.1 Pinout Configuration SNSK2 20 SNS3 N/C 19 N/C 18 N/C 17 SNS2 SNSK1 SNS1 SNSK0 SNS0 1 2 3 4 5 16 15 14 SNSK3 OUT2 OUT3 OUT1 OUT0 QT1040 13 12 6 N/C 7 N/C 8 VSS 9 VDD 11 10 N/C Table 1-1. Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Pin Listing Name SNS2 SNSK1 SNS1 SNSK0 SNS0 N/C N/C Vss Vdd N/C OUT0 OUT1 OUT3 OUT2 SNSK3 SNS3 N/C N/C N/C SNSK2 Type I/O I/O I/O I/O I/O – – P P – OD OD OD OD I/O I/O – – – I/O Function Sense pin Sense pin and option detect Sense pin Sense pin and option detect Sense pin – – Supply ground Power – Out 0 Out 1 Out 3 Out 2 Sense pin Sense pin – – – Sense pin To Cs2 + key To Cs3 + key To Cs3 Alternative function: Debug CLK Alternative function: Debug DATA Notes To Cs2 To Cs1 and option resistor + key To Cs1 To Cs0 and option resistor + key To Cs0 If Unused... Leave open Connect to option resistor* Leave open Connect to option resistor* Leave open – – – – – Leave open Leave open Leave open Leave open Leave open Leave open – – – Leave open * Option resistor should always be fitted even if channel is unused and Cs capacitor is not fixed. I/O 2 CMOS input and output OD CMOS open drain output P Ground or power AT42QT1040 9524B–AT42–04/09 AT42QT1040 1.2 Schematic Typical Circuit NOTES: VUNREG VREG 1) The central pad on the underside of the VQFN chip is a Vss pin and should be connected to ground. Do not put any other tracks underneath the body of the chip. 2) It is important to place all Cs and Rs components physically near to the chip. Figure 1-1. Creg Creg VDD 1 J1 ON OFF AKS SELECT Follow regulator manufacturer's recommended values for input and output bypass capacitors (Creg). GND Add a 100 nF capacitor close to pin 9. VDD RAKS 2 3 LED3 LED2 LED1 LED0 VDD 1 J2 FAST SLOW RFS 9 2 3 RL0 RL1 RL2 RL3 Example use of output pins 11 12 14 13 VDD OUT0 OUT1 OUT2 OUT3 SPEED SELECT SNSK0 SNS0 4 5 Rs0 Cs0 Key0 J3 5 4 3 2 1 5 4 3 2 1 6 7 10 17 18 19 SNSK1 SNS1 2 3 Rs1 Cs1 Key1 QT1040 SNSK2 N/C N/C N/C N/C N/C VSS N/C SNSK3 SNS3 SNS2 20 1 Rs2 Cs2 Key2 15 16 Rs3 Cs3 Key3 Suggested regulator manufacturers: • Torex (XC6215 series) • Seiko (S817 series) • BCDSemi (AP2121 series) Re Figure 1-1 check the following sections for component values: • Section 3.1 on page 6: Cs capacitors (Cs0 – Cs3) • Section 3.5 on page 7: Voltage levels • Section 3.3 on page 6: LED traces 8 3 9524B–AT42–04/09 2. Overview of the AT42QT1040 2.1 Introduction The AT42QT1040 (QT1040) is a digital burst mode charge-transfer (QT™) capacitive sensor driver designed for touch-key applications. The device can sense from one to four keys; one to three keys can be disabled by not installing their respective sense capacitors. Any of the four channels can be disabled in this way. The device includes all signal processing functions necessary to provide stable sensing under a wide variety of changing conditions, and the outputs are fully debounced. Only a few external parts are required for operation. The QT1040 modulates its bursts in a spread-spectrum fashion in order to heavily suppress the effects of external noise, and to suppress RF emissions. 2.2 2.2.1 Signal Processing Detect Threshold The internal signal threshold level is fixed at 10 counts of change with respect to the internal reference level. This in turn adjusts itself slowly in accordance with the drift compensation mechanism. See Section 3.1 on page 6 for details on how to adjust each key’s sensitivity. When going out of detect there is a hysteresis element to the detection. The signal threshold must drop below 8 counts of change with respect to the internal reference level to register as untouched. 2.2.2 Detection Integrator The device features a detection integration mechanism, which acts to confirm a detection in a robust fashion. A per-key counter is incremented each time the key has exceeded its threshold, and a key is only finally declared to be touched when this counter reaches a fixed limit of 5. In other words, the device has to exceed its threshold, and stay there for 5 acquisitions in succession without going below the threshold level, before the key is declared to be touched. Burst Length Limitations Burst length is the number of times the charge transfer process is performed on a given channel; that is, the number of pulses it takes to measure the key’s capacitance. The maximum burst length is 2048 pulses. The recommended design is to use a capacitor that gives a signal of