User Manual

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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

9524A–AT42–03/09

Summary of content (18 pages)

PAGE 1
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 par
PAGE 2
1. Pinout and Schematic 1.1 Pinout Configuration 5 SNS3 SNS0 17 16 QT1040 7 8 9 15 SNSK3 14 OUT2 13 OUT3 12 OUT1 11 10 OUT0 N/C 6 VDD 4 N/C SNSK0 18 VSS 3 N/C SNS1 19 N/C 2 N/C SNSK1 20 N/C 1 SNSK2 Table 1-1. SNS2 Pin Listing Pin Name Type Function Notes If Unused...
PAGE 3
AT42QT1040 1.2 Schematic Figure 1-1. Typical Circuit NOTES: VUNREG 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. VREG 2) It is important to place all Cs and Rs components physically near to the chip. Creg Creg J1 VDD 1 Follow regulator manufacturer's recommended values for input and output bypass capacitors (Creg). GND Add a 100 nF capacitor close to pin 9.
PAGE 4
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.
PAGE 5
AT42QT1040 The use of AKS is selected by connecting a 1 M resisitor between Vdd and the SNSK0 pin (see Section 4.1 on page 8 for more information). When AKS is disabled, any combinations of keys can enter detect. 2.2.5 Auto 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, non-detections, and sensitivity shifts will follow.
PAGE 6
3. Wiring and Parts 3.1 Cs Sample Capacitors Cs0 – Cs3 are the charge sensing sample capacitors; normally they are identical in nominal value. The optimal Cs values depend on the corresponding keys electrode design, the thickness of the panel and its dielectric constant. Thicker panels require larger values of Cs. Values can be in the range 2.2 nF (for faster operation) to 22 nF (for best sensitivity); typical values are 4.7 nF to 10 nF.
PAGE 7
AT42QT1040 3.5 Power Supply See Section 5.2 on page 13 for the power supply range. If the power supply fluctuates slowly with temperature, the device tracks and compensates for these changes automatically with only minor changes in sensitivity. 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 usual power supply considerations with QT parts apply to the device.
PAGE 8
4. Detailed Operations 4.1 Adjacent Key Suppression The use of AKS is selected by the connection of a 1 M resistor (RAKS resistor) between the SNSK0 pin and either Vdd (AKS mode on) or Vss (AKS mode off). Table 4-1. RAKS Resistor RAKS Connected To... Mode Vdd AKS on Vss AKS off The RAKS resistor should always be connected to either Vdd or Vss and should not be changed during operation of the device. Note: 4.2 Changing the RAKS option will affect the sensitivity of the particular key.
PAGE 9
AT42QT1040 Figure 4-1. ~500 ns Pulse On OUT2 Pin SNS0K OUT2 Power-on/ Reset ~20 ms Pulse on OUT2 SNS0K OUT2 4.3 Speed Selection Speed selection is determined by a 1 M resistor (RFS resistor) connected between SNSK1 and either Vdd (Fast Mode) or Vss (Slow Mode). Table 4-2. RFS Resistor RFS Connected To... Mode Vdd Fast mode Vss Slow mode In Fast Mode, the device sleeps for 16 ms between burst acquisitions. In Slow Mode, the device sleeps for 64 ms between acquisitions.
PAGE 10
4.4 Calibration Calibration is the process by which the sensor chip assesses the background capacitance on each channel. During calibration, a number of samples are taken in quick succession to get a baseline for the channel’s reference value. Calibration takes place ~50 ms after power is applied to the device. Calibration also occurs if the Max On-duration is exceeded or a positive re-calibration occurs. 4.
PAGE 11
AT42QT1040 Table 4-3. Serial Data Output (Continued) Byte Purpose Notes 18 Delta 0 Low Byte 19 Delta 0 High Byte 20 Delta 1 Low Byte 21 Delta 1 High Byte 22 Delta 2 Low Byte 23 Delta 2 High Byte 24 Delta 3 Low Byte 25 Delta 3 High Byte 26 Flags 27 Flags2 Various operational flags Unsigned bytes 28 Status Byte Unsigned byte.
PAGE 12
Figure 4-3. Byte Following Byte (~ 30 µs Period) Figure 4-4. Full Debug Send (30 Bytes) Figure 4-5.
PAGE 13
AT42QT1040 5. Specifications 5.1 Absolute Maximum Specifications Vdd -0.5 to +6.0V Max continuous pin current, any control or drive pin ±10 mA Voltage forced onto any pin -0.5V to (Vdd + 0.5) Volts CAUTION: Stresses beyond those listed under Absolute Maximum Specifications may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied.
PAGE 14
5.4 Timing Specifications Parameter Description TBS Burst duration – 3.5 Fc Burst center frequency – 119 Fm Burst modulation, percentage -7.5 – +7.5 % TPW Burst pulse width – 2 – µs 5.5 Typ Max – Units Notes ms Cx = 5 pF, Cs = 18 nF kHz Power Consumption Vdd (V) AKS Mode (RAKS) Speed (RFS) Power Consumption (µA) 1.
PAGE 15
AT42QT1040 5.6 Mechanical Dimensions D C y Pin 1 ID E SIDE VIEW TOP VIEW A1 A D2 16 17 18 19 20 COMMON DIMENSIONS (Unit of Measure = mm) C0.18 (8X) 15 Pin #1 Chamfer (C 0.3) 14 2 e E2 13 MIN NOM MAX A 0.75 0.80 0.85 A1 0.00 0.02 0.05 b 0.17 0.22 0.27 SYMBOL 1 3 C 12 4 11 5 b 10 9 8 7 K L BOTTOM VIEW 0.3 Ref (4x) 0.152 D 2.90 3.00 3.10 D2 1.40 1.55 1.70 E 2.90 3.00 3.10 E2 1.40 1.55 1.70 – 0.45 – L 0.35 0.40 0.45 K 0.20 – – y 0.
PAGE 16
5.7 Marking Either of the following two markings may be used: Abbreviation of Part Number: Pin 1 ID 140 Code Revision: 1.0 Released AT42QT1040 R1 Program Week Code Number 1-52 Where: A = 1 B = 2 ... Z = 26 then using the underscore A = 27...Z = 52 Pin 1 ID Code Revision: R1 = 1.
PAGE 17
AT42QT1040 5.8 Part Number Part Number AT42QT1040-MMH 5.9 Description 20-pin 3 x 3 mm VQFN RoHS compliant Moisture Sensitivity Level (MSL) MSL Rating MSL1 Peak Body Temperature o 260 C Specifications IPC/JEDEC J-STD-020 Revision History Revision No. History Revision A – March 2009  Initial release for chip revision 1.
PAGE 18
Headquarters International Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: 1(408) 441-0311 Fax: 1(408) 487-2600 Atmel Asia Unit 01-05 & 16, 19/F BEA Tower, Millennium City 5 418 Kwun Tong Road Kwun Tong Kowloon Hong Kong Tel: (852) 2245-6100 Fax: (852) 2722-1369 Atmel Europe Le Krebs 8, Rue Jean-Pierre Timbaud BP 309 78054 Saint-Quentin-enYvelines Cedex France Tel: (33) 1-30-60-70-00 Fax: (33) 1-30-60-71-11 Atmel Japan 9F, Tonetsu Shinkawa Bldg.