at42qt2100 ATMEL Corporation, at42qt2100 Datasheet - Page 5

• Manufacturer Part Number: at42qt2100
• Description: Qtouch Touch Sensor Ic
• Manufacturer: ATMEL Corporation

2. Overview
2.1
2.2
9554CX–AT42–11/11
Burst Operation
Introduction
The AT42QT2100 (QT2100) is an easy to use sensor IC based on Atmel’s patented
charge-transfer (“QT”) principles for robust operation and ease of design. This device has
many advanced features which provide for reliable, trouble-free operation over the life of the
product. In particular the QT2100 features advanced self-calibration, drift compensation, and
fast thermal tracking. The QT2100 can tolerate some fluctuations in the power supply, and in
many applications will not require a dedicated voltage regulator.
The QT2100 is capable of detecting near-proximity or touch on up to seven electrodes and a
slider/wheel. It allows electrodes to project sense fields through any dielectric such as glass or
plastic. These electrodes are laid out as a scroller (slider or wheel), plus seven additional
independent keys.
Each key channel can be tuned for a unique sensitivity level by simply changing a
corresponding external Cs capacitor, whereas the slider/wheel's sensitivity can be changed
dynamically through SPI commands. Any number of key channels can be optimized for
operation as hand proximity sensors by increasing the sensitivity for the corresponding
channel.
Note:
The slider/wheel uses a simple, inexpensive sensing element between three connection
points. The QT2100 can report a single rapid touch anywhere along the sense elements, or it
can track a finger moving along the slider/wheel's surface in real time.
By using the charge-transfer principle, this device delivers a level of performance clearly
superior to older technologies yet is highly cost-effective. Spread-spectrum burst technology
provides superior noise rejection.
The device operates in burst mode. Each key is acquired using a burst of charge-transfer
sensing pulses whose count varies depending on the value of the sense capacitors
(CsA1 to CSA3 and CsB1 to CSB7) and the load capacitance Cx (finger touch capacitance
and circuit stray capacitance).
The channels’ signals are acquired using three successive bursts of pulses:
where B1 to B7 are the individual key sensors and A1 to A3 are the slider/wheel sensors.
Bursts operate in sequence and occur one after the other with minimum delay. During each
burst the DRDY pin is held low. The groups are separated by an interval of 500 µs when
DRDY is held high to signal an appropriate time for SPI communications. Communications
may be carried out at any time, however, regardless of the state of the DRDY pin.
Burst 1: B1, B2, B3
Burst 2: B4, B5, B6, B7
Burst 3: A1, A2, A3
There are special circumstances if using AKS (see
Section 4.3.6 on page
AT42QT2100
15).
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