MXT224 Datasheet, PDF (9/12 Pages) ATMEL Corporation – maXTouch 224-channel Touchscreen Sensor IC

mXT224
2. Overview of the mXT224
2.1 Introduction
The mXT224 (AT42QT602240) uses a unique charge-transfer acquisition engine to implement
the QMatrix^™ capacitive sensing method patented by Atmel^®. This allows the measurement of
up to 224 mutual capacitance nodes in under 1 ms. Coupled with a state-of-the-art XMEGA^™
CPU, the entire touchscreen sensing solution can measure, classify and track a single finger
touch every 4 ms if required.
The acquisition engine uses an optimal measurement approach to ensure almost complete
immunity from parasitic capacitance on the receiver inputs (Y lines). The engine includes
sufficient dynamic range to cope with touchscreen mutual capacitances spanning 0.5 pF to 5 pF,
allowing great flexibility for use with Atmel’s proprietary ITO pattern designs. One and two layer
ITO sensors are possible using glass or PET substrates.
The main AVR^® XMEGA CPU has, under its control, two powerful, yet low power,
microsequencer coprocessors. These combine to allow the signal acquisition, preprocessing,
postprocessing and housekeeping to be partitioned in an efficient and flexible way. This gives
ample scope for sensing algorithms, touch tracking or advanced shape-based filtering. An
in-circuit reflash can be performed over the chip’s hardware-driven two-wire interface
(I²C-compatible).
Overall, the mXT224 represents a step improvement over competing technologies, providing a
near optimal mix of low power, small size and low part count, while offering unrivalled true
multitouch performance.
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9530BS–AT42–10/09