Peripherals ICs

The mXT224 uses a unique charge-transfer acquisition engine to implement the QMatrix capacitive sensing method patented by . 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 touch screen 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 touch screen mutual capacitances spanning 0.5 pF to 5 pF, allowing great flexibility for use with 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, micro sequencer coprocessors. These combine to allow the signal acquisition, preprocessing, post processing 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.

• maXTouch™ Touch screen
  • True 12-bit multi-touch with independent XY tracking for up to 10 concurrent touches in real time with touch size reporting
  • Up to 4.3 inch diagonal screen size supported with 10 mm “pinch” separation
  • Up to 10.1 inch support with correspondingly wider “pinch”
• Number of Channels
  • Up to 224 (subject to other configuration limitations)
  • Electrode grid configurations up to 20 X by 10 Y lines supported (subject to 30 total pins and a maximum of 14 Y lines)
• maXTouch Touch Key Support
  • Up to 32 channels can be allocated as fixed keys (subject to other configurations)
• Zero Additional Part Count
  • 16 X by 14 Y matrix (224 channels) implementable with power bypass capacitors only
• Signal Processing
  • Advanced digital filtering using both hardware engine and firmware
  • Self-calibration
  • Auto drift compensation
  • Adjacent Key Suppression® (AKS™) technology
  • Grip and face suppression
  • Reports one-touch and two-touch gestures
  • Down-scaling and clipping support to match LCD resolution
  • Ultra-fast start-up and calibration for best user experience
  • Supports axis flipping and axis switch-over for portrait and landscape modes
• Scan Speed
  • Maximum single touch >250Hz, subject to configuration
  • Configurable to allow power/speed optimization
  • Programmable timeout for automatic transition from active to idle states
• Response Times
  • Initial latency <10 ms for first touch from idle, subject to configuration
• Sensors
  • Works with PET or glass sensors
  • Works with all proprietary sensor patterns recommended
  • Works with passive stylus
• Panel Thickness
  • Glass up to 3 mm, screen size dependent
  • Plastic up to 1.5 mm, screen size dependent
• Interface
  • I²C-compatible slave mode 400 kHz
• Dual-rail Power
  • Interface 1.8V to 3.3V nominal, analog 2.7V to 3.3V nominal
• Power Consumption
  • Idle 80Hz: <1.8 mW, subject to configuration
  • One Touch Active 80Hz: 3.9 mW, subject to configuration
  • Sleep: 4.5 µW
• Package
  • 49-ball UFBGA 5 x 5 x 0.6 mm, 0.65 ball pitch
  • 49-ball VFBGA 5 x 5 x 1 mm, 0.65 ball pitch
  • 48-pin QFN 6 x 6 x 0.6 mm, 0.4 mm pin pitch