MAX11800_10 Datasheet, PDF (16/57 Pages) Maxim Integrated Products – Low-Power, Ultra-Small Resistive Touch-Screen Controllers with I2C/SPI Interface

Low-Power, Ultra-Small Resistive Touch-Screen
Controllers with I²C/SPI Interface
Detailed Description
The MAX11800–MAX11803 contain standard features
found in a typical resistive touch-screen controller as
well as advanced features. Standard features included
in the MAX11800–MAX11803 are:
• 4-wire touch-screen interface
• X/Y coordinate measurement
• Touch pressure measurement
• Direct conversion operation—requires direct AP
involvement
• Single commands—AP initiates all activity one com-
mand at a time
• Ratiometric measurement
• 12-bit SAR ADC
• Single 1.8V to 3.3V supply
• Programmable touch-detect pullup—50kΩ or
100kΩ
• Auto power-down control for low-power operation
• 400kHz I²C interface (MAX11801/MAX11803)
Advanced features found in the MAX11800–MAX11803
include:
• Autonomous conversion operation—minimal AP
involvement (MAX11800/MAX11801)
• On-chip FIFO—buffers up to 16 consecutive mea-
surements (MAX11800/MAX11801)
• Data tagging—records measurement and touch-
event information
• Filtering—reduces noise using straight or median
averaging
• Aperture mode—provides spatial filtering
(MAX11800/MAX11801)
• Combined commands—multiple operations per-
formed with a single AP command
• Digital processing to reduce serial bus activity
• Digital processing to reduce interrupt generation
• User-programmable acquisition modes
• Programmable interrupt output drive
• 25MHz SPI interface (MAX11800/MAX11802)
The MAX11800–MAX11803 operate in one of two top-
level modes: direct conversion mode (DCM) or
autonomous conversion mode (ACM). Direct conversion
mode requires the AP to initiate all activity to and from
the MAX11800–MAX11803. DCM is the operating mode
that most standard resistive touch-screen controllers
use. ACM allows the MAX11800/MAX11801 to perform
measurements automatically and inform the AP when
they are complete, reducing data transfers on the serial
bus as well as generating fewer interrupt requests. The
MAX11800/MAX11801 can operate in the standard
mode that is familiar to users, or in the advanced fea-
tures mode to provide additional flexibility.
Both DCM and ACM support averaging, data tagging,
and combined commands. Certain commands and
operations are only available in DCM, while others are
only available in ACM. See Figures 3a and 3b and
Table 2 for details.
Position Measurements
Position measurements determine either the X or Y
coordinates of the point of contact on the panel sensor.
Allow adequate time for the panel to settle when switch-
ing between X and Y measurements. Figure 4 shows
the physical setup of the panel when performing posi-
tion measurements.
The element R_TOUCH represents the resistance between
the X and Y planes of the panel sensor. R_TOUCH does
not contribute to the error when performing position mea-
surements. R_TOUCH affects the panel settling time
required between each valid measurement.
The panel end-to-end resistance in the direction of
measurement determines the power applied across the
panel. The panel dissipates power in the X elements
when performing an X direction measurement and dis-
sipates power in the Y elements when performing a Y
direction measurement.
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