MAX11800–MAX11803
Low-Power, Ultra-Small Resistive Touch-Screen
Controllers with I2C/SPI Interface
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Detailed Description
The MAX11800–MAX11803 contain standard features
found in a typical resistive touch-screen controller as
well as advanced features found only on Maxim touch-
screen controllers. 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
command at a time
Ratiometric measurement
12-bit SAR ADC
Single 1.7V to 3.6V supply
Programmable touch-detect pullup—50kΩ or
100k
Ω
Auto power-down control for low-power operation
Advanced features found in the MAX11800/MAX11801
include:
Autonomous conversion operation—minimal AP
involvement
On-chip FIFO—buffers up to 16 consecutive mea-
surements
Data tagging—records measurement and touch-
event information
Filtering—reduces noise using straight or median
averaging
Aperture mode—provides spatial filtering
Combined commands—multiple operations per-
formed with a single AP command
User-programmable acquisition modes
Programmable interrupt output drive
Advanced features found in the MAX11802/MAX11803
include:
Data tagging—records measurement and touch
event information
Filtering—reduces noise using straight or median
averaging
Combined commands—multiple operations per-
formed with a single AP command
User-programmable acquisition modes
Programmable interrupt output drive
The MAX11800/MAX11801 operate in one of two top-
level modes: direct conversion mode (DCM) or
autonomous conversion mode (ACM). Direct conver-
sion mode requires the AP to initiate all activity to and
from the MAX11800/MAX11801. DCM is the operating
mode that most standard resistive touch-screen con-
trollers 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 MAX11802/MAX11803 operate in DCM
only. DCM requires the AP to initiate all activity to and
from the MAX11802/MAX11803. DCM is the operating
mode that most standard resistive touch-screen con-
trollers use.
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 RTOUCH represents the resistance between
the X and Y planes of the panel sensor. RTOUCH does
not contribute to the error when performing position
measurements. RTOUCH 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.