MAX11803 Maxim Integrated Products, MAX11803 Datasheet - Page 21

• Manufacturer Part Number: MAX11803
• Description: (MAX11800 - MAX11803) Ultra-Small Resistive Touch-Screen Controllers
• Manufacturer: Maxim Integrated Products

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readback. The characteristics of the return to TDM and
the timing of the decision are configurable through the
touch-detect pullup timing configuration register (0x07).
Program the MAX11800–MAX11803 in the context of
the application to maximize power efficiency and
achieve the desired scan throughput.
PUR is a fast pullup mode, which uses the main X+
switch in parallel with the resistive pullup to quickly slew
the panel capacitance. PUF uses only the touch-detect
pullup resistor, R
tion as TDM, but are timed so that the panel can settle
after completing measurements and before rendering
any decisions on the touch status of the panel.
Use the optional PUR mode to reduce the time to tag
data by momentarily placing the panel in a low-imped-
ance (< 10Ω) pullup mode instead of using the avail-
able 50kΩ/100kΩ touch-detection pullup resistors. This
operation forces the monitored TSC input high during
the PUR interval. Once the PUR interval expires, a PUF
interval must be allowed so that the panel can recover
and pull the TSC input low in case a touch is present.
The purpose of the PUR mode is to reduce the time
required to determine touch status by avoiding long
pullup time constants caused by high-capacitance
touch panels and the high-impedance on-chip pullup
resistors (R
intervals, the current through the low-impedance pullup
(XPSW) and panel combination is significantly higher
than that observed in the PUF mode. The durations in
the PUR mode must be matched to the panel charac-
Figure 6. Touch-Detection Circuitry
Low-Power, Ultra-Small Resistive Touch-Screen
X-
Y+
PANEL
TD
). When a touch is present during PUR
TD
______________________________________________________________________________________
. PUR and PUF serve the same func-
YMSW
XPSW
X+
Y-
V
DD
PUR
PUR, PUF, TDM
RTD
TSW
PSW
Controllers with I
RTD
PUR, PUF, TDM
TDRSEL
PUR and PUF
MAX11800–
MAX11803
MAX11801 LOGIC)
(TO MAX11800/
TOUCH
teristics and the desired scan throughput rates to mini-
mize power dissipation.
While use of the PUR mode is optional, the PUF period
is required for all applications. The PUF interval allows
the panel to resettle following scan or optional PUR
intervals. When a touch is not present, the panel capac-
itance settles toward V
switch and a portion of the panel resistance (with the
optional PUR mode disabled). When a touch is present,
the panel capacitance settles toward ground through a
portion of the panel resistance, ideally significantly
lower than the selected pullup impedance, R
enough recovery time for settling through the panel
when using a PUR mode. Figure 7 illustrates the touch-
detection operations.
Once the PUF period expires, the preceding measure-
ment data is tagged and made available for readback.
The MAX11800–MAX11803 transition to an appropriate
mode depending on the conversion and interrupt mode
selected.
The MAX11800–MAX11803 contain a programmable
averaging filter. When enabled, this feature allows col-
lecting 4, 8, or 16 consecutive samples for each mea-
surement type requested. The number of the samples
for each measurement type is controlled by configura-
tion register 0x03. The AUX depth input is selected in
configuration register 0x0A. Averaging can be
assigned to each measurement type. For example, X
and Y measurements can use an average of 16 sam-
ples, while Z measurements can use one or four sam-
ples to save power.
The MAX11800–MAX11803 can be configured to per-
form one of two statistical operations. One option is a
median averaging filter (MAF). The MAF first removes
outliers before taking the average of the remaining
sample set. The second is a straight averaging filter
(SAF), which takes the average of the entire sample set.
Averaging modes are supported in both direct and
autonomous conversion modes. Both filter types and
position/pressure averaging are controlled by configu-
ration register 0x0B. This allows switching between
direct and autonomous modes using a single configu-
ration write through the serial interface (SIF). Table 4
presents the details of the median averaging operations
of the MAX11800–MAX11803.
2
C/SPI Interface
Averaging Modes and Options
Features Common to the
DD
MAX11800–MAX11803
through the internal pullup
Idle Modes
TD
. Allow
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