Datasheet

10
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TSC2000
SBAS257
FIGURE 4. Simplified Diagram of the Analog Input Section.
In some applications, external capacitors may be required
across the touch screen for filtering noise picked up by the
touch screen; i.e., noise generated by the LCD panel or
back-light circuitry. The value of these capacitors will provide
a low-pass filter to reduce the noise, but will cause an
additional settling time requirement when the panel is touched.
Several solutions to this problem are available in the TSC2000.
A programmable delay time is available which sets the delay
between turning the drivers on and making a conversion.
This is referred to as the Panel Voltage Stabilization time,
and is used in some of the modes available in the TSC2000.
In other modes, the TSC2000 can be commanded to turn on
the drivers only without performing a conversion. Time can
then be allowed before a conversion is started.
The TSC2000 touch screen interface can measure position (X
and Y) and pressure (Z). Determination of these coordinates
is possible under three different modes of the A/D converter:
conversion controlled by the TSC2000, initiated by detection of
a touch; conversion controlled by the TSC2000, initiated by the
host responding to the
PENIRQ signal; or conversion com-
pletely controlled by the host processor.
A/D CONVERTER
The analog inputs of the TSC2000 are shown in Figure 4. The
analog inputs (X, Y, and Z touch panel coordinates, battery
voltage monitors, chip temperature, and auxiliary inputs) are
provided via a multiplexer to the Successive Approximation
Register (SAR) A/D converter. The A/D converter architecture
is based on capacitive redistribution architecture which inher-
ently includes a sample-and-hold function.
Converter
–REF
+REF
+IN
–IN
V
BAT1
AUX1
Battery
On
AUX2
GND
2.5V
Reference
Ref ON/OFF
X+
X–
+V
DD
TEMP1
Y+
Y–
V
REF
TEMP0
7.5kΩ
V
BAT2
2.5kΩ
2.5kΩ
Battery
On
2.5kΩ