TSC2007-Q1
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SBAS545 –SEPTEMBER 2011
The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-position and
Y-position, and Z1. Equation 2 also calculates the touch resistance:
RX−plate @ XPosition
YPosition
4096
4096
Z1
ǒ Ǔ ǒ Ǔ
RTOUCH
+
*1 *RY−plate @ 1*
4096
(2)
Measure X-Position
X+
Y+
Touch
X-Position
X-
Y-
Measure Z1-Position
Y+
X+
Touch
Z1-Position
X-
Y-
Y+
X+
Touch
Z2-Position
X-
Y-
Measure Z2-Position
Figure 21. Pressure Measurement
When the touch panel is pressed or touched and the drivers to the panel are turned on, the voltage across the
touch panel often overshoots and then slowly settles down (decays) to a stable dc value. This effect is a result of
mechanical bouncing caused by vibration of the top layer sheet of the touch panel when the panel is pressed.
This settling time must be accounted for, or else the converted value is incorrect. Therefore, a delay must be
introduced between the time the driver for a particular measurement is turned on, and the time a measurement is
made.
In some applications, external capacitors may be required across the touch screen for filtering noise picked up by
the touch screen (for example, noise generated by the LCD panel or back-light circuitry). The value of these
capacitors provides a low-pass filter to reduce the noise, but creates an additional settling time requirement when
the panel is touched. The settling time typically shows up as gain error.
To solve this problem, the TSC2007-Q1 can be commanded to turn on the drivers only, without performing a
conversion. Time can then be allowed to perform a conversion before the command is issued.
The TSC2007-Q1 touch screen interface can measure position (X,Y) and pressure (Z).
Copyright © 2011, Texas Instruments Incorporated
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