Datasheet

R
TOUCH
+
R
X−plate
@ X
Postition
4096
ǒ
4096
Z
1
*1
Ǔ
*R
Y−plate
@
ǒ
1*
Y
Position
4096
Ǔ
(2)
X-Position
MeasureX-Position
MeasureZ -Position
1
Touch
X+ Y+
X
-
Y-
Z -Position
1
Touch
X+
Y+
Y
-X-
MeasureZ -Position
2
Z -Position
2
Touch
X+
Y+
Y
-X-
TSC2008
www.ti.com
.......................................................................................................................................................... SBAS406B JUNE 2008 REVISED MARCH 2009
The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and
Y-Position, and Z
1
. Equation 2 also calculates the touch resistance:
Figure 22. 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 will often overshoot and then slowly settle down (decay) 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. The TSC2008 has a built-in noise filter
(see the Preprocessing section). These capacitors can be reduced to minimal value or not installed.
The TSC2008 touch screen interface can measure position (X,Y) and pressure (Z).
Copyright © 2008 2009, Texas Instruments Incorporated Submit Documentation Feedback 13
Product Folder Link(s): TSC2008