Datasheet

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-
TSC2006
www.ti.com ......................................................................................................................................................... SBAS415C – JUNE 2007 – REVISED MARCH 2009
Figure 25. 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 TSC2006 offers several solutions to this problem. A programmable delay time is available that sets the delay
between turning the drivers on and making a conversion. This delay is referred to as the panel voltage
stabilization time, and is used in some of the TSC2006 modes. In other modes, the TSC2006 can be
commanded to turn on the drivers only without performing a conversion. Time can then be allowed before the
command is issued to perform a conversion.
The TSC2006 touch screen interface can measure position (X,Y) and pressure (Z). Determination of these
coordinates is possible under three different modes of the A/D converter:
• TSMode1 — conversion controlled by the TSC2006 initiated by TSC;
• TSMode2 — conversion controlled by the TSC2006 initiated by the host responding to the PENIRQ signal; or
• TSMode3 — conversion completely controlled by the host processor.
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