www.ti.com

R

TOUCH

+

R

X−plate

4096

4096

Z

1

Y

Position

4096

(2)

X-Position

MeasureX-Position

MeasureZ -Position

1

Touch

X+

Y+

Z -Position

1

Touch

X+

Y+

MeasureZ -Position

2

Z -Position

2

Touch

X+

Y+

TSC2007

SBAS405 – MARCH 2007

OVERVIEW (continued)

The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and

Y-Position, and Z

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 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 will be in error. 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 will cause an additional settling time requirement

when the panel is touched. The setlling time will typically show up as gain error.

To solve this problem, the TSC2007 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 touch screen interface can measure position (X,Y) and pressure (Z).

14

Submit Documentation Feedback