TSC2004 datasheet(15/62 Pages) TI2

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TOUCH

+ RX−plate @

Postition

4096

* 1

(1)

TOUCH

X−plate

@ XPostition

4096

*1 *RY−plate @ 1*

Position

4096

(2)

X-Position

MeasureX-Position

MeasureZ -Position

Touch

X+

Y+

Z -Position

Touch

X+

Y+

MeasureZ -Position

Z -Position

Touch

X+

Y+

TSC2004

SBAS408E – JUNE 2007 – REVISED MARCH 2008

The A/D converter converts the voltage measured at the point where the panel is touched. A measurement of the

Y position of the pointing device is made by connecting the X+ input to a data converter chip, turning on the Y+

and Y– drivers, and digitizing the voltage seen at the X+ input. The voltage measured is determined by the

voltage divider developed at the point of touch. For this measurement, the horizontal panel resistance in the X+

lead does not affect the conversion because of the high input impedance of the A/D converter.

Voltage is then applied to the other axis, and the A/D converter converts the voltage representing the X position

on the screen. This process provides the X and Y coordinates to the associated processor.

Measuring touch pressure (Z) can also be done with the TSC2004. To determine pen or finger touch, the

pressure of the touch must be determined. Generally, it is not necessary to have very high performance for this

test; therefore, 10-bit resolution mode is recommended (however, data sheet calculations are shown using the

12-bit resolution mode). There are several different ways of performing this measurement. The TSC2004

supports two methods. The first method requires knowing the X-plate resistance, the measurement of the

X-Position, and two additional cross panel measurements (Z2 and Z1) of the touch screen (see Figure 26).

Equation 1 calculates the touch resistance:

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:

Figure 26. Pressure Measurement

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