Revision V1.5/June 2010

©2010 Semtech Corp.

SX8652

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Page 13

ADVANCED COMMUNICATIONS & SENSING

DATASHEET

15kV ESD Low Power 4-Wire / 5-Wire Resistive

Touchscreen Controller with SPI Interface

4. 4-wire Touch Screen Detailed Description

4.1. Touch Screen Operation

A 4-wire resistive touch screen consists of two (resistive) conductive sheets separated by an insulator when not pressed.

Each sheet is connected through 2 electrodes at the border of the sheet (Figure 12). When a pressure is applied on the top

sheet, a connection with the lower sheet is established. Figure 13 shows how the Y coordinate can be measured. The

electrode plates are connected through terminals X+, X- and Y+, Y- to an analog to digital converter (ADC) and a reference

voltage. The resistance between the terminals X+ and X- is defined by Rxtot. Rxtot will be split in 2 resistors, R1 and R2, in

case the screen is touched. The resistance between the terminals Y+ and Y- is represented by R3 and R4. The connection

Figure 12. 4-wire Touch Screen

Figure 13. Touch Screen Operation ordinate measurement (Y)

X-

Y+

Y-

X+

top conductive sheet

bottom conductive sheet

electrodes

electrodes

X-

X+

Y-

Y+

R3

R4

R2

R1

+

-

ADC

Ypos

Vref

+

-