SX8650 Datasheet, PDF (22/56 Pages) Semtech Corporation – World’s Lowest Power & Smallest Footprint 4-wire Resistive Touchscreen Controller with 15kV ESD

SX8650
World’s Lowest Power & Smallest Footprint 4-wire
Resistive Touchscreen Controller with 15kV ESD
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
4. Detailed Description
4.1. Touch Screen Operation
A 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 18). When a pressure is applied on the top
sheet, a connection with the lower sheet is established. Figure 19 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
between the top and bottom sheet is represented by the touch resistance (R_T).
Y+
top conductive sheet
electrodes
+
X-
Vr-ef
Y-
X+
electrodes
X-
bottom conductive sheet
Figure 18. Touch Screen
Y+
R3
R2
R_{T R1 X+}
R4
+
ADC
-
Ypos
Y-
Figure 19. Touch Screen Operation ordinate measurement (Y)
ACS Revision V2.15/October 2009
©2009 Semtech Corp.
Page 21
www.semtech.com