sx8652 Semtech Corporation, sx8652 Datasheet - Page 16

• Manufacturer Part Number: sx8652
• Description: 15kv Esd Low Power 4-wire / 5-wire Resistive Touchscreen Controller With Spi Interface
• Manufacturer: Semtech Corporation

5. 5-wire Touch Screen Detailed Description
5.1. Touch Screen Operation
A 5-wire resistive touch screen consists of two (resistive) conductive sheets separated by an insulator when not pressed.
4 wires are connected on the 4 corners of the bottom conductive sheet. They are referred as Top Left, Top Right, Bottom
Left, Bottom Right.
The fifth wire is used for sensing the electrode voltage and is referred as the wiper. It is embedded in the top sheet.
Higher reliability and better endurance are the advantages of 5-wire touchscreen.
On the other hand, 5-wire touchscreen does not permit pressure measurement.
5.2. Coordinates Measurement
The top resistive sheet is biased with a voltage source. Resistors R3 and R4 determine a voltage divider proportional to the
Y position of the contact point. Since the converter has a high input impedance, no current flows through R1 so that the
voltage X+ at the converter input is given by the voltage divider created by R3 and R4.
The X coordinate is measured in a similar fashion with the bottom resistive sheet biased to create a voltage divider by R1
and R2, while the voltage on the top sheet is measured through R3. Figure 18 shows the coordinates measurement setup.
The X and Y position are found by:
Revision V1.6/July 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
Y p o s
bottom conductive sheet
electrodes
wiper
W i p e r
Figure 18. Ordinate (Y) and abscissa (X) coordinates measurement setup
T L
B L
Xpos
TL
T R
B R
R 4
R 3
=
Figure 17. 5-wire touchscreen
V r e f
4095
BL
+
-
------------------- -
R1
15kV ESD Low Power 4-Wire / 5-Wire Resistive
R2
+
Page 16
R2
TR
Touchscreen Controller with SPI Interface
Ypos
top conductive sheet
BR
V r e f
+
-
=
Linearisation pattern
4095
R 1
R 2
B R
B L
------------------- -
R3
R4
electrodes
+
T R
T L
R4
W ip e r
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SX8652
X p o s