SX8652ICSTRT Semtech, SX8652ICSTRT Datasheet - Page 14

• Manufacturer Part Number: SX8652ICSTRT
• Description: 4/5-wire Resistive Touch Screen Controller (SPI)
• Manufacturer: Semtech

4.2. Coordinates Measurement
The top resistive sheet (Y) 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 (X) biased to create a voltage divider by
R1 and R2, while the voltage on the top sheet is measured through R3. Figure 14 shows the coordinates measurement
setup. The resistance R
area of the X and Y resistive sheet and varies with the applied pressure.
The X and Y position are found by:
4.3. Pressure Measurement
The pressure measurement consists of two additional setups: z1 and z2 (see Figure 15).
Revision V1.6/July 2010
©2010 Semtech Corp.
ADVANCED COMMUNICATIONS & SENSING
Ypos
Vref
+
-
Figure 14. Ordinate (Y) and abscissa (X) coordinates measurement setup
R2
R2
R1
R1
T
X+
X+
X-
X-
is the resistance obtained when a pressure is applied on the screen. R
Figure 15. z1 and z2 pressure measurement setup
R
R
T
T
Xpos
Y-
Y+
Y-
Y+
=
R3
R4
R3
R4
4095
Vref
z1
+
------------------- -
R1
-
15kV ESD Low Power 4-Wire / 5-Wire Resistive
R2
+
Page 14
R2
Touchscreen Controller with SPI Interface
Ypos
Vref
Vref
+
+
-
-
=
4095
z2
R2
R1
X+
X-
R2
R1
------------------- -
R3
X+
X-
R4
+
R4
R
T
R
T
T
is created by the contact
Y-
Y+
R3
R4
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DATASHEET
Y-
Y+
SX8652
R3
R4
Xpos