SX8654ICSTRT SEMTECH [Semtech Corporation], SX8654ICSTRT Datasheet - Page 15

• Manufacturer Part Number: SX8654ICSTRT
• Description: Haptics Enabled 4/5-Wire Resistive Touchscreen Controller with Proximity Sensing
• Manufacturer: SEMTECH [Semtech Corporation]

ADVANCED COMMUNICATIONS & SENSING
4.2.2
5-wire touchscreen coordinates measurement is performed similarly by biasing opposite corner pairs in either X
or Y directions on the lower panel, and converting the voltage appearing on the wiper panel with the ADC.
The X and Y positions output by the ADC correspond to the formulas below:
4095 corresponds to the max output value of the ADC (12 bits => 2
For example, a touch in the center of the screen will output (Xpos, Ypos) = ~(2048, 2048)
4.3
The pressure measurement consists in extracting the touch resistance R
illustrated below. The smaller R
and hence the more “pressure” there is by the user.
The z1 and z2 values output by the ADC correspond to the formulas below:
The X and Y total sheet resistance (Rxtot = R1+R2, Rytot = R3+R4) are known from the touch screen supplier.
R4 is proportional to the Y coordinate and its value is given by the total Y plate resistance Rytot multiplied by the
fraction of the Y position over the full coordinate range.
Rev 1 – 25
Pressure Measurement (4-wire only)
5-wire Touchscreen
th
July 2011
Figure 13 – 5-wire Touchscreen Coordinates Measurement
z1
T
, the more common touched surface there is between top and bottom plates
Xpos
=
4095
Figure 14 – Pressure Measurement
=
4095
--------------------------------- -
R1 R4
+
R4
-------------------- -
R1
R2
+
+
Resistive Touchscreen Controller with Proximity Sensing
R
R2
T
15
Y pos
z2
=
=
4095
4095
SX8654/SX8655/SX8656
12
----------------- - --------------- -
R1
– 1).
-------------------- -
R3 R4
R4
+
R4
R4 R
+
+
T
Rt
via two additional setups z1 and z2
+
T
Haptics Enabled 4/5-Wire
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