ak4184 AKM Semiconductor, Inc., ak4184 Datasheet - Page 11

• Manufacturer Part Number: ak4184
• Description: Tsc With Keypad Scanner And Gpio Expander
• Manufacturer: AKM Semiconductor, Inc.

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Touch screen pen pressure can be derived from the measurement of the contact resistor between two plates. The
contact resistance depends on the size of the depressed area and the pressure. The area of the spot is proportional to
the contact resistance. This resistance (Rtouch) can be calculated using two different methods.
The first method is when the total resistance of the X-plate sheet is already known. The resistance, Rtouch, is
calculated from the results of three A/D conversions: X-position, Z1-Position, and Z2-Position, using the following
formula:
Rtouch = (Rxplate) * (Xposition/4096) * [(Z2/Z1) – 1]
The second method is when both the resistances of the X-plate and Y-plate are known. The resistance, Rtouch, is
calculated from the results of three A/D conversions: X-position, Y-Position, and Z1-Position, using the following
formula:
Rtouch = (Rxplate*Xposition/4096)*[(4096/Z1) – 1] – Ryplate*[1 – (Yposition/4096)]
MS0603-E-00
YP-Driver SW ON
XN-Driver SW ON
ADC
Pen Pressure Measurement
VREF+
VREF-
a)
Z1-Position Measurement
AVDD
AIN+
AIN-
YP
XP
XN
YN
Figure 4. Pen Pressure Measurements
Rtouch
11
XN-Driver SW ON
YP-Driver SW ON
ADC
VREF+
VREF-
b)
AVDD
Z2-Position Measurement
AIN+
AIN-
YP
XP
XN
YN
2007/04
Rtouch
[AK4184]