ak4183 AKM Semiconductor, Inc., ak4183 Datasheet - Page 7

• Manufacturer Part Number: ak4183
• Description: I 2 C Touch Screen Controller
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
The differential mode position detection is typically more accurate than the single-ended mode. As the full scale of single-ended
mode is fixed to the VCC, input voltage may exceed the full-scale reference voltage. This problem does not occur in differential
mode. In addition to this, the differential mode is less influenced by power supply voltage variation due to the ratio-metric
measurement.
The 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 that when the total resistance of the X-plate sheet is already known. The resistance, Rtouch, is calculated from
the results of three conversions, X-position, Z1-Position, and Z2-Position, and then using the following formula:
Rtouch = (Rxplate) * (Xposition/4096) * [(Z2/Z1) – 1]
The second method is that when both the resistances of the X-plate and Y-plate are known. The resistance, Rtouch, is calculated
from the results of three conversions, X-position, Y-Position, and Z1-Position, and then using the following formula:
Rtouch = (Rxplate*Xposition/4096)*[(4096/Z1) – 1] – Ryplate*[1 – (Yposition/4096)]
MS0500-E-00
YP-Driver SW ON
ADC
XN-Driver SWON
The Pen Pressure Measurement
VREF+
VREF-
a)
Z1-Position Measurement
VCC
AIN+
AIN-
YP
XP
XN
YN
Figure 3 Pen Pressure Measurements
Rtouch
7
XN-Driver SW ON
YP-Driver SW ON
ADC
VREF+
VREF-
b)
Z2-Position Measurement
VCC
AIN+
AIN-
YP
XP
XN
YN
Rtouch
2006/04
[AK4183]