ak4183 AKM Semiconductor, Inc., ak4183 Datasheet - Page 6

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

ASAHI KASEI
The AK4183 incorporates a 12-bit successive approximation resistor (SAR) A/D converter for position measurement. The
architecture is based on a capacitive redistribution algorithm, and an internal capacitor array functions as the sample/hold (S/H)
circuit.
The SAR A/D converter output is a straight binary format as shown below:
A position detecting (X, Y position) on the touch panel is selected by the control command via the A2, A1, A0 bits in the control
register. The mode of the position detecting is differential mode, the full scale (∆VREF) is the differential voltage between the non-
inverting terminal and the inverting terminal of the measured axis (e.g. X-axis measurement: ∆VREF = V
difference on the A/D converter (∆AIN) is the voltage between non-inverting terminals of the non-measured axis and the inverting
terminal of the measured axis. (E.g. ∆AIN= (AIN+) - (AIN-) = V
capacitor array during the sampling period. No current flows into the internal capacitor after the capacitor has been charged
completely.
The required settling time to charge the internal capacitor array depends on the source impedance (Rin). If the source impedance is
600 ohm, the settling time needs at least 2.5µs (1 clock cycle period of SCL 400 KHz)
The position on the touch screen is detected by taking the voltage of one axis when the voltage is supplied between the two
terminals of another axis. At least two A/D conversions are needed to get the two-dimensional (X/Y axis) position.
MS0500-E-00
ADC
A/D Converter for Touch Screen
The Position Detection of Touch Screen
a)
VREF+
VREF-
XN-Driver SW ON
X-Position Measurement Differential Mode
XP-Driver SW ON
The X-plate and Y-plate are connected on the dotted line when the panel is touched.
AIN+
AIN-
VCC
XN
YN
(∆VREF-2.5LSB) ~ (∆VREF-1.5LSB)
(∆VREF-1.5LSB)~ ∆VREF
XP
YP
XN
YN
XP
c)
0.5LSB ~ 1.5LSB
Input Voltage
4-wire Touch Screen Construction
0 ~ 0.5LSB
∆VREF: (VREF+) – (VREF-)
---------
Figure 2 Axis Measurements
X-Plate
Table 1 Output Code
Y-Plate
YP
6
YP
-V
ADC
XN
) The voltage difference (∆AIN) is charged to the internal
b)
VREF+
VREF-
Y-Position Measurement Differential Mode
YN-Driver SW ON
YP-Driver SW ON
Output Code
---------
FFEH
FFFH
001H
000H
X-Plate (Top side)
Y-Plate (Bottom side)
AIN+
AIN-
VCC
XP
– V
XP
YP
XN
YN
XN
). The voltage
Touch Screen
X-Plate
2006/04
[AK4183]
Y-Plate