ak4182 AKM Semiconductor, Inc., ak4182 Datasheet - Page 7

• Manufacturer Part Number: ak4182
• Description: Touch Screen Controllers
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
The AK4182 incorporates a 12-bit successive approximation resistor (SAR) A/D converter for position measurement, temperature,
and battery voltage. The architecture is based on 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:
The full scale (∆VREF) of the A/D converter depends on the input mode. The AK4182 is controlled by the 8 bit serial command
on DIN.
Analog input is selected via the A2, A1, A0 and SER/ DFR bits in the control register. If the analog inputs are selected to the X
or Y-axis, SER/ DFR = “0”, which means 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 :(XP) – (XN)). Analog non-inverting
input to A/D converter is the non-inverting terminal of the non-measured axis while the inverting input is the inverting terminal of
the measured axis. If the SER/ DFR bit is set to “1” which means single-ended mode, the full scale of A/D converter (∆VREF)
is the internal reference voltage or external reference voltage. Note that SER/ DFR bit should be set to”0” if IN2 is selected as
analog input; nevertheless, IN2 is actually measured by single-ended mode.
Tracking time is the period from the falling edge of 5
CSN=”L”.
The required settling time to charge the internal capacitor array depends on the source impedance (Rin). If the source impedance is
600Ω, the settling time needs at least 1.428µs (3tDCLKat 2.1MHz). The maximum throughput of A/D converter is 125 kHz.
If the source impedance of analog input or battery input is larger than 600Ω, longer tracking time is required.
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.
MS0411-E-00
A/D Converter for Touch Screen
Analog Inputs
The Position Detection of Touch Screen
(∆VREF-2.5LSB) ~ (∆VREF-1.5LSB)
(∆VREF-1.5LSB)~ ∆VREF
0.5LSB ~ 1.5LSB
Input Voltage
0 ~ 0.5LSB
∆VREF: (VREF+) – (VREF-)
---------
th
Table 1 Output Code
DCLK to that of 8
7
th
DCLK after the detection of START bit during
Output Code
---------
FFEH
FFFH
001H
000H
2005/08
[AK4182]