ak4182a AKM Semiconductor, Inc., ak4182a Datasheet - Page 7

• Manufacturer Part Number: ak4182a
• Description: Touch Screen Controller
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
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The AK4182A 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 (ΔVREF) of the A/D converter depends on the input mode. The AK4182A is controlled by the 8 bit serial command
on DIN.
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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 (ΔVREF) 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 (ΔVREF)
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 needs at least 1.428μs (3tDCLKat 2.1MHz). The maximum
throughput of A/D converter is 125 kHz.
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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.
MS0482-E-01
A/D Converter for Touch Screen
Analog Inputs
The Position Detection of Touch Screen
(ΔVREF-2.5LSB) ~ (ΔVREF-1.5LSB)
(ΔVREF-1.5LSB)~ ΔVREF
0.5LSB ~ 1.5LSB
Input Voltage
0 ~ 0.5LSB
ΔVREF: (VREF+) – (VREF-)
---------
th
Table 1 Output Code
DCLK to that of 8
7
th
DCLK after the detection of START bit during
Output Code
---------
FFFH
FFEH
001H
000H
[AK4182A]
2006/12