AK4185 AKM [Asahi Kasei Microsystems], AK4185 Datasheet - Page 7

• Manufacturer Part Number: AK4185
• Manufacturer: AKM [Asahi Kasei Microsystems]

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The AK4185 consists of the following blocks:
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The AK4185 incorporates a 12bit successive approximation resistor (SAR) A/D converter for position measurement,
temperature, and auxiliary input. 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 AK4185 can select SCLK of the digital interface and internal clock within oscillator for A/D conversion clock. The
full scale (ΔVREF) of the A/D converter depends on the input mode. Position and pen pressure is actually measured by
differential mode, then IN and temperature is actually measured by single-ended mode. The AK4185 is controlled by the
8bit serial command on the DIN pin. A/D conversion result is 12bit data output on the DOUT pin.
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Analog input is selected via the A2, A1, and A0 bits in the converter register. If the analog inputs are selected to the X, Y,
or Z-axis, at differential mode, the full scale (ΔVREF) is the voltage difference 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. At single-ended mode, the full scale of A/D converter (ΔVREF) is the external reference voltage (VDD).
The analog input of A/D converter (ΔAIN) is the voltage difference between the selected channel (IN, TEMP) and the
VSS. In case of external clock mode, tracking time is the period from the falling edge of 5th SCLK to that of 8th SCLK
after the detection of START bit during CSN = “L”.
If the source impedance of analog input is larger than 600Ω, longer tracking time is required. Then A/D conversion should
be started.
MS0954-E-00
Analog Inputs
Function Overview
A/D Converter for Touch Screen
● 1.6V Successive Approximation Resister (SAR) A/D converter
● 4-wire or 5-wire resistive touch screen controller interface
● Single or Continuous A/D conversion
● SAR A/D Converter conversion clock select function
● SPI
- External Clock (SCLK)
- Internal Clock
TM
I/F
(ΔVREF-2.5LSB) ~ (ΔVREF-1.5LSB)
(ΔVREF-1.5LSB)~ ΔVREF
0.5LSB ~ 1.5LSB
Input Voltage
OPERATION OVERVIEW
0 ~ 0.5LSB
ΔVREF: (VREF+) – (VREF-)
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Table 1. Output Code
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Output Code
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FFFH
FFEH
001H
000H
[AK4185]
2008/05