AK4180VT 参数 Datasheet PDF下载

[ASAHI KASEI]

[AK4180]

A/D Converter for Touch Screen

The AK4180 incorporates a12-bit successive approximation resistor 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 circuit.

The A/D converter output is a straight binary format as shown below:

Input Voltage

Output Code

FFF

(∆VREF-1.5LSB)~

∆VREF

FFE

(∆VREF-2.5LSB) ~ (∆VREF-1.5LSB)

---------

---------

0.5LSB ~ 1.5LSB

001

0 ~ 0.5LSB

000

∆VREF:

(VREF+) – (VREF-)

Table 1 Output Code

The A/D converter’s full scale measurements depend on the input mode.

Analog Inputs

Analog input is selected via the A2, A1, A0 and SER/ DFR bits in the control register. If the analog inputs are the X or Y-axis,

use 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. (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

th

DCLK to the falling edge of 8

th

DCLK after the detection of START bit.

the required settling time to charge the internal capacitors depends on the source impedance. If the source impedance, Rin, is 600

ohm, the settling time needs at least 1.5

µs

(3 tDCLK@2MHz). The maximum throughput of A/D converter is 125kHz.

If the source impedance of analog input is larger than 600 ohm, longer tracking time is required.

The Position Detection of Touch Screen

The selected touch screen position is detected by the voltage measurement of one axis when the voltage is supplied between the

two terminals of the other axis. At least two A/D conversions are needed to get the two-dimensional (X/Y axis) position.

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2003/02