AK4184 Datasheet, PDF (9/36 Pages) Asahi Kasei Microsystems – TSC with Keypad Scanner and GPIO Expander

[AK4184]
OPERATION OVERVIEW
The AK4184 consists of the following blocks:
z 4-wire resistive touch screen controller interface
z 6 columns by 5 rows keypad interface
z 8 GPIO pins
z PWM control circuit for LED bias control
z Successive approximation resister (SAR) A/D converter
z Pen interrupt and key interrupt circuit
z Oscillation circuit
AK4184 interfaces to the host processor through standard SPI™ serial interface.
SPI™ is the trademark of Motorola
■ Touch Screen A/D Converter
The AK4184 incorporates a 12-bit successive approximation resistor (SAR) A/D converter for determining the touch
position and pressure 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 in straight binary format
as shown below:
Input Voltage
Output Code
(ΔVREF-1.5LSB) ~ ΔVREF
FFFH
(ΔVREF-2.5LSB) ~ (ΔVREF-1.5LSB)
FFEH
---------
---------
0.5LSB ~ 1.5LSB
001H
0 ~ 0.5LSB
000H
ΔVREF: (VREF+) – (VREF-)
Table 1. Output Code
MS0603-E-00
9
2007/04