AKD4184 View Datasheet(PDF) - Asahi Kasei Microdevices

Part Name

Description

Manufacturer

AKD4184

TSC with Keypad Scanner and GPIO Expander

Asahi Kasei Microdevices 

[AK4184]

■ Touch Screen Position Detection

XY-coordinate detection (XY-position) from the touch panel is determined by the control command (A1, A0) bits of

the touch screen control command. Coordinate detection is in 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: ΔVREF = VXP – VXN). The input (ΔAIN) of the A/D converter is the voltage between the non-inverting

terminal (VXP) of the non-target axis and the inverting terminal (VXN) of the target axis. (E.g. ΔAIN = (AIN+)-(AIN-)

= VYP – VXN) The input voltage charges the internal capacitor during the sampling time period. No current flows into

the internal capacitors after the capacitor has been fully charged. The required settling time to charge the internal

capacitor array depends on the source impedance (Rin). The source impedance is the resistance of the touch panel

plate. If the source impedance is 600Ω, the settling time needs to be at least 1.5μs. The maximum throughput of the

A/D converter is 125kHz. If the source impedance of the analog input is larger than 600Ω, longer settling time is

required. The position from 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.

AVDD

XP-Driver SW ON

VREF+

ADC

VREF-

AIN+

AIN-

XN-Driver SW ON

X-Plate

XP

Y-Plate

AVDD

YP-Driver SW ON

VREF+

AIN+

YP

ADC

VREF-

AIN-

XN

X-Plate

XP

Y-Plate

YP

XN

YN

YN Touch Screen

YN-Driver SW ON

a) X-Position Measurement Differential Mode

b) Y-Position Measurement Differential Mode

The X-Plate and Y-plate are connected on the dotted line when the panel is touched.

XP

XN

YN

YP

c) 4-wire Touch Screen

X-Plate (Top side)

Y-Plate (Bottom side)

Figure 3. Axis Measurement

MS0603-E-00

10

2007/04

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