ak4184 AKM Semiconductor, Inc., ak4184 Datasheet - Page 10

• Manufacturer Part Number: ak4184
• Description: Tsc With Keypad Scanner And Gpio Expander
• Manufacturer: AKM Semiconductor, Inc.

L
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 ( VREF) is the
differential voltage between the non-inverting terminal and the inverting terminal of the measured axis (e.g. X-axis
measurement: VREF = V
terminal (V
= V
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 600 , the settling time needs to be at least 1.5 s. The maximum throughput of the
A/D converter is 125kHz. If the source impedance of the analog input is larger than 600 , 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.
MS0603-E-00
Touch Screen Position Detection
YP
– V
ADC
XN
XP
) The input voltage charges the internal capacitor during the sampling time period. No current flows into
) of the non-target axis and the inverting terminal (V
a) X-Position Measurement Differential Mode
VREF+
VREF-
XN-Driver SW ON
XP-Driver SW ON
The X-Plate and Y-plate are connected on the dotted line when the panel is touched.
AIN+
AIN-
XP
AVDD
– V
XN
XN
YN
). The input ( AIN) of the A/D converter is the voltage between the non-inverting
XP
XP
YP
XN
YN
Figure 3. Axis Measurement
c) 4-wire Touch Screen
X-Plate
Y-Plate
10
YP
ADC
XN
VREF+
VREF-
b) Y-Position Measurement Differential Mode
) of the target axis. (E.g. AIN = (AIN+)-(AIN-)
YN-Driver SW ON
YP-Driver SW ON
X-Plate (Top side)
Y-Plate (Bottom side)
AIN+
AIN-
AVDD
YP
XN
YN
XP
Touch Screen
X-Plate
Y-Plate
2007/04
[AK4184]