BU21025GUL Datasheet, PDF (11/19 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21025GUL
Datasheet
●Operation
Position Detection of Touch Screen
The 4-wire resistive touch screen is mainly constituted in two resistive plates, X and Y. If screen is pressed, these 2 plates
are connected.
A position of touch screen is detected by applying voltage to one plate and measuring voltage of another plate. This
measurement voltage is divided by touch position. In X-position detection, X-plate is applied voltage. And Voltage of Y-plate
is measured. In Y-position detection, Y-plate is applied voltage. And Voltage of Y-plate is measured. The master needs to
detection 2 times for detecting X and Y position
When screen is not touched, a measuring plate is high impedance from another plate. So, it can’t get voltage. And a value
of the A/D conversion became unknown. If unknown values are used for calculating the coordinates, the coordinates will not
show touch points. So it is require to filter unknown values when the calculate coordinates.
VDD
VDD
ON
XP
YP
ON
XP
YP
VREFP
VREFP
AIN
AIN
VREFN
VREFN
XN
YN
ON
XN
YN
ON
GND
Figure 5. X-Position Detection Mode
GND
Figure 6. Y-Position Detection Mode
Touch Resistance Measurement
These are two methods for measuring touch resistance. The first method requires that a resistance of X-plate (RX-plate) is
known. In this method, the calculation of touch resistance (RTOUCH) needs X position and 2 additional measurement data (Z1
and Z2) that shown in Figure 7 and 8. The equation is as follows,
R _TOUCH
= R _X-plate
⋅
X _postion
4096
⎜⎜⎝⎛
Z₂
Z₁
−1_{⎟⎟⎠⎞}
The second method requires that both resistance of X-plate and resistance of Y-plate (RY-plate) are known. In this method,
the calculation of RTOUCH needs X and Y position and Z1. The equation is as follows,
R _TOUCH
= ^{R X-plate - Xposition}
4096
⋅
⎜⎜⎝⎛
4096
Z₁
−1_{⎟⎟⎠⎞} - R _Y-plate
⋅ _{⎜⎜⎝⎛}1-
Y_position
4096
⎟⎟⎠⎞
VDD
VDD
ON
XP
YP
ON
XP
YP
VREFP
AIN
VREFN
XN
YN
ON
GND
Figure 7. Z1-Position Detection Mode
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© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
11/15
VREFP
AIN
VREFN
XN
YN
ON
GND
Figure 8. Z2-Position Detection Mode
TSZ02201-0Y2Y0F300050-1-2
7.AUG.2012 Rev.002