BU21028FV-M Datasheet, PDF (13/36 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21028FV-M
Specification of Touch Detection
BU21028FV-M executes its touch detection function by outputting an interrupt signal at pin INT once it is able to detect
touch. The circuit diagram of the touch detection function is shown on the following figure.
VDDP
INT
Connected when touch
screen is touched
YP
XP
50kΩ
90kΩ
PU90K
(register)
Control
Logic
High when XP or YP
dirvers ON
Touch screen
YN
XN
ON
GNDP
GND
Figure 4. Touch detection circuit
When the touch panel is connected to the panel interface terminals (XP, XN, YP, YN), pin XP is connected to VDDP through
an internal pull-up resistor inside the IC and pin YN is connected to GNDP. During a no-touch state, BU21028FV-M will be
on standby. During this time, INT outputs "H" through an internal pull-up resistor. Since pins XP and YN are connected to
the touch screen through contact resistance, the resistance ratio of the internal pull-up resistance and the touch screen
resistance is able to detect the voltage drop at pin XP whenever the screen is touched. This results to an "L" output at INT.
When touch is detected and pins XP and YP is put to drive state by each scanning operation, the internal pull-up resistance
is disconnected from pin XP and the output of pin INT is held at "L".
www.rohm.com
© 2016 ROHM Co., Ltd. All rights reserved.
TSZ22111 • 15 • 001
13/32
TSZ02201-0L5L0F300720-1-2
27.May.2016 Rev.002