BU21029GUL Datasheet, PDF (3/29 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21029GUL
●Block Diagram
XP
XN
YP
YN
AUX
PVDD
LDO
Touch
Screen
Drivers
& I/F
PGND
VDD
LDO
M
U
X
VREF
OSC
PENIRQ
SAR
ADC
Control
Logic
&
2 wire
Serial
I/F
POR
GND
Datasheet
INT
SDA
SCL
AD0
AD1
RSTB
●OVERVIEW
BU21029GUL is a controller for 4-wire resistive touch screens. It has built-in 12-bit SAR A/D converter, clock oscillator,
power on reset circuit, and LDO regulator for internal blocks and operates with 1.65-3.60V single power supply. Aside from
being able to detect single point coordinates and touch pressure like existing 4-wire resistive touch screen controllers can,
it can also detect dual coordinates by generating data based on the prearranged touch screen parameters.
Communication between BU21029GUL controller and the host processor uses 2-wire serial interface. The BU21029GUL,
being the I2C slave device, is controlled by the host processor by writing to its registers. This way, the host processor sets
whether the touch screen controller operates under command control mode or under automatic control mode. In automatic
control mode, the host processor reads the touch data saved by the controller in its internal registers at any time.
Preprocess
A/D conversion is continuously done for several times in one driving time. Data is median average processed; meaning
data is sorted and calculation that takes the average from the center of the sorted data is performed.
Interrupt control
The BU21029GUL sends an interrupt signal to the host processor through INT, an active-low pin, whenever it detects touch
on the screen. In automatic control mode, this happens after the scan of the first touch is completed.
2-point detection function
The 2-point detection function of BU21029GUL can be used by calibrating the circuit for 2-point detection based on the
inherent panel perimeters (registers 0x3, 0x4). Since the characteristics of each touch panel differ significantly, it is
necessary for the host processor to execute the calibration of parameters to match the 2-point detection circuit of
BU21029GUL with every touch panel.
Power control
After a conversion function has been completed, the BU21029GUL automatically powers down in order to reduce current
consumption. In automatic control mode, scanning restarts automatically from power down when the touch screen is
operated.
Power on reset
BU21029GUL has built-in power-on-reset circuit. If the host processor will not be used to control RSTB pin, RSTB pin can
be shorted to VDD. This way, the registers of BU21029GUL initialize upon power-on.
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11.Nov.2013 Rev.002