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

BU21028FV-M
Block Diagram(s)
VDDP
DVDD
VDD _OUT VREF DVDD_IN
XP
XN
YP
YN
AUX
PVDD
LDO
DVDD
LDO
Touch
Screen
M
Drivers
& I/F
U
X
OSC
PENIRQ
SAR
ADC
Control
Logic
&
2 wire
Serial
I/F
INT
SDA
SCL
AD0
AD1
RSTB
GNDP GND
OVERVIEW
BU21028FV-M is a controller for 4-wire resistive touch screens. It has built-in 12-bit SAR A/D converter, clock oscillator, and
LDO regulator for internal blocks and operates with 2.7 to 3.6V 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.
 Host interface
Communication between BU21028FV-M controller and the host processor uses 2-wire serial interface. The
BU21028FV-M, 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 BU21028FV-M sends an interrupt signal to the host processor through INT terminal, 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 BU21028FV-M 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
BU21028FV-M with every touch panel.
 Auto power-down, power-on function(Power control)
After a conversion function has been completed, the BU21028FV-M 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.
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27.May.2016 Rev.002