BW7381 Datasheet, PDF (7/11 Pages) Bruckewell Technology LTD – Universal High Brightness LED Driver

BW7381
Universal High Brightness LED Driver
APPLICATION INFORMATION
1. Function Description
The BW7381 is a high performance controller
which monitors actual output current. These results
BW7381 enable tight line and load regulation. The
BW7381 uses constant off-time peak current mode
control to control the switching current in the
MOSFET.
At Initial, VDD capacitor charged through
start-up resistor until it achieves 18V. Then BW7381
turns-on the MOSFET and make its shape of peak
current flow input sine wave. This performs high
power factor and low total harmonic distortion. The
output current flow through a current sensing
resistor and feedback to FLT pin. The controller
always adjusts the amplitude of current command
base on the potential of FLT pin. Once the peak
current reaches the current command, controller
turns off the MOSFET. The resistor connected at RT
pin determines the off-time. At the switching on-time,
controller senses and limits the maximum switch
current by CS pin. This ensures the current in
MOSFET be limited in safe operating area.
The BW7381 built-in output short-circuit and
over-voltage protection. While the MOSFET turns
off at the off-time, the VDD capacitor can get charge
by output voltage, and controller can set output over
voltage protection threshold by specified zener
diode. If the LED string is open, the output voltage
will be boost over the designed level until the VDD
arrive to 28V. The BW7381 goes into over-voltage
protection and latches the MOSFET. The controller
starts up the system again while the VDD falls to
8.5V (UVLO). Therefore, the converter
Rev.1.4 Jan. 2013Ä¡
auto-recovery output while the output open circuit
condition removed. In case of output short-circuit
condition. The VDD capacitor cannot get charge
from output voltage. So, the converter repeats
start-up and UVLO. However, the BW7381provides
full protections such as OCP, OVP, gate-voltage
clamp and cycle-by-cycle current limit.
2. Pin Detail
2-1. CS
MOSFET current sensing, use for cycle by cycle
switch peak current control.
I _{L(lim it )}
0.7V
R₄
2-2. GND
GND is the reference node of internal circuit.
2-3. FLT
Actual output current sensing, the signal
feedback to error amplifier and compare with the
internal reference voltage (0.2V).
0.2V
I_O
R₂
2-4. COMP
This is the output of the Gm amplifier. Connect
with a suitable RC network to ground.