BW7385 Datasheet, PDF (6/7 Pages) Bruckewell Technology LTD – Non-isolation Buck current control IC with High PFC for LED Lighting

BW7385
Non-isolation Buck current control IC with High PFC for LED Lighting
APPLICATION INFORMATION
Start-up Current
The typical start-up current is around 45uA. Very
low start-up current allows the PWM controller to
increase the value of start-up resistor and then
reduce the power dissipation on it.
UVLO(Under Voltage Lockout)
A hysteresis UVLO comparator is implemented in
BW7385 the turn-on and turn-off thresholds level
are fixed at 17.5V and 8V respectively. This
hysteresis shown in Fig.3 ensures that the start-up
capacitor will be adequate to supply the chip
during start-up. For quickly star-tup the LED driver,
the start-up resistor should be matched with the
start-up capacitor. Due to the low UVLO on level,
so the turn-on delay time will also never greater
than the general PWM IC.
OCP(Over Current Protection)
The BW7385 is built cycle by cycle over current
protection function on CS pin. As the CS pin
voltage is larger than V_OCP (1.4V), the gate output
will be turned off immediately to avoid the driver
board be burned out.
OVP (Over Voltage Protection) on VCC
To prevent the LED driver from being damaged,
the BW7385 is implemented an OVP function on
VCC. When the VCC voltage is higher than the
V_OVP (31V), the output gate driver circuit will be
shut down immediately to stop the switching of
power MOSFET. The VCC pin OVP function is an
auto recovery type protection. If the OVP condition
happens, the pulses will be stopped until the VCC
pin voltage is down to the UVLO off level. The
BW7385 is working in an auto-recovery mode as
shown in Fig. 4.
Fig. 3
LEB(Leading-Edge Blanking)
Each time the power MOSFET is switched on, a
turn-on spike will inevitably occur at the sense
resistor. To avoid fault trigger, a 400ns
leading-edge blanking time is built in.
Conventional RC filtering can therefore be omitted.
During this blanking period, the current-limit
comparator is disabled and cannot switch off the
gate driver.
Fig. 4
Gate Clamp
Driver is clamped to 12.5V by an internal clamping
circuit to avoid the Gate of MOSFET be damage.
Ver 1.01 Mar. 2014
6