BW7385A Datasheet, PDF (6/9 Pages) Bruckewell Technology LTD – TM (Transition Mode) Fixed On -Time PFC Control

Preliminary BW7385A
Application Information
Start-up Current
The typical start-up current is around 10uA. 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
BW7385A, then the turn-on and turn-off thresholds
level are fixed at 15V and 6.5V respectively. This
hysteresis shown in Fig.1 ensures that the start-up
capacitor will be adequate to supply the chip during
start-up. For quickly startup the LED driver, the
start-up resistor should be matched with the startup
capacitor. Due to the low UVLO on level, so the
turn-on delay time will also never greater than the
general PWM IC.
threshold voltage 31.5V, 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 and never recovery unless the
VCC pin voltage is down to the UVLO off level. The
BW7385A is working in an auto-recovery mode as
shown in Fig.2.
Fig.1
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 450ns 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
can not switch off the gate driver.
OVP (Over Voltage Protection) on VCC
To prevent the LED driver from being damaged,
the BW7385A is implemented an OVP function on
VCC. When the VCC voltage is higher than the
OVP
Fig. 2
Gate Clamp
Driver is clamped to 15V by an internal clamping
circuit. Those damages usually come from
undesired over-voltage gate signals. Under the
conditions listed below, the gate output will turn off
immediately to protect the power circuit.
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