BW7386 Datasheet, PDF (7/8 Pages) Bruckewell Technology LTD – Accuracy Constant Current LED Driver

BW7386
Accuracy Constant Current LED Driver
APPLICATION INFORMATION
Start-up Current
The typical start-up current is around 8uA.
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)
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 410ns 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.
A hysteresis UVLO comparator is implemented in
BW7386 then the turn-on an turn-off thresholds level
are fixed at 18V and 8V 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.
UVLO(on) 18V
UVLO(off) 8V
Fig. 1
Oscillator
The maximum duty-cycle of internal oscillator is up
to 90% for driving high LED voltage string. The
frequency of the oscillator is fixed to 45KHZ by
internal setting.
OCP(Over Current Protection)
The BW7386 has an over current protection function
on CS pin. An internal circuit detects the current
level, when the current is larger than a threshold
level, the gate output will keep on low level. Then
VCC decreases below UVLO off level, the controller
resets again.
OVP (Over Voltage Protection) on VCC
The prevent the LED driver from being damaged,
the BW7386 is implemented an OVP function on
VCC. When the VCC voltage is higher than the OVP
threshold voltage 28V, 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 (latch off type
optional). 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
BW7386 is working in an auto-recovery mode as
shown in Fig. 2.
Rev 2.0 Aug. 2013Ä¡
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