BW7381 Datasheet, PDF (10/11 Pages) Bruckewell Technology LTD – Universal High Brightness LED Driver

BW7381
Universal High Brightness LED Driver
In buck-boost converter, the average of
current flow in MOSFET is equal to the input
current. If given a ratio of maximum inductor
current ripple to maximum inductor peak current,Ä¡
ȋŊ_LİŊ_L(pk)įġThen the inductor peak current can be
estimated by the equation:
I _{L( pk )}
2I _{in( pk)}
¨§
¨©
2

'I _L
I _{L( pk )}
¸·
¸¹
u
Duty_{( pk)}
The maximum inductor current ripple, ȋŊ_L
is :
'I _L
I
L(
pk )
u
'I _L
I _{L( pk )}
From the basic inductor equation, the
inductance is :
the CS pin goes execss of 700mV, the BW7381
force MOSFET switcher turn off. Design the peak
inductor current to 75 percent of switcher
current limit is recommend.
R₄
0.53V
I _{L( peak )}
I _{L(limit )}
0.7V
R₄
L
V_O
'I _L
u toff
Follow the equations above, the inductance
and maximum inductor current can be computed.
The magnetic design of the inductor must ensure
that there is a sufficient flux density margin to
avoid saturation with operating current being
applied.
3-10. Switch Current Sensing Resistor
The BW7381sense switch current from CS
pin to provide cycle-by-cycle current limit. While
Rev.1.4 Jan. 2013Ä¡