YB1509
High-Power White LED Driver
Functional Block Diagram
VBAT
CIN
L1
Charge Enable
EN
VIN
SW
Cout
Bypass
VFB
1.23V
VREF
D1
Set Q
Reset
O ff Tim e
Control
Q1
10nF
I
SET
G ND
60O HM
Figure 9. Block Diagram
Functional Description
The YB1509 is a constant current
high-power white LED driver. It can drive up
to 10 LEDs in series or 18 LEDs in
parallel/series configuration. The IC uses a
peak current, 1µs off-time PFM scheme.
The inductor current ramp up when power
NPN is turn on. Once the inductor current
reaches the preset value determined by the
I
SET
pin, output power NPN is shut off and
the energy stored in inductor is delivered to
the output capacitor. Once the discharge
cycle is completed, the power NPN is on
again. If the FB voltage has not yet reached
the designated value of 1.23V, the inductor
current will be charged up again. This
charging and discharging sequence will
repeat itself until the FB voltage gets to the
designated value and triggers the on-off
YB1509 MRev.1.1
latch to hold off the power NPN regardless
the inductor current value.
LED Current and Brightness control
The LED’s current is set by the resistor
connected at FB pin to GND using:
I
LED
=
1.23
V
R
FB
LED’s brightness is accomplished by
applying a PWM signal with a frequency
range between 100Hz and 50KHz to the
EN pin.
Inductor Current Set
Using a resistor connected from I
SET
to
GND is able to set inductor current. An 8µA
current source is coming out of the YB1509
5
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YOBON [ YOBON TECHNOLOGIES,INC. ]
