YB1521 Datasheet, PDF (7/9 Pages) YOBON TECHNOLOGIES,INC. – High Power Step-Up DC-DC Converter & WLED Driver

YB1521
High Power Step-Up DC-DC Converter & WLED Driver
be reduced by pulse width modulating the
EN. A better approach is to adjust the
internal reference voltage for dimming
control by a logic signal illustrated in Figure
5. YB1521 contains circuitry to support this
automatically. The typical dimming frequency is
50KHz and recommended not to lower
than 20KHz. Besides the EN dimming
control scheme, either a DC level signal or
a filtered PWM signal can be used to
control the LED current as illustrated in
Figure 6 and Figure 7 respectively. The
average current through the LEDs will
increase linearly to the duty cycle of the
controlling PWM signal.
YB1521
EN
FB
Figure 5: PWM Dimming Control Using a Logic
Signal
YB1521
FB
R1
R2
80K
20K
VDC
Figure 6: Dimming Control Using a DC Voltage
YB1521
FB
R1
R2
R3
20K
80K
20K
0.1uF
Figure 7: Dimming Control Using a Filtered
PWM Signal
Over Voltage Protection
The YB1521 has an internal over voltage
protection circuit which also acts as an
open-circuit protection. In the case of open
circuit or the LEDs failure, the LEDs are
disconnected from the circuit, and the
feedback voltage will be zero. The YB1521
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW voltage to exceed its
maximum 18V rating. The YB1521 will
shutdown automatically until the power is
recycled.
Inductor Selection
A 6.8µH is recommended to drive 39 LEDs
in series/parallel. Although small size and
high efficiency are major concerns, the
inductor should have low core losses at
1.3MHz and low DCR (copper wire
resistance). A higher 10µH inductor is
recommended to improve efficiency.
Diode Selection
To maintain high efficiency, the average
current rating of the Schottky diode should
be larger than the peak inductor current.
Schottky diode with a low forward drop and
fast switching speeds are idea for
increasing efficiency in portable application.
Choose a reverse breakdown of the
YB1521 MRev.1.1
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