YB1508
Step-up DC-DC Converter , White LED Driver
Inrush Current
The maximum switch current is limited to
about 300 mA by the chip. Typically, this
large current will occur for about 40us
during start up. A larger Cout will increase
the duration of high current. However,
when Vin is first connected, an even
larger current can flow into Cout. This
occurs when the SW pin is open circuit
and and the Cout voltage changes from
0V to Vin in a few microseconds. Because
the duration of this large current is short, it
will usually not cause problems.
LED Current and Dimming Control
The LED current can be reduced by pulse
width modulating the CTRL voltage from
0.4V to 1.8V. Using the PWM mode, the
LED current can be controlled from 0% to
100%.
Open Circuit Protection
The YB1508 has an internal open-circuit
protection circuit. When the LEDs are
disconnected from the circuit or fail
open, the YB1508 will then shutdown
until Vin goes low or CTRL goes lower
than 0.4V.
Different maximum Vout
can be requested from YoBon.
Board Layout Consideration
To maximize efficiency, rise and fall
times of switch should be made as
short as possible. Proper layout of the
high frequency switching path is
important to prevent electromagnetic
interference (EMI) problems. Place
COUT close to the VOUT pin. A
ground plane under the switching
regulator is needed to minimize
interplane coupling. In addition, the
feedback resistor Rs should be tied
directly to the GND Pin without any
other connection to ensure a clean,
noise-free connection.
Figure 4. Dimming Control Using a DC Voltage
Figure 5. Dimming Control Using a Filtered PWM
Signal
YB1508 MRev1.4
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YOBON [ YOBON TECHNOLOGIES,INC. ]
