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