YB1508 datasheet(5/7 Pages) YOBON

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YB1508

Step-up DC-DC Converter , White LED Driver

YB1508 MRev1.4

WWW.YOBON.COM.TW

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

needed

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

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