YB1518 查看數據表（PDF） - YOBON TECHNOLOGIES,INC.

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产品描述 (功能)

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YB1518

Step-up DC-DC Converter White LED Driver

YOBON TECHNOLOGIES,INC. 

Functional Block

YB1518

Step-up DC-DC Converter White LED Driver

Operation

Figure 3: YB1518 Block Diagram

The YB1518 uses a constant frequency,

current mode control scheme to regulate

the output LED current. Its operation can

be understood by referring to the block

diagram in Figure 3. At the start of each

oscillator cycle, a voltage proportional to

the switch current is added to a ramp

output and the resulting sum is fed into the

positive terminal of the PWM comparator

(comparator-1). When this voltage exceeds

the level of the comparator negative input,

the peak current has been reached, and

the SR latch (in Control Logic) is reset and

turns off the power switch. The voltage at

the negative input of the comparator comes

from the output of the error amplifier. The

error amplifier sets the correct peak current

level to keep the output in regulation. If the

error amplifier’s output increases, more

current is delivered to the output; if it

decreases, less current is delivered.

Application Information

Soft Start and Current Limit

The internal soft start circuit minimizes the

inrush current during turning on YB1518.

The maximum switch current is limited to

about 230 mA by the chip.

LED Current and Dimming Control

The LED’s current is set by a resistor

connected at FB pin to GND using:

I LED

= 100mV

RLED

The maximum LED current set initially can

be reduced by pulse width modulating the

CTRL. A better approach is to adjust the

feedback voltage for dimming control.

Either a DC level signal or a filtered PWM

signal can be used to control the LED

current as illustrated in Figure 4 and Figure

YB1518 Rev.1.3

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