YB1520 View Datasheet(PDF) - YOBON TECHNOLOGIES,INC.

Part Name

Description

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YB1520

Step-up DC-DC Converter, White LED Driver

YOBON TECHNOLOGIES,INC. 

Function Block

YB1520

Step-up DC-DC Converter, White LED Driver

Figure 3: YB1520 Block Diagram

Operation

The YB1520 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.

When this voltage exceeds the level of the

comparator negative input, the peak current

has been reached, and the SR latch 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

Inrush Current

The maximum switch current is limited to

about 450mA by the chip. Typically, 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 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. If

this current is not desirable, an external

soft-start circuit can be added to

significantly reduce this inrush current.

LED Current and Dimming Control

The LED’s current is set by a resistor

connected at FB pin to GND using:

I LED

=

200mV

RLED

The maximum LED current set initially can

YB1520 Rev.1.4

www.yobon.com.tw

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