YB1521 Datasheet, PDF (6/9 Pages) YOBON TECHNOLOGIES,INC. – High Power Step-Up DC-DC Converter & WLED Driver

YB1521
High Power Step-Up DC-DC Converter & WLED Driver
Functional Block
Figure 4: Function Block
Operation
The YB1521 features 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 output of error
amplifier increases, more current is
delivered to the output; if it decreases, less
current is delivered.
Application Information
Inrush Current
The YB1521 has internal soft-start to limit
the amount of current through the IN pin at
startup and to also limit the amount of
overshoot on the output. The current limit is
increased by 4 steps to give a total
soft-start time of 160µs.
LED Current and Dimming Control
The LED’s current is set by a resistor
connected at FB pin to GND:
I_LED = 200mV / R₁.
The maximum LED current set initially can
YB1521 MRev.1.1
www.yobon.com.tw
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