YB1508
Step-up DC-DC Converter , White LED Driver
Functional Block Diagram
Figure 3. Block Diagram
Application Information
Operation
The operation of YB1508 can be
understood by referring to the block
diagram in Figure 3.
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.
small size and high efficiency are major
concerns, the inductor should have low
core losses at 1MHz and low DCR
(copper wire resistance).
Capacitor Selection
The small size of ceramic capacitors
makes them ideal for YB1508
applications. X5R and X7R types are
recommended because they retain their
capacitance over wider voltage and
temperature ranges than other types.
Diode selection
To maintain high efficiency, the average
current rating of the schottky diode
should be larger than the peak inductor
current, IPK. Schottky diode with a low
forward drop and fast switching speeds
are ideal for increasing efficiency in
portable applications. The reverse
breakdown voltage of the schottky diode
must be larger than the output voltage.
Inductor Selection
A 22uH inductor is recommended for most
YB1508 applications. Although
YB1508 MRev1.4
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