YB1517 Ver la hoja de datos (PDF) - YOBON TECHNOLOGIES,INC.
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YB1517 Datasheet PDF : 10 Pages
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Function Block
YB1517
Step-up DC-DC Converter & White LED Driver
Figure 4: YB1517 Block Diagram
Operation
The YB1517 uses a constant frequency,
current mode control scheme to regulate
the output voltage. Its operation can be
understood by referring to the block
diagram in Figure 4. 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 YB1517.
The maximum switch current is limited to
about 900mA by the chip.
Over Voltage Protection
The YB1517 has an internal over voltage
protection circuit which also acts as an
open-circuit protection. In the cases of
open circuit or the LEDs failure, the LEDs
are disconnected from the circuit, and the
feedback voltage will be zero. The YB1517
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW pin voltage to exceed its
maximum 24V rating. The YB1517 will
shutdown automatically until input condition
changes to bring it out of the shutdown
mode.
YB1517 Rev.1.4
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