|YB1522ST||Step-up DC-DC Converter White LED Driver|
|YB1522ST Datasheet PDF : 12 Pages |
Step-up DC-DC Converter White LED Driver
Over Voltage Protection
The YB1522 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 YB1522
will then switch to a high duty cycle
resulting in a high output voltage, which
may cause SW pin voltage to exceed its
maximum 30V rating. The YB1522 will
shutdown automatically until input condition
changes to bring it out of the shutdown
A 33uH inductor is recommended for most
applications to drive more than 3x7 WLEDs.
Although small size and high efficiency are
major concerns, the inductor should have
low core losses at 1MHz and low DCR
(copper wire resistance).
To maintain high efficiency, the average
current rating of the Schottky diode should
be large than the peak inductor current, IPK.
Schottky diode with a low forward drop and
fast switching speeds are ideal for increase
efficiency in portable application. Choose a
reverse breakdown of the Schottky diode
large than the output voltage.
Choose low ESR capacitors for the output
to minimize output voltage ripple. Multilayer
capacitors are a good choice for this as well.
A 10uF capacitor is sufficient for 3x7
WLEDs applications. For additional
bypassing, a 100nF ceramic capacitor can
be used to shunt high frequency ripple on
The input bypass capacitor CIN, as shown
in Figure 1, must be placed close to the IC.
This will reduce copper trace resistance
which affects input voltage ripple of the IC.
For additional input voltage filtering, a
100nF bypass capacitor can be placed in
parallel with CIN to shunt any high
frequency noise to ground. The output
capacitor, COUT, should also be placed
close to the IC. Any copper trace
connections for the COUT capacitor can
increase the series resistance, which
directly effect output voltage ripple.
The feedback network, resister R2 should
be kept close to the FB pin to minimize
copper trace connections that can inject
noise into the system. The ground
connection for the feedback resistor
network should connect directly to an
analog ground plane. The analog ground
plane should tie directly to the GND pin. If
no analog ground plane is available, the
ground connection for the feedback
network should tie directly to the GND pin.
Trace connections made to the inductor
and Schottky diode should be minimized to
reduce power dissipation and increase
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