Rainbow Electronics MAX1524 - Manual (Page 11)

MAX1522/MAX1523/MAX1524
Simple SOT23 Boost Controllers
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Diode Selection
The MAX1522/MAX1523/MAX1524s’ high switching fre-
quency demands a high-speed rectifier. Schottky
diodes are recommended for most applications
because of their fast recovery time and low forward
voltage. Ensure that the diode’s current rating is ade-
quate to withstand the diode’s RMS current:
Also, the diode reverse breakdown voltage must
exceed V
OUT . For high output voltages (50V or above),
Schottky diodes may not be practical because of this
voltage requirement. In these cases, use a high-speed
silicon rectifier with adequate reverse voltage. Another
consideration for high input voltages is reverse leakage
of the diode. This should be considered using the man-
ufacturer’s specification due to its direct influence on
system efficiency.
Layout Considerations
High switching frequencies and large peak currents
make PC board layout a very important part of design.
Good design minimizes excessive EMI on the feedback
paths and voltage gradients in the ground plane, both
of which can result in instability or regulation errors.
Connect the inductor, input filter capacitor, and output
filter capacitor as close together as possible, and keep
their traces short, direct, and wide. Connect their
ground pins at a single common node in a star-ground
configuration. The external voltage-feedback network
should be very close to the FB pin, within 0.2in (5mm).
Keep noisy traces (such as the trace from the junction
of the inductor and MOSFET) away from the voltage-
feedback network; also keep them separate, using
grounded copper. The MAX1522/MAX1523/ MAX1524
evaluation kit manual shows an example PC board lay-
out and routing scheme.
Generating Resistance
with PC Board Traces
If the output capacitor’s ESR is too low for proper regu-
lation, it can be increased artificially directly on the PC
board. For example, an additional 50m
Ω
of ESR added
to the output capacitor provides best regulation. The
resistivity of a 10mil trace using 1oz copper is about
50m
Ω
per inch. Therefore, a 10mil trace 1in long gener-
ates the required resistance.
I I I
DIODE RMS OUT PEAK ( )
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