Solving for C
f
gives:
or 22pF, whichever is greater.
Standard Application Circuits
Figures 3 and 4 are standard applications circuits for
the MAX1927/MAX1928. Figure 3 illustrates the preset
output voltages (MAX1928), while Figure 4 shows the
adjustable configuration (MAX1927). Table 2 lists part
numbers and suppliers for the components used in
these circuits.
PC Board Layout and Routing
High switching frequencies and large peak currents
make PC board layout a very important part of design.
Good design minimizes EMI, noise on the feedback
paths, and voltage gradients in the ground plane, all 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 those from the LX pin, away
from the voltage feedback network. Position the bypass
capacitors as close as possible to their respective pins
to minimize noise coupling. For optimum performance,
place input and output capacitors as close to the
device as possible. Connect GND and PGND to the
highest quality system ground. The MAX1928 evalua-
tion kit illustrates an example PC board layout and rout-
ing scheme.
Chip Information
TRANSISTORS: 3282
PROCESS: BiCMOS
