Datasheet
LMR61428
www.ti.com
SNVS815A –JUNE 2012–REVISED APRIL 2013
OUTPUT DIODE SELECTION
A Schottky diode should be used for the output diode. The forward current rating of the diode should be higher
than the load current, and the reverse voltage rating must be higher than the output voltage. Do not use ordinary
rectifier diodes, since slow switching speeds and long recovery times cause the efficiency and the load regulation
to suffer.
INPUT AND OUTPUT FILTER CAPACITORS SELECTION
While tantalum chip capacitors are recommended for the input and output filter capacitors, ceramic caps can also
be used. A 22µF capacitor is suggested for the input filter capacitor. It should have a DC working voltage rating
higher than the maximum input voltage. A 68µF tantalum capacitor is suggested for the output capacitor. The DC
working voltage rating should be greater than the output voltage. Very high ESR values (>3Ω) should be avoided.
PC BOARD LAYOUT
High switching frequencies and high peak currents make a proper layout of the PC board an important part of
design. Poor design can cause excessive EMI and ground-bounce, both of which can cause malfunction and loss
of regulation by corrupting voltage feedback signal and injecting noise into the control section.
Power components - such as the inductor, input and output filter capacitors, and output diode - should be placed
as close to the regulator IC as possible, and their traces should be kept short, direct and wide. The ground pins
of the input and output filter capacitors and the PGND and SGND pins of LMR61428 should be connected using
short, direct and wide traces. The voltage feedback network (R
fbt
, R
fbb
, and C
ff
) should be kept very close to the
FB pin. Noisy traces, such as from the SW pin, should be kept away from the FB and V
DD
pins. The traces that
run between V
out
and the FB pin of the IC should be kept away from the inductor flux. Always provide sufficient
copper area to dissipate the heat due to power loss in the circuitry and prevent the thermal protection circuitry in
the IC from shutting the IC down. Additional ground planes as intermediate levels help with shielding and
improve EMI mitigation.
Copyright © 2012–2013, Texas Instruments Incorporated Submit Documentation Feedback 11
Product Folder Links: LMR61428