MIC26903ZA_14 Datasheet, PDF (23/29 Pages) Micrel Semiconductor – 28V, 9A Hyper Speed Control Synchronous DC/DC Buck Regulator

Micrel, Inc.
PCB Layout Guidelines
Note: To minimize EMI and output noise, follow these
layout recommendations.
PCB layout is critical to achieve reliable, stable, and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power, signal,
and return paths.
Follow these guidelines to ensure proper MIC26903-ZA
regulator operation:
IC
• A 2.2µF ceramic capacitor, which is connected to the
PVDD pin, must be located right at the IC. The PVDD
pin is very noise sensitive, so placement of the
capacitor is critical. Use wide traces to connect to the
PVDD and PGND pins.
• A 1µF ceramic capacitor must be placed right
between VDD and the signal ground (SGND). SGND
must be connected directly to the ground planes. Do
not route the SGND pin to the PGND pad on the top
layer.
• Place the IC close to the point-of-load (POL).
• Use fat traces to route the input and output power
lines.
• Keep signal and power grounds separate and
connected at only one location.
Input Capacitor
• Place the input capacitor next.
• Place the input capacitor on the same side of the
board and as close to the IC as possible.
• Keep both the PVIN pin and PGND connections
short.
• Place several vias to the ground plane close to the
input capacitor ground terminal.
• Use either X7R or X5R dielectric input capacitors. Do
not use Y5V or Z5U type capacitors.
• Do not replace the ceramic input capacitor with any
other type of capacitor. Any type of capacitor can be
placed in parallel with the input capacitor.
• If a Tantalum input capacitor is placed in parallel with
the input capacitor, it must be recommended for
switching regulator applications and the operating
voltage must be derated by 50%.
• In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be used to limit the
overvoltage spike seen on the input supply when
power is suddenly applied.
MIC26903-ZA
Inductor
• Keep the inductor connection to the switch node
(SW) short.
• Do not route any digital lines underneath or close to
the inductor.
• Keep the switch node (SW) away from the feedback
(FB) pin.
• Connect the CS pin directly to the SW pin to
accurately sense the voltage across the low-side
MOSFET.
• To minimize noise, place a ground plane underneath
the inductor.
• The inductor can be placed on the opposite side of
the PCB with respect to the IC. It does not matter
whether the IC or inductor is on the top or bottom as
long as there is enough air flow to keep the power
components within their temperature limits. The input
and output capacitors must be placed on the same
side of the board as the IC.
Output Capacitor
• Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
• Phase margin changes as the output capacitor value
and ESR changes. Contact the factory if the output
capacitor is different from what is shown in the BOM.
• The feedback trace should be separate from the
power trace and connected as near as possible to the
output capacitor. Sensing a long high current load
trace can degrade the DC load regulation.
Optional RC Snubber
• Place the RC snubber on either side of the board and
as close to the SW pin as possible.
July 22, 2014
23
Revision 1.1