MIC2164 Datasheet, PDF (20/36 Pages) Micrel Semiconductor – Constant Frequency, Synchronous Buck Controllers Featuring Adaptive On-Time Control

Micrel, Inc.
PCB Layout Guideline
Warning!!! 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.
The following guidelines should be followed to insure
proper operation of the MIC2164/-2/-3 converter.
IC
• Place the IC and MOSFETs close to the point of
load (POL).
• Use fat traces to route the input and output power
lines.
• Signal and power grounds should be kept separate
and connected at only one location.
Input Capacitor
• Place the HSD input capacitor next.
• Place the HSD input capacitors on the same side of
the board and as close to the MOSFETs as
possible.
• Keep both the HSD and PGND connections short.
• Place several vias to the ground plane close to the
HSD 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 over-
voltage spike seen on the input supply with power is
suddenly applied.
• An additional Tantalum or Electrolytic bypass input
capacitor of 22uF or higher is required at the input
power connection.
• The 1µF and 0.1µF capacitors, which connect to the
V_IN terminal, must be located right at the IC. The V_IN
terminal is very noise sensitive and placement of the
MIC2164/-2/-3
capacitor is very critical. Connections must be made
with wide trace.
Inductor
• Keep the inductor connection to the switch node
(LX) short.
• Do not route any digital lines underneath or close to
the inductor.
• Keep the switch node (LX) away from the feedback
(FB) pin.
• The LX pin should be connected directly to the drain
of the low-side MOSFET to accurate sense the
voltage across the low-side MOSFET.
• To minimize noise, place a ground plane underneath
the inductor.
Output Capacitor
• Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
• Phase margin will change 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 close as possible to
the output capacitor. Sensing a long high current
load trace can degrade the DC load regulation.
Schottky Diode (Optional)
• Place the Schottky diode on the same side of the
board as the MOSFETs and HSD input capacitor.
• The connection from the Schottky diode’s Anode to
the input capacitors ground terminal must be as
short as possible.
• The diode’s Cathode connection to the switch node
(LX) must be keep as short as possible.
RC Snubber
• Place the RC snubber on the same side of the board
and as close to the MOSFETs as possible.
September 2009
20
M9999-090409-B