MAX8543/MAX8544
Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
______________________________________________________________________________________ 25
3.43kHz << f
C
< 120kHz; select f
C
= 120kHz.
Since f
zMOD
< f
C
:
Select the nearest standard value: C
C
= 220pF
Select the nearest standard value: C
F
= 10pF:
R3 = R
C
= 220kΩ
C8 = C
C
= 220pF
C7 = C
F
= 10pF
Applications Information
PC Board Layout Guidelines
Careful PC board layout is critical to achieve low
switching losses and clean, stable operation. The
switching power stage requires particular attention.
Follow these guidelines for good PC board layout:
1) Place IC decoupling capacitors as close to IC pins
as possible. Keep separate the power ground
plane and the signal ground plane. Place the input
ceramic decoupling capacitor directly across and
as close as possible to the high-side MOSFET’s
drain and the low-side MOSFET’s source. This is to
help contain the high switching current within this
small loop.
2) For output current greater than 10A, a four-layer PC
board is recommended. Pour a signal ground
plane in the second layer underneath the IC to min-
imize noise coupling.
3) Connect input, output, snubber, and VL capacitors
to the power ground plane; connect all other
capacitors to the signal ground plane.
4) Place the inductor current-sense resistor and capaci-
tor as close to the inductor as possible. Make a
Kelvin connection to minimize the effect of PC board
trace resistance. Place the input bias balance resistor
and bypass capacitor (R5 and C10 in Figures 7 and
8) near CS-. Run two closely parallel traces from
across the capacitor (C9 in Figures 7 and 8) to CS+
and CS-. Place the decoupling capacitor C11 close
to CS+ and CS- pins.
5) Place the MOSFET as close as possible to the IC to
minimize trace inductance of the gate-drive loop. If
parallel MOSFETs are used, keep the trace lengths
to both gates equal.
6) Connect the drain leads of the power MOSFET to a
large copper area to help cool the device. Refer to
the power MOSFET data sheet for recommended
copper area.
7) Place the feedback and compensation components
as close to the IC pins as possible. Connect the
feedback-divider resistor from FB to the output as
close as possible to the farthest output capacitor.
Refer to the MAX8544 evaluation kit for an example layout.
