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SC416
26
For placement, power devices for side1 should be
grouped together near the gate drive pins for side1
(pins 23-24 and 1-8). Power devices for side2 should be
grouped together near the gate-drive pins for side2 (pins
15-20).
The feedback and VOUT sense components should be
located near the FBx/VOUTx pins. This includes the feed-
back resistors and capacitors if used.
Ground Connections
When doing placement, be aware that there are four
grounds to consider on the pcb. ‘
Power ground for Side1
Power ground for Side2
Analog ground for Side1
Analog ground for Side2
Note that grounds (1) and (2) are high-current and con-
tain high noise. These grounds carry the DL gate drive
current as well as the high switching current through the
MOSFETs and low-side diode. It is important to note that
the SC416 has only one power ground pin (PAD, pin 25),
which must drive DL for both side1 and side2. As such,
the low-side MOSFET and diode will need to be near the
IC.
Grounds (3) and (4) are low-current and intended for
low-noise VOUT/FB ripple sensing. Note that there is
only one analog ground pin (RTN, pin 9) which shared
between sides 1 and 2
Proper connection between the grounds is needed for
good operation. Generally, all ground connections be-
tween the power components and the SC416 should
be short and direct, without vias where possible. Each
side has significant high-current switching in the ground
path, moving between the input capacitors, the low-side
MOSFET, the low-side diode if used, and the output ca-
pacitors. Moreover, each side has significant high-cur-
rent pulses to/from the ground PAD, created by the DL
1.
2.
3.
4.
drive to the low-side MOSFETs. The DL gate-drive cur-
rent peaks can be 2 amps or more, with fast switching. As
such the ground connection between the low-side MOS-
FETs and the ground PAD should be as short and wide as
practical.
Note that the ground PAD, which is the return path for
the high-noise DL drive current, is not accessible on the
top layer of the pcb, due to the other pins. The ground
PAD connection to the MOSFETs must therefore be done
on an inner or bottom layer. For this reason, it is best to
place the low-side MOSFET on the opposite side of the
pcb, to allow a wide and direct connection to the ground
PAD on the bottom layer. Otherwise an inner layer must
be used for the ground PAD connection; if needed, this
should be done with many vias to minimize the high-fre-
quency impedance. This applies to both side1 and side2
MOSFETs.
The remaining power devices should then be placed
with their ground pins near each other, and near the IC.
That is, the ground connections between the IC, the low-
side MOSFET, the low-side diode (if used), the input ca-
pacitors, and the output capacitor, should be short. The
other non-ground power connections (from input cap to
high-side MOSFET, from MOSFETs to inductor, and from
inductor to output capacitor) should be short and wide
as well, to minimize the loop length and area.
Use short, wide traces from the DL/DH pins to the MOS-
FETs to reduce parasitic impedance; the low-side MOS-
FET is most critical. Maintain a length to width ratio of
<20:1 for gate drive signals. Use multiple vias as required
for current handling (and to reduce parasitics) if routed
on more than one layer.
When placing the power components, also be aware that
the VOUT signal must route back to the analog compo-
nents. It is important that this feedback signal not cross
the DH/DL/BST or other high-noise power signals. Place
and rotate the power components in a way that allows
the VOUT trace to get from the output capacitor to the
Applications Information (continued)