SC411EVB SEMTECH [Semtech Corporation], SC411EVB Datasheet - Page 17

• Manufacturer Part Number: SC411EVB
• Description: Synchronous Buck Pseudo-Fixed Frequency Power Supply Controller
• Manufacturer: SEMTECH [Semtech Corporation]

Layout Guidelines
One (or more) ground planes is/are recommended to minimize the effect of switching noise and copper losses, and
maximize heat dissipation. The IC ground reference, VSSA, and the power ground pin, PGND, should both connect
directly to the device thermal pad. The thermal pad should connect to the ground plane(s) using multiple vias.
The VOUT feedback trace must be kept far away from noise sources such as switching nodes, inductors and gate
drives. Route the feedback trace in a quiet layer (if possible) from the output capacitor back to the chip. All compo-
nents should be located adjacent to their respective pins with an emphasis on the chip decoupling capacitors (VCCA
and VDDP) and the components that are shown connecting to VSSA in the above schematic. Make any ground con-
nections simply to the ground plane.
Power sections should connect directly to the ground plane(s) using multiple vias as required for current handling (in-
cluding the chip power ground connections). Power components should be placed to minimize loops and reduce loss-
es. Make all the connections on one side of the PCB using wide copper fi lled areas if possible. Do not use “minimum”
land patterns for power components. Minimize trace lengths between the gate drivers and the gates of the MOSFETs
to reduce parasitic impedances (and MOSFET switching losses), the low-side MOSFET is most critical. Maintain a
length to width ratio of <20:1 for gate drive signals. Use multiple vias as required by current handling requirements
(and to reduce parasitics) if routed on more than one layer. Current sense connections must always be made using
Kelvin connections to ensure an accurate signal, with the current limit resistor located at the device.
We will examine the reference design used in the Design Procedure section while explaining the layout guidelines in
more detail.
© 2007 Semtech Corp.
POWER MANAGEMENT
PGOOD
VBAT = 8V to 20V
VOUT = 1.2V @ 6A
VBAT
R1
1M
0402
C8
1nF
0402
C5
56p
0402
VOUT
R3
20k0
0402
R5
14k3
0402
R2
10R
0402
5VSUS
C9
1uF
0603
1
2
3
4
VOUT
VCCA
FB
PGD
U1
Figure 4: Reference Design
SC411
VDDP
ILIM
17
DH
LX
12
11
10
9
5VSUS
C10
1uF
0603
R4 7k87
0402
D1
SOD323
C1 0u1
0603
IRF7811AV
FDS6676S
Q1
Q2
VBAT
C2
2n2/50V
0402
L1
2u2
C3
0u1/25V
0603
+
C6
220u/25m
7343
C4
10u/25V
1210
+
C7
220u/25m
7343
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SC411
VOUT