SC486 Semtech Corporation, SC486 Datasheet - Page 23

• Manufacturer Part Number: SC486
• Description: Complete DDR1/2/3 Memory Power Supply
• Manufacturer: Semtech Corporation

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Layout Guidelines (Cont.)
Key points for the switcher power section:
1) there should be a very small input loop, well decoupled.
2) the phase node should be a large copper pour, but compact since this is the noisiest node.
3) input power ground and output power ground should not connect directly, but through the ground planes instead.
Connecting the control and switcher power sections should be accomplished as follows (see Figure 12 below):
1) Route VDDQ feedback trace in a “quiet” layer away from noise sources.
2) Route DL, DH and LX (low side FET gate drive, high side FET gate drive and phase node) to chip using wide traces
with multiple vias if using more than one layer. These connections are to be as short as possible for loop minimization,
with a length to width ratio less than 20:1 to minimize impedance. DL is the most critical gate drive, with power
ground as its return path. LX is the noisiest node in the circuit, switching between VBAT and ground at high frequencies,
thus should be kept as short as practical. DH has LX as its return path.
3) BST is also a noisy node and should be kept as short as possible.
4) Connect PGND pins on the chip directly to the VDDP decoupling capacitor and then drop vias directly to the
ground plane.
Phase nodes (black) to be copper islands (preferred) or wide copper traces. Gate drive traces (red) and phase node
traces (blue) to be wide copper traces (L:W < 20:1) and as short as possible, with DL the most critical. Use multiple
vias when switching between layers. Locate the current limit resistor (R10) at the chip with a kelvin connection to
the phase node.
POWER MANAGEMENT
2006 Semtech Corp.
11
10
14
15
12
13
16
17
3
2
6
8
9
5
4
U1
VTTEN
VDDQS
TON
FB
REF
COMP
VTTS
VCCA
VSSA
VTT
VTT
VTTIN
VTTIN
PGND2
PGND2
Figure 12: Connecting Control and Switcher Power Sections
PAD
EN/PSV
PGND1
VDDP
SC486
PGD
ILIM
BST
DH
DL
LX
7
1
24
23
21
22
19
20
18
R10 13k0
23
Q1
IRF7811AV
Q2
FDS6676S
L1
1u5
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SC486