SC486 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC486' PDF : 26 Pages View PDF
SC486
POWER MANAGEMENT
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.
U1
11 VTTEN
3 VDDQS
2 TON
6 FB
8 REF
9 COMP
SC486
PGD 7
EN/PSV 1
BST 24
10 VTTS
5 VCCA
4 VSSA
14
15
VTT
VTT
12
13
VTTIN
VTTIN
16
17
PGND2
PGND2
PAD
DH 23
ILIM 21
LX 22
DL 19
VDDP 20
PGND1 18
R10 13k0
Q1
IRF7811AV
Q2
FDS6676S
L1 1u5
Figure 12: Connecting Control and Switcher Power Sections
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.
2006 Semtech Corp.
23
www.semtech.com
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