Rainbow Electronics MAX1625 - Manual (Page 22)

MAX1624/MAX1625
High-Speed Step-Down Controllers with
Synchronous Rectification for CPU Power
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• Minimize high-current path trace lengths. Use
very short and wide traces. From C1 to N1: 0.4 in.
(10mm) max length; D1 cathode to N2: 0.2 in.
(5mm) max length; LX node (N1 source, N2 drain,
D1 cathode, inductor L1): 0.6 in. (15mm) max
length.
2) Place the MAX1624/MAX1625 and supporting
components following these rules:
• Minimize trace lengths to the current-sense
resistor.
The IC must be no farther than 0.4 in.
(10mm) from the current-sense resistor. Use a
Kelvin connection.
• Minimize ground trace lengths between the
MAX1624/MAX1625 and supporting compo-
nents.
Connect components for the REF, CC1,
CC2, and FREQ pin directly to AGND. Connect
AGND and PGND at the IC.
• Keep noisy nodes and components away from
sensitive analog nodes,
such as the current-
sense, voltage-feedback, REF, CC1, CC2, and
FREQ pins. Placing the IC and analog compo-
nents on the opposite side of the board from the
power-switching node is desirable. Noisy nodes
include the main switching node (LX), inductor,
and gate-drive outputs.
• Place components for the FREQ, REF, CC1,
and CC2 pins as close to the IC as possible,
within 0.2 in. (5mm).
• Keep the gate-drive traces (DH, DL, and BST)
shorter than 20mm, and route them away from
CSH, CSL, REF, FB, etc.
• Filter the V CC supply input to the IC. Bypass the
IC directly from V DD to PGND using a 0.1µF
ceramic capacitor and 4.7µF electrolytic capacitor
placed within 0.2 in. (5mm) of the IC.
• Place the voltage-feedback components close to
the FB pin of the MAX1625, within 0.2 in. (5mm).
Connect the voltage-feedback trace directly to the
CPU’s power input and route it to avoid noisy
traces.