ltc3729euh-trpbf Linear Technology Corporation, ltc3729euh-trpbf Datasheet - Page 24

• Manufacturer Part Number: ltc3729euh-trpbf
• Description: 550khz, Polyphase, High Efficiency, Synchronous Step-down Switching Regulator
• Manufacturer: Linear Technology Corporation

LTC3729
APPLICATIO S I FOR ATIO
The diagram in Figure 9 illustrates all branch currents in a
2-phase switching regulator. It becomes very clear after
studying the current waveforms why it is critical to keep
the high-switching-current paths to a small physical size.
High electric and magnetic fields will radiate from these
“loops” just as radio stations transmit signals. The output
capacitor ground should return to the negative terminal
of the input capacitor and not share a common ground
path with any switched current paths. The left half of the
circuit gives rise to the “noise” generated by a switching
regulator. The ground terminations of the sychronous
MOSFETs and Schottky diodes should return to the
24
R
IN
V
IN
C
IN
BOLD LINES INDICATE
HIGH, SWITCHING
CURRENT LINES.
KEEP LINES TO A
MINIMUM LENGTH.
+
U
Figure 9. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator
U
W
SW1
SW2
U
D1
D2
bottom plate(s) of the input capacitor(s) with a short
isolated PC trace since very high switched currents are
present. A separate isolated path from the bottom plate(s)
of the input capacitor(s) should be used to tie in the IC
power ground pin (PGND) and the signal ground pin
(SGND). This technique keeps inherent signals generated
by high current pulses from taking alternate current paths
that have finite impedances during the total period of the
switching regulator. External OPTI-LOOP compensation
allows overcompensation for PC layouts which are
not optimized but this is not the recommended design
procedure.
L1
L2
R
R
SENSE1
SENSE2
+
C
V
OUT
OUT
3729
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F09
R
L