ltc3730 Linear Technology Corporation, ltc3730 Datasheet - Page 23

• Manufacturer Part Number: ltc3730
• Description: 3-phase, 5-bit Intel Mobile Vid, 600khz, Synchronous Buck Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
7) Minimize trace impedances of TG, BG and SW nets. TG
and SW must be routed in parallel with minimum distance.
Figure 12 illustrates all branch currents in a three-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 elec-
tric 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
V
IN
R
BOLD LINES INDICATE HIGH
SWITCHING CURRENTS.
KEEP LINES TO A MININMUM
LENGTH.
IN
+
C
IN
U
U
W
SW1
SW2
SW3
U
D2
D1
D3
Figure 12
L1
L2
L3
to the “noise” generated by a switching regulator. The
ground terminations of the synchronous MOSFETs and
Schottky diodes should return to the 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 and output capacitor(s)
should be used to tie in the IC power ground pin (PGND).
This technique keeps inherent signals generated by high
current pulses taking alternate current paths that have fi-
nite impedances during the total period of the switching
regulator. External OPTI-LOOP compensation allows over-
compensation for PC layouts which are not optimized but
this is not the recommended design procedure.
R
R
R
SENSE2
SENSE3
SENSE1
C
OUT
3730 F12
V
+
OUT
LTC3730
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R
L
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