LTC3735 LINER [Linear Technology], LTC3735 Datasheet - Page 26

• Manufacturer Part Number: LTC3735
• Description: 2-Phase, High Efficiency DC/DC Controller for Intel Mobile CPUs
• Manufacturer: LINER [Linear Technology]

The ground terminations of the sychronous MOSFETs and
Schottky diodes should return to the negative 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 negative 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.
LTC3735
APPLICATIONS INFORMATION
26
R
IN
V
IN
C
IN
BOLD LINES INDICATE
HIGH, SWITCHING
CURRENT LINES.
KEEP LINES TO A
MINIMUM LENGTH.
+
Figure 12. Instantaneous Current Path Flow in a Multiple Phase Switching Regulator
SW1
SW2
D1
D2
Simplified Visual Explanation of How a 2-Phase
Controller Reduces Both Input and Output RMS Ripple
Current
A multiphase power supply significantly reduces the
amount of ripple current in both the input and output
capacitors. The RMS input ripple current is divided by,
and the effective ripple frequency is multiplied up by the
number of phases used (assuming that the input voltage
is greater than the number of phases used times the out-
put voltage). The output ripple amplitude is also reduced
by, and the effective ripple frequency is increased by the
number of phases used. Figure 13 graphically illustrates
the principle.
L1
L2
R
R
SENSE1
SENSE2
3735 F12
+
C
V
OUT
OUT
R
L
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