LTM4628
applicaTions inForMaTion
Pulse-Skipping Mode Operation
should be used. Forced continuous operation can be
enabled by tying the MODE_PLLIN pin to SGND. In this
mode, inductor current is allowed to reverse during low
output loads, the COMP voltage is in control of the current
comparator threshold throughout, and the top MOSFET
alwaysturnsonwitheachoscillatorpulse.Duringstart-up,
forced continuous mode is disabled and inductor current
is prevented from reversing until the LTM4628’s output
voltage is in regulation. Either regulator can be configured
for forced continuous mode.
Inapplicationswherelowoutputrippleandhighefficiency
at intermediate currents are desired, pulse-skipping
mode should be used. Pulse-skipping operation allows
the LTM4628 to skip cycles at low output loads, thus
increasing efficiency by reducing switching loss. Tying
the MODE_PLLIN pin to INTV enables pulse-skipping
CC
operation. At light loads the internal current comparator
may remain tripped for several cycles and force the top
MOSFETtostayoffforseveralcycles,thusskippingcycles.
The inductor current does not reverse in this mode. This
modewillmaintainhighereffectivefrequenciesthuslower
output ripple and lower noise than Burst Mode operation.
Eitherregulatorcanbeconfiguredforpulse-skippingmode.
Multiphase Operation
For output loads that demand more than 8A of current,
two outputs in LTM4628 or even multiple LTM4628s can
be paralleled to run out of phase to provide more output
currentwithoutincreasinginputandoutputvoltageripple.
TheMODE_PLLINpinallowstheLTM4628tosynchronize
to an external clock (between 400kHz and 780kHz) and
theinternalphase-lockedloopallowstheLTM4628tolock
Forced Continuous Operation
In applications where fixed frequency operation is more
critical than low current efficiency, and where the lowest
output ripple is desired, forced continuous operation
PHASMD PIN STATUS AND CORRESPONDING
PHASE RELATIONSHIP
2-PHASE DESIGN
FLOAT
CLKOUT
MODE_PLLIN
PHASMD SGND FLOAT INTV
CC
CONTROLLER1
CONTROLLER2
CLKOUT
0°
0°
0°
180°
60°
180°
90°
240°
120°
0 PHASE
180 PHASE
V
OUT1
V
OUT2
SGND OR FLOAT
PHASMD
4-PHASE DESIGN
90 DEGREE
CLKOUT
MODE_PLLIN
CLKOUT
MODE_PLLIN
0 PHASE
FLOAT
180 PHASE
90 PHASE
270 PHASE
V
OUT1
V
V
OUT1
V
OUT2
OUT2
FLOAT
PHASMD
PHASMD
6-PHASE DESIGN
60 DEGREE
60 DEGREE
CLKOUT
MODE_PLLIN
CLKOUT
CLKOUT
MODE_PLLIN
MODE_PLLIN
0 PHASE
SGND
180 PHASE
60 PHASE
SGND
240 PHASE
120 PHASE
FLOAT
300 PHASE
V
OUT1
V
V
V
V
OUT1
V
OUT2
OUT2
OUT1
OUT2
PHASMD
PHASMD
PHASMD
4628 F03
Figure 3. Examples of 2-Phase, 4-Phase, and 6-Phase Operation with PHASMD ꢁable
4628fd
13
LINEAR_DIMENSIONS [ Linear Dimensions ]
