Datasheet

LTM4608A
13
4608afd
applicaTions inForMaTion
provide more output current without increasing input and
output voltage ripple. The CLKIN pin allows the LTM4608A
to synchronize to an external clock (between 0.75MHz
and 2.25MHz) and the internal phase locked loop allows
the LTM4608A to lock onto CLKIN’s phase as well. The
CLKOUT signal can be connected to the CLKIN pin of the
following LTM4608A stage to line up both the frequency
and the phase of the entire system. Tying the PHMODE
pin to SV
IN
, SGND or SV
IN
/2 (floating) generates a phase
difference (between CLKIN and CLKOUT) of 180°, 120°
or 90° respectively, which corresponds to a 2-phase,
3-phase or 4-phase operation. A total of 6 phases can be
cascaded to run simultaneously with respect to each other
by programming the PHMODE pin of each LTM4608A to
different levels. For a 6-phase example in Figure 2, the
2nd stage that is 120° out of phase from the 1st stage
can generate a 240° (PHMODE = 0) CLKOUT signal for
the 3rd stage, which then can generate a CLKOUT signal
that’s 420°, or 60° (PHMODE = SV
IN
) for the 4th stage.
With the 60° CLKIN input, the next two stages can shift
120° (PHMODE = 0) for each to generate a 300° signal
for the 6th stage. Finally, the signal with a 60° phase shift
on the 6th stage (PHMODE is floating) goes back to the
1st stage. Figure 3 shows the configuration for 12-phase
operation.
A multiphase power supply significantly reduces the
amount of ripple current in both the input and output
capacitors. The RMS input ripple current is reduced by,
and the effective ripple frequency is multiplied by, the
number of phases used (assuming that the input voltage
is greater than the number of phases used times the output
voltage). The output ripple amplitude is also reduced by
the number of phases used.
Figure 2. 6-Phase Operation
Figure 3. 12-Phase Operation
4608A F02
0
+120
PHASE 1
CLKOUTCLKIN
PHMODE
120
PHASE 3
CLKOUTCLKIN
PHMODE
240
+180+120
PHASE 5
CLKOUTCLKIN
PHMODES
VIN
(420)
60
PHASE 2
CLKOUTCLKIN
PHMODE
+120
180
PHASE 4
CLKOUTCLKIN
PHMODE
+120
300
PHASE 6
CLKOUTCLKIN
PHMODE
4608 F02
0
+120
PHASE 1
CLKOUTCLKIN
PHMODE
120
PHASE 5
CLKOUTCLKIN
PHMODE
240
+180+120
PHASE 9
CLKOUTCLKIN
PHMODES
VIN
(420)
60
PHASE 3
CLKOUTCLKIN
PHMODE
+120
180
PHASE 7
CLKOUTCLKIN
PHMODE
+120
300
PHASE 11
CLKOUTCLKIN
PHMODE
4608A F03
90
+120
PHASE 4
CLKOUTCLKIN
PHMODE
OUT1
OUT2
V
+
LTC6908-2
210
PHASE 8
CLKOUTCLKIN
PHMODE
330
+180+120
PHASE 12
CLKOUTCLKIN
PHMODES
VIN
(510)
150
PHASE 6
CLKOUTCLKIN
PHMODE
+120
270
PHASE 10
CLKOUTCLKIN
PHMODE
+120
(390)
30
PHASE 2
CLKOUTCLKIN
PHMODE