LTM4608 LINER [Linear Technology], LTM4608 Datasheet - Page 13

• Manufacturer Part Number: LTM4608
• Description: Low VIN, 8A DC/DC ?ModuleTM with Tracking, Margining, and Frequency Synchronization
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
loop allows the LTM4608 to lock onto CLKIN’s phase as
well. The CLKOUT signal can be connected to the CLKIN
pin of the following LTM4608 stage to line up both the
frequency and the phase of the entire system. Tying the
PHMODE pin to SV
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 12 phases can
be cascaded to run simultaneously with respect to each
other by programming the PHMODE pin of each LTM4608
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
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
CLKIN
PHMODE
PHASE 1
0
CLKOUT
CLKIN
PHMODE
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 1
PHASE 5
PHASE 9
IN
+120
120
240
0
CLKOUT
CLKOUT
CLKOUT
, SGND or SV
CLKIN
PHMODE
+90
+90
+90
PHASE 3
120
CLKOUT
IN
CLKIN
PHMODE
CLKIN
PHMODE
CLKIN
PHMODE
/2 (fl oating) generates
IN
PHASE 12
PHASE 4
PHASE 8
) for the 4th stage.
+120
210
330
S
90
VIN
CLKOUT
CLKOUT
CLKOUT
CLKIN
PHMODE
Figure 3. 12-Phase Operation
Figure 2. 6-Phase Operation
+90
+90
PHASE 5
240
CLKOUT
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 11
PHASE 7
+180
180
300
CLKOUT
CLKOUT
the 6th stage (PHMODE is fl oating) goes back to the 1st
stage. Figure 3 shows the confi guration for a 12 phase
confi guration
A multiphase power supply signifi cantly 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.
The LTM4608 device is an inherently current mode con-
trolled device. Parallel modules will have very good current
sharing. This will balance the thermals on the design.
Tie the I
current evenly. To reduce ground potential noise, tie the
I
THM
CLKIN
PHMODE
+120
+90
pins of all LTM4608s together and then connect to
PHASE 2
(420)
60
TH
CLKOUT
pins of each LTM4608 together to share the
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 10
PHASE 3
(420)
+120
270
60
CLKOUT
CLKOUT
CLKIN
PHMODE
+120
+90
PHASE 4
180
CLKOUT
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 2
PHASE 6
(390)
+120
150
30
CLKOUT
CLKOUT
LTM4608
CLKIN
PHMODE
+90
+90
4608 F03
PHASE 6
300
CLKOUT
13
4608 F02
4608f