ltm4608a Linear Technology Corporation, ltm4608a Datasheet - Page 13

• Manufacturer Part Number: ltm4608a
• Description: Low Vin, 8a Dc/dc ?module With Tracking, Margining, And Frequency Synchronization
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
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
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 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
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
CLKIN
PHMODE
PHASE 1
0
CLKOUT
CLKIN
PHMODE
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 1
PHASE 5
PHASE 9
+120
IN
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
+120
) for the 4th stage.
S
210
330
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
on the 6th stage (PHMODE is fl oating) goes back to the
1st stage. Figure 3 shows the confi guration for 12-phase
operation.
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 LTM4608A 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 LTM4608As together and then connect to
PHASE 2
(420)
60
CLKOUT
TH
pins of each LTM4608A together to share the
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 10
PHASE 3
+120
(420)
270
60
CLKOUT
CLKOUT
CLKIN
PHMODE
+120
+90
PHASE 4
180
CLKOUT
CLKIN
PHMODE
CLKIN
PHMODE
PHASE 2
PHASE 6
+120
(390)
150
30
LTM4608A
CLKOUT
CLKOUT
CLKIN
PHMODE
4608A F03
PHASE 6
+90
+90
300
CLKOUT
13
4608af
4608A F02