Datasheet
LTM4601AHV
12
4601ahvfc
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Multiphase operation with multiple LTM4601AHV devices
in parallel will lower the effective output ripple current due
to the interleaving operation of the regulators. For example,
each LTM4601AHV’s inductor current in a 12V to 2.5V
multiphase design can be read from the Inductor Ripple
Current versus Duty Cycle graph (Figure 3). The large
ripple current at low duty cycle and high output voltage
can be reduced by adding an external resistor from f
SET
to
ground which increases the frequency. If the duty cycle is
DC = 2.5V/12V = 0.21, the inductor ripple current for 2.5V
output at 21% duty cycle is ~6A in Figure 3.
Figure 4 provides a ratio of peak-to-peak output ripple cur
-
rent to the inductor current as a function of duty cycle and
the
number
of paralleled phases. Pick the corresponding
duty cycle and the number of phases to arrive at the correct
output ripple current ratio value. If a 2-phase operation is
chosen at a duty cycle of 21%, then 0.6 is the ratio. This
0.6 ratio of output ripple current to inductor ripple of 6A
equals 3.6A of effective output ripple current. Refer to
Application Note 77 for a detailed explanation of output
ripple current reduction as a function of paralleled phases.
The output ripple voltage has two components that are
related to the amount of bulk capacitance and effective
series resistance (ESR) of the output bulk capacitance.
Figure 4. Normalized Output Ripple Current vs Duty Cycle, Dlr = V
O
T/L
I
, Dlr = Each Phase’s Inductor Current
DUTY CYCLE (V
O
/V
IN
)
0.1 0.15 0.2 0.25 0.350.3 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85
0.9
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
4601AHV F04
6-PHASE
4-PHASE
3-PHASE
2-PHASE
1-PHASE
PEAK-TO-PEAK OUTPUT RIPPLE CURRENT
DIr
RATIO =
Figure 3. Inductor Ripple Current vs Duty Cycle
DUTY CYCLE (V
OUT
/V
IN
)
0
0
I
L
(A)
2
4
6
8
10
12
0.2 0.4 0.6 0.8
4601AHV F03
2.5V OUTPUT
5V OUTPUT
1.8V OUTPUT
1.5V OUTPUT
1.2V OUTPUT
3.3V OUTPUT WITH
130k ADDED FROM
V
OUT
TO f
SET
5V OUTPUT WITH
100k ADDED FROM
f
SET
TO GND
applicaTions inForMaTion