Datasheet

LTM4622
12
Rev. G
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The LTM4622 device is an inherently current mode con-
trolled device, so parallel modules will have very good
current sharing. This will balance the thermals on the
design. Please tie RUN, TRACK/SS, FB and COMP pin
of each paralleling channel together. Figure28 shows an
example of parallel operation and pin connection.
INPUT RMS Ripple Current Cancellation
Application Note 77 provides a detailed explanation of
multiphase operation. The input RMS ripple current can-
cellation mathematical derivations are presented, and
a graph is displayed representing the RMS ripple cur-
rent reduction as a function of the number of interleaved
phases. Figure3 shows this graph.
Soft-Start and Output Voltage Tracking
The TRACK/SS pin provides a means to either soft-start
the regulator or track it to a different power supply. A
capacitor on the TRACK/SS pin will program the ramp
rate of the output voltage. An internal 1.4µA current
source will charge up the external soft-start capacitor
towards INTV
CC
voltage. When the TRACK/SS voltage is
below 0.6V, it will take over the internal 0.6V reference
voltage to control the output voltage. The total soft-start
time can be calculated as:
t
SS
= 0.6 •
C
SS
1.4µA
where C
SS
is the capacitance on the TRACK/SS pin.
Current foldback and force continuous mode are disabled
during the soft-start process.
The LTM4622 has internal 400μs soft-start time when
TRACK/SS leave floating.
Output voltage tracking can also be programmed
externally using the TRACK/SS pin. The output can be
APPLICATIONS INFORMATION
Figure3. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle
0.75
0.8
4622 F03
0.70.650.60.550.50.450.40.350.30.250.20.150.1
0.85
0.9
DUTY FACTOR (V
OUT
/V
IN
)
0
DC LOAD CURRENT
RMS INPUT RIPPLE CURRENT
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
1-PHASE
2-PHASE
3-PHASE
4-PHASE
6-PHASE
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