LTM4644 datasheet(16/36 Pages) LINER

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LTM4650A-1

4650a1f

For more information www.linear.com/LTM4650A-1

APPLICATIONS INFORMATION

Figure 6. Input RMS Current Ratios to DC Load Current as a Function of Duty Cycle

DUTY FACTOR (VOUT/VIN)

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9

0.60

0.55

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

4650a1 F06

6-PHASE

4-PHASE

3-PHASE

2-PHASE

1-PHASE

A multiphase power supply significantly reduces the

amount of ripple current in both the input and output ca-

pacitors. 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 when all of the outputs are tied together

to achieve a single high output current design.

In multi LTM4650A-1s parallel applications, CTH and RTH

valuesinTable6arestillvalidtoachievetransientresponse

in a 25% load step. Connect one set of RC (RTH and CTH)

network to the COMP pin of each paralleling module like

a dual phase single output setup. Then connect the COMP

pins, FB pins, TRACK/SS pin and VOUT pins from different

modules together. See Figure 35 and 37 for examples of

parallel operation. LTpowerCAD Power Design Tool can

also be used to optimize loop compensation and transient

performance if only one set of RC (RTH and CTH) network

is to be added to the common COMP pins.

The LTM4650A-1 device is an inherently current mode

controlled device, so parallel modules will have very

good current sharing. This will balance the thermals on

the design.

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 current

reductionasafunctionofthenumberofinterleavedphases.

Figure 6 shows this graph.

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