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LTM4650A

4650afb

For more information www.linear.com/LTM4650A

APPLICATIONS INFORMATION

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.

The LTM4650A device is an inherently current mode con-

trolled device, so parallel modules will have very good cur-

rent sharing. This will balance the thermals on the design.

Connect the COMP pins, FB pins, TRACK/SS pin and VOUT

pins from different modules together. See Figure 33 and

35 for examples of parallel operation.

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 4 shows this graph.

Figure 4. 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

4650A F04

6-PHASE

4-PHASE

3-PHASE

2-PHASE

1-PHASE

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