Data Sheet

LTM4640

analog.com

Rev. 0

18 of 38

Table 8. PHMODE Pin Status and Corresponding Phase Relationship (Relative to CLKIN)

PHMODE

INTVCC

GND

FLOAT

CLKOUT

180°

120°

90°

Figure 19. 4-Phase Operation with an External Clock IC and Low-Pass Filters

A multiphase power supply significantly reduces the amount of ripple current in both the input and the output

capacitors. The RMS input ripple current is reduced by, and the effective ripple frequency is multiplied by, the

number of phases used (if the input voltage exceeds the number of phases used times the output voltage). The

output ripple amplitude is also reduced by the number of phases used when all the outputs are connected to

achieve a single high output current design.

The LTM4640 is an inherently current mode-controlled device, which ensures good current sharing in parallel

operation. This balances the thermals on the design. Connect the RUN, TRACK/SS, FB, and COMPa pins of each

paralleling channel together. Figure 39 shows an example of a parallel operation and the pins connection.

Input RMS Ripple Current Cancellation

Analog Devices Application Note 77 provides a detailed explanation of a multiphase operation. The input RMS ripple

current cancellation mathematical derivations are presented, and a graph is displayed representing the RMS ripple

current reduction as a function of the number of interleaved phases. Figure 20 shows this graph.

Figure 20. The RMS Input Ripple Current to DC Load Current Ratio as a Function of the Duty Cycle

1kΩ

1kΩ

1kΩ

1kΩ

68pF

68pF

68pF

68pF

PHASE 1

MODE/CLKIN

CLK1

CLK2

CLK4

CLK3

0°

90°

180°

270°

VOUT

LTC6902

LTM4640

MODE/CLKIN

VOUT

LTM4640

MODE/CLKIN

VOUT

LTM4640

MODE/CLKIN

VOUT

LTM4640

PHASE 2

PHASE 3

PHASE 4

0.75 0.8

0.7

0.65

0.6

0.55

0.5

0.45

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.85 0.9

DUTY CYCLE (VOUT/VIN)

0

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