LTM4650 datasheet(17/38 Pages) AD

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LTM4652

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Figure 5. Examples of 2-Phase, 4-Phase, and 6-Phase Operation with PHASMD Table

4652 F05

VOUT2

180-PHASE

0-PHASE

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

2-PHASE DESIGN

4-PHASE DESIGN

6-PHASE DESIGN

90-DEGREE

FLOAT

VOUT2

180-PHASE

0-PHASE

FLOAT

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

VOUT2

270-PHASE

90-PHASE

FLOAT

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

60-DEGREE

VOUT2

180-PHASE

0-PHASE

SGND

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

VOUT2

240-PHASE

60-PHASE

SGND

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

VOUT2

300-PHASE

120-PHASE

FLOAT

MODE_PLLIN

VOUT1

PHASMD

CLKOUT

PHASMD SGND

CONTROLLER1

CONTROLLER2

CLKOUT

FLOAT

INTVCC

180

240

120

onto incoming clock phase as well. The CLKOUT signal

can be connected to the MODE_PLLIN pin of the following

stage to line up both the frequency and the phase of the

entire system. Tying the PHASMD pin to INTVCC, SGND, or

(floating) generates a phase difference (between

MODE_PLLIN and CLKOUT) of 120 degrees, 60 degrees,

or 90 degrees respectively. A total of 12 phases can be

cascaded to run simultaneously with respect to each other

by programming the PHASMD pin of each LTM4652 chan-

nel to different levels. Figure 5 shows a 2-phase design,

4-phase design and a 6-phase design example for clock

phasing with the PHASMD table.

A multiphase power supply significantly reduces the

amount of ripple current in both the input and output

capacitors. 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 LTM4652s parallel applications, CTH and RTH val-

ues in Table 6 are still valid to achieve transient response in

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

work to the COMP pin of each paralleling module like a dual

phase single output setup. Then connect the COMP pins,

FB pins, TRACK pins and VOUT pins from different mod-

ules together. See Figure 32, Figure 34 and Figure 35 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 LTM4652 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.

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

reduction as a function of the number of interleaved

phases. Figure 6 shows this graph.

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