LTM4645 datasheet(13/34 Pages) LINER

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LTM4645

4645f

For more information www.linear.com/LTM4645

applicaTions inForMaTion

PLL and Frequency Synchronization

Forsomeswitchingnoisesensitiveapplications,LTM4645

can be synchronized from 300kHz to 1MHz subject to

minimum on-time and inductor current ripple limitation

with an input clock that has a high level above 2V and a

low level below 0.8V at the MODE_PLLIN pin. Once the

LTM4645 is synchronizing to an external clock frequency,

it will always be running in forced continuous current

operation. The 300kHz low end operation frequency limit

is suggested to limit inductor ripple current.

Multiphase Operation

For outputs that demand more than 25A of load current,

multiple LTM4645 devices can be paralleled to provide

more output current without increasing input and output

voltage ripple.

The MODE_PLLIN pin allows the LTM4645 to synchronize

to an external clock (between 300kHz and 1MHz) and the

internal phase-locked loop allows the LTM4645 to lock

onto an 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, three-

fourths of INTVCC, floating or, SGND generates a phase

difference (between VOUT and CLKOUT) of 180 degrees,

60 degrees, 120 degrees, 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 LTM4645 channel to different levels. Figure 3

shows a 2-phase, 3-phase, 4-phase, and 6-phase design

example for clock phasing.

VFREQ (V)

0.4

900

1100

1300

1.0

1.4

4645 F02

700

500

0.6

0.8

1.2

1.6

1.8

300

100

Figure 2. Relationship Between Switching Frequency

and FREQ Pin Voltage

Figure 3. Phase Selection Examples

LTM4645

180 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

3/4 INTVCC

LTM4645

240 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

3/4 INTVCC

LTM4645

300 PHASE

MODE_PLLIN

PHASMD

4645 F03

CLKOUT

VOUT

3/4 INTVCC

LTM4645

0 PHASE

MODE_PLLIN

PHASMD

10k

30.1k

CLKOUT

VOUT

LTM4645

0 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

90 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

180 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

270 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

3/4 INTVCC

INTVCC

LTM4645

60 PHASE

SIX PHASE

FOUR PHASE

LTM4645

0 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

120 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

240 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

THREE PHASE

LTM4645

0 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

LTM4645

180 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

INTVCC

TWO PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

3/4 INTVCC

LTM4645

120 PHASE

MODE_PLLIN

PHASMD

CLKOUT

VOUT

3/4 INTVCC

VOUT

PHASE

CLKOUT

PHASE

120

180

PHASMD

(V)

1/4 INTVCC

FLOAT

3/4 INTVCC

INTVCC

PHASE SELECTION

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