LTM8045 datasheet(13/30 Pages) LINER

13 / 30 page

LTM4649

4649fc

For more information www.linear.com/LTM4649

APPLICATIONS INFORMATION

PLL and Frequency Synchronization

The LTM4649 device operates over a range of frequen-

cies to improve power conversion efficiency. The nominal

switchingfrequencyis450kHz.Itcanalsobesynchronized

from 400kHz to 800kHz with an input clock that has a high

level above 2V and a low level below 0.8V at the CLKIN pin.

Once the LTM4649 is synchronizing to an external clock

frequency, it will always be running in Forced Continuous

operation.Althoughsynchronizationto250kHzispossible,

400kHz is the lowest recommended operating frequency

to limit inductor ripple current.

Multiphase Operation

For outputs that demand more than 10A of load current,

multiple LTM4649 devices can be paralleled to provide

more output current and reduced input and output volt-

age ripple.

The CLKOUT signal together with CLKIN pin can be used

tocascadeadditionalpowerstagestoachieveamultiphase

power supply solution. Tying the PHMODE pin to INTVCC,

GND, or leaving it floating generates a phase difference

(between CLKIN and CLKOUT) of 180°, 120°, or 90°

respectively as shown in Table 2. A total of 4 phases can

be cascaded to run simultaneously with respect to each

other by programming the PHMODE pin of each LTM4649

channel to different levels. Figure 3 shows a 3-phase de-

sign and 4-phase design example for clock phasing with

the PHMODE table.

Table 2. PHMODE and CLKOUT Signal Relationship

PHMODE

GND

FLOAT

INTVCC

CLKOUT

120°

90°

180°

The LTM4649 device is an inherently current mode con-

trolled device, so parallel modules will have good current

sharing. This will balance the thermals in the design. Tie

the COMP, VFB,TRACK/SSandRUNpinsofeachLTM4649

together to share the current evenly. Figures 19 and 20

each show a schematic of a parallel design.

4649 F03

4-PHASE DESIGN

3-PHASE DESIGN

90 DEGREE

0 PHASE

FLOAT

CLKIN

VOUT

PHMODE

CLKOUT

90 PHASE

CLKIN

VOUT

PHMODE

CLKOUT

180 PHASE

CLKIN

VOUT

PHMODE

CLKOUT

270 PHASE

CLKIN

VOUT

PHMODE

CLKOUT

120 DEGREE

0 PHASE

GND

CLKIN

VOUT

PHMODE

CLKOUT

120 PHASE

CLKIN

VOUT

PHMODE

CLKOUT

240 PHASE

CLKIN

VOUT

PHMODE

CLKOUT

Figure 3. Examples of 3-Phase, 4-Phase Operation with PHMODE Table

FREQ PIN VOLTAGE (V)

900

800

600

400

100

200

700

500

300

4649 F02

2.5

1.5

0.5

Figure 2. Operating Frequency vs FREQ Pin Voltage

LTM8045 데이터시트(PDF) 13 Page - Linear Technology

LTM8045 데이터시트(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

데이터시트 다운로드

링크 URL