LTM4609 datasheet(14/38 Pages) LINER

14 / 38 page

LTM4636-1

46361fa

For more information www.linear.com/LTM4636-1

Multiphase Operation

For outputs that demand more than 40A of load current,

multiple LTM4636-1 devices can be paralleled to provide

more output current without increasing input and output

ripplevoltage.TheMODE_PLLINpinallowstheLTM4636-1

to be synchronized to an external clock and the internal

phase-locked loop allows the LTM4636-1 to lock onto

input clock phase as well. The FREQ resistor is selected

for normal frequency, then the incoming clock can syn-

chronize the device over the specified range.

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. See Application Note 77.

The LTM4636-1 device is an inherently current mode

controlled device, so parallel modules will have good cur-

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

Tie the COMPA to COMPB and then tie the COMPA pins

together, tie VFBpinsofeachLTM4636-1togethertoshare

the current evenly. Figure 21 shows a schematic of the

parallel design. For external compensation and parallel

operation only tie COMP A pins together with external

compensation.

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

(see Figure 2).

PLL, Frequency Adjustment and Synchronization

The LTM4636-1 switching frequency is set by a resistor

(RFREQ)fromtheFREQpintosignalground.A20µAcurrent

(IFREQ)flowingoutoftheFREQpinthroughRFREQdevelops

a voltage on the FREQ pin. RFREQ can be calculated as:

RFREQ

FREQV

20µA

APPLICATIONS INFORMATION

Figure 2. Normalized Input RMS Ripple Current vs Duty Cycle for One to Six µModule Regulators (Phases)

0.75 0.8

46361 F02

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)

0.05

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

LTM4609 Datasheet(PDF) 14 Page - Linear Technology

LTM4609 Datasheet(HTML) 14 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 31 32 33 34 35 36 37 38

Datasheet Download

Link URL