LTM4611



4611f

enabled by tying the MODE_PLLIN pin to GND. In this

mode, inductor current is allowed to reverse during low

comparator threshold throughout, and the top MOSFET

alwaysturnsonwitheachoscillatorpulse.Duringstart-up,

forced continuous mode is disabled and inductor current

is prevented from reversing until the LTM4611’s output

voltage is in regulation.

Multiphase Operation

For outputs that demand more than 15A of load current,

multiple LTM4611 devices can be paralleled to provide

more output current without increasing input and output

voltageripples.TheMODE_PLLINpinallowstheLTM4611

to be synchronized to an external clock (between 360kHz

to 710kHz) and the internal phase-locked loop allows the

LTM4611 to lock onto input clock phase as well. The PLL-

Figures 18 and 19 for a synchronizing example circuit.

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 LTM4611 device is an inherently current mode con-

trolled device, so parallel modules will have good current

sharing. This will balance the thermals on the design.

together to share the current evenly. In addition, tie the

respectiveTRACK/SSandRUNpinsofparalleledLTM4611

devices together, to ensure proper start-up and shutdown

behavior. Figures 18 and 19 show schematics of LTM4611

devices operating in parallel.

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).

applicaTions inForMaTion

Figure 2. Normalized Input RMS Ripple Current vs Duty Factor for One to Six µModules (Phases)

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

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