LTM4615 datasheet(13/32 Pages) LINER

13 / 32 page

LTM4642

4642fb

For more information www.linear.com/LTM4642

Mode Selections and Phase-Locked Loop

The LTM4642 can be enabled to operate in discontinuous

orforcedcontinuousmode.Toselecttheforcedcontinuous

operation, tie the MODE/PLLIN pin to INTVCC. To select

discontinuous operation, or tie the MODE/PLLIN pin to

ground. This will improve the light load efficiency.

Frequency Selection and External Clock

Synchronization

An internal oscillator (clock generator) provides phase

interleaved internal clock signals for individual channels

to lock on to. The switching frequency and phase of each

switching channel is independently controlled by adjust-

ing the top MOSFET turn-on time (on-time) through the

one-shot timer. This is achieved by sensing the phase

relationship between a top MOSFET turn-on signal and

its internal reference clock through a phase detector, and

the time interval of the one-shot timer is adjusted on a

cycle-by-cycle basis, so that the rising edge of the top

MOSFET turn-on is always trying to synchronize to the

internal reference clock signal for the respective channel.

Thefrequencyoftheinternaloscillatorcanbeprogrammed

from 600kHz to 1.4MHz by connecting a resistor, RFREQ,

from the FREQ pin to signal ground (SGND). The equation:

RFREQ kΩ

( )=

41550

FREQ kHz

(

)

– 2.2

For applications with stringent frequency or interference

requirements, an external clock source connected to the

MODE/PLLIN pin can be used to synchronize the internal

clock signals through a clock phase-locked loop (Clock

PLL). The LTM4642 operates in forced continuous mode

of operation when it is synchronized to the external clock.

The external clock frequency has to be within ±30% of the

internal oscillator frequency for successful synchroniza-

tion. The clock input levels should be no less than 2V for

“high” and no greater than 0.5V for “low”. The MODE/

PLLIN pin has an internal 600k pull-down resistor.

PHASMD Pin Programming

The PHASMD pin determines the relative phases between

the internal reference clock signals for the two channels

applicaTions inForMaTion

as well as the CLKOUT signal, as shown in Table 2. The

phases tabulated are relative to zero degree (0°) being

defined as the rising edge of the internal reference clock

signal of channel 1. The CLKOUT signal can be used to

synchronize additional power regulator modules. The

system can be configured for up to 12-phase operation

with a multichannel solution. Typical configurations are

shown in Table 3 to interleave the phases of the channels.

The applications will validate a 6 phase multiple regulator

solution with multiple outputs.

Each of the LTM4642 channels can be paralleled up to 8A

of output, but cannot be paralleled from one module to

the other modules. Twelve phases can be paralleled with

no more than two phases per module.

Table 2

PHASMD

SGND

FLOAT

INTVCC

Channel 1

0°

Channel 2

180°

240°

CLKOUT

60°

90°

120°

Table 3

NUMBER OF

PHASES

NUMBER OF

LTM4642*

PIN CONNECTIONS

[PIN NAME (CHIP NUMBER)]

PHASMD(1) = FLOAT or SGND

2 or

1 + ½(LTM4642)

PHASMD(1) = INTVCC

MODE/PLLIN(2) = CLKOUT(1)

PHASMD(1) = FLOAT

PHASEMD(2) = FLOAT or SGND

MODE/PLLIN(2) = CLKOUT(1)

PHASMD(1) = SGND

PHASMD(2) = SGND

MODE/PLLIN(2) = CLKOUT(1)

PHASMD(3) = FLOAT or SGND

MODE/PLLIN(3) = CLKOUT(2)

*No more than two channels of any one module may be paralleled.

Soft-Start and Tracking

The LTM4642 has the ability to either soft-start by itself

with a capacitor or track the output of another channel or

externalsupply.Whenoneparticularchannelisconfigured

to soft-start by itself, a capacitor should be connected to

its TRACK/SS pin. This channel is in the shutdown state

if its RUN pin voltage is below 1.2V. Its TRACK/SS pin is

actively pulled to ground in this shutdown state.

LTM4615 Datasheet(PDF) 13 Page - Linear Technology

LTM4615 Datasheet(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 31 32

Datasheet Download

Link URL