LTC6902 datasheet(11/28 Pages) LINER

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LTM4632

4632fc

For more information www.linear.com/LTM4632

APPLICATIONS INFORMATION

Force Continuous Current Mode (CCM) Operation

In applications where fixed frequency operation is more

critical than low current efficiency, and where the low-

est output ripple is desired, forced continuous opera-

tion should be used. Forced continuous operation can

be enabled by tying the SYNC/MODE pin to GND. In this

mode, inductor current is allowed to reverse during low

output loads, the COMP voltage is in control of the current

comparator threshold throughout, and the top MOSFET

always turns on with each oscillator pulse. During start-

up, forced continuous mode is disabled and inductor

current is prevented from reversing until the LTM4632’s

output voltage is in regulation.

Operating Frequency

The operating frequency of the LTM4632 is optimized to

achieve the compact package size and the minimum output

ripple voltage while still keeping high efficiency. The default

operating frequency is internally set to 1MHz. In most appli-

cations, no additional frequency adjusting is required.

Frequency Synchronization

The power module has a phase-locked loop comprised

of an internal voltage controlled oscillator and a phase

detector. This allows the internal top MOSFET turn-on to

be locked to the rising edge of the external clock. The

external clock frequency range must be within ±30%

around the set operating frequency. A pulse detection

circuit is used to detect a clock on the SYNC/MODE pin

to turn on the phase locked loop. The pulse width of the

clock has to be at least 100ns. The clock high level must

be above 2V and clock low level below 0.3V. The presence

of an external clock will place both regulator channels into

forced continuous mode operation. During the start-up of

the regulator, the phase-locked loop function is disabled.

Multiphase Operation (Configured as Multiphase

Single Output VTT)

For VTT termination output loads that demand more than

3A of current, two outputs in the LTM4632 or even mul-

tiple LTM4632s can be paralleled to run out of phase to

provide a multiphase single output VTT termination supply

capable of souring and sinking higher current.

33.2k

3.3

INTVCC

V+

MOD

VOUT1

VOUT2

OUT1

0°

90°

270°

4632 F02

180°

VTT

12A

90°

OUT2

SET

SYNC/

MODE

VOUT1

VOUT2

SYNC/

MODE

DIV

GND

LTC6902

LTM4632

Figure 2. Example of Clock Phasing for 4-Phase

Single Output VTT Operation with LTC6902

The two switching mode regulator channels inside the

LTM4632 are internally set to operate 180° out of phase.

Multiple LTM4632s could easily operate 90 degrees,

60 degrees or 45 degrees shift which corresponds to

4-phase, 6-phase or 8-phase operation by letting SYNC/

MODE of the LTM4632 synchronize to an external multi-

phase oscillator like LTC6902. Figure 2 shows a 4-phase

single output VTT termination supply design example for

clock phasing.

Tie FB1 pin of the LTM4632 to its INTVCC pin to put the

module into two phase single VTT output operation mode.

This will internally switch the Channel 1 error amplifier

reference voltage from 0.6V to VTTR voltage, which is the

same as Channel 2. Repeat this for each LTM4632 module

in multiple LTM4632s paralleling application.

Also tie RUN, TRACK/SS and COMP pin of each paral-

leling channel together. Figure 20 shows an example of

paralleled multiphase single output VTT termination sup-

ply operation and pin connection.

The LTM4632 device is an inherently current mode con-

trolled device, so parallel modules will have very good cur-

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

Multiphase Operation (Configured as VDDQ+VTT)

For application which both VDDQ and VTT termination

output loads demand more than 3A of current, two or

multiple Channel 1 outputs from different LTM4632 mod-

ules can be easily paralleled to provide a multiphase sin-

gle VDDQ output while Channel 2 outputs from different

LTM4632 modules can paralleled to provide a multiphase

single VTT output.

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