LTM4677 datasheet(24/110 Pages) AD

24 / 110 page

LTC3888-1

Rev. 0

For more information www.analog.com

OPERATION

PWM phase relationships and frequency are independent

of each other, providing numerous application options.

Multiple LTC3888-1 ICs can be synchronized to real-

ize a PolyPhase array. Two LTC3888-1 devices can be

combined to expand phase count while maintaining ideal

phase separation of 360/n degrees, where n is the num-

ber of phases driving the output voltage rail. Refer to the

Applications Information section for additional details.

POLYPHASE LOAD SHARING

Multiple LTC3888-1 devices can be combined to provide

a balanced load-share solution by configuring the neces-

sary pins. The SHARE_CLK and SYNC pins of all load-

sharing ICs should be bussed together. Connecting the

SYNC pins synchronizes the PWM controllers with each

other. Bussing the SHARE_CLK pins together allows the

phases to start synchronously. Refer to the discussion in

the previous Power-Up and Initialization section. The last

device to see all start-up conditions satisfied controls the

initiation of power sequencing for all phases.

The outputs of multiple LTC3888-1 error amplifiers (ITH

pins) may be wired together in large PolyPhase applica-

tions if VOUT sensing for those channels is also shared.

The error amplifier of only one master phase can also be

designated for voltage control by redefining any remain-

ing master phases as slaves using bit 4 of MFR_PWM_

MODE_LTC3888-1. Additional details for properly con-

structing various PolyPhase designs are covered in the

Applications Information section.

VOLTAGE CONTROL LOOP COMPENSATION

Because the LTC3888-1 uses an operational transcon-

ductance amplifier (OTA) architecture for its error ampli-

fier, Type II compensation is most commonly applied for

stabilizing the voltage control loop. The LTC3888-1 offers

several programmable features for flexability in designing

and operating the PWM with optimum transient behavior

over a wide range of output capacitance without additional

hardware changes.

Bits[4:0] of MFR_PWM_COMP adjust an internal resis-

tor which can be used to set the dominant zero against

the primary compensation capacitance. This resistance

appears between the ITH and ITHR pins.

The transconductance of the error amplifier itself can also

be adjusted using bits[7:5] of MFR_PWM_COMP.

Both of these parameters can be modified when the device

is in operation, affording real-time evaluation of compen-

sation settings. Refer to the Applications Information sec-

ton for additional details related to loop compensation.

LOAD STEP EMULATION

Basic assembly integrity, PWM regulator loop response,

and passive component aging or thermal degredation

are best evaluated by analyzing load current transient

response. The LTC3888-1 features a flexible load step

emulation capability that allows in-situ transient response

evaluation without the need to actually generate and apply

large, regulated load current pulses at the regulator out-

put. These features can find use in the design, debug,

prototyping and preventative maintenence phases of a

product life cycle.

Load step emulation is controlled by MFR_LOAD_

EMULATION. All phases associated with each master

channel can be programmed to emulate a load step of

known amplitude (bits[1:0]). Bit 2 of the command deter-

mines whether the emulated load is applied as a con-

tinuous increase or as a 100μs pulse. Because internal

application of data from a PMBus command is an asyn-

chronous event, bit 3 of the command allows the PGOOD

output to be repurposed to provide a trigger at the actual

start of the emulated load step, if necessary.

INPUT SUPPLY MONITORING

The input supply voltage is sensed by the LTC3888-1 at

the VIN pin. Undervoltage, overvoltage, and valid on/off

levels can be programmed for VIN. Refer to the following

PMBus Command Details section for more information

on programming input supply thresholds. In addition, the

telemetry ADC monitors VIN relative to GND. Conversion

results are returned by READ_VIN.

LTM4677 Datasheet(PDF) 24 Page - Analog Devices

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