LTM4686B datasheet(64/132 Pages) AD

64 / 132 page

LTM4683

Rev. 0

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APPLICATIONS INFORMATION

increased by decreasing CCOMPna. If RCOMP is increased

by the same factor that CCOMP is decreased, the zero fre-

quency will be kept the same, thereby keeping the phase

shift the same in the most critical frequency range of the

feedback loop. The gain of the loop will be proportional to

the transconductance of the error amplifier, gm, which is

set using bits[7:5] of the MFR_PWM_COMP command.

The output voltage settling behavior is related to the sta-

bility of the closed-loop system and will demonstrate the

actual overall supply performance. A second, more severe

transient is caused by switching in loads with large (>1µF)

supply bypass capacitors. The discharged bypass capaci-

tors are effectively put in parallel with COUT, causing a

rapid drop in VOUT. No regulator can alter its delivery of

current quickly enough to prevent this sudden step change

in output voltage if the load switch resistance is low and if

it is driven quickly. If the ratio of CLOAD to COUT is greater

than 1:50, the switch rise time should be controlled so that

the load rise time is limited to approximately 25 • CLOAD.

Thus, a 10µF capacitor would require a 250µs rise time,

limiting the charging current to about 200mA.

PolyPhase Configuration

When configuring a PolyPhase rail with multiple LTM4683s,

the user must share the SYNC, COMP, SHARE_CLK, FAULT,

and ALERT pins of these parts. Be sure to use pull-up resis-

tors on FAULT, SHARE_CLK and ALERT. One of the part’s

SYNC pins must be set to the desired switching frequency,

and all other FREQUENCY_SWITCH commands must be

set to External Clock. If an external oscillator is provided,

set the FREQUENCY_SWITCH command to External Clock

for all parts. The relative phasing of all the channels should

be spaced equally. The MFR_RAIL_ADDRESS of all the

devices should be set to the same value.

Multiple channels need to tie all the VSENSEn+ pins

together, and all the VSENSEn– pins together, COMPna and

COMPnb pins together as well. Do not assert bit[4] of

MFR_CONFIG_ALL except in a PolyPhase application. See

the Typical Applications section (Figure 50).

CONNECTING THE USB TO I2C/SMBUS/PMBUS

CONTROLLER TO THE LTM4683 IN SYSTEM

The ADI USB-to-I2C/SMBus/PMBus adapter (DC1613A

or equivalent) can be interfaced with the LTM4683 on

the user’s board for programming, telemetry, and sys-

tem debugging. The adapter, when used in conjunction

with LTpowerPlay, provides a powerful way to debug an

entire power system. Faults are quickly diagnosed using

telemetry, fault status commands and the fault log. The

VINnn

VIN

VDD33_nn

VDD25_nn

SDA_nn

1µF

VGS MAX ON THE TP0101K IS 8V IF VIN > 14V

CHANGE THE RESISTOR DIVIDER ON THE PFET GATE

LTM4683 HAS TWO INTERNAL CONTROLLERS

4683 F30

10k

100k

TP0101K

ISOLATED

3.3V

SDA

SCL

TP0101K

100k

ADI

CONTROLLER

HEADER

TO ADI DC1613A

USB TO I2C/SMBus/PMBus

CONTROLLER

SCL_nn

WP_nn PGND/SGND_nn

LTM4683

1/2

VINnn

VDD33_nn

SDA_nn

SCL_nn

WP_nn PGND/SGND_nn

LTM4683

1/2

10k

VDD25_nn

Figure 30. Controller Connection

LTM4686B Datasheet(PDF) 64 Page - Analog Devices

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