LTC2977 datasheet(73/138 Pages) AD

73 / 138 page

LTM4664A

Rev. 0

For more information www.analog.com

Because of the adapter’s limited current sourcing capa-

bility, only the LTM4664As, PSM their associated pull-up

resistors and the I2C pull-up resistors should be powered

from the ORed 3.3V supply. In addition any device sharing

the I2C bus connections with the LTM4664A PSM should

not have body diodes between the SDA/SCL pins and their

respective VDD node because this will interfere with bus

communication in the absence of system power. If VINS3

is applied, the DC1613A will not supply the power to the

LTM4664As PSM on the board. It is recommended the

RUN_Cn pins be held low or no voltage configuration

resistors inserted to avoid providing power to the load

until the part is fully configured.

The LTM4664A PSM is fully isolated from the host PC’s

ground by the DC1613A.The 3.3V from the adapter

and the LTM4664A VDD33 pin must be driven to each

LTM4664A with a separate PFET. If both VINS3 and EXTVCC

are not applied, the VDD33 pins can be in parallel because

the on-chip LDO is off. The controller 3.3V current limit

is 100mA but typical VDD33 currents are under 15mA. The

VDD33 does back drive the INTVCC/EXTVCC pin. Normally

this is not an issue if VIN is open.

LTpowerPlay: AN INTERACTIVE GUI FOR DIGITAL

POWER

LTpowerPlay (Figure 35) is a powerful Windows-based

development environment that supports Analog Devices

digital power system management ICs including the

LTM4664A PSM section. The software supports a variety

of different tasks. LTpowerPlay can be used to evaluate

Analog Devices ICs by connecting to a demo board or

the user application. LTpowerPlay can also be used in

an off-line mode (with no hardware present) in order to

build multiple IC configuration files that can be saved and

reloaded at a later time. LTpowerPlay provides unprec-

edented diagnostic and debug features. It becomes a

valuable diagnostic tool during board bring-up to pro-

gram or tweak the power system or to diagnose power

issues when bring up rails. LTpowerPlay utilizes Analog

Devices’ USB-to-I2C/SMBus/PMBus adapter to commu-

nication with one of the many potential targets includ-

ing the DC2165A demo board, the DC2298A socketed

programming board, or a customer target system. The

software also provides an automatic update feature to

keep the revisions current with the latest set of device

drivers and documentation.

A great deal of context sensitive help is available with

LTpowerPlay along with several tutorial demos. Complete

information is available at:

LTpowerPlay

PMBus COMMUNICATION AND COMMAND

PROCESSING

The LTM4664A PSM has a one deep buffer to hold the

last data written for each supported command prior to

processing as shown in Figure 36, Write Command Data

Processing. When the part receives a new command from

the bus, it copies the data into the Write Command Data

Buffer, indicates to the internal processor that this com-

mand data needs to be fetched, and converts the com-

mand to its internal format so that it can be executed.

Two distinct parallel blocks manage command buffering

and command processing (fetch, convert, and execute) to

ensure the last data written to any command is never lost.

Command data buffering handles incoming PMBus writes

by storing the command data to the Write Command Data

Buffer and marking these commands for future process-

ing. The internal processor runs in parallel and handles

the sometimes slower task of fetching, converting and

executing commands marked for processing. Some com-

putationally intensive commands (e.g., timing parame-

ters, temperatures, voltages and currents) have internal

processor execution times that may be long relative to

PMBus timing. If the part is busy processing a command,

and new command(s) arrive, execution may be delayed or

processed in a different order than received. The part indi-

cates when internal calculations are in process via bit 5 of

MFR_COMMON (“calculations not pending”). When the

part is busy calculating, bit 5 is cleared. When this bit is

set, the part is ready for another command. An example

polling loop is provided in Figure 37 which ensures that

commands are processed in order while simplifying error

handling routines.

DUAL 25A/30A PSM APPLICATIONS INFORMATION

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