LTC4449 datasheet(32/108 Pages) LINER

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LTC3882-1

Rev A

For more information www.analog.com

OPERATION

Serial Interface

TheLTC3882-1hasaPMBuscompliantserialinterfacethat

can operate at any frequency between 10kHz and 400kHz.

The LTC3882-1 is a bus slave device that communicates

bidirectionally with a host (master) using standard PMBus

protocols. The Timing Diagram found earlier in this docu-

ment, along with related Electrical Characteristics table

entries, define the timing relationships of the SDA and SCL

bus signals. SDA and SCL must be high when the bus is

not in use. External pull-up resistors or current sources

are required on these lines.

PMBus, an incremental extension of the SMBus standard,

offersmorerobustoperationthana2-wireI2Cinterface.In

addition to adding a protocol layer to improve interoper-

ability and facilitate reuse, PMBus supports bus timeout

recoveryforsystemreliability,optionalpacketerrorcheck-

ing to ensure data integrity, and peripheral hardware alerts

for system fault management. In general, a programmable

device capable of functioning as an I2C bus master can be

configuredforPMBusmanagementwithlittleornochange

tohardware.However,notallI2Ccontrollerssupportrepeat

start (restart) required for PMBus reads.

For a description of the minor extensions and exceptions

PMBus makes to the SMBus standard, refer to PMBus

SpecificationPartIRevision1.2Paragraph5onTransport.

For a description of the differences between SMBus and

I2C, refer to System Management Bus (SMBus) Specifi-

cation Version 2.0 Appendix B on Differences Between

SMBus and I2C.

The user is encouraged to reference Part I of the latest

PMBus Power System Management Protocol Specifica-

tion to understand how to interface the LTC3882-1 to a

PMBus system. This specification can be found at http://

www.pmbus.org/specs.html.

TheLTC3882-1usesthefollowingstandardserialinterface

protocolsdefinedintheSMBusandPMBusspecifications:

• Quick Command

• Send Byte

• Write Byte

• Write Word

• Read Byte

• Read Word

• Block Read

• Block Write – Block Read Process Call

• Alert Response Address

The LTC3882-1 does not require PEC for Quick Command

under any circumstances. The LTC3882-1 also supports

group command protocol (GCP) as required by PMBus

specificationPartI,section5.2.3.GCPisusedtosendcom-

mands to more than one PMBus device in one continuous

transmission. It should not be used with commands that

require the receiving device to respond with data, such as

a STATUS_BYTE command. Refer to Part I of the PMBus

specification for additional details on using GCP.

AllLTC3882-1messagetransmissiontypesallowforpacket

error checking. The later section on Serial Communication

Errors provides more detail on packet error checking.

Figure 4 to Figure 20 illustrate these protocols. Figure 3

provides a key to the protocol diagrams. Not all protocol

elements will be present in every data packet. For instance,

not all packets are required to include the packet error

code. A number shown above a field in these diagrams

indicates the number of bits in that field. All data transfers

are initiated by the present bus master regardless of how

many times data direction flow may change during the

subsequent transmission. The LTC3882-1 never functions

as a bus master.

This device includes handshaking features to ensure ro-

bust system communication. Please refer to the PMBus

Communication and Command Processing section in

Applications Information for more details.

Serial Bus Addressing

The LTC3882-1 supports four types of serial bus ad-

dressing:

• Global Bus Addressing

• Power Rail Addressing

• Individual Device Addressing

• Page+ Channel Addressing

LTC4449 Datasheet(PDF) 32 Page - Linear Technology

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