LTM4686BEVPBF datasheet(77/130 Pages) AD

77 / 130 page

LTM4686B

Rev. 0

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APPENDIX A

SIMILARITY BETWEEN PMBUS, SMBUS AND I2C

2-WIRE INTERFACE

The PMBus 2-wire interface is an incremental extension

of the SMBus. SMBus is built upon I2C with some minor

differences in timing, DC parameters and protocol. The

PMBus/SMBus protocols are more robust than simple I2C

byte commands because PMBus/SMBus provide time-

outs to prevent bus errors and optional packet error check-

ing (PEC) to ensure data integrity. In general, a master

device that can be configured for I2C communication can

be used for PMBus communication with little or no change

to hardware or firmware. Repeat start (restart) is not

supported by all I2C controllers but is required for SMBus/

PMBus reads. If a general purpose I2C controller is used,

check that repeat start is supported.

For a description of the minor extensions and exceptions

PMBus makes to SMBus, refer to PMBus Specification

Part 1 Revision 1.2: Paragraph 5: Transport.

For a description of the differences between SMBus

and I2C, refer to System Management Bus (SMBus)

Specification Version 2.0: Appendix B—Differences

Between SMBus and I2C.

PMBus data format terminology and abbreviations used

in ADI data sheets (see Appendix C: PMBus Command

Details, for example), application notes, and the

LTpowerPlay GUI are indicated in Table 21.

Table 21. Data Format Terminology

PMBus TERMINOLOGY

MEANING

TERMINOLOGY FOR: SPECS, GUI,

APPLICATION NOTES

ABBREVIATIONS FOR SUMMARY

COMMAND TABLE

Linear

Linear_5s_11s

L11

Linear (for Voltage Related Commands)

Linear

Linear_16u

L16

Direct

Direct-Manufacturer Customized

DirectMfr

Hex

I16

ASCII

ASC

Reg

Handshaking features are included to ensure robust system communication. Please refer to the PMBus Communication and Command Processing

subsection of the Applications Information section for further details.

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