ADM1276-3ACPZ-RL(Rev0) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

ADM1276-3ACPZ-RL
(Rev.:Rev0)

Hot Swap Controller and Digital Power and Energy Monitoring with PMBus Interface

Analog Devices 

ADM1276

PMBus INTERFACE

The I2C bus is a common, simple serial bus used by many devices

to communicate. It defines the electrical specifications, the bus

timing, the physical layer, and some basic protocol rules.

SMBus is based on I2C and aims to provide a more robust and

fault tolerant bus. Functions such as bus timeout and packet

error checking are added to help achieve this robustness, along

with more specific definitions of the bus messages used to read

and write data to devices on the bus.

PMBus is layered on top of SMBus and, in turn, on I2C. Using the

SMBus defined bus messages, PMBus defines a set of standard

commands that can be used to control a device that is part of a

power chain.

The ADM1276 command set is based upon the PMBus™ Power

System Management Protocol Specification, Part I and Part II,

Revision 1.2. This version of the standard is intended to provide

a common set of commands for communicating with dc-to-dc

type devices. However, many of the standard PMBus commands

can be mapped directly to the functions of a hot swap controller.

Part I and Part II of the PMBus standard describe the basic

commands and how they can be used in a typical PMBus setup.

The following sections describe how the PMBus standard and

the ADM1276 specific commands are used.

DEVICE ADDRESSING

The ADM1276 is available in one model: the ADM1276-3. The

PMBus address is 7 bits in size. The upper 5 bits (MSBs) of the

address word are fixed. The base address for the ADM1276 is

01000xx (0x20).

The ADM1276 has a single ADR pin that is used to select one of

four possible addresses. The ADR pin connection selects the

lowest two bits (LSBs) of the 7-bit address word (see Table 6).

Table 6. PMBus Addresses and ADR Pin Connection

Value of Address LSBs

ADR Pin Connection

00

Connect to GND

01

150 kΩ resistor to GND

10

No connection (floating)

11

Connect to VCAP

SMBus PROTOCOL USAGE

All I2C transactions on the ADM1276 are done using SMBus

defined bus protocols. The following SMBus protocols are

implemented by the ADM1276:

 Send byte

 Receive byte

 Write byte

 Read byte

 Write word

 Read word

 Block read

PACKET ERROR CHECKING

The ADM1276 PMBus interface supports the use of the packet

error checking (PEC) byte that is defined in the SMBus standard.

The PEC byte is transmitted by the ADM1276 during a read

transaction or sent by the bus host to the ADM1276 during a

write transaction. The ADM1276 supports the use of PEC with

all the SMBus protocols that it implements.

The use of the PEC byte is optional. The bus host can decide

whether to use the PEC byte with the ADM1276 on a message-

by-message basis. There is no need to enable or disable PEC in

the ADM1276.

The PEC byte is used by the bus host or the ADM1276 to detect

errors during a bus transaction, depending on whether the trans-

action is a read or a write. If the host determines that the PEC

byte read during a read transaction is incorrect, it can decide to

repeat the read if necessary. If the ADM1276 determines that the

PEC byte sent during a write transaction is incorrect, it ignores

the command (does not execute it) and sets a status flag.

Within a group command, the host can choose to send or not

send a PEC byte as part of the message to the ADM1276.

Rev. 0 | Page 24 of 48

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