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ADP1052

Data Sheet

Rev. B | Page 46 of 113

PMBus/I2C COMMUNICATION

The PMBus slave allows a device to interface with a PMBus-

compliant master device, as specified by the PMBus Power

System Management Protocol Specification (Revision 1.2,

September 6, 2010). The PMBus slave is a 2-wire interface that

can communicate with other PMBus-compliant devices and is

compatible in a multimaster, multislave bus configuration.

PMBus FEATURES

The function of the PMBus slave is to decode the command

that is sent from the master device and respond as requested.

Communication is established using a 2-wire interface with a

clock line (SCL) and data line (SDA) that is similar to an I2C

interface. The PMBus slave design externally moves chunks of

8-bit data (bytes) while maintaining compliance with the PMBus

protocol. The PMBus protocol is based on the System Management

Bus (SMBus) Specification, Version 2.0, August 2000. The SMBus

specification is, in turn, based on the Philips I2C Bus Specifica-

tion, Version 2.1, dated January 2000. The PMBus incorporates

the following features:

•

Slave operation on multiple device systems

•

7-bit addressing

•

100 kbps and 400 kbps data rates

•

General call address support

•

Support for clock low extension (clock stretching)

•

Separate multibyte receive and transmit FIFOs

•

Extensive fault monitoring

OVERVIEW

The PMBus slave module is a 2-wire interface that communicates

with other PMBus-compliant devices. Its transfer protocol is

based on the Philips I2C transfer mechanism. The ADP1052 is

always configured as a slave device in the overall system. The

ADP1052 communicates with the master device using one data

pin (SDA, Pin 15) and one clock pin (SCL, Pin 14). Because the

ADP1052 is a slave device, it cannot generate the clock signal;

however, it is capable of stretching the SCL line to put the master

device in a wait state when it is not ready to respond to the request

of the master.

Communication initiates when the master device sends a

command to the PMBus slave device. Commands can be read

or write commands, and data transfers between the devices in a

byte wide format. Commands can also be send commands; in

that case, the command is executed by the slave device upon

receiving the stop bit. The stop bit is the last bit in a complete

data transfer, as defined in the PMBus/I2C communication

protocol. During communication, the master and slave devices

send acknowledge (A) or no acknowledge (A) bits as a method

of handshaking between devices. See the PMBus specification

for a more detailed description of the communication protocol.

When communicating with the master device, it is possible for

the PMBus slave to receive illegal or corrupted data. In this case,

the PMBus slave must respond to the invalid command or data,

as defined by the PMBus specification, and indicate to the

master device that an error or fault condition has occurred. This

method of handshaking is the first level of defense against

inadvertent programming of the slave device that can

potentially damage the chip or system.

The PMBus specification defines a set of generic PMBus

commands that is recommended for a power management

system; however, each PMBus device manufacturer can choose

to implement and support certain commands that are deemed

fit for the system. In addition, the PMBus device manufacturer can

implement manufacturer specific commands, the functions of

which are not included in the generic PMBus command set. The

list of standard PMBus and manufacturer specific commands are

found in the PMBus Command Set and Extended Command

List: Manufacturer Specific sections.

PMBus/I2C ADDRESS

The PMBus address of the ADP1052 is set by connecting an

external resistor from the ADD pin (Pin 22) to AGND. Table 10

lists the recommended resistor values and the associated PMBus

addresses. Eight different addresses can be used.

Table 10. PMBus Address Settings and Resistor Values

PMBus Address

Resistor Value (kΩ)

0x70

10 (or connect the ADD pin directly to AGND)

0x71

31.6

0x72

51.1

0x73

71.5

0x74

90.9

0x75

110

0x76

130

0x77

150 (or connect the ADD pin directly to VDD)

The recommended resistor values in Table 10 can vary by ±2 kΩ.

Therefore, it is recommended to use 1% tolerance resistors on the

ADD pin.

The ADP1052 responds to the standard PMBus broadcast

address (general call) of 0x00. However, when more than one

ADP1052 device is connected to the master device, do not use

the general call address because the data returned by multiple

slave devices is corrupted. For more information, see the

General Call Support section.

DATA TRANSFER

Format Overview

The PMBus slave follows the transfer protocol of the SMBus

specification, which is based on the fundamental transfer protocol

format of the I2C bus specification. Data transfers are byte wide,

lower byte first. Each byte is transmitted serially, most significant

bit (MSB) first. A typical transfer is shown in Figure 46. See the

SMBus and I2C specifications for detailed descriptions of the

transfer protocols. Figure 46 through Figure 53 use the

abbreviations listed in Table 11.

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