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ADP1050

Data Sheet

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 be used to 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 an I2C-like, 2-wire interface

with a clock line (SCL) and data line (SDA). The PMBus slave is

designed to externally move 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 Specification, 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 can be used to

communicate with other PMBus compliant devices. Its transfer

protocol is based on the Philips I2C transfer mechanism. The

ADP1050 is always configured as a slave device in the overall

system. The ADP1050 communicates with the master device

using one data pin (SDA, Pin 12) and one clock pin (SCL, Pin 11).

Because the ADP1050 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 is initiated when the master device sends

a command to the PMBus slave device. Commands can be read

or write commands, and data is transferred 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

illegal or corrupted data to be received by the PMBus slave.

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 can be used as a 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 choose to 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 can be found in the PMBus Command Set

and Manufacturer Specific Extended Command List sections.

PMBus/I2C ADDRESS

The PMBus address of the ADP1050 is set by connecting an

external resistor from the ADD pin (Pin 19) to AGND. Table 9

lists the recommended resistor values and the associated PMBus

addresses. Eight different addresses can be used.

Table 9. 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 9 can vary by ±2 kΩ.

Therefore, it is recommended that 1% tolerance resistors be used

on the ADD pin.

The ADP1050 responds to the standard PMBus broadcast

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

ADP1050 device is connected to the master device, it is not

recommended that the general call address be used 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 37. See the

Rev. A | Page 38 of 92

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