Datasheet

ADP1053 Data Sheet
Rev. A | Page 34 of 84
PMBus/I
2
C COMMUNICATION
The PMBus slave allows a device to interface to a PMBus-
compliant master device, as specified by the PMBus Power
System Management Protocol Specification (Revision 1.1,
February 5, 2007). 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.
FEATURES
The function of the PMBus slave is to decode the command sent
from the master device and respond as requested. Communi-
cation is established using an I
2
C-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 SMBus Specification (Version 2.0,
August 2000). The SMBus specification is, in turn, based on
the Philips I
2
C Bus Specification (Version 2.1, January 2000).
The PMBus incorporates the following features:
• Slave operation on multiple device systems
• 7-bit addressing
• 100 kHz and 400 kHz data rates
• General call address support
• Support for clock low extension (clock stretching)
• Separate multibyte receive and transmit FIFO
• 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 trans-
fer protocol is based on the Philips I
2
C transfer mechanism. The
ADP1053 is always configured as a slave device in the overall
system. The ADP1053 communicates with the master device
using one data pin (SDA) and one clock pin (SCL). Because the
ADP1053 is a slave device, it cannot generate the clock signal.
However, it is capable of clock-stretching the SCL line to put the
master device in a wait state when it is not ready to respond to
the master’s request.
Communication is initiated when the master device sends a
command to the PMBus slave device. Commands can be read
or write commands, in which case data is transferred between
the devices in a byte wide format. Commands can also be send
commands, in which 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/I
2
C communi-
cation protocol. During communication, the master and slave
devices send acknowledge (A) or not-acknowledge (
A
) bits as a
method of handshaking between devices. See the PMBus speci-
fication 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
device. In this case, the PMBus slave device should respond to
the invalid command or data, as defined by the PMBus specifi-
cation, 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 as it deems fit for
its system. In addition, the PMBus device manufacturer can
choose to implement manufacturer-specific commands whose
functions 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 (Supported by the
ADP1053) section and the Manufacturer-Specific Extended
Command List section.
PMBus/I
2
C ADDRESS
The PMBus address of the ADP1053 is set by connecting an
external resistor from the ADD pin to AGND. Table 11 lists the
recommended resistor values and associated PMBus addresses.
Seven different addresses can be used.
Table 11. PMBus Address Settings and Resistor Values
PMBus Address ADD Pin Resistor Value (kΩ)
0x60 10 (or connect directly to AGND)
0x61 28.7
0x62 48.7
0x63 68.1
0x64 88.7
0x65 109
0x67 200 (or connect directly to VDD)
The recommended resistor values in Table 11 can vary by ±2 k.
Therefore, it is recommended that 1% tolerance resistors be used
on the ADD pin.
The part responds to the standard PMBus broadcast address
(general call) of 0x00. However, it is not recommended that the
general call address be used when more than one ADP1053 is
connected to the master device because the data returned by
multiple slave devices will be corrupted.
For more information, see the General Call Support section.