
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)
10 (or connect the ADD pin directly to AGND)
0x71 31.6
0x72 51.1
0x73 71.5
0x74 90.9
0x75 110
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
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