Datasheet

MAX34451 PMBus 16-Channel V/I Monitor and
12-Channel Sequencer/Marginer
www.maximintegrated.com
Maxim Integrated │ 20
PMBus Operation
From a software perspective, the device appears as a
PMBus device capable of executing a subset of PMBus
commands. A PMBus 1.1-compliant device uses the
SMBus version 1.1 for transport protocol and responds
totheSMBusslaveaddress.Inthisdatasheet,theterm
SMBus is used to refer to the electrical characteristics
of the PMBus communication using the SMBusphysical
layer.ThetermPMBusisusedtorefertothePMBuscom-
mand protocol. The device employs a number of standard
SMBus protocols (e.g., Write Word, Read Word, Write
Byte,ReadByte,SendByte,etc.)toprogramoutputvolt-
ageandwarning/faultthresholds,readmonitoreddata,and
provide access to all manufacturer-specific commands.
The device supports the group command. The group
command is used to send commands to more than one
PMBus device. It is not required that all the devices
receive the same command. However, no more than one
command can be sent to any one device in one group
command packet. The group command must not be used
with commands that require receiving devices to respond
withdata,suchastheSTATUS_WORDcommand.When
the device receives a command through this protocol, it
immediately begins execution of the received command
afterdetectingtheSTOPcondition.
ThedevicesupportsthePAGEcommandandusesitto
selectwhichindividualchanneltoaccess.Whenadata
word is transmitted, the lower order byte is sent first
and the higher order byteissentlast. Within any byte,
themost-significantbit(MSB)issentfirstandtheleast-
significantbit(LSB)issentlast.
PMBus Protocol Support
The device supports a subset of the commands defined
in the PMBus Power System Management Protocol
SpecificationPartII-CommandLanguageRevision1.1.
FordetailedspecificationsandthecompletelistofPMBus
commands, refer to Part II of the PMBus specification
available at www.PMBus.org. The supported PMBus
commands and the corresponding device behavior are
described in this document. All data values are represent-
edinDIRECTformat,unlessotherwisestated.Whenever
the PMBus specification refersto the PMBus device, it
is referring to the device operating in conjunction with a
powersupply.Whilethecommandcancallforturningon
oroffthePMBusdevice,thedevicealwaysremainson
tocontinuecommunicatingwiththePMBus master and
transfers the command to the power supply accordingly.
Data Format
Voltage data for commanding or reading the output
voltage or related parameters (such as the overvoltage
threshold) are presented in DIRECT format. DIRECT
format data is a 2-byte, two’s complement binary value.
DIRECTformatdatacanbeusedwithanycommandthat
sendsorreadsaparametricvalue.TheDIRECTformat
uses an equation and defined coefficients to calculate
the desired values. Table 5 lists coefficients used by the
device.
Interpreting Received DIRECT
Format Values
The host system uses the following equation to convert
thevaluereceivedfromthePMBusdevice—inthiscase
theMAX34451—intoareadingofvolts,degreesCelsius,
orotherunitsasappropriate:
X=(1/m)x(Yx10
–R
-b)
where X is the calculated real-world value in the appro-
priateunits(V,°C, etc.);mistheslopecoefficient;Yis
the 2-byte, two’s complement integer received from the
PMBusdevice;bistheoffset;andRistheexponent.