Introduction To The PMBus™
Presented By
Robert V. White, Artesyn Technologies;
Chair, PMBus Specification Working GroupMay 2005
www.powerSIG.org©2005 System Management Interface Forum. All Rights Reserved

What Is PMBus?

©2005 System Management Interface Forum

2What Is PMBus?
A Standard Way
To Communicate
With Power Converters
Over A Digital
Communications Bus©2005 System Management Interface Forum3

Configure

SystemConfigure©2005 System Management Interface Forum

PMBus
DevicePMBus
Device4

Configure
Control

PMBus
DeviceSystemConfigure©2005 System Management Interface ForumControl

PMBus
Device5

Configure
Control
Monitor

SystemPMBus
DeviceMonitorConfigure©2005 System Management Interface ForumControl

PMBus
Device6Configure
Control

SystemConfigure©2005 System Management Interface ForumPMBus
System Maintenance
ProcessorMonitor– Or –Device
Spare Gates In An FPGA
– Or –Laptop Computer
Monitor– Or –Control Dedicated Controller
PMBus IC
– Or –Device
General Purpose
Microcontroller– Or –Automatic Test Equipment
7

PMBus Is An Open Standard• Owned By The
System Management Interface Forum (SM-IF)– SM-IF Membership Is Open To All• Royalty Free
• Released Specifications Freely Available• Works With All Types Of Power Converters– AC-DC Power Supplies– Isolated DC-DC And Bus Converters– Non-Isolated Point-Of-Load Converters– Microprocessor Power Converters©2005 System Management Interface Forum

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PMBus: What It Is Not• Not A Standard For A Power Supplies Or
DC-DC Converters– No Form Factor, Pin Out, Efficiency, Etc.
– Alliances Like POLA And DOSA Will Define• No Converter-To-Converter Communication– Such As Current Share And Analog Voltage Tracking– Left To The IC And Power Supply Manufacturers– Including These Would Inhibit Future Innovation©2005 System Management Interface Forum

9Some Basic PMBus Requirements• PMBus Devices Must Start Up Safely WithoutBus Communication• PMBus Devices Can Be Used With Or Without
A Power System Manager/Controller• PMBus Devices Support “Set And Forget”– Can Be Programmed Once At Time Of Manufacture– Then Operate Forevermore Without BusCommunication• Defaults From Either/Or– Non-Volatile Memory– Pin Programming©2005 System Management Interface Forum

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Who Is PMBus?

©2005 System Management Interface Forum

11

PMBus Founders And Supporters
Founders
Artesyn Technologies

Emerson/Astec

Texas Instruments

IntersilMicrochip Technology

Summit Microelectronics

Volterra Semiconductor

Zilker LabsSupporters©2005 System Management Interface Forum

12

System Management Interface Forum, Inc.

©2005 System Management Interface Forum

13

System Management Interface Forum, Inc.

www.powerSIG.org©2005 System Management Interface Forum

14

System Management Interface Forum, Inc.
SM-IF MembershipOpen To Any And All

www.powerSIG.org©2005 System Management Interface Forum

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PMBus Specification©2005 System Management Interface Forum

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PMBus Specifications• Part I: Transport– SMBus V1.1 Plus Extensions– Addressing– Hardwired Signals• Example: CONTROL Signal (On/Off Function)• Part II: Command Language– Configuration– Control– Status Monitoring– Fault Management– Information Storage: Inventory, User Data, Etc.
©2005 System Management Interface Forum17

Why SMBus?
• Low Cost Like I²C• More Robust Than I²C– Timeouts Force Bus Reset• More Features Than I²C– SMBALERT# Line For Interrupts– Packet Error Checking (PEC)– Host Notify Protocol• Generally Electrically Compatible With I²C©2005 System Management Interface Forum

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Addressing I²C Shortcomings• “Noise Sensitivity” – Edge Triggering– False START: Timeouts Force Reset– False STOP: PMBus Devices Detect FailedTransmissions As Faults• “Noise Sensitivity” – Corrupt Data
– Data Rates Permit Digital Filtering– Packet Error Checking (PEC)– Every Value That Can Be Written Can Be Read©2005 System Management Interface Forum

19

Addressing I²C Shortcomings• Slave Device Hangs Bus– Timeouts Force Device Reset• Requires Retrieving Device Information
By Polling– SMBALERT# Line Acts As An Interrupt– Automatic Bitwise Arbitration Of SimultaneousRequests• No More Than 8 Devices Of A Type On One Bus– No Central Address Control Bureaucracy– Over 100 Device Addresses Available©2005 System Management Interface Forum

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Other Issues• Fault Tolerance– Physically Failed Devices Are AProblem With Any Bus– Must Add Isolating Switches And Multiplexers• 400 pF Maximum Bus Capacitance
Requires Repeaters Or Bridges For:– Large Numbers Of Devices– Long Distance©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections

DataClock©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections

Optional
CONTROL
Signal Is For
On/Off Control©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections

Optional
SMBALERT#Signal Acts As AnInterrupt Line And
Activates TheAlert Protocol©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections

RequiredHardwired Pins
To SetPhysical Address©2005 System Management Interface Forum

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SYSTEM HOST/
BUS MASTER

PMBus™ Connections

Optional
Write Protect
Pin To Prevent
Unwanted Data
Changes©2005 System Management Interface Forum

27

PMBus™ In A Large System
SystemPower BusBus
Converter

Local/On-Board
Power Bus

Host — Power System
Communication Bus(e.g. IPMI Or RS-485)
HostSystem

PowerSystem
Interface

PMBus

POL w/
PMBus

VOUT1

POL w/
PMBus

VOUT2

POL w/PMBus

VOUT3STD
POL

VOUT4

STD
POL

VOUT5PMBus
InterfaceIC©2005 System Management Interface Forum

Analog Control
Lines (Sense,Enable, Trim,Power Good)28

PMBus™ In A Large System
SystemPower BusBus
Converter

Local/On-Board
Power Bus

Existing System Processor– Or –
Extra Gates In An FPGA– Or –General Purpose
Microcontroller
Host — Power System
Communication Bus(e.g. IPMI Or RS-485)
HostSystem

PowerSystem
Interface

PMBus

POL w/
PMBus

VOUT1

POL w/
PMBus

VOUT2

POL w/
PMBus

VOUT3

STD
POL

VOUT4

STD
POL

VOUT5

PMBus
InterfaceIC©2005 System Management Interface Forum

Analog Control
Lines (Sense,Enable, Trim,Power Good)29

Typical Packet Structure
ADDRESS BYTECOMMAND BYTEDATA BYTE 1

S 7 6 5 4 3 2 1 0 A 7 6 5 4 3 2 1 0 A 7 6 5 4 3 2 1 0 A
DATA BYTE 2

DATA BYTE N

7 6 5 4 3 2 1 0 A

START Signal FromS Host System

7 6 5 4 3 2 1 0 A 7 6 5 4 3 2 1 0 A P

READ/WRITE#0 Bit©2005 System Management Interface ForumOPTIONAL PEC BYTEACKNOWLEDGE

A Signal From Converter

STOP Signal FromP Host System30

Addressing• PMBus Devices Use A 7 Bit Address
Per The SMBus Specification– Provides More Than 100 Possible Device Addresses
After Allowing For Reserved Addresses• No I²C Style Address Control Assignments
Or Limitations• PMBus Users Can Expect Device Addresses To
Be Set By A Mix Of:– Hardwired Address Pins
– High Order Address Bits Set By The
PMBus Device Manufacturer©2005 System Management Interface Forum31

Addressing (cont’d)• PMBus Device Manufacturers Will Trade Off
Cost Of Pins Versus Address Flexibility• Expect Device Makers To Offer Tri-State Pins
Or Resistor Value Programming• Examples Of The Possibilities– 3 Tri-State Pins => 27 Addresses– 1 Resistor Programmed Pin => 16–32 Addresses©2005 System Management Interface Forum

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Multiple Output Units And Paging• Paging Allows One Physical Address To Be
Used To Control Multiple Outputs– One Address Per Physical Unit
– One Page Per Output– Pages Contain All The Settings Of Each Output• Paging Process– Set Page For Output Of Interest– Send Commands• Configure, Control, Read Status©2005 System Management Interface Forum

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Paging: Multiple Output Units©2005 System Management Interface Forum

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Paging: Non-PMBus Device Adapter©2005 System Management Interface Forum

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Paging: Non-PMBus Device Adapter
Example Device:
Analog Margin/Sequence
Controller With
PMBus Interface©2005 System Management Interface Forum

Example Device:
POL Converter
With An
Analog Interface

36

Command Language• Extensive And Comprehensive• Commands Take Effect Immediately• Every Value That Can Be Written
Can Be Read©2005 System Management Interface Forum

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Command Language• Extensive And Comprehensive• Commands Take Effect Immediately• Every Value That Can Be Written
Can Be Read
Not All Devices Support All Commands!
Devices Will Support Commands Appropriate
To Their Intended Application
And Price Point©2005 System Management Interface Forum38Concept: Setting The Output Voltage©2005 System Management Interface Forum

39

Memory And Startup Concepts
Hard Coded
Parameters

1

PinProgrammed
Values23

OperatingMemory(Volatile)

STORE_DEFAULT

45©2005 System Management Interface ForumRESTORE_DEFAULTRESTORE_USERSTORE_USER

Default
Store(Non-Volatile)
User
Store
(Non-Volatile)

BUS
COMMUNICATION
40

Memory And Startup Concepts
Hard Coded
Parameters

1

PinProgrammed
Values2

RESTORE_
Operating Memory
3 DEFAULTDefault
STORE_DEFAULT
ConceptualStore
Volatile(Non-Volatile)

OperatingMemory(Volatile)45©2005 System Management Interface Forum

Memory Store For Device’sRESTORE_USER
User
Operating Parameters
STORE_USERStore(Non-Volatile)

BUS
COMMUNICATION
41

Memory And Startup Concepts
Hard CodedParameters

1PinProgrammed
2Values
Hard Coded Parameters
RESTORE_3 DEFAULT
Default
Store Up,At Device PowerSTORE_DEFAULT(Non-Volatile)

OperatingMemory(Volatile)

4

Values Hard Coded Into The
RESTORE_USER
PMBus Device AreUser
Loaded FirstStoreMemory
STORE_USERInto
The Operating(Non-Volatile)

5©2005 System Management Interface Forum

BUS
COMMUNICATION
42

Memory And Startup Concepts
Hard CodedParameters

123Operating
Memory(Volatile)

DefaultStore
STORE_DEFAULT
Pin Programmed
Values(Non-Volatile)45©2005 System Management Interface ForumRESTORE_DEFAULT

Pin
Programmed
ValuesRESTORE_USER

User
Next, Pin Programmed
ValuesStore
STORE_USER(Non-Volatile)
Are Loaded IntoOperatingMemory. This Overwrites Any
BUS Values.
Previously Loaded
COMMUNICATION

43

Memory And Startup Concepts
1

Default Values

Hard Coded
Parameters

Next, Values From The Non-Volatile Default
PinStore (If Provided) Are Loaded. This Overwrites
Programmed
2
Any Previously
Loaded Values.
Values3OperatingMemory(Volatile)

STORE_DEFAULT

45©2005 System Management Interface ForumRESTORE_DEFAULTRESTORE_USERSTORE_USER

Default
Store(Non-Volatile)
UserStore(Non-Volatile)

BUS
COMMUNICATION
44

Memory And Startup Concepts
User Stored Values

1Hard Coded
Parameters

Next, Values From The Non-Volatile User Store
Pin(If Provided) Are Loaded. This Overwrites
Any
Programmed
2
Previously
Loaded Values.
Values3

OperatingMemory(Volatile)

STORE_DEFAULT

45©2005 System Management Interface ForumRESTORE_DEFAULTRESTORE_USERSTORE_USER

Default
Store(Non-Volatile)
UserStore(Non-Volatile)

BUS
COMMUNICATION
45

Memory And Startup Concepts
1Bus Communication

Hard Coded
Parameters

Next, Values Sent Via The SMBus Are PinLoaded.
This Overwrites AnyValues.
Programmed
2 Previously Loaded
3OperatingMemory(Volatile)

STORE_DEFAULT

45©2005 System Management Interface Forum

ValuesRESTORE_DEFAULTRESTORE_USERSTORE_USER

Default
Store(Non-Volatile)
UserStore(Non-Volatile)

BUS
COMMUNICATION
46

Memory And Startup Concepts
Hard Coded

Used To 1Store A Snapshot Of The
Device’sParameters
Operating State. When Power Removed And
Pin From Its
Restored, Device Can Resume Operation
Programmed
Last2 Programmed State.Values
3

OperatingMemory(Volatile)

STORE_DEFAULT

45©2005 System Management Interface ForumRESTORE_DEFAULTRESTORE_USERSTORE_USER

Default
Store(Non-Volatile)
UserStore(Non-Volatile)

BUS
COMMUNICATION
47

Setting The Output Voltage• Two Step Process• Step 1: Set Or Determine
Voltage Command Mode
• Step 2: Send Output Voltage Command• Output Voltage Command Modes– Linear In LSB– Popular VIDs
– “IPMI Like” Equation Mode©2005 System Management Interface Forum48

On/Off Control• Two Inputs Control Whether A PMBus Device Is
Operating Or Not– Hardwired CONTROL Pin (Programmable Polarity)– OPERATION Command From The Bus• On/Off Control Totally Programmable• CONTROL Pin Options– Active High Or Active Low– Followed Programmed Sequencing Or
Shutdown Immediately©2005 System Management Interface Forum49

On/Off Control Options• “Always On”– Device Providing Output Power Anytime
Input Power Is Present• Respond To CONTROL Pin,
Ignore OPERATION Command• Respond To OPERATION Command,
Ignore Control Pin• Respond To Both CONTROL Pin
And OPERATION Command– An “Off” From Either Turns Output Off©2005 System Management Interface Forum50

OPERATION Command Data Byte
One Command Used To Set Operation Mode: On/Off/Margin©2005 System Management Interface Forum51Group Commands/Operation• Used When Multiple Units Need To Execute A
Command Simultaneously• One SMBus Transaction Used To Send
Commands To Multiple Addresses– Sent In One Large Packet Using Repeated STARTs• Can Be Same Or Different Commands– Example: Command One Unit To Margin Low
And All Others To Margin High• Commands Are Executed When SMBus STOP
Condition Received©2005 System Management Interface Forum52

Interleaving• INTERLEAVE
CommandSets– GroupNumber– Number Of
Units In TheGroup– Switching
Order WithinThe Group©2005 System Management Interface Forum

Tdelay (Unit X ) =Interleave Order Of Unit X• TS
Number In Group53

Many Other Configuration Commands• Maximum Output Voltage• Maximum Output Power• Voltage Scale For External Divider Network• Maximum Duty Cycle• Switching Frequency• Turn On/Off Levels For Input Voltage• Current Scale For Current Sense Resistance• Current Measurement Calibration©2005 System Management Interface Forum

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Sequencing: Event Driven• Event Driven Sequencing Is Closed Loop
• Requires Power System Manager
To Close The Loop©2005 System Management Interface Forum

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Sequencing: Time Driven Commands• Open Loop: Does Not Require
Power System ManagerOnOffTon-RiseToff-Delay

OutputTimeTon-Delay©2005 System Management Interface ForumTon-Max
Fault

Toff-Fall Toff-Max
Fault

56

Converter

Fault Management: Input©2005 System Management Interface Forum57

Faults

Converter

Fault Management: Input

Faults Cause Action.
Response To A Fault Can
Be Programmed©2005 System Management Interface Forum58

Fault Management: Input

Warnings
Converter

Warnings Do Not Directly
Cause Action. Status Bits
Are Set And Host Notified(If Device Supports)©2005 System Management Interface Forum

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Fault Management: Output

Converter

Voltage

Current

OV FAULTOC FAULTOV WARN

OC WARNUV WARNUV FAULTUC FAULT

Related Commands:
POWER_GOOD_ON, POWER_GOOD_OFF©2005 System Management Interface Forum

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Other Fault ManagementConverter©2005 System Management Interface Forum

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Fault Response Programming Byte

©2005 System Management Interface Forum

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Notifying The Host Of A Fault• Host Can Continuously Poll PMBus Devices• PMBus Device Can Send An Interrupt– SMBALERT# Signal Is Optional– See The SMBus Specification For Details• PMBus Device Can Become A Bus Master AndTransmit Notice To System Host– Optional– Requires A More Sophisticated Host©2005 System Management Interface Forum63

Handling Unsupported Commands & Bad Data
• Choice 1– PMBus Device NACKS Command Or Data Byte
– Reason Put Into Status Registers• Choice 2– PMBus Device ACKs Everything, Processes Later– If An Unsupported Command Or
Data Out Of Bounds Is Received:• Set CML Bit In STATUS_BYTE• Set Appropriate Bit In Status Registers (If Supported)• Notify Host (If Supported)©2005 System Management Interface Forum64

Status Reporting: 3 Levels Of Detail
Level 1:STATUS_BYTE
Most Critical InfoLevel 2:
STATUS_WORD
Adds More Important Info

Level 3:Status Registers
Detailed Information©2005 System Management Interface Forum65

STATUS_BYTE & STATUS_WORD©2005 System Management Interface Forum66

Status Registers
STATUS_WORD
High Byte

Low Byte

UNKNOWN FAULT OR WARNING
ReservedReserved
POWER_GOOD Negated
MFR SPECIFIC²INPUT FAULT OR WARNINGIOUT FAULT OR WARNING
VOUT FAULTS OR WARNINGSSTATUS_BYTE
UNIT IS BUSYUNIT IS OFF
VOUT_OV FAULT
IOUT_OC FAULTVIN_UV FAULTTEMPERATURE FAULT OR WARNING
COMM, LOGIC, MEMORY EVENTOTHER FAULT OR WARNING

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
STATUS_VOUT
Register

STATUS_OTHER
Register

STATUS_IOUT
Register

STATUS_CML¹
Register

STATUS_INPUT
Register

STATUS_TEMPERATURERegister

STATUS_MFR²Register©2005 System Management Interface Forum¹: CML: Communication, Memory, Logic²: MFR SPECIFIC: Manufacturer Specific67

Parametric Information••••••

Input Voltage
Input Current
Output Voltage
Output Current
Hold Up Capacitor Voltage
Temperature– Up To 3 Sensors• Fan Speed– Up To 2 Fans

• Duty Cycle• Switching Frequency©2005 System Management Interface Forum68

Parametric Information••••••

Input Voltage
Input Current
Output Voltage
Output Current
Hold Up Capacitor Voltage
Temperature– Up To 3 Sensors• Fan Speed– Up To 2 Fans

• Duty Cycle• Switching Frequency©2005 System Management Interface ForumREMEMBER!
Not All PMBus
Devices Will
Support AllCommands!
Support Based
On Application
And Price Point

69

Manufacturer And User Data
• Manufacturer’s Information– Inventory Information (Model Number, Etc.)– Ratings Information (Input Voltage Range, Etc.)• User Data
– 32 Command Codes For PMBus Device Makers To
Support User Inventory And Configuration Data
– Example: Digital Control Loop Coefficients• Manufacturer Specific Commands– 45 Command Codes Reserved For PMBus Device
Makers To Implement Manufacturer SpecificCommands©2005 System Management Interface Forum70

Data Integrity And Security• Protecting Against Corrupted Transmissions– Packet Error Checking Can Be Used

• Unwanted Or Unintentional Data Changes– Write Protect Pin– WRITE_PROTECT Command©2005 System Management Interface Forum

71

Summary• PMBus Is A Flexible, Powerful Tool For
Digital Power System Management• Supports Both Embedded, Discrete Converters
As Well As Complete, Purchased Converters• Has The Features Needed By Nearly All Users• Application Oriented Feature Sets Control Cost

More Information And Specifications At:

www.powerSIG.org©2005 System Management Interface Forum72