Using The PMBus™ Protocolpmbus.org/Assets/PDFS/Public/Using_The_PMBus_20051012.pdfOct 12, 2005...
Transcript of Using The PMBus™ Protocolpmbus.org/Assets/PDFS/Public/Using_The_PMBus_20051012.pdfOct 12, 2005...
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Using The PMBus™ Protocol
Robert V. WhiteStaff Engineer
Artesyn TechnologiesChair, PMBus™ Specification Working Group
12 October 2005
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Presentation Overview• What Is The PMBus™?• PMBus Basics• Using The PMBus In
The Lab…• Implementing PMBus• Command Language
Overview• Data Formats• Setting The Output
Voltage
• On/Off Control• Sequencing• Status Reporting• Fault Management And
Reporting• Monitoring Voltage,
Current And Temperature
• Some Other Topics(As Time Allows)
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What Is PMBus?A Standard WayTo Communicate
With Power ConvertersOver A Digital
Communications Bus
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SystemPMBusDevice
PMBusDevice
Configure
Configure
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SystemPMBusDevice
PMBusDevice
Configure
Configure
Control
Control
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SystemPMBusDevice
PMBusDevice
Configure
Configure
Control
Control
Monitor
Monitor
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SystemPMBusDevice
PMBusDevice
Configure
Configure
Control
Control
Monitor
Monitor
System Maintenance Processor– Or –
Spare Gates In An FPGA– Or –
Laptop Computer– Or –
Dedicated Controller IC– Or –
General Purpose Microcontroller
– Or –Automatic Test Equipment
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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
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PMBus: What It Is Not
• Not A Product Or Product Line• 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
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Some Basic PMBus Requirements
• PMBus Devices Must Start Up Safely Without Bus 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 Bus Communication
• Defaults From Either/Or– Non-Volatile Memory– Pin Programming
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Who Is PMBus?
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PMBus Adopters• Alliance Semiconductor• Artesyn Technologies• Emerson/Astec• International Rectifier• Intersil Corporation• Magnetek, Inc. • Micro Computer Control
Corporation (MCC) • Microchip Technology
• Primarion• Silicon Laboratories • Summit
Microelectronics, Inc. • Texas Instruments • Tyco Electronics Corp. • Volterra Semiconductor
Corporation • Zilker Labs
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System Management Interface Forum, Inc.
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System Management Interface Forum, Inc.
www.powerSIG.org
SM-IF MembershipOpen To Any And All
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Use Of PMBus™Logo And Trademark• Only Adopters Are Permitted To Use The
PMBus™ Trademarks And Logo For Commercial Purposes– Commercial Purpose Is Anything Related To The
Sale Of Products And Services– Helps Assure That PMBus Device Manufacturers
Understand The Specification• The Press May Use The Trademarks And Logo
In Articles That Do Not Promote Products Or Services
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Specification Structure
• Part I – Physical Layer And Transport– Bus & Protocols– Discrete Signals– Electrical Levels
• Part II – Command Language– Commands– Data Formats– Fault Management “Tutorial”– Status Reporting “Tutorial”– Information Storage
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
Clock
Data
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
OptionalCONTROL
Signal Is ForOn/Off Control
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
OptionalSMBALERT#
Signal Acts As AnInterrupt Line And
Activates The Alert Protocol
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
RequiredHardwired Pins
To SetPhysical Address
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PMBus™ Connections
SYST
EM H
OST
/B
US
MA
STER
OptionalWrite Protect
Pin To PreventUnwanted Data
Changes
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What Is SMBus?
• A Long Existing Standard Bus• Similar To I²C
– Synchronous (Clock And Data Lines)– Byte Oriented– Same Addressing Scheme– Same Transmission Control
• START, STOP, ACK, NACK
• Did Not Require Royalties To Philips
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Why SMBus?
• Low Cost Like I²C• More Robust Than I²C• More Features Than I²C
– SMBALERT# Line For Interrupts– Packet Error Checking (PEC)– Host Notify Protocol
• Generally Electrically Compatible With I²C• Widely Used In Personal Computers And
Small To Medium Servers
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SMBus Improvements
• I²C “Noise Sensitivity” – Edge Triggering– False START: Timeouts Force Reset– False STOP: PMBus Devices Detect Failed
Transmissions As Faults• I²C “Noise Sensitivity” – Corrupt Data
– Data Rates Permit Digital Filtering– Packet Error Checking (PEC)– Every Value That Can Be Written Can Be Read
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SMBus Improvements
• I²C Slave Device Hangs Bus– Timeouts Force Device Reset
• I²C Requires Retrieving Device Information By Polling– SMBALERT# Line Acts As An Interrupt– Automatic, Lossless Bitwise Arbitration Of
Simultaneous Requests• I²C: 8 Devices Max Of One Type On A Bus
– No Central Address Control Bureaucracy– Over 100 Device Addresses Available
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SMBus Limitations
• SMBus and PMBus Specifications Say 100 kHz– I²C Says 400 kHz – Which Is Possible If
SMBus Setup And Hold Times Are Obeyed• Capacitance Is A Concern
– No Explicit Maximum– Excessive Capacitance Causes A Violation Of
Bus Timing By Slowing Rise Times– Minimize Capacitance In Layout
• Stubs And Branches Not A Concern
– See SMBus Specification For Details
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SMBus Limitations
• SMBus and PMBus Specifications Say 100 kHz– I²C Says 400 kHz – Which Is Possible If
SMBus Setup And Hold Times Are Obeyed• Capacitance Is A Concern
– No Explicit Maximum– Excessive Capacitance Causes A Violation Of
Bus Timing By Slowing Rise Times– Minimize Capacitance In Layout
• Stubs And Branches Not A Concern
– See SMBus Specification For Details
PMBus Going To400 kHz
In Revision 1.1
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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
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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
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Basic Packet Structure
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Write Word Packet
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Write Word Packet
Packet Error Checking (PEC)Is Optional In The Specification
But It Is Expected To Be Very Popular With System OEMs!
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Read Word Packet
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Read Word Packet
This Data Is Being TransmittedBy The Slave Device
To The Host
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Using PMBus In The Lab
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Using PMBus In The Factory
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Using PMBus In A System
PMBus
InputPower A
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
InputPower B
POL w/PMBus
Front End Power
Supply A
Front End Power
Supply B
N/C
SetAndForget
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Using PMBus In A System
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PMBus In A System
PMBus
InputPower A
RemoteHost
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
SystemMaintenance
Processor
InputPower B
POL w/PMBus
Front End Power
Supply A
Front End Power
Supply B
Remote SystemMaintenanceComm Bus
(IPMI, RS-485, …)
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PMBus In A System
PMBus
SystemPower Bus
RemoteHost
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
SystemMaintenance
Processor
POL w/PMBus
BusConverter
Remote SystemMaintenanceComm Bus
(IPMI, RS-485, …)
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PMBus In A System
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PMBus In A System
PMBus
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
Power/System
Interface
POL w/PMBus
BusConverter
PMBus
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
Power/System
Interface
POL w/PMBus
BusConverter
SystemPower Bus
SystemHost
PMBus
PMBusInterface
IC
POL w/PMBus
POL w/PMBus
STDPOL
STDPOL
VOUT3
VOUT4
VOUT2
VOUT1
VOUT5
Analog ControlLines (Sense, Enable, Trim,Power Good)
Local/On-BoardPower Bus
Pwr System/Host System
Interface
POL w/PMBus
BusConverter
SystemMaintenanceComm Bus
(IPMI, RS-485, …)
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PMBus In A System
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PMBus Bridge To Other Buses
Extra Gates In An FPGA– Or –
General Purpose Microcontroller– Or –
Application Specific IC
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Simple ElectricalBi-Directional Isolation
A B
3.3 V A 3.3 V B
DATA A DATA B
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Bus Extensions
Mul
tiple
xor
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Redundant Buses
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What’s Needed To Make A PMBus Device?• Physical/Data Link Layer To Receive & Send
Data Over The Bus– Plus CONTROL, SMBALERT#, WP,
Address Pin Interface
• Memory– Received Configuration– Device Status And Parametric Information
• The Rest Of The Device– Such As Power Control And Conversion Circuits That
Use/Supply Stored Information– Note That PMBus Does Not Depend On The Type Of
Controller: Analog, Digital, Hybrid
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PMBus Device Concept
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How to Make A PMBus Device
Integrated Solution
ASSP ASIC
Piece Part Solution
Bus Interface Control & Monitor
ASIC
FPGA
GP Microcontroller
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Making A PMBus Device
Pro Con Risk
ASSP
ASIC
FPGA
GeneralPurpose
Microcontroller
MinimalInvestment
Hard ToDifferentiate
Low TechnicalMedium Economic
Have ItYour Way
$$$$$Design Skills
Medium TechnicalHigh Economic
Have ItYour Way
$$$Design Skills
Medium TechnicalMedium Economic
Flexibility &Added
Functionality
$Programming
Skills
Medium TechnicalMedium Economic
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Conceptual View OfMemory And Startup
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Conceptual View OfMemory And Startup
Operating Memory
Conceptual Volatile Memory Store For Device’s
Operating Parameters
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Conceptual View OfMemory And Startup
Hard Coded Parameters
At Device Power Up,Values Hard Coded Into The
PMBus Device Are Loaded First Into The Operating Memory
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Conceptual View OfMemory And Startup
Pin Programmed Values
Next, Pin Programmed Values Are Loaded Into Operating
Memory. This Overwrites Any Previously Loaded Values.
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Conceptual View OfMemory And Startup
Default Values
Next, Values From The Non-Volatile Default
Store (If Provided) Are Loaded. This Overwrites Any Previously Loaded
Values.
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Conceptual View OfMemory And Startup
User Stored Values
Next, Values From The Non-Volatile User Store (If Provided) Are Loaded. This
Overwrites Any Previously Loaded Values.
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Conceptual View OfMemory And Startup
Bus Communication
Next, Values Sent Via The SMBus Are Loaded. This Overwrites Any Previously Loaded Values.
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Conceptual View OfMemory And Startup
Used To Store A Snapshot Of The Device’s Operating State. When Power Removed And
Restored, Device Can Resume Operation From Its Last Programmed State.
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PMBus–Host Interface
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PMBus–Host Interface
Someone Will Have ToWrite Code For This
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PMBus–Host Interface
Calculation And ConversionFor Input To D/A Converters
And Output From A/D Converters
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PMBus–Host Interface
Highly Platform Dependent!
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PMBus/SMBus Interface
• “Bit Banging” With A General PurposeI/O Port On A Microcontroller– Can Be Done & Can Be Done Well– Pay Attention To The Specification– Timing Is Important
• Integrated Into Silicon– Many Microcontrollers Have An I²C Port
That Can Be Used To Drive SMBus– Look For PMBus To Be Built Into I²Cs
For Power Conversion And System Monitoring
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Command Language
• Commands Consist Of:– A Command Code
• 256 Command Codes (00h To FFh)
– Zero Or More Data Bytes• Command Code
– Not A Register Location!– Devices Must Map Command Code To
Memory Location Themselves• Data Byte(s)
– Defined In The Specification
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Data Formats
• More Time Spent On This By Specification Working Group Than Any Other Topic!
• Challenges– Wide Range Of Values (Millivolts To Kiloamperes)– Wide Range Of Resolution
• Millivolts For Microprocessors• Volts And Amperes For AC Power
– Positive And Negative Values– Limited Computing Power In PMBus Devices
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Data Format ChoicesR
esol
utio
nGeneral
Purpose:10 Bits
OutputVoltageRelated:16 Bits
Low:DirectMode
Higher:Literal
Com
pute Power
VRM Mode
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Data Format ChoicesR
esol
utio
nGeneral
Purpose:10 Bits
OutputVoltageRelated:16 Bits
Low:DirectMode
Higher:Literal
Com
pute Power
VRM Mode
Refers To Compute PowerNeeded In The PMBus Device
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Literal Format
• X = Y·2N Y = X·2–N
– X = “Real World” Value (Example: 3.3)– Y = Binary Value Sent Over The PMBus– N = Scale Factor
• Y (Binary Signed Integer)– General Purpose Case: 11 Bits– Output Voltage Related Data: 16 Bits
• N (Binary Signed Integer)– 5 Bits In Both General Purpose Data And
Output Voltage Related Data
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Literal Format
• X = Y·2N Y = X·2–N
– X = “Real World” Value (Example: 3.3)– Y = Binary Value Sent Over The PMBus– N = Scale Factor
• Y (Binary Signed Integer)– General Purpose Case: 11 Bits– Output Voltage Related Data: 16 Bits
• N (Binary Signed Integer)– 5 Bits In Both General Purpose Data And
Output Voltage Related Data
NOTICE!
This Is The Form That Will AppearIn The PMBus Specification Revision 1.1
This Is “Backwards” From What Is InSpecification 1.0 Section 7
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Literal Format
• Two Ways to Think Of This Format• “Binary Floating Point”
X = Y·2N
N = ExponentY = Mantissa
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Literal Format
• Two Ways to Think Of This Format• “Binary Floating Point”
– Y = Mantissa– N = Exponent
• Number Of LSBs
X = Y·2N
2N Equals SizeOf LSBY = Number Of LSBs
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Literal Format
• Two Ways to Think Of This Format• “Binary Floating Point”
– Y = Mantissa– N = Exponent
• Number Of LSBs
X = Y·2N
2N Equals SizeOf LSBY = Number Of LSBs
Example: N = –102–10 = 1/1024 = 9.766 × 10–4 =>
977 microunits/bit
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General Purpose Literal Format
• 10 Bit Resolution• Wide Range Of Values Possible
– Maximum Positive: 1023 × 215 = 33.5217 × 106
– Minimum Value: ±1 × 2-16 = ±1.526 × 10-5
– Maximum Negative: -1024 × 215 = -33.5544 × 106
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Example Conversion WithMaximum Resolution• Given X = 3.3 V;
Calculate Y And N• Maximum Resolution With Largest Possible Y
– Ymax = 1023• Largest Possible Y => Smallest 2–N
– Smallest LSB– Largest |N|
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Example Conversion WithMaximum Resolution• Start By Finding N• Can Solve Directly
– But Complicated
• Or: Start By Dividing Ymax By X
• Examine Result And Find Largest 2–N That Is Less Than The Result– This Gives N
• Multiply X By 2–N
To Get Y– Convert To 11 Bit Signed
Binary Integer
2
lnint log int
ln 2MAX
MAX
XYXN
Y
⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟⎛ ⎞⎛ ⎞ ⎝ ⎠⎜ ⎟= =⎜ ⎟⎜ ⎟ ⎜ ⎟⎝ ⎠⎝ ⎠ ⎜ ⎟⎜ ⎟⎝ ⎠
1023 310.03.3
MAXYX
= =
max(2 ) 310.0 2568 11000b
N
N
− < ⇒⇒ = − =
83.3 2 3.3 23.3 256844.8 845
845 01101001101b
N
Y
−× = ×= ×= ⇒⇒ =
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Literal ModeResult Sent Over The PMBus
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
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Literal Mode As A Non-Integer Binary Value• Can Think Of N As
Telling The Device How Many Binary Places To Move The Binary Point:11.0100110b
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
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Literal Mode As A Non-Integer Binary Value• Can Think Of N As
Telling The Device How Many Binary Places To Move The Binary Point:11.0100110b
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
N = –8
Move Binary Point 8 PlacesTo The Left
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Literal Mode As A Non-Integer Binary Value• Can Think Of N As
Telling The Device How Many Binary Places To Move The Binary Point:11.0100110b
• Can Also Think Of This As A Sum Of Powers Of 2
1 11 2 1 1 0 12 4
1 1 10 0 18 16 321 1 11 0 164 128 256
+ + + +
+ + +
+ +
i i i i …
i i i
i i i
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
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Literal Mode As A Non-Integer Binary Value• Can Think Of N As
Telling The Device How Many Binary Places To Move The Binary Point:11.0100110b
• Can Also Think Of This As A Sum Of Powers Of 2
• Result = 3.0078
1 11 2 1 1 0 12 4
1 1 10 0 18 16 321 1 11 0 164 128 256
+ + + +
+ + +
+ +
i i i i …
i i i
i i i
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
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Literal Mode As A Non-Integer Binary Value• Can Think Of N As
Telling The Device How Many Binary Places To Move The Binary Point:11.0100110b
• Can Also Think Of This As A Sum Of Powers Of 2
• Result = 3.0078
1 11 2 1 1 0 12 4
1 1 10 0 18 16 321 1 11 0 164 128 256
+ + + +
+ + +
+ +
i i i i …
i i i
i i i
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
Error Of 7.8 mV (0.0236%)Is From Rounding
848.8 To 845And Quantization Errors
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Literal Mode AsLSB Size & Number Of LSBs• Also Can Think Of This As
– The LSB Size (2N)– The Number Of LSBs (Y)
• LSB = 2N = 2–8
= 0.00390625• Y = Number Of LSBs
= 845• X = 845 × 0.00390625
= 3.30078125
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
N Y
Data Byte High Data Byte Low
MSBMSB
1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1
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Example Decode• Received Value:
High Byte(Received Second)
Low Byte(Received First)
11100011 01100111
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Example Decode• Received Value:
• Separate Into N And Y
11100011 01100111
11100 0110110011111100b 401101100111b 871
NY= = −= =
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Example Decode• Received Value:
• Separate Into N And Y
• Calculate X
11100011 01100111
11100 0110110011111100b 401101100111b 871
NY= = −= =
42 871 2871 54.43816
NX Y −= = ×
= =
i
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Example Decode• Received Value:
• Separate Into N And Y
• Calculate X
• Original Value: 54.46– Error: 22 mV => 0.040%
11100011 01100111
11100 0110110011111100b 401101100111b 871
NY= = −= =
42 871 2871 54.43816
NX Y −= = ×
= =
i
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Error: We Got Lucky!
• Suppose Full Scale Was 60 V• Resolution:
60 V ÷ 1023 = 58.65 mV/bit
• Some Applications , Such As ATelecomm Rectifier, Need A Much Finer Resolution– Typically 10-20 mV/bit
• But Range Of Interest Is Not 0 V to 60 V,More Like 42 V To 58 V
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Scaling With Offset
0123
2N–42N–32N–22N–1
XMAX
YMAX
YMIN
XMIN
Human/Analog/“Real
World”Value
PMBusDigitalValue
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Scaling With Offset
0123
2N–42N–32N–22N–1
XMAX
YMAX
YMIN
XMIN
Human/Analog/“Real
World”Value
PMBusDigitalValue
Can We MapFrom:
Real WorldRange
Of ValuesOf Interest
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Scaling With Offset
0123
2N–42N–32N–22N–1
XMAX
YMAX
YMIN
XMIN
Human/Analog/“Real
World”Value
PMBusDigitalValue
To:The Range Of Values
Accepted By ThePMBus Device?
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0123
2N–42N–32N–22N–1
XMAX
YMAX
YMIN
XMIN
Human/Analog/“Real
World”Value
PMBusDigitalValue
Scaling With Offset
This Is One Of TheMotivations For TheDirect Mode/Format
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More Direct Mode Motivation
No “Floating Point”Computation!
Value From PMBusIs Used Directly
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Direct Mode Equation
• The Direct Mode Uses An Equation As Follows:
• Where:– Y Is The Value Transmitted To Or Received From
The PMBus Device (16 Bits, Signed)– X Is The “Human” Value To Be Encoded– m Is The Scaling Coefficient (16 Bits, Signed)– b Is The Offset Coefficient (16 Bits, Signed)– R Is The Scaling Coefficient (8 Bits, Signed)
=( ) 10RY mX b+ i
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Direct Mode Equation
• The Direct Mode Uses An Equation As Follows:
• Where:– Y Is The Value Transmitted To Or Received From
The PMBus Device– X Is The “Human” Value To Be Encoded– m Is The Scaling Coefficient (16 Bits, Signed)– b Is The Offset Coefficient (16 Bits, Signed)– R Is The Scaling Coefficient (8 Bits, Signed)
=( ) 10RY mX b+ iNOTICE!
This Is The Form That Will AppearIn The PMBus Specification Revision 1.1
This Is “Backwards” From What Is InSpecification 1.0 Section 7
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Direct Mode: m, b And R
• m, b And R Are Known As The Coefficients• They Are Supplied By The PMBus Device
Manufacturer• Preferred:
Coefficients Stored In The Device And Retrieved By The Host With The COEFFICIENTS Command
• Alternative:Coefficients Are Provided In The Product Literature (Data Sheet, Application Note)
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Calculating The Coefficients
• Problem– 3 Unknowns (m, b, R)– 2 Constraints
• The Two Constraints– Xmin => Ymin And Xmax => Ymax
• Solution Procedure– Assume R Is Known And Fixed– Solve For m And b In Terms Of Xmin, Xmax, Ymin, Ymax– Use A Tool Like Excel To Solve For m And b For
Several Values Of R– Choose Largest Possible Values Of m And b
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Calculating The Coefficients• The Constraints
• Substituting Into The Direct Mode Equation
• Solving For m And b
min min
max max
02 1n
X YX Y
⇒ =
⇒ = −
min min
max max
( ) 10( ) 10
R
R
Y mX bY mX b
= +
= +
ii
max min
max min
max minmin min
max min
max minmax max
max min
10
10
10
R
R
R
Y YmX X
Y Yb Y XX X
Y YY XX X
−
−
−
⎛ ⎞−= ⎜ ⎟−⎝ ⎠⎛ ⎞−
= −⎜ ⎟−⎝ ⎠⎛ ⎞−
= −⎜ ⎟−⎝ ⎠
i
i
i
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Calculating The CoefficientsExample• AC-DC Rectifier For Telecom Applications
– Wide Range Of Output Voltage To Control Battery Charging
– Resolution In Range Of 10–20 mV• Number Of Bits For Input: 10
– Ymin = 000h– Ymax = 1023d = 3FFh = 1111111111b
• Output Voltage Range– Xmin = 44 Vdc– Xmax = 58 Vdc– Resolution: 13.69 mV/bit
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Calculating The CoefficientsExample• Using Microsoft Excel to Solve For m And B
For Various Values Of R Yields:
R m (calculated) b (calculated) m (rounded) b (rounded)-4 730714.2857 -32151428.57 730714 -32151429-3 73071.42857 -3215142.857 73071 -3215143-2 7307.142857 -321514.2857 7307 -321514-1 730.7142857 -32151.42857 731 -321510 73.07142857 -3215.142857 73 -32151 7.307142857 -321.5142857 7 -3222 0.730714286 -32.15142857 1 -323 0.073071429 -3.215142857 0 -34 0.007307143 -0.321514286 0 05 0.000730714 -0.032151429 0 0
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Calculating The CoefficientsExample• Using Microsoft Excel to Solve For m And B
For Various Values Of R Yields:
R m (calculated) b (calculated) m (rounded) b (rounded)-4 730714.2857 -32151428.57 730714 -32151429-3 73071.42857 -3215142.857 73071 -3215143-2 7307.142857 -321514.2857 7307 -321514-1 730.7142857 -32151.42857 731 -321510 73.07142857 -3215.142857 73 -32151 7.307142857 -321.5142857 7 -3222 0.730714286 -32.15142857 1 -323 0.073071429 -3.215142857 0 -34 0.007307143 -0.321514286 0 05 0.000730714 -0.032151429 0 0
Values In Red ExceedThe Range Of ValuesAvailable To A 16 Bit
Signed Integer(+32,767 To –32,768)
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Calculating The CoefficientsExample• Using Microsoft Excel to Solve For m And B
For Various Values Of R Yields:
R m (calculated) b (calculated) m (rounded) b (rounded)-4 730714.2857 -32151428.57 730714 -32151429-3 73071.42857 -3215142.857 73071 -3215143-2 7307.142857 -321514.2857 7307 -321514-1 730.7142857 -32151.42857 731 -321510 73.07142857 -3215.142857 73 -32151 7.307142857 -321.5142857 7 -3222 0.730714286 -32.15142857 1 -323 0.073071429 -3.215142857 0 -34 0.007307143 -0.321514286 0 05 0.000730714 -0.032151429 0 0
For Best Resolution,Choose Largest Possible
Values Of m And bm = 731b = -32151R = –1
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Calculating The CoefficientsExample• Chosen Solution
m: 731b: –32151R: –1
• Double Check Calculation
min min1
( ) 10(731 44 32,151) 101.3 0
RY mX b−
= +
= −= ≠
ii i
max max1
( ) 10
(731 58 32,151) 101024.7 1023
RY mX b−
= +
= −= ≠
ii i
More Rounding AndQuantization Errors!
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Calculating The CoefficientsExample• Example
– Minimum Voltage (Xmin): 44 V– Maximum Voltage (Xmax): 58 V– PMBus Device Resolution: 16 Bits
R m (calculated) b (calculated) m (rounded) b (rounded)-2 468107.1429 -20596714.29 468107 -20596714-1 46810.71429 -2059671.429 46811 -20596710 4681.071429 -205967.1429 4681 -2059671 468.1071429 -20596.71429 468 -205972 46.81071429 -2059.671429 47 -20603 4.681071429 -205.9671429 5 -2064 0.468107143 -20.59671429 0 -21
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Calculating The CoefficientsExample• Chosen Solution
m: 468b: –20597R: 1
• Double Check Calculationmin min
1
( ) 10(468 44 20,597) 105 0
RY mX b+
= +
= −= − ≠
ii i
Still Have Rounding AndQuantization Errors!
max max1
( ) 10
(468 58 20,597) 1065,470 65,535
RY mX b+
= +
= −= ≠
ii i
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What To Do?
• Choices– Live With It– Adjust The Slope (m)– Adjust the Offset (b)– Adjust Both– Adjust Xmax And Xmin
• Optimization Is Left As An Exercise For The Student
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What To Do?
• Choices– Live With It– Adjust The Slope (m)– Adjust the Offset (b)– Adjust Both– Adjust Xmax And Xmin
• Optimization Is Left As An Exercise For The Student
Lesson:You Must Pay Attention To ErrorsIntroduced By Discrete Arithmetic!
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Decoding Direct ModeExample• Example Of Reading The Output Current Of An
Isolated DC-DC Bus Converter• Using COEFFICIENTS Command Returns
Values For m, b And R As:– m = 850– b = 0– R = –2
• Using READ_IOUT Command ReturnsThe Value 0000000001101001b => 105d
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Decoding Direct ModeExample• Use The Inverse Of The
Equation Used To Encode
• Substitute Values And Solve
• Output Current = 12.35 A
( ) 101 ( 10 )
R
R
Y mX b
X Y bm
−
= +
= −
i
i
( 2)1 (105 10 0)85010500 12.35850
X − −= −
= =
i
Note That These Calculations Are Done In The Host And Not The PMBus Device!
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Setting The Output Voltage
Step 1Which Data Format?
(aka Which Mode)
Linear
Direct
VIDVOUT_MODE Command
Step 2Set The Output Voltage Using The
VOUT_COMMAND Command
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VOUT_MODE Command• VOUT_MODE
Command Is Sent Separately From Any Other Command, Such As VOUT_COMMAND
• Sent Only When Necessary To Change The Mode– Only Once?
• Applies For All Output Voltage Related Commands
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VOUT_MODE &VOUT_COMMAND
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VOUT_MODE &VOUT_COMMAND
Voltage = Y·2N
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7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Y
Data Byte High
Mode= 010b
7 6 5 4 3 2 1 0
Data Byte Low
VOUT_COMMAND Data BytesFor DIRECT Mode
Value =00000b
VOUT_MODEData Byte ForDIRECT Mode
VOUT_MODE &VOUT_COMMAND
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Fine Tuning The Output Voltage
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Margin Testing
Margin Testing UsesPre-Stored Values
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Margin Testing
Margin Testing UsesPre-Stored Values
OPERATION CommandSelects Between Stored Setpoint
And Upper And Lower Margin Voltages
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Fine Tuning The Output Voltage
VOUT_TRIMIntended Mostly For End User.
Example: Adjust Voltage On ASICTerminals In Manufacturing
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Fine Tuning The Output Voltage
VOUT_CALIntended Mostly ForDevice Manufacturer
Example: Calibrate OutReference Voltage Error
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Fine Tuning The Output Voltage
VOUT_DROOPUse For Either
Adaptive Voltage Positioning OrPassive Current Sharing
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Fine Tuning The Output Voltage
VOUT_MAXHelps Prevent “Oops!”
Protect Devices By LimitingThe Maximum Voltage Than
Can Be Generated
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Using And External Divider
PMBus Device
VOUT KRVOUT_
SCALE_LOOP
VOUT_COMMAND K
ErrorProcessing/
Control Loop
RESISTORDIVIDERRATIO
16
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Using And External Divider
PMBus Device
VOUT KRVOUT_
SCALE_LOOP
VOUT_COMMAND K
ErrorProcessing/
Control Loop
RESISTORDIVIDERRATIO
16
Simplifies Life For The End User
They Do Not Need To Think About The Voltage Divider
Just Send Command Voltage As They Want It
Example: 1.80 V
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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
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ON_OFF_CONFIGDevicePower
On/OffControl Mode
CONTROLInput
BusCommand
If Power,Then ON X X
If Power,Respond
To CONTROLAnd Bus
CommandsAs
Programmed
Active High IgnoreBus
CommandsActive Low
Ignore CONTROL
RespondTo Bus
CommandsActive High
Active Low
AlwaysON
Respond ToCONTROL
Only
Respond ToBus Only
RespondTo Both
CONTROLAnd Bus
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OPERATION Command
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OPERATION Command
Ignore Fault
Prevents Sending An AlarmOr Responding To An
Output Undervoltage ConditionThat Was Deliberately Caused
By Margin Testing
This Allows System Testing ToProceed Without Special ModificationsTo The Power Supply/DC-DC Converter
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OPERATION Command
Act On Fault
The PMBus Device Will Send An AlarmOr Respond To An
Output Undervoltage ConditionThat Was Deliberately Caused
By Margin Testing
This May Be Desired To ProtectThe System From
Extreme Output Voltages
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Sequencing: Event Driven
• Event Driven Sequencing Is Closed Loop• Requires Power System Manager
To Close The Loop
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Sequencing:Time Driven Commands• Open Loop: Does Not Require
Power System Manager
Time
Ton-Rise
Ton-Delay Ton-MaxFault
Toff-Fall
Toff-Delay
Output
On
Off
Toff-MaxFault
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Open Loop Tracking• To Implement An Open
Loop Tracking Turn On, Need To Know:– Each Output Voltage– Desired Rise Time
(TON_RISE) For Just One Output Voltage
• Calculate TON_RISE Of All Other Outputs As Follows:
2_ ( 2) _ ( 1)13_ ( 3) _ ( 1)1
VTON RISE V TON RISE VVVTON RISE V TON RISE VV
=
=
i
i
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Status Reporting AndFault Management• The PMBus Protocol Supports Two Alarm
Levels– Warnings (Minor Alarms)– Faults (Major Alarms)
• Warnings Only Result In Host Being Notified That Attention Is Needed
• Faults Cause The PMBus Device To Respond And Take Action Internally As Programmed
• Parametric Information (e.g. Voltage) Can Also Be Read From PMBus Devices
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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 And Transmit Notice To System Host– Optional– Requires A More Sophisticated Host And
More Sophisticated PMBus Devices
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Status Reporting: 3 Levels Of Detail
Level 1:STATUS_BYTE
Most Critical Info
Level 2:STATUS_WORD
Adds More Important Info
Level 3:Status Registers
Detailed Information
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STATUS_BYTE & STATUS_WORD
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Status RegistersSTATUS_WORD
STATUS_BYTE
7 6 5 4 3 2 1 0
OTHER FAULT OR WARNINGCOMM, LOGIC, MEMORY EVENT
TEMPERATURE FAULT OR WARNING
IOUT_OC FAULTVOUT_OV FAULT
VIN_UV FAULT
UNIT IS OFFUNIT IS BUSY
7 6 5 4 3 2 1 0
UNKNOWN FAULT OR WARNINGReserved
ReservedPOWER_GOOD Negated
MFR SPECIFIC²INPUT FAULT OR WARNING
IOUT FAULT OR WARNINGVOUT FAULTS OR WARNINGS
STATUS_VOUTRegister
STATUS_IOUTRegister
STATUS_INPUTRegister
STATUS_TEMPERATURERegister
STATUS_OTHERRegister
STATUS_CML¹Register
STATUS_MFR²Register
¹: CML: Communication, Memory, Logic²: MFR SPECIFIC: Manufacturer Specific
Low ByteHigh Byte
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Clearing Status Bits• Any warning or fault bits set in the status registers
remain set, even if the fault or warning condition is removed or corrected, until:– The device receives a CLEAR_FAULTS command,– A RESET signal (if one exists) is asserted,– The output is commanded through the CONTROL pin, the
OPERATION command, or the combined action of the CONTROL pin and OPERATION command, to turn off and then to turn back on
– Bias power is removed from the PMBus device.• If the warning or fault condition is present when the bit
is cleared, the bit is immediately set again. The device shall respond as described in Section 10.2.1 or Section 10.2.2 as appropriate.
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Fault Management: Input
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Fault Management: Output
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Other Fault Management
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Voltage Or TemperatureFault Response Programming Byte
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Fault Response Examples
Shut Down And Latch Off
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Fault Response Examples
Shutdown And Latch OffContinuous Hiccup Mode
1 0 1 1 1 0 0 0
DON’T CARE111 = CONTINUOUS RETRY
10 = SHUTDOWN AND RETRY
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Fault Response Examples
Keep Operating For 3 Time Units.If Fault Still Exists At That Time,
Shut Down And Latch Off
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Fault Response Examples
Keep Operating For 3 Time Units.If Fault Still Exists At That Time,
Shut Down And Latch Off
“Time Units” Are Defined In Each
Device’s Product Literature
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Current Fault Options
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Parametric Information• Input Voltage (READ_VIN)• Input Current (READ_IIN)• Output Voltage (READ_VOUT)• Output Current (READ_IOUT)• Hold Up Capacitor Voltage (READ_VCAP)• Temperature (READ_TEMPERTURE_1, _2, _3)
– Up To 3 Sensors• Fan Speed (READ_VFAN_1,_2)
– Up To 2 Fans• Duty Cycle (READ_DUTY_CYCLE)• Switching Frequency (READ_FREQUENCY)
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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
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Interleaving
• INTERLEAVE Command Sets– Group
Number– Number Of
Units In The Group
– Switching Order Within The Group ( ) S
Interleave Order Of Unit XTdelay Unit X TNumber In Group
= i
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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
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Paging: Multiple Output Units
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Paging:Non-PMBus Device Adapter
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Paging:Non-PMBus Device Adapter Example Device:
POL ConverterWith An
Analog InterfaceExample Device:Analog Margin/
Sequence Controller With
PMBus Interface
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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
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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 Specific Commands
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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
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