What is PMBus?

Topic 6
Using PMBus for Improved
System-Level Power Management
KKurt t Hesse
H

PMBus overview
Agenda
Some tasks and PMBus solutions
Brief design example
6-2

Evolution
Newer systems require more advanced
capabilities
Supplies evolving in:
Si Size and d iintegration i
Functionality
Flexibility
Monitoring and control
PMBus is an answer
6-3

Open standard
What is PMBus?
Serial interface to controller
Electrical ect ca spec specification cat o pprotocol otoco aand d co command a d language a guage
Anyone can use – royalty free
Controlled by Special Interest Group (SIG):
www.pmbus.org
Communication only
NNo fform factor f t
No I/O specification
No specific functionality requirement
No pinout
Implementation of the physical supply is
completely open
6-4

Si Single l master t – HHost t
Typical PMBus System
One or more slaves – Supplies
Bus:
CLOCK and DATA
required
Central Control Unit:
System Host/Bus Master
CNTL and SMBALRT optional
Each device has unique address
Only communication between
host and supplies – no intersupply
communication
Power Supply:
Bus Slave
CLK
DATA
CNTL
SMBALRT
Write Protect Address 1
Power Supply:
Bus Slave
CLK
DATA
CNTL
SMBALRT
Write Protect Address 2
Power Supply:
Bus Slave
CLK
DATA
CNTL
SMBALRT
Write Protect Address 3
6-5

PC
Development stage
Automatic Test
What is the Host?
Central Control Unit:
Equipment
System Host/Bus Master
Production testing
Final parameter trim
Microcontroller/
Power Supply:
Bus Slave
CLK
DATA
CNTL
SMBALRT
Write Protect Address 1
Power Supply:
Bus Slave
CLK
DATA
CNTL
SMBALRT
Write Protect Address 2
Microprocessor
CLK
DATA
CNTL
Power Supply:
Bus Slave
SMBALRT
In the field
Power sequencing, fault
management, etc.
Write Protect Address 3
6-6

PMBus-Converter Architecture
Si Similar il tto standard t d d controller t ll
PMBus interface addon is typical
Hooks into controller for PMBus functions
NVRAM
Store operating parameters, user data, etc.
Input
Power Current
Sense
PMBus to
System
Host
RReference f
Voltage
SSense
CLK
DATA
SMBALRT
CNTL
Error Amplifier
and Pulse-Width
Pulse Width
Modulator
PMBus Interface
Power Stage
Current Sense
Voltage Sense
Nonvolatile
Memory
Output
PPower
6-7

Ancestry of PMBus
Inter-Integrated Circuit – Philips development
Simple serial 2-wire bus
VVulnerable l bl
Excessive clock stretching causing bus lockup
No standard error check
6-8

Ancestry of PMBus
System y Management g Bus – www.smbus.orgg
Fixes bus lockup from clock stretching issues
Bus times out and resets
Standard error checking defined
HHost-notify t tif protocol t l defined d fi d
Slave device can alert master when needed
6-9

Ancestry of PMBus
Power Management Bus – www.pmbus.org
Outgrowth of SMBus
Notable differences
Host-notify protocol is optional
Group-command protocol
Multiple devices can execute commands at the same time
6-10

PMBus Compliance
PMBus specification is in two parts
Compliant converters must:
Meet all Part I specifications
Hardware interface (electrical, timing)
Implement at least one command
Other than manufacturer specific
Supported commands must comply with Part II of
the specification
Command language
Non-supported Non supported command
Also:
Respond according to Part II
Must be able start without PMBus communication
6-11

Not hard!
Simple sequential
commands
Example sets
converter’s:
OOvercurrent t limit li it
Input turn-on voltage
Soft-start time
Usage Mechanics
Parameters to power-up p p
defaults
Prior parts of
the host
program
IOUT_OC_FAULT_LIMIT (Converter A, 10 A);
VIN_ON (Converter A, 10 V);
TON_RISE (Converter A, 5 ms);
STORE STORE_DEFAULT_ALL DEFAULT ALL (Converter A);
Remainder of
the host
program
6-12

PMBus Command
1 7 1 1 8 1 8
One or more Data Bytes
1 8 1 8 1 1
S Device Address W A Command Code A Data Byte A ... Data Byte A PEC A P
CLK CLK
DATA DATA
START Condition STOP Condition
PMBus command is fairly simple
START and STOP conditions have DATA-change
state while CLK is high.
Normal transfer: DATA is stable while CLK is high
6-13

Types of Commands Available
On, off, and margin
testing
OOutput t t voltage lt related l t d
Addressing, memory
communication communication, and
capability
Fault au handling a d g
Sequencing
Status
Telemetry
Other
Deal with turning
converter on and off,
output margining
Commands in group:
OPERATION
ON_OFF_CONFIG
VOUT_MARGIN_HIGH
VOUT_MARGIN_LOW
6-14

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Commands affect the
output voltage of the
converter
Commands in group:
VOUT_COMMAND
VOUT_TRIM
VOUT_CAL_OFFSET
VOUT_SCALE_LOOP
6-15

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Deal with device
addressing, memory,
communication, and
capability of the converter
Commands in group:
STORE_DEFAULT_ALL
STORE STORE_DEFAULT_CODE
DEFAULT CODE
PHASE, PAGE
WRITE_PROTECT
6-16

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Determine how converter
responds to faults
Defines what fault and
warning levels are
Commands in group:
IOUT_OC_WARN_LIMIT
IOUT_OC_FAULT_LIMIT
IOUT_OC_FAULT_RESPONSE
Many others
6-17

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Deals with timing of
startup and shutdown
Commands in group:
TON_DELAY
TON_RISE
TOFF_DELAY
TOFF_FALL
6-18

Enable
CNTL
VIN_ON
OPERATION
Power-On Sequencing
0
Enable
TON_DELAY
TON_RISE
Output
Voltage
Time
6-19

Enable
CNTL
VIN_OFF
OPERATION
Power-Off Sequencing
0
Enable
TOFF_ DELAY
Output
Voltage
TOFF_FALL
Time
6-20

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Information about
status of converter
Commands in group:
STATUS_BYTE
STATUS_WORD
STATUS_IOUT
STATUS_CML
6-21

STATUS_BYTE and STATUS_WORD
STATUS_WORD
High Byte
7– VOUT OU
6– IOUT/POUT
5– INPUT
4– MFR
33– POWER POWER_GOOD GOOD
2– FANS
1– OTHER
0– UNKNOWN
7– BUSY
6– OFF
Low Byte
5–VOUT 5– VOUT_OV OV
4– IOUT_OC
3– VIN_UV
2– TEMPERATURE
1– CML
0– None of the above
STATUS_BYTE part of
STATUS_WORD
Most flags have more
detailed status commands
STATUS_BYTE
7– BUSY
6– OFF
5–VOUT 5– VOUT_OV OV
4– IOUT_OC
3– VIN_UV
2– TEMPERATURE
1– CML
0– None of the above
6-22

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Report back converter
operating conditions
Commands in group:
READ_VIN
READ_VOUT
READ_IIN
READ READ_IOUT IOUT
READ_DUTY_CYCLE
READ READ_FREQUENCY
FREQUENCY
Several others
6-23

Types of Commands Available
On, off, and margin
testing
Output voltage related
Addressing, memory
communication communication, and
capability
Fault handlingg
Sequencing
Status
Telemetry
Other
Commands that don’t
really fit elsewhere:
FREQUENCY FREQUENCY_SWITCH SWITCH
VIN_ON
VIN_OFF
IOUT_CAL_GAIN
IOUT_CAL_OFFSET
Other classes not
mentioned:
Manufacturer data
User data
6-24

PMBus overview
Agenda
Some tasks and PMBus solutions
Brief design example
6-25

PMBus in the System
Converter may not support all PMBus
commands
Consider tasks needed
Match capability to task requirements
For example
Sequencing
Margining g g
Monitoring, etc.
6-26

Sequencing
Several ways to accomplish with PMBus
facilities:
Remote enable
CNTRL pin
OPERATION command
Time delay
Open-loop Open loop tracking
6-27

System
Host
CNTL
Remote Enable
PMBus
Converter A
Power Good
Converter B
PMBus
CNTL
PPower Good G d
Vout
Vout
0
Output
Voltage
Simple p – not really y PMBus solution
CNTL is like ENABLE pin
CNTL A
CNTL B
TON_RISE(A)
TON_RISE(B)
Controlled individually – conventional
Similar operation possible using OPERATION
commands over PMBus
Time
Converter B
Converter A
6-28

0
Output
Voltage
Time-Delay Sequencing
EEnable bl
TON_DELAY(B)
TON_RISE(A)
TON TON_RISE(B) RISE(B)
Time
Converter B
Converter A
Converters programmed with startup delay (TON_RISE)
Enabled simultaneously
Eases burden on system host
6-29

0
Enable
Output
Voltage g
Time-Delay Off
Time
Similar to previous – using TOFF_DELAY
Watch fall times if TOFF TOFF_FALL FALL not supported
Both converters disabled simultaneously
6-30

0
Tracking
Startup methodology keeping multiplevoltage
rails close
Startup
Possibly shutdown
Startup and shutdown only here - Not for DDR
Output
Voltage
Rail 1
Rail 2
Time
6-31

0
PMBus-Tracking Startup
Enable
TON_RISE(B)
TON_RISE(A)
Converter B
Converter A
V V
OOutput t t
out(A) out(B)
Voltage =
Time
Set slopes of rise times equal
TON _ RISE(A) TON _ RISE(B)
Requires very fine control of TON_RISE
6-32

0
PMBus-Tracking Shutdown
Converter B
Converter A
Enable
TOFF TOFF_DELAY(A) DELAY(A)
Output
Voltage
Time
Vout(A) Vout(B)
=
TOFF_FALL(A) TOFF_FALL(B)
TOFF_FALL(B)
TOFF_FALL(A)
Set down slopes equal – Requires TOFF_FALL support
Note off delay required for lower voltage output
6-33

Margining
Vary output voltages to test system
Requires q either
Converter support
External device(s) to implement
PMBus support
Variable margin g voltages g
Variable transition rate
Programmable g fault response p during g margin g
Set margin voltages and use OPERATION
command to execute
6-34

Margin
Output
Voltage
Margin Illustrated
VOUT_TTRANSITION_RATE
Time
VOUT_MARGIN_HIGH
Margin initiated using OPERATION command
Transition rate and margin voltage are variable
MMuch ch more flexible fle ible than hard hardware are sol solution
tion
6-35

Timing Issue
How to synchronize PMBus commands
Startup/tracking require known timing relationships
Serial bus not inherently good
PMBus solution:
Group Command Protocol
6-36

PMBus Group Command
OneormoreDataBytes
One or more Data Bytes
1 7 1 1 8 1 8 1 8 1 8 1
S Device 1 Address W A Command Code A Data Byte A ... Data Byte A PEC 1 A
1 7 1 1 8 1 8
One or more Data Bytes
1 8 1 8 1
S Device 2 Address W A Command Code A Data Byte A ... Data Byte A PEC 2 A
One or more Data Bytes
1 7 1 1 8 1 8 1 8 1 8 1 1
S Device N Address W A Command Code A Data Byte A ... Data Byte A PEC N A P
S START Bit P STOP Bit A ACK Bit Device N Address
Seven-bit
device
address
Lik Like single i l command d except: t
No STOP after first command
PEC
Packet-error
check byte.
START repeats and next command is issued
STOP issued after final command
W
...
...
Read/Write eighth
bit of address byte
set to WRITE mode.
Commands simultaneously executed after the STOP
6-37

PMBus Group Command
Group command caveats:
1. No more than one command in a group
can be addressed to a single slave
device
2. No command in the group can require
the slave to respond over the PMBus
6-38

Other Uses of PMBus
Change system power parameters
Factory or field
No hardware modification
Accidental overvoltage protection
Inadvertent/erroneous command
System monitoring
Compensation and capacitive loading
Fault and incident tracking
6-39

PMBus overview
Agenda
Some tasks and PMBus solutions
Brief design example
6-40

Design Example
Important: Not all converters support all
functions
Determine necessary functions
Select converter or controller accordingly
6-41

Target Specifications
Power supply for two processors in communications rack
Core and I/O for each
Input voltage: 12 V
Core output voltage: 1.2 V at 10 A per processor
Must be able to change from 1.1 V to 1.2 V
I/O output voltage: 3.3 V at 3 A per processor
Sequencing required: Core up first, then I/O’s
Margin testing support for field and factory
Output voltage and current monitoring
Minimal cost
6-42

PMBus Features Required
Nonvolatile memory
Store default operating parameters
PPower-on sequencing i
TON_DELAY
VOUT VOUT_TRIM TRIM command
To adjust nominal output voltage on cores
Margin commands
VOUT_MARGIN_HIGH, VOUT_MARGIN_LOW, OPERATION
VOUT_TRANSITION_RATE nice to have
READ_VOUT, READ_IOUT
Monitor output power
READ READ_POUT POUT would ld work k too
t
6-43

Proposed Solution
FFusion i PPower Peripherals
P i h l
UCD9240
UCD9240
Digital PMBus controller
Features
Up to 4 independent rail control
±1-mV feedback resolution
HHardware d accelerated l t d di digital it l
compensator
12-bit monitoring of supply
parameters t
Programmable softstart and stop
Nonvolatile memory with ECC
Supports voltage tracking
Programmable margining and
sequencing q g
PC-based design tools
PWR
GND
BPCAP
EAP4
EAN4
EAP3
EAN3
EAP2
EAN2
EAP1
EAN1
5
6
ADDR-00
ADDR-01
CS-1A
CS-1B
CS-2A
CS-2B
CS-3A
CS-3B
CS-4A
CS-4B
VIN
Vtrack
Temperature
Diff
Amp
Error ADC
Error ADC
ADC
12-Bit
200 ksps
Error ADC
Error ADC
Ref
Error
Amp
6
6
6
6-Bit
ADC
Analog Comparators
Ref 1
Ref 2
Compensator
3P/3Z IIR
Compensator
3P/3Z IIR
Compensator
3P/3Z IIR
TRIP 1
TRIP 2
16
16
16
Compensator
6
IIR
3P/3Z
Coeff.
Regs
16
ARM-7 Flash
Core Memory
with ECC
Digital
High-Res
PWM
Digital
High High-Res Res
PWM
Digital
High-Res
PWM
Digital
High-Res
PWM
SRE
Control
DPWM-4A
DPWM-4B
FAULT-4A
FAULT-4B
DPWM-3A
DPWM-3B
FAULT FAULT-3A 3A
FAULT-3B
DPWM-2A
DPWM-2B
FAULT-2A
FAULT-2B
DPWM-1A
DPWM-1B
FAULT-1A
FAULT-1B
SYNC-IN
SYNC-OUT
SRE-4B
SRE-4A
SRE-3B
SRE-3A
SRE SRE-2B 2B
SRE-2A
SRE-1B
SRE-1A
TRIP 3
Ref 3
Vreg
PMBus-Clk
PMBus-Data
Osc
PMBus PMBus-Alert
TRIP 4 PMBus PMBus-Cntl
Cntl
Ref 4 POR/BOR
6-44

Vin
+Vsens-rail1
-Vsens-rail1
+Vsens-rail2
-Vsens-rail2
+Vsens-rail3
-Vsens-rail3 Vsens rail3
+Vsens-rail4
-Vsens-rail4
Isens-rail1
Isens Isens-rail2 rail2
Isens-rail3
Isens-rail4
To
PMBus
host
Power
Good
3.3 V
50 EAp1
51 EAn1
52 EAp2
53 EAn2
54 EAp3
55 EAn3
56 EAp4
57 EAn4
61 AddrSens0
60 AddrSens1
V33FB
V33A
V33D
3.3 V
58 46 45 7 44 47
V33DIO-1
V33DIO-2
BPCap
UCD9240
Proposed Solution
DPWM-1A 17
DPWM-1B 18
DPWM-2A 19
DPWM-2B 20
DPWM-3A 21
DPWM DPWM-4A 4A 23
FAULT -1A 11
FAULT -1B 12
FAULT -2A 13
FAULT -2B 14
FAULT -3A 25
FAULT -4A 34
TLV1117-ADJ
Vin
Vout
8V
Isens-rail1
+Vsens-rail1
-Vsens-rail1
59 CS-1A (COMP1)
SRE-1A 22
Isens-rail2
3 CS CS-2A 2A (COMP2)
SRE-1B 24
+V +Vsens-rail2 il2
2 CS-3A (COMP3)
SRE-2A 33
-Vsens-rail2
1 CS-4A (COMP4)
SRE-2B 35
63 CS-1B
SRE-3A 29
62 CS-2B
SRE-4A 30
4 Vin
5 Vtrack
6 Temp
15 PMBus PMBus-CLK CLK
16 PMBus-DATA
27 PMBus-ALERT
28 PMBus-CTRL
39 PowerGood
9 /Reset
AGND-1
AGND-2
AGND-3
DGND-1
DGND-2
DGND-3
49 48 64 8 26 43
TMUX-0 31
TMUX-1 32
TMUX-2 42
FAN FAN-PWM PWM 41
FAN-TACH 36
SYNC-IN 38
SYNC-OUT 37
/TRST 40
TRCK 10
Isens-rail3
+Vsens-rail3
-Vsens-rail3
Isens-rail4
+Vsens-rail4
-Vsens-rail4
8 V
UCD72XX
8 V
8 V
8 V
Power Stage
Power Stage
Vcore1
Vin Vcore2
Vin
Power Stage
Vin
Power Stage g
VI/O1
VI/O2
6-45

Conclusions
PMBus as a standard supports a wide range
of functionality
Many system-level tasks can be accomplished
by the facilities provided by PMBus
Converters won’t generally fully support
PMBus command set
Match system requirements to converter capability
6-46