Power management bus (pmbus)

1 Introduce

1.1 brief introduction

Power management bus （PMBus） System management bus （SMBus） A variation of the , It aims to realize the digital management of power supply . And SMBus equally , It is based on I²C Relatively slow two-wire communication protocol . Different from either of these two standards , It defines a number of domain specific commands , Not just how to communicate using reader defined commands .
Power management bus (PMBus) Is an open standard digital power management protocol : Simple 、 robust 、 Scalable .

1.2 background

PMBus To regulate in 2005 Released in , Designed to help redefine power management in embedded systems .
SMBus It is based on I2C The agreement above , It was created as a means of managing smart batteries and other systems and power management devices .SMBus And I2C Same low cost , But its functions and features are more powerful .
because PMBus yes SMBus Protocol extension , Therefore, it shares most of its physical layer and the operation mode of the bus . however ,PMBus Defines a specific set of commands and data structures required for power control and management components .

1.3 function

The physical layer / transmission

PMBus It is a low-cost two-wire interface , yes SMBus Standard extension , This standard is based on I2C Agreement building . And SMBus similar ,PMBus At least two wires are required for communication , Including clock signal SMBCLK And data signals SMBDAT. The optional signal will be replaced by two GPIO Pin , Include CONTROL and SMBALERT# The signal .
And I2C comparison ,PMBus Support stronger protocols , because PMBus Provides timeout and optional packet error checking （PEC） To enhance data integrity . Timeout prevents the slower slave from holding the clock line beyond the specified timeout interval , So as to avoid bus hang up .PEC Bytes are used CRC-8 Algorithm generated , The algorithm is used to verify the integrity of transactions , This is often critical in power management systems .
And SMBus equally ,PMBus Including the system host for communication / Bus master and slave devices （PMBus equipment ）.

data format

And I2C similar ,PMBus It's a by 8 A variable length packet consisting of bits and bytes .PMBus The basic packet structure of includes an address byte , The address byte consists of a 7 Bit address composition , With 1 Bit reads or writes to the end of the signal . And then a 8 Bit command byte （ Including command code ）, Then there is one or more 8 Bit data byte .（ Optional ） There may also be one 8 position PEC byte . Each byte contains its own receiver acknowledgement , And each transaction is included in the host " start-up " Bit and " stop it " Between bits .

electrical

PMBus The electrical interface shall comply with SMBus Specifications similar specifications . For power supply voltage requirements , Operating voltage range （V Interrupter ) The voltage may be 3 V to 5 V±10%（2.7 V to 5.5 V）.
about 400 kHz PMBus equipment , The required pull-down current is 4 mA.

Use PMBus The location of

PMBus It has been increasingly used for digital power management in the system .PMBus It can be used with various power management products , for example AC-DC Power Supply 、 Isolated DC-DC Disconnect the converter 、 Non isolated load points （POL） converter 、 Power sequencer and load point voltage programmer , And monitor and fan controller .

1.4 history

• 2005 Released in PMBus standard .

• 2014 year 3 month ,AVSBus As PMBus Standard No 1.3 Part of the release .AVSBus yes PMBus A subset of , Used to FPGA、ASIC、 Processors and other large digital devices IC Provide adaptive voltage scaling .

1.5 Focus on the direction

A more ambitious work is also under way ,PMBus and AVSBus Will be upgraded to 2.0, This will be PMBus/AVSBus Command set and SMBus Provide a clear separation between the physical layer and the transport layer . Will make PMBus In the future, it is easier to adopt additional physical layer and transport layer . At the same time, in order to improve the security in the field of digital power communication , More changes are being considered .

PMBus Application profile working group （PMBus ApplicaTIon Profile Work Group） Focus on the following areas ：

• Extend existing point-to-point AVSBus Architecture behavior , Allow multiple slaves on the bus , And make relevant commands and monitor changes .

• For industry 、 Medical care 、 Definition of front-end power supply in communication and computing market PMBus Application configuration files . The specification will include AC input ,48V Input , High voltage DC input .

• The definition is universal （ Or neutral ） Characteristics of file format , It is used to configure the products from multiple suppliers on the newly manufactured circuit board PMBus device .

• The physical bus realizes unification （ Physical bus implementation ）. This will be in the coming PMBus 2.0 Got support from .SMBus Has always been a PMBus Default PHY, But some have achieved others PHY, In order to transmit over a long distance PMBus command （ENET、CAN、RS485 etc. ）. This work will create a standard approach to support PMBus Not through other PHY Realization .

1.6 command

PMBus The agreement currently includes about 200 An order , These commands can be classified as follows ：

To configure

Output voltage
Working frequency
OVT/OCT/OTP threshold
Power Supply “ good ” window
Troubleshooting
Soft start mode
Sync
And other things

control

Enable / Ban
Output voltage
Working frequency
Phase throttling
margin
And other things

monitor

Input and output voltages
Input and output currents
Duty cycle
temperature
And other things

2 Advantages and disadvantages

2.1 advantage

• Easy to design .

• Shorten the design time .

• Be able to monitor the power supply , And screen out the circuit board with poor design .

• Use new purpose specific integrated circuits (ASIC) when , It can optimize the power level （ Measure the actual drawn current value , And there is no need to over design the output inductor and output capacitor ）.

• PMBus You can do this without the need for external simulation components , Easily create a new power design , In this case , You don't have to endure the pain of smoky fire when trying new resistors and capacitors on the workbench .

• Through a graphical user interface (GUI),PMBus Can realize programming 、 Sort 、 To configure 、 control 、 Voltage margin regulation 、 Output voltage regulation 、 And parameter and fault monitoring , In this way, redesign can be realized quickly , And respond more intelligently to parameters and observed faults .

• PMBus IC External hardware monitors can be exempted 、 monitor 、 Temperature sensor , And the need of discrete logic circuits for delay .

  

  
   

3 Example

3.1 MW

application ： Autopilot （AGV）
model ：RPB-1600-48（ built-in PMBus）
communication interface ：PMBus

This application uses two RPB-1600-48 Charging station of automatic guided vehicle installed in parallel in logistics warehouse . When the truck returns to the charging station , The system will detect the connection status of the port , And use PMBus Turn on the charger to charge the battery . Pictured 3 Shown , The system will also select the appropriate charging current , adopt PMBus Charge the truck's six battery packs , And send back charging information and power status through communication .

4、I2C And PMBUS The difference between

I2C

I2C It is the standard formulated by Philips semiconductor before , It's today's NXP.

I2C The bus consists of a data line （SDA） And a clock line （SCL） form . Equipment is divided into master and slave , The master device provides a clock , And initiate the operation . 

SMBUS

SMBUS It's based on I2C And the extended protocol . There are some more complex operations , But the principles are still based on I2C Of . 

PMBUS

PMBUS Is based on SMBUS, It defines many commands related to power management . In physical transmission , and SMBUS It's exactly the same .