Application Note 304 Flex Power Modules Microcontroller Programming for 3E Digital Products UMA NIBH VITAE DIAM volumpat wisi Introduction Flex’s 3E Digital products are designed with state-of-the- Abstract art digital controllers. This provides the user with superior electrical performance and a broad capability to configure, control and monitor the products in the engineering lab, in The 3E Digital products can be configured, controlled the factory, and in the field. This capability is provided by the and monitored through a digital serial interface use of the open-standard PMBus™ digital power using the PMBus™ power management protocol. management protocol. This application note provides an introduction to the The PMBus protocol was created by the System serial bus interface of the 3E Digital products and Management Interface Forum (SMIF) and Power accessing the 3E products using a general purpose Management Bus (PMBus) Implementers Forum to microcontroller. This application note is not a detailed standardize communication with a wide range of power tutorial on the PMBus power management protocol. conversion devices. The resulting PMBus standard is It is recommended that you study the SMBus and written in two parts. The first, “Specification Part I – General PMBus specification documents before attempting Requirements Transport and Electrical Interface”, specifies to access a 3E product via the serial bus interface. the transport including the physical layer, addressing, and packet structure. The second, “Specification Part II – While it is possible to write firmware for the Command Language”, specifies the command language microcontroller that creates a serial bus by “bit to be used when communicating with PMBus compliant banging” general purpose I/O pins, this is not devices. The PMBus specifications are freely available at recommended. It is highly recommended that the the PMBus Web site, user choose a microcontroller that includes a hardware implementation of an I²C or SMBus http://www.pmbus.org interface. For such an interface, the programmer is generally only concerned with transferring data to In addition to the capabilities provided by the PMBus, Flex’s and from transmit and receive buffers and monitoring 3E POL regulators feature the Group Command Bus (GCB). The flags for the status of the data transmission. GCB is an inter-device communication bus that provides addition capabilities like digital current sharing and fault The details of working with a microcontroller’s I²C or propagation management. SMBus interface are dependent on the microcontroller being used and are not discussed in this application This document, to be used in conjunction with the PMBus note. This application note will assume that a specifications and the Technical Specifications for each micro-controller with a hardware I²C or SMBus product, describes how to interface a microcontroller based port is being used. system controller to the Flex 3E digital bus converters and regulators. The focus of this document is more on the issues involved in programming the microcontroller than in the details of the physical layer and bit-by-bit operation of the bus. Application Note 304 2 LZT 146 261 R1G ©Flex, Dec 2017 Contents Introduction 2 11 Bit Linear Format 15 Example 1: 11 Bit Linear Data To Be Written Forum Websites 4 To A PMBus Device 15 The System Management Interface Forum (SMIF) 4 Example 2: 11 Decoding 11 Bit Linear Data Power Management Bus Implementers Forum Received From A PMBUS Device 16 (PMBUS-IF) 4 Non-Numeric Data 16 PMBus – Power System Management Bus PMBus Commands On The Bus 17 Protocol Documents 4 Example PMBus Transaction 1: Specification Part I – General Requirements A Command With One Byte Of Data Transport And Electrical Interface 4 Written To A PMBus Device 17 Specification Part II – Command Language 4 Example PMBus Transaction 2: A Command That Reads Two Bytes Of Data From SMBus – System Management Bus Documents 4 A PMBus Device 18 System Management Bus Specification, Example PMBus Transaction 3: Version 20, August 3, 2000 4 A Command That Reads A Block Of Data From A PMBus Device 19 Applicability 5 Responding To A NACK From A PMBus Device 19 SMBus Basics 6 Packet Error Checking 20 SMBus Signals 6 SMBus Packet Error Checking 20 PHY Layer And Electrical Interface 6 Calculating The Checksum 20 Addressing 6 Checking PEC Support In A Slave Device 20 Transaction Basics 6 Writing Data With A PEC Byte 20 Bit And Bytes – The Data Link Layer 7 Reading Data With A PEC Byte 21 Bits And Data Validity 7 Using Packet Error Checking With A START, ACK, NACK and STOP Conditions 7 PMBus Device That Does Not Support NACK (Not Acknowledge) 8 Packet Error Checking 22 STOP Condition 8 Handling A Failed Checksum Comparison 22 Clock Stretching 9 Bus Timeout Limits 9 SALERT (SMBALERT#) Protocol 22 SMBus Data Transfer Protocols 10 Bit and Byte Order 10 Other PMBus Signals 24 WRITE BYTE Protocol Example 10 CTRL (PMBus CONTROL) 24 READ WORD Protocol Example 11 WP (Write Protect) 24 PMBus Data Formats 12 PMBus Variations From SMBus Specification 24 16 Bit Linear For Output Voltage Related Signals 24 Commands 12 Speed 24 Data Format For The 3E Digital POL Regulators 13 GROUP Protocol 24 Data Format 13 Example 1: Setting The Output Voltage 13 Summary 25 Example 2: Trimming The Output Voltage 13 Data Format For The 3E Digital Intermediate Reference Documents 26 Bus Converters 14 Flex Technical Specifications Data Format 14 For The Following Products: 26 Example 1: Setting The Output Voltage 14 Example 2: Trimming The Output Voltage 14 Appendix 1: Example PEC Checksum Calculation Code 26 Application Note 304 3 LZT 146 261 R1G ©Flex, Dec 2017 Forum Websites The System Management Interface Forum (SMIF) Power Management Bus Implementers Forum (PMBUS-IF) http://www.powersig.org/ http://pmbus.org/ The System Management Interface Forum (SMIF) supports the The PMBus-IF supports the advancement and early rapid advancement of an efficient and compatible adoption of the PMBus protocol for power management. This technology base that promotes power management and website offers recent PMBus specification documents, PMBus systems technology implementations. The SMIF provides a articles, as well as upcoming PMBus presentations and membership path for any company or individual to be seminars, PMBus Document Review Board (DRB) meeting active participants in any or all of the various working notes, and other PMBus related news. groups established by the implementer forums. PMBus – Power System Management Bus Protocol Documents These specification documents may be obtained from the Specification Part I – General Requirements Transport And PMBus-IF website described above. These are required Electrical Interface reading for complete understanding of the PMBus Includes the general requirements, defines the transport implementation. This application note will not re-address and electrical interface and timing requirements of all of the details contained within the two PMBus hardwired signals. Specification documents. Specification Part II – Command Language Describes the operation of commands, data formats, fault management and defines the command language used with the PMBus. SMBus – System Management Bus Documents System Management Bus Specification, Version 2.0, August specification is freely available from the System 3, 2000 Management Interface Forum Web site at: This specification specifies the version of the SMBus on which Revision 1.2 of the PMBus Specification is based. This http://www.smbus.org/specs/ Application Note 304 4 LZT 146 261 R1G ©Flex, Dec 2017 Applicability This document applies to all versions of the Most PMBus commands have the same data format and following products: effect for these products. However, there are some exceptions. For example, a command may be available for > BMR450 digital POL regulator the BMR450 and BMR451 products but not the BMR46x > BMR451 digital POL regulator products. In other cases the same command code may have different meanings and effects depending on the specific > BMR46x digital POL regulators model. The details of these differences are described in > BMR 453 digital intermediate bus converter AN302 PMBus Command Set and the technical > BMR 454 digital intermediate bus converter specification for each product. Application Note 304 5 LZT 146 261 R1G ©Flex, Dec 2017 SMBus Basics We start with an introduction to the SMBus because the fall times are one of the most common causes of unreliable PMBus protocol is based on SMBus Version 2. The PMBus bus operation. protocol does have some unique extensions to the SMBus interface that will be discussed later. Some microcontrollers offer the option of configuring the serial bus port for I²C or SMBus signal levels. If the The SMBus is a two wire serial bus with electrical microcontroller being used offers this option, configure the characteristics very similar to the I²C bus invented by serial bus pins for the SMBus signal levels. Philips. If you are familiar with using a microcontroller to manage I²C devices then you will have little difficulty Addressing accessing the 3E Digital products via the serial bus The SMBus specification, like the I²C specification, provides interface. for each device to have a seven bit physical address. Each device on the bus must have a unique address. It is left to For a detailed description of how the SMBus differs from the system engineer to assure that there are no address the I²C bus, including detailed electrical and timing conflicts. characteristics, please see Appendix B – Differences between SMBus and I²C of the SMBus Specification (Version The 3E products use resistors to program the bus address 2.0) of each device. The device address is not configurable through the serial bus interface. Consult the technical SMBus Signals specification for the 3E product being used for the details The SMBus has two required signal wires. SMBCLK is the on setting the device’s bus address.