DATA CENTER PSUs PMBus: Telemetry in data center power supply units

Related Vendors

MRS Electronic GmbH & Co. KG

Diotec Semiconductor AG

MERSEN France SB

PMBus, the “power management bus,” isn’t a conductor or a device like a bus bar; it is a communications protocol layered on top of the system management bus (SMBus), which is based on another protocol known as inter-integrated circuit (I2C). In simple words, PMBus is a communications protocol that facilitates digital management of power supplies in data centers.

What is PMBus?

PMBus is a communications protocol that allows enterprises to talk to their power systems. With the help of PMBus, enterprises can read system values, configure them, and monitor the ongoing status and overall health of the power system. Without PMBus, enterprise users cannot understand the health of their power systems; in short, they cannot prevent failure.

A host controller, which could be a baseboard management controller (BMC), outside the data center PSU functions as a bus master. This means that the BMC host wants to monitor and control the power of the data center PSU. Power Supply Management Controller (PSMC) is a chip built into the data center PSU that runs and oversees the supply.

Now, the BMC host targets data center PSUs, which must respond. PMBus is a two-wire interface that enables communication between the host BMC and the PSMC of the data center PSU. In short, power managers or hosts can exchange information on power-related values using digital communications.

Like many other communications protocols, PMBus is an open standard. Power and semiconductor companies developed it around 2004-2005. The specification is now maintained and developed by the System Management Interface Forum (SMIF).

To be precise, the subgroup of the same forum, Power Management Bus Implementers Forum (PMBus-IF), manages PMBus. About 40+ enterprises, mostly semiconductor manufacturers and vendors, are part of the forum to promote and improve the standard. In this way, telemetry becomes accessible across vendors.

PMBus features for data center PSUs

PMBus ensures communication between power managers and data center PSUs. Hosts can change only a few values and extract accurate data. Further action is based on the administrator's call. Continuous monitoring helps run data center PSUs at peak performance. It’s a part of a predictive maintenance strategy where continuous monitoring can flag and prevent future problems. Some of the PMBus features are listed below.

• Live power status monitoring: Using PMBus for data center PSUs, users can read live voltages, currents, speeds, temperatures, and many more things.

• Interoperability: Every compliant device that runs PMBus, based on its own limits, can expose similar controls, telemetry, faults, and warning signs. This means each device exposes different functions based on what it can do.

• Self-query: Enterprise users can query PMBus to know about capabilities.

• Configuration: With the help of PMBus, enterprise users can set output voltages, currents, and many other values digitally. Because PMBus accepts readable and writable commands. For example, VOUT_COMMAND, which sets the output voltage, is a writable command that tells the rail what voltage to produce. A few commands are as simple as:

READ_VOUT: Reads the present output voltage.
READ_IOUT: Reads the present output current.
READ_TEMPERATURE: Reads the device’s measured temperature.
STATUS_WORD: Reports the overall fault or warning status flags.
SMBALERT#: Notifies the host about faults.

• Logging: PMBus can store data in EEPROM-based semiconductor memories for troubleshooting, future use, and analytics. Optional packet error check (PEC) ensures that transmitted or stored data is accurate because noise can corrupt digital signals.

• Fault protection: PMBus provides built-in fault protection features, such as over-current (OC), over-voltage (OV), output short-circuit protection, over-temperature (OT), and many more, to keep the data center PSU healthy.

• Replacement: PMBus enables users to read records and notify an administrator to connect field-replaceable units (FRUs) in place of a faulty PSU. The host can instantly recognize new PSUs.

PMBus allows users to monitor the power status of power systems deployed in data centers, servers, embedded systems, industrial automation tools, telecommunications equipment, workstations, and many more automation applications.

Without this organized digital management layer, data center power supplies look like a car without a dashboard or a speedometer. The car, if considered analogous to data centers, can still run, but without any readouts and warnings.

References

https://pmbus.org/

https://www.fsp-group.com/en/knowledge-tec-67.html

https://www.totalphase.com/blog/2021/02/what-is-pmbus/?srsltid=AfmBOop_rUKbjx1s-CuwyzfFU108wQkHHRxuDy46zahBxxuioX_zQ6a3

https://www.us.lambda.tdk.com/resources/blogs/20220927.html

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