Has the Modern Data Center Outstripped I2C and SMBus? I3C May Be the Answer

June 05, 2020 by Gary Elinoff

An upgrade in serial communication interfaces may be in order. Renesas is stepping up to support the transition.

We recently discussed the heightened demands on modern data centers, especially with more employees working from home. Some of these demands involve security and component authentication, advanced thermal control loops, fault tolerance, and recovery. Interfaces like I2C and SMBus, which are sometimes outdated by decades, may struggle to meet these challenges.  

I3C Basic may be a useful solution. I3C, which stands for improved inter-integrated circuit, is a serial communication interface specification spearheaded by the MIPI Alliance. MIPI 13C is said to improve the "features, performance, and power use of I2C, while maintaining backward compatibility for most devices." I3C Basic is the same as I3C, minus the RAND-Z licensing and other feature sets. 

I3C Basic can remedy many of the burdens of the modern data center, allowing users to manage a system architecture with detailed information about a server's resource status during bootup and runtime. This can help system managers effectively migrate workloads and load balance a server when necessary. 

To bolster I3C Basic, Renesas has announced a new product family designed to implement I3C Basic as a system management bus in applications where there may be multiple masters and long traces to multiple endpoint devices.


New family of I3C bus extension devices from Renesas

New family of I3C bus extension devices from Renesas. Image used courtesy of Renesas

Critically, an integrated thermal sensor is supported by selected members of the family.


The Case for the I3C Bus

The MIPI Alliance is a global organization that promotes standards for hardware and software interfaces. MIPI I3C combines the best features of I2C and SPI and adds higher throughput, enables interrupts from slave to master, improves power management, and provides dynamic addressing. It also supports hot-join, which allows slave devices to join an already configured bus.

I3C is backward compatible with I2C and uses less power. I3C has two signal lines: Data (SDA) and Clock (SCL).


Renesas I3C Basic Expanders

Family members include two bus multiplexers and two general-purpose I/O expanders.

The IMX3102 2:1 bus multiplexer is designed for the use case of two masters controlling a single peripheral or slave devices. The IMX3112 1:2 bus multiplexer supports applications in which one master controls two slaves. 


Block diagrams of IM3102/IM3112

The IM3102 (left) and the IM3112 (right). Image (modified) used courtesy of Renesas


Both devices present a single device load to the host bus and support up to a 12.5 MHz transfer rate. They also support a range of I/O voltage levels and require a single 1.8 V power supply. 

Renesas says the devices feature a temperature sensor with 0.5°C accuracy and 0.25°C resolution. This feature allows users to integrate thermal management into the bus design itself, lowering the overall BoM.

The IXP3114/IXP3104 is a 1:4 general-purpose I/O expander, with four GPIO pins that can be configured as either output only, input only, or input/output on a local interface.



Block diagram of the IXP3114/IXP3104. Image used courtesy of Renesas


The IXP3114/IXP3104 offers most of the same specifications as the bus multiplexers, however, the internal thermal sensor isn’t featured in the IXP3104.

All four family members are available in 2 mm x 3 mm DFN packages and can be specified to operate over the industrial temperature range of -40°C to 125°C.


More Complex Subsystems May Need I3C

The new components are pin-compatible, and Renesas says they're faster and more power-efficient than their predecessors. That, and the fact that JEDEC has adapted the I3C Basic standard for the DDR5 memory sideband, are powerful inducements for these devices to be incorporated into new designs and old ones undergoing revisions.

Looking ahead, subsystems are only going to get more complex. They'll require higher sideband bus bandwidth, and the I3C bus is a much-needed step forward to this end.



If you’re a systems designer, have you found that the I2C is not quite as useful as it used to be? Share your thoughts in the comments below.

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    sckid June 05, 2020

    Overall I like the idea of I3C.  An area of potential concern is that with the faster edge and data rates of I3C is that signal integrity becomes a more prominent issue than the older slower I2C.  A nice feature is that I2C just sorta works even if your circuit is a couple wire between bread boards and some bad soldering.  I2C will have a place for a long time to come.

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  • S
    sckid June 05, 2020

    Sorry, one other point is that in order to get really popular I3C needs to be integrated into Arm Cortex based devices and the like.

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