Electronic Design

Support Chips Electrify Thunderbolt

Ever look what's under the hood of Intel's Thunderbolt interface (see Thunderbolt and Light Peak)? It is not as simple as the cabling system might imply. The system delivers bidirectional 10 Gbit/s connections as well as bidirectional power distribution. It requires active retiming at both ends of the cable so there is more in the cable than just wires and connectors.

Texas Instrument's Thunderbolt chipset (Fig. 1) delivers the analog and power portion Intel's Thunderbolt interface. This includes power distribution and management as well as timing.

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Figure 1. Texas Instrument's Thunderbolt chipset delivers the timing, analog and power portion Intel's Thunderbolt interface.

Thunderbolt uses a single cabling system to deliver PCI Express and DisplayPort. It has been found on Apple laptops and is making its way into other laptops as Intel pushes its Ultrabook architecture. It provides a way to bring display and interface support to almost any device or display.

Intel is only supplier of Thunderbolt controllers at this point but they are only part of the story albeit the more expensive part. The Intel controllers expose the PCI Express and DisplayPort interfaces. On the other side, they expose the Thunderbolt interface and this is where the TI parts come into play.

The host and device require a power load switch like the TPS22980. This is a smart power load switch designed to handle voltages and current limits on cable. These can be 18V or 3.3V. They chips enable power negotiation for charging applications with high current capability for fast charging.

The TPS22985 is an automatic supply selection chip. It is used to detect the power available at both ends of the cable. It maintains switching between power supplies at both ends of the cable to prevent brownouts. The chip also provides UART signal buffering.

The LMZ10501 is a DC-DC step down load switch with overcurrent limiting. It is normally found at both ends of a Thunderbolt cable. It also assists in power negotiation for charging applications.

The LM3017 Boost and Battery Disconnect chip is usually used as a boost converter for battery operated devices. It does the heavy lifting to connect between different power sources and protects the other chips from excessive current draw. The LM3017 can deliver up to 30W of power. An enforced start up time allows output to charge up to input voltage in less than 20 milliseconds. The 430kHz fixed switching frequency delivers low ripple and high efficiency (93%). The tiny 3mm by 2.5mm chip incorporates an inductor and handles input voltages from 2.7V to 5.5V. It is fully WEBENCH enabled. This is TI's web-based design center.

The HD3SS0001 10 GHz Differential Switch provides muxing of high speed and low speed signals. It supports AUX and DDC muxing.

The DS100TB211 Retimer is needed at both ends of the cable to guarantee a clean signal in both directions. The chip has smart eye monitor capability. It is designed to support 4-layer boards and it does not need extra clock.

Thunderbolt has yet to take the world by storm but its use is growing.

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