Building Multi-Port USB Type-C Adapters for Power

Brian King, Texas Instruments
EETimes (5/17/2016 10:00 AM EDT)

In the a previous blog, we discussed some of the challenges when designing AC/DC adapters for USB Type-C power delivery (PD). In that article, we focused on an adapter with a single Type-C output connector. In this article, we'll examine the complexities introduced when architecting a multi-port Type-C adapter.

Before getting into the details, it is helpful to review some of the power requirements of a Type-C PD output:

• The standard Type-C cable is rated for 3A of output current. (There are also provisions for up to 5A of output current with a special active cable.)
• The voltage on the Type-C bus is adjustable from 5V to 20V, with standardized levels of 5V, 9V, 15V, and 20V.
• A Type-C connector that serves as a power source is known as a downward facing port (DFP). The DFP’s supported voltage/current profiles are advertised on a pair of communication wires (CC1 and CC2) within the Type-C cable.
• When a load is connected to the other end of the cable, it can communicate back to the DFP which of the available profiles it wants. A port controller device is used in the DFP to provide this handshaking and interface back to the switching power supply within the DFP.

The first decision to make is which voltage profiles to support. This will be driven by the application and the voltage profiles supported by the devices that the adapter is intended to charge. The 5V level is mostly used by legacy phones and tablets, as well as small devices like thumb drives. As Type-C is more widely adopted, we should see more of the phone and tablet market migrate away from the 5V level.

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