UNIVERSAL SERIAL BUS (USB) POWER-DISTRIBUTION REQUIREMENTS

TPS2552

TPS2553, TPS2552-1, TPS2553-1

One application for this device is for current limiting in universal serial bus (USB) applications. The original USB

interface was a 12-Mb/s or 1.5-Mb/s, multiplexed serial bus designed for low-to-medium bandwidth PC

peripherals (e.g., keyboards, printers, scanners, and mice). As the demand for more bandwidth increased, the

USB 2.0 standard was introduced increasing the maximum data rate to 480-Mb/s. The four-wire USB interface is

conceived for dynamic attach-detach (hot plug-unplug) of peripherals. Two lines are provided for differential data,

and two lines are provided for 5-V power distribution.

USB data is a 3.3-V level signal, but power is distributed at 5 V to allow for voltage drops in cases where power

is distributed through more than one hub across long cables. Each function must provide its own regulated 3.3 V

from the 5-V input or its own internal power supply. The USB specification classifies two different classes of

devices depending on its maximum current draw. A device classified as low-power can draw up to 100 mA as

defined by the standard. A device classified as high-power can draw up to 500 mA. It is important that the

minimum current-limit threshold of the current-limiting power-switch exceed the maximum current-limit draw of

the intended application. The latest USB standard should always be referenced when considering the

current-limit threshold

The USB specification defines two types of devices as hubs and functions. A USB hub is a device that contains

multiple ports for different USB devices to connect and can be self-powered (SPH) or bus-powered (BPH). A

function is a USB device that is able to transmit or receive data or control information over the bus. A USB

function can be embedded in a USB hub. A USB function can be one of three types included in the list below.

• Low-power, bus-powered function

• High-power, bus-powered function

• Self-powered function

SPHs and BPHs distribute data and power to downstream functions. The TPS2552/53 has higher current

capability than required for a single USB port allowing it to power multiple downstream ports.

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Product Folder Link(s): TPS2552 TPS2553 TPS2552-1 TPS2553-1