UNIVERSAL SERIAL BUS (USB) POWER-DISTRIBUTION REQUIREMENTS

TPS2552

TPS2553, TPS2552-1, TPS2553-1

Where:

θ

Compare the calculated junction temperature with the initial estimate. If they are not within a few degrees, repeat

iterations are generally sufficient to achieve the desired result. The final junction temperature is highly dependent

on thermal resistance

θ

layout. The Dissipating Rating Table provides example thermal resistances for specific packages and board

layouts.

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