SELF-POWERED AND BUS-POWERED HUBS

LOW-POWER BUS-POWERED AND HIGH-POWER BUS-POWERED FUNCTIONS

USB POWER-DISTRIBUTION REQUIREMENTS

TPS2552

TPS2553, TPS2552-1, TPS2553-1

A SPH has a local power supply that powers embedded functions and downstream ports. This power supply

must provide between 4.75 V to 5.25 V to downstream facing devices under full-load and no-load conditions.

SPHs are required to have current-limit protection and must report overcurrent conditions to the USB controller.

Typical SPHs are desktop PCs, monitors, printers, and stand-alone hubs.

A BPH obtains all power from an upstream port and often contains an embedded function. It must power up with

less than 100 mA. The BPH usually has one embedded function, and power is always available to the controller

of the hub. If the embedded function and hub require more than 100 mA on power up, the power to the

embedded function may need to be kept off until enumeration is completed. This is accomplished by removing

power or by shutting off the clock to the embedded function. Power switching the embedded function is not

necessary if the aggregate power draw for the function and controller is less than 100 mA. The total current

drawn by the bus-powered device is the sum of the current to the controller, the embedded function, and the

downstream ports, and it is limited to 500 mA from an upstream port.

Both low-power and high-power bus-powered functions obtain all power from upstream ports. Low-power

functions always draw less than 100 mA; high-power functions must draw less than 100 mA at power up and can

draw up to 500 mA after enumeration. If the load of the function is more than the parallel combination of 44

Ω

and 10

µF at power up, the device must implement inrush current limiting.

USB can be implemented in several ways regardless of the type of USB device being developed. Several

power-distribution features must be implemented.

• SPHs must:

–

Current limit downstream ports

–

Report overcurrent conditions

• BPHs must:

–

Enable/disable power to downstream ports

–

Power up at <100 mA

–

Limit inrush current (<44

Ω and 10

µF)

• Functions must:

–

Limit inrush currents

–

Power up at <100 mA

The feature set of the TPS2552/53 and TPS2552-1/53-1 meets each of these requirements. The integrated

current limiting and overcurrent reporting is required by self-powered hubs. The logic-level enable and controlled

rise times meet the need of both input and output ports on bus-powered hubs and the input ports for

bus-powered functions.

Copyright © 2008–2009, Texas Instruments Incorporated

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