TPS2074, TPS2075

FOUR-PORT USB HUB POWER CONTROLLERS

SLVS288A – SEPTEMBER 2000 – REVISED FEBRUARY 2001

20

POST OFFICE BOX 655303

APPLICATION INFORMATION

undervoltage lockout (UVLO)

An undervoltage lockout ensures that the device (LDO and switches) is in the off state at power up. The UVLO

will also keep the device from being turned on until the power supply has reached the start threshold (see

undervoltage lockout table), even if the switches are enabled. The UVLO will activate whenever the input

voltage falls below the stop threshold as defined in the undervoltage lockout table. This facilitates the design

of hot-insertion systems where it is not possible to turn off the power switches before input power is removed.

Upon reinsertion, the power switches will be turned on with a controlled rise time to reduce EMI and voltage

overshoots.

self-power to bus-power or bus-power to self-power transition

An autoswitching function between bus-powered mode and self-powered mode is a feature of the TPS2074 and

TPS2075. When this feature is enabled (BP_DIS is inactive) and SP is removed or applied, a transition will be

initiated. The transition sequence begins with the internal LDO being turned off and its external capacitance

discharged. Any enabled switches are also turned off and the external capacitors discharged. Once the LDO

and switch outputs are low, the internal logic will turn the LDO back on. This entire sequence occurs whenever

power to the SP input is removed or applied, regardless of the source of power, i.e., an external power supply

or the use of the external regulator.

universal serial bus (USB) applications

The universal serial bus (USB 1.1) interface is a 12-Mb/s, 1.5-Mb/s, or 480 Mb/s (USB 2.0), multiplexed serial

bus designed for low-to-medium bandwidth PC peripherals (e.g., keyboards, printers, scanners, and mice). 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 or 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 defines the following five classes of devices, each differentiated by power-consumption

requirements:

Self-powered and bus-powered hubs distribute data and power to downstream functions. The TPS2074 and

TPS2075 can provide power-distribution solutions for hybrid hubs that need switching between BPH and SPH

according to power availability and application requirements.