FOUR-PORT USB HUB POWER CONTROLLERS
SLVS288A – SEPTEMBER 2000 – REVISED FEBRUARY 2001
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
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
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
D Hosts/self-powered hubs (SPH)
D Bus-powered hubs (BPH)
D Low-power, bus-powered functions
D High-power, bus-powered functions
D Self-powered functions
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.