Datasheet
SLVS399A − JANUARY 2002 − REVISED MAY 2006
21
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APPLICATION INFORMATION
undervoltage lockout (UVLO)
An undervoltage lockout ensures that the device (LDO and switch) is in the off state at power up. The UVLO
also keeps 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 is also activated whenever the input
voltage falls below the stop threshold as defined in the undervoltage lockout table. This function 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 are turned on with a controlled rise time to reduce EMI and
voltage overshoots.
universal serial bus (USB) applications
The universal serial bus (USB) interface is a multiplexed serial bus operating at either 12 Mbps, or 1.5 Mbps
for USB 1.1, or 480 Mbps for USB 2.0. The USB interface is designed to accommodate the bandwidth required
by PC peripherals such as keyboards, printers, scanners, and mice. The four-wire USB interface was 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 defines the following five classes of devices, each differentiated by power-consumption
requirements:
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
The TPS2140/41/50/51 are well suited for USB hub and peripheral applications. The internal LDO can be used
to provide the 3.3-V power needed by the controller while the switch distributes power to the downstream
functions.
USB power-distribution requirements
USB can be implemented in several ways, and, regardless of the type of USB device being developed, several
power-distribution features must be implemented.
D Hosts/self-powered hubs must:
− Current-limit downstream ports
− Report overcurrent conditions on USB V
BUS
D Bus−powered hubs must:
− Enable/disable power to downstream ports
− Power up at <100 mA
− Limit inrush current (<44 Ω and 10 µF)
D Functions must:
− Limit inrush currents
− Power up at <100 mA