Datasheet

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SLVS401 − AUGUST 2001
15
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APPLICATION INFORMATION
universal serial bus (USB) applications (continued)
The TPS2149 and TPS2159 are well suited for USB bus-powered hub applications. The internal LDO can be
used to provide the 3.3 V power needed by the controller while the dual switches distribute 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.
• 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
The feature set of the TPS2149 and TPS2159 is designed to help USB bus-powered hubs meet the
requirements. The integrated current-limiting and overcurrent reporting is required by hosts and self-powered
hubs. The logic-level enable and controlled rise times meet the need of both input and output ports on
bus-powered hubs, as well as the input ports for bus-powered functions.
USB applications
Figure 17 shows the TPS2149 being used in a USB bus-powered two-port hub design. The internal 3.3-V LDO
is used to provide power for the USB function controller as well as to the 1.5-kΩ pullup resistor.
Switches 1 and 2 provide power to the downstream ports. Both are separately enabled to control power being
sent downstream. They are also disabled during enumeration to satisfy the 100 mA requirement.
Figure 18 shows the TPS2149 being used in a USB bus-powered four-port hub design. The internal 3.3-V LDO
is used to provide power for the USB function controller as well as to the 1.5 kΩ pullup resistor.