Datasheet

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 
SLVS333 − AUGUST 2001
19
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APPLICATION INFORMATION
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
The feature set of the TPS2145 and TPS2147 allows them to meet each of these 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 19 shows the TPS2147 being used in a USB bus-powered/self-powered peripheral 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.
In bus-powered mode, switch 1 provides power to the 5-V circuitry. In self-powered mode, switch 2 provides
power to the 5-V circuitry while the USB 5-V still provides power to the 3.3-V LDO (USB allows self-powered
devices to draw up to 100 mA from V
BUS
).