Datasheet



SLVS373 − AUGUST 2001
16
www.ti.com
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.
• 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
USB applications
Figure 17 shows the TPS2148 being used in a USB bus-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.
Switch 1 provides power to the 5-V circuitry which is only enabled after enumeration is complete to ensure
meeting the 100-mA USB power up requirement. Switch 2 provides power to the 3.3-V circuitry. Switch 2 is also
enabled only after enumeration is complete to satisfy the 100 mA requirement.