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TPS205X Datasheet(PDF) 8 Page - Texas Instruments

No. de Pieza. TPS205X
Descripción  USB POWER DISTRIBUTION
Descarga  19 Pages
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Fabricante  TI [Texas Instruments]
Página de inicio  http://www.ti.com
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TPS205X Datasheet(HTML) 8 Page - Texas Instruments

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USB Power Distribution
4
SLVA049
USB Power Distribution
The USB power distribution requirements are designed so that 4.35 V is the
minimum voltage supplied to downstream functions. The USB power distribution
system is supplied power from a host or self-powered hub and distributed
downstream. Resistive voltage drops are associated with each connection, PCB
trace, cable, or other component on the power distribution system.
USB specification 1.1 dictates the minimum voltages on the downstream ports
of the self-powered hubs, bus-powered hubs, and on a downstream function
when operating in continuous load current states and transient states during
hot-plug events (see Figure 1).
The minimum dc voltage on self-powered hubs at the board side of the
connection is 4.75 V; it is 4.4 V on a bus-powered hub. Bus-powered hubs are
allowed a 100-mV voltage drop leaving a 250-mV voltage drop for the cable.
During hot-plug connections, the self-powered hub voltage is allowed to drop
330 mV to 4.42 V and 4.07 V on the bus-powered hub. Downstream functions
should have a dc voltage of 4.35 V. All hubs and functions must be able to provide
configuration information with a minimum voltage of 4.4 V at the connector end
of the upstream cables.
The specification also dictates that all downstream devices (self-powered hubs,
bus-powered hubs, bus-powered functions, and self-powered functions) can only
sink (draw) current from the source voltage. All USB downstream devices must
be able to enter into the suspend state to reduce current consumption. Suspend
current is a function of unit load allocation. All devices initially default to low power
and are limited to 500
µA of suspend current. Devices configured for high power
and enabled as a wake up source may draw 2.5 mA. Configured bus-powered
hubs may consume 500
µA of suspend current per port and 500 µA for the hub
and nonremovable function for a total of 2.5 mA. When determining the suspend
current, the current through the pull-up (1.5 k
Ω) and pull-down (15 kΩ) resistors
on the data lines must be included. Figure 1 summarizes the voltage drops and
droops in the USB power distribution system.
Host
or
Self-Powered Hub
Bus-Powered
Hub
Low-Power
Bus-Power
Function
4.75 V/4.42 V
Minimum
4.4 V/4.07 V
Minimum
4.35 V
Minimum
Figure 1. Maximum Voltage Drops and Droops on the USB Power Distribution System


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