TPS2042DR Datasheet, PDF (18/26 Pages) Texas Instruments – DUAL POWER-DISTRIBUTION SWITCHES

TPS2042, TPS2052
DUAL POWER-DISTRIBUTION SWITCHES
SLVS173A – AUGUST 1998 – REVISED APRIL 1999
APPLICATION INFORMATION
host/self-powered and bus-powered hubs (continued)
Bus-powered hubs obtain all power from upstream ports and often contain an embedded function. The hubs
are required to power up with less than one unit load. The BPH usually has one embedded function, and power
is always available to the controller of the hub. If the embedded function and hub require more than 100 mA
on power up, the power to the embedded function may need to be kept off until enumeration is completed. This
can be accomplished by removing power or by shutting off the clock to the embedded function. Power switching
the embedded function is not necessary if the aggregate power draw for the function and controller is less than
one unit load. The total current drawn by the bus-powered device is the sum of the current to the controller, the
embedded function, and the downstream ports, and it is limited to 500 mA from an upstream port.
low-power bus-powered functions and high-power bus-powered functions
Both low-power and high-power bus-powered functions obtain all power from upstream ports; low-power
functions always draw less than 100 mA, and high-power functions must draw less than 100 mA at power up
and can draw up to 500 mA after enumeration. If the load of the function is more than the parallel combination
of 44 Ω and 10 µF at power up, the device must implement inrush current limiting (see Figure 32).
D+
D–
VBUS
GND
Power Supply
3.3 V
10 µF
0.1 µF
TPS2042
2
IN
7
OUT1
0.1 µF
10 µF
Internal
Function
USB
Control
8
OC1
3 _EN1
5
OC2
4
EN2
6
OUT2
GND
1
0.1 µF
10 µF
Internal
Function
Figure 32. High-Power Bus-Powered Function
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