Datasheet

TPS2044, TPS2054
QUAD POWER-DISTRIBUTION SWITCHES
SLVS174B – JULY 1998 – REVISED FEBRUARY 1999
19
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
host/self-powered and bus-powered hubs
Hosts and self-powered hubs have a local power supply that powers the embedded functions and the
downstream ports (see Figure 31). This power supply must provide from 5.25 V to 4.75 V to the board side of
the downstream connection under full-load and no-load conditions. Hosts and SPHs must have current-limit
protection and must report overcurrent conditions to the USB controller. Typical SPHs are desktop PCs,
monitors, printers, and stand-alone hubs.
IN1
OC1
EN1
OC2
EN2
GND1
0.1 µF
2
11
3
13
4
15
14
33 µF
33 µF
GND
1
OUT1
OUT2
TPS2044
Power Supply
D+
D–
V
BUS
GND
D+
D–
V
BUS
Downstream
USB Ports
USB
Controller
3.3 V 5 V
OC3
EN3
OC4
EN4
12
7
9
8
6
IN2
+
+
5
GND2
11
10
33 µF
33 µF
GND
OUT3
OUT4
D+
D–
V
BUS
GND
D+
D–
V
BUS
+
+
†
†
†
†
†
An RC filter may be needed, see Figure 36
Figure 31. Typical Four-Port USB Host/Self-Powered Hub
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.