Datasheet
TPS2041, TPS2051
POWER-DISTRIBUTION SWITCHES
SLVS172A –AUGUST 1998 – REVISED APRIL 1999
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
The USB specification defines the following five classes of devices, each differentiated by power-consumption
requirements:
Hosts/self-powered hubs (SPH)
Bus-powered hubs (BPH)
Low-power, bus-powered functions
High-power, bus-powered functions
Self-powered functions
Self-powered and bus-powered hubs distribute data and power to downstream functions. The TPS2041 and
TPS2051 can provide power-distribution solutions for many of these classes of devices.
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 are required to have
current limit protection and must report overcurrent conditions to the USB controller. Typical SPHs are desktop
PCs, monitors, printers, and stand-alone hubs.
IN
OC
EN
GND
0.1 µF
2, 3
5
4
7
0.1 µF 120 µF
GND
OUT
TPS2041
Power Supply
D+
D–
V
BUS
Downstream
USB Ports
USB
Control
3.3 V 5 V
†
†
May need RC Filter (see Figure 34)
Figure 31. One-Port Solution
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 powerup, 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.