Datasheet

TPS2042, TPS2052
DUAL POWER-DISTRIBUTION SWITCHES
SLVS173A – AUGUST 1998 – REVISED APRIL 1999
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
universal serial bus (USB) applications
The universal serial bus (USB) interface is a 12-Mb/s, or 1.5-Mb/s, multiplexed serial bus designed for
low-to-medium bandwidth PC peripherals (e.g., keyboards, printers, scanners, and mice). The four-wire USB
interface is conceived for dynamic attach-detach (hot plug-unplug) of peripherals. Two lines are provided for
differential data, and two lines are provided for 5-V power distribution.
USB data is a 3.3-V level signal, but power is distributed at 5 V to allow for voltage drops in cases where power
is distributed through more than one hub across long cables. Each function must provide its own regulated 3.3 V
from the 5-V input or its own internal power supply.
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 TPS2042 and
TPS2052 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
OC1
EN1
OC2
EN2
GND
0.1 µF
2
8
3
5
4
7
6
0.1 µF 68 µF
0.1 µF 68 µF
GND
1
OUT1
OUT2
TPS2042
Power Supply
D+
D–
V
BUS
GND
D+
D–
V
BUS
Downstream
USB Ports
USB
Control
3.3 V 5 V
†
†
†
May need RC filter (see Figure 36)
Figure 31. Typical Two-Port USB Host/Self-Powered Hub