参数资料
型号: TPS2046BDR
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 2-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8
封装: GREEN, PLASTIC, MS-012AA, SOIC-8
文件页数: 8/29页
文件大小: 901K
代理商: TPS2046BDR
www.ti.com
UNIVERSAL SERIAL BUS (USB) APPLICATIONS
HOST/SELF-POWERED AND BUS-POWERED HUBS
LOW-POWER BUS-POWERED AND HIGH-POWER BUS-POWERED FUNCTIONS
SLVS532C – JULY 2004 – REVISED OCTOBER 2007
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
TPS204xB/TPS2055B can provide-power distribution solutions to many of these classes of devices.
Hosts and self-powered hubs have a local power supply that powers the embedded functions and the
downstream ports. 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.
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.
Both low-power and high-power bus-powered functions obtain all power from upstream ports; low-power
functions always draw less than 100 mA; 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
and 10
μF at power up, the device must implement inrush current limiting (see Figure 25).
16
Copyright 2004–2007, Texas Instruments Incorporated
Product Folder Link(s): TPS2045B TPS2055B TPS2046B TPS2047B
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