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參數(shù)資料
| 型號(hào)： | APPNOTE17 |
| 英文描述： | Universal Serial Bus Power Management |
| 中文描述： | 通用串行總線電源管理 |
| 文件頁(yè)數(shù)： | 9/12頁(yè) |
| 文件大?。?/td> | 125K |
| 代理商： | APPNOTE17 |
October 1998
9
Application Note 17
Application Note 17
Printed Circuit Layout Hints
Power Traces
wide, heavy copper
short, straight traces
“star” from input filter capacitor
same side, no vias
Ground
wide ground plane
same side, no vias
Switches
wide power input traces
0.1
μ
F ceramic input bypass close to IC
wide power output traces
IC placed near output port
“star” power traces from input capacitor
power traces on same side, no vias
Output Filter
close to output port
120
μ
F tantalum, 10V
0.01
μ
F ceramic 25V bypass
ferrite bead on power lead
ferrite bead on ground lead
connector shield to ground plane
Thermal Management
ground plane under switch
wide traces to all IC pins
thermal paste or adhesive under IC
maximum copper area, both sides
air circulation inside and outside
Micrel
Definitions
Controller
A microprocessor which implements the Universal Serial Bus
protocols.
Host
The root hub host computer system where the Universal
Serial Bus host controller is installed. This includes the host
hardware platform (CPU, bus, etc.) and the operating system
in use.
Host Controller
The host’s Universal Serial Bus interface.
Hub
A Universal Serial Bus device which repeats data and pro-
vides additional connections to the Universal Serial Bus.
Bus-Powered Hub
Receives operating power from the upstream port, up to
500mA.
Root Hub
A Universal Serial Bus hub directly attached to the host
controller. This hub is attached to the host; tier 0.
Self-Powered Hub
Draws less than 100mA from upstream port, provides down-
stream power from 5V +5/–3% internal power supply and up
to 500mA per port, 3.5A per protection device.
Port
Point of access to or from a system or circuit. For Universal
Serial Bus, the point where a Universal Serial Bus is attached.
Downstream Port
The direction of data flow away from the host. A downstream
port is the port on a device electrically farthest from the host
that generates downstream data traffic from the hub. Down-
stream ports receive upstream data traffic.
Root Port
The upstream port on a hub.
Upstream Port
The direction of data flow toward the host. An upstream port
is the port on a device electrically closest to the host that
generates upstream data traffic from the hub. Upstream ports
receive downstream data traffic.
Unit Load
Not more than 100mA power drain under normal operating
conditions, with a 4.4V bus.
Universal Serial Bus (USB)
A collection of Universal Serial Bus devices, software, and
hardware that allows them to connect the capabilities pro-
vided by functions to the host.
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