www.德州仪器.com
IN1
OC1
EN1
OC2
EN2
地
0.1
µ
F
2
16
3
13
4
15
14
33
µ
F
33
µ
F
地
1
OUT1
OUT2
TPS2044B
电源 供应
D+
D−
V
总线
地
D+
D−
V
总线
Downstream
usb 端口
USB
控制
3.3 v 5 v
OC3
EN3
OC4
EN4
12
7
9
8
6
IN2
+
+
5
地
11
10
33
µ
F
33
µ
F
地
OUT3
OUT4
D+
D−
V
总线
地
D+
D−
V
总线
+
+
低-powerbus-poweredandhigh-powerbus-poweredfunctions
tps2041b,,tps2042b
tps2043b,tps2044b,tps2051b
tps2052b,tps2053b,tps2054b
SLVS514E–APRIL2004–REVISEDJANUARY2006
applicationinformation(持续)
figure31.typicalfour-portusbhost/自-poweredhub
总线-poweredhubsobtainallpowerfromupstreamportsandoftencontainanembeddedfunction.thehubsare
requiredtopowerupwithlessthanoneunitload.thebphusuallyhasoneembeddedfunction,andpoweris
alwaysavailabletothecontrollerofthehub.iftheembeddedfunctionandhubrequiremorethan100maon
powerup,thepowertotheembeddedfunctionmayneedtobekeptoffuntilenumerationiscompleted.thiscan
beaccomplishedbyremovingpowerorbyshuttingofftheclocktotheembeddedfunction.powerswitchingthe
embeddedfunctionisnotnecessaryiftheaggregatepowerdrawforthefunctionandcontrollerislessthanone
unitload.thetotalcurrentdrawnbythebus-powereddeviceisthesumofthecurrenttothecontroller,这
embeddedfunction,andthedownstreamports,anditislimitedto500mafromanupstreamport.
bothlow-powerandhigh-powerbus-poweredfunctionsobtainallpowerfromupstreamports;低-电源
functionsalwaysdrawlessthan100ma;高-powerfunctionsmustdrawlessthan100maatpowerupandcan
drawupto500maafterenumeration.iftheloadofthefunctionismorethantheparallelcombinationof44
Ω
and10µfatpowerup,thedevicemustimplementinrushcurrentlimiting(看Figure32).
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