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Simple USB power management Q.

Mohammad Ali Koteich
Intellectual 365 points
Other Parts Discussed in Thread: OMAP-L138, TPS2068, TPS2087

Hi

I'm desiging a PCB based on the OMAP-L138. Looking at the Hawkboard schematics, I see they did the following for the USB powermanagement:

http://img823.imageshack.us/img823/3200/hawkusb.png

Now I'm not experienced with power management at all, but my question is: Is there any rational reason for why they're using a seperate switch (TPS2068) for supplying the VCC_5VD net instead of just utilizing the IN1-OUT1 ports on the TPS2087???...

Well the only reason I can see is if the TPS2087 limits the current (I'm starting to think that is the case), since datasheet states a 500mA continous current pr channel. But it also states that "The power switch supplies a minimum of 500 mA per switch." on page 6. I interpret that as "can supply more than 500mA, just not less".. but maybe I'm reading this all wrong?

Thanks for your time!

PS: Maybe there is a better chip out there for this exact purpose which is newer? If that is the case a recommendation of such a chip would be highly appreciated!

-Koteich