Author Topic: USB Bus Power using ULPI transceiver  (Read 10253 times)

aclark

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USB Bus Power using ULPI transceiver
« on: May 04, 2011, 04:27:00 pm »
A common USB implementation problem is managing power in a bus powered application.

ULPI transceivers are commonly employed to simplify support when using FPGAs, DSPs or many fast MCUs. These devices are primed to take advantage of high speed USB since they have sufficient MIPs.

This leads to my question. If an external processor is acting as the USB Controller, then how can it do this when it can't really consume current (<2.5mA in suspend). It is even difficult to meet the 100mA pre-enumeration limit in many cases.

I have thought about using a slow low power processor (maybe PIC24) that would act as a temporary controller but these processors don't operate at 60MHz.

It seems like a catch 22.  I realize that many people ignore the suspend requirement (which makes their solution non compliant), but there must be a more clever solution.

Can anyone point to an application note or share their secret sauce for this problem? Do I need to wait for Jan's 5th edition ;) ?


Thanks

Al Clark
aclark@danvillesignal.com



Barry Twycross

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Re: USB Bus Power using ULPI transceiver
« Reply #1 on: May 04, 2011, 07:58:50 pm »
In general terms, you stop the processor in suspend, so hopefully it doesn't draw much power. The PHY detects resumes and generates an interrupt to restart the processor when needed.