Question on A5 power routing

Andy Green andy at
Wed Feb 27 03:06:06 CET 2008

Hash: SHA1

Somebody in the thread at some point said:

> I can see using the GTA02 being used in research labs or in product
> development labs as an embedded and connected controller for
> prototyping, using the USB port in host mode to interface to arbitrary

For non-phone uses I will replace my current mailserver that is based on
180MHz ARM9 and 1G USB memory stick with one of these with a 4G MicroSD
for sure, but that is ok with USB as device and incoming power.

> external electronics. In this case I would want to power the GTA02 via
> USB, with the battery installed to satisfy instantaneous current draw.

I think we maybe need to characterize this "instantaneous current draw"
which is blamed, because it can be managed in other ways than a battery
if it is understood.

> Assuming the user is comfortable hacking at driver code in order to
> enable this, is there anything in the hardware which prevents accepting
> power from the USB port in host mode, powering the GTA02 (except for
> those modules you mention below) and charging the battery at the same time?
> Would any of the changes proposed for A6 prevent this?

There is special regulation circuitry U4904

to create the 5V needed in host mode to power the device that is plugged
in, right now the same signal EN_USBHOST starts that up AND enables
other USB OTG configuration for host mode (15K pullups).  The plugin
detect pullup is separately controlled though.

Quite possibly the regulator will be fine with being powered at the same
time external 5V comes in, it may react by just going pretty much idle,
it will have to be tested since another possibility is we let the magic
black smoke "that makes it work" out of it.  If it is okay with it then
no problem with the "external power with USB host mode" hack scenario.

- -Andy
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