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Olimex LPC-P2148 Question

Started by deliconn January 5, 2006
I was wondering, on the Olimex LPC2148 demo board, if it could be
powered from a wall wart and have the USB connected. I see a diode
there in the 5V line from the USB, is that enough to make it safe?

Thanks,

Vern


An Engineer's Guide to the LPC2100 Series


Are you referring to D1, at the top from the +5V_USB to the regulator? The
purpose of that is to prevent the wall port from giving power to the USB
line. What do you mean "enough to make it safe?"

At 07:51 PM 1/5/2006, you wrote:
>I was wondering, on the Olimex LPC2148 demo board, if it could be
>powered from a wall wart and have the USB connected. I see a diode
>there in the 5V line from the USB, is that enough to make it safe?
>
>Thanks,
>
>Vern




It's been 3 months and there still hasn't been an updated datasheet, and a
lot of the current values in the static characteristics section are
<tbd>. Has there been any progress on updating these? Would anyone happen
to know the I(BAT) and I(DD) values?

Thanks

-- Sean


Well.

Ibat I found to be the same as the lpc2138
Idd is about the same, but i can't be so sure because my application is
running @ 12Mhz
But I'm not sure if i'm doing something wrong because my Ipd (powerdown)
is about 1000uA, and falls to about 400uA if I put 2 470K pulldowns in
D- and D+.
I really hope i'm doing something wrong, bacause with this powerdoen
current I can run an MSP430 @ 8Mhz....
Sean wrote:
> It's been 3 months and there still hasn't been an updated datasheet,
> and a
> lot of the current values in the static characteristics section are
> <tbd>. Has there been any progress on updating these? Would anyone
> happen
> to know the I(BAT) and I(DD) values?
>
> Thanks
>
> -- Sean >
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Vern,

to add to Sean's comment:

No, to make it safe you will need some basic understanding of hardware :o)

D1 is just preventing that you put power on your USB line, to be sure you
are not trying to feed power into your power adapter in the case that you
only apply USB power (believe me, this will not result in a 110/230 V
output ...) you need to make sure that is also not possible.

Maybe an extra diode will do, maybe there is already a diode there.
Just check the schematics.

Rob

> Are you referring to D1, at the top from the +5V_USB to the regulator?
> The
> purpose of that is to prevent the wall port from giving power to the USB
> line. What do you mean "enough to make it safe?"
>
> At 07:51 PM 1/5/2006, you wrote:
>>I was wondering, on the Olimex LPC2148 demo board, if it could be
>>powered from a wall wart and have the USB connected. I see a diode
>>there in the 5V line from the USB, is that enough to make it safe?
>>
>>Thanks,
>>
>>Vern


Vern,

>I was wondering, on the Olimex LPC2148 demo board, if it could be
> powered from a wall wart and have the USB connected. I see a diode
> there in the 5V line from the USB, is that enough to make it safe?

I'd say so, as long as your wall wart supplies
voltage as spec'ed.

* 6VAC, giving you about 7.8V DC at Vin
* 9VDC, giving you about 8.3V DC at Vin

For both variants, the "+5V_USB-diode" would not be
conducting due to the cathode, that is being connected
to Vin, is at a higher potential then the anode, connected
to 5V from USB and the board would be powered from the wall
wart solely.

Even if your wall warts outputs leads to Vin less then that,
it still would be safe.

There would be a small range of output voltage from your wall
wart (about 4.7V-5.7V DC), where both would be contributing to
the supply of the board.

Below that range the board would be supplied by USB solely,
due to the rectifier bridge G1, but at no time there would
be flowing any current from one supply into the other.

So, from my understanding of electronics, it should be safe
to connect a wall wart and USB simultaneously.

-uwe