Run DK xDot on external power

[Mark Ruys]

We want to run an MTMDK-XDOT (with USB plug) on external power. This is to perform a stress test for our battery to see how long they keep the xDot up and running.

When I look at the schematics, I think it is safe to use pin 2 from JP30 for this (VDD_XDOT). It will power up only the xDot. I don’t think this will hurt other hardware (as long as we don’t use the USB), but I might be wrong. Does anyone know if this is allowable?

Thanks, Mark

[Leon Lindenfelser]

Hi Mark,

That is safe to do. The buffer chips U12, U13, U16 & U17 are what connect to the xDot from the developer card. If they are not powered, they should not draw current. If you are uneasy about that, you can power the developer card with JP5 installed then power the xDot. Either way, configure the xDot IO that connect to U12, U13, U16 & U17 as analog no pull to obtain least power draw. Also pay attention to GPIO0 as it connects to an LED. Again analog no pull would be least power.

Kind regards,
Leon

[Mike Fiore]

Mark,

I checked with one of our HW guys. Leaving the USB unplugged won’t work because the reset pin will end up floating instead of being pulled high.

You don’t need to unplug the USB to power the xDot externally though. You can connect your battery VDD to pin 2 of JP30 and leave JP5 connected. Your battery ground can connect to P2 or P14 on the DK.

With JP5 connected, your UARTs won’t work and you won’t be able to program the xDot, but LED1 and the IOs (P1 – P24) should still be functional.

Cheers,
Mike

[Mark Ruys]

Sounds great guys. This kind of support is why we’ve chosen the xDot above other competitive modules 😉

Thanks & all the best,
Mark

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