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Powering Launchpad from external 3.3 or 5 volts

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Noticed some good basic info here http://processors.wi...Power_Interface

about powering the LaunchPad from a source other than the USB port.

 

5 Volts is preferred but 3.3 will work also. Just don't connect both at the same time and set the power selector switch to not get power from a connected USB port.

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You can use the Stellaris Launchpad with a single cell LiPo on the +VBUS connector, if you disable the onboard voltage supervisor. More details can be found on my blog: http://blog.psten.de...tellaris-rocket

I posted this on 43oh.com and bluehash asked me to post it here, too, so there you have it ;)

Thanks Blue!

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As the regulator used is a LDO one (with 0,2V Vdo,max), the best solution IMHO would be replacing the voltage supervisor with one resetting the chip when voltage drops below 3,7V ~ 3,6V (depending on the battery used). This way the battery will not continue draining when discharged. But of course, the most economic way is cutting a trace or removing the voltage supervisor.

 

Nice hack!

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I'm intending to run my Launchpad from a LiPo so Philipp's tip will be really helpful. I've actually go a 3S (11.1V) battery to power some stepper drivers and intend to "steal" 3.7V from the connector used for balance charging. I figure as the Launchpad will be drawing minimal current compared to the motors that this should be OK. If anyone feels like shouting "NO! Don't do it." then now would be a good time...

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Have you measured the voltage with a scope? Is the line clean? How much ripple does it have?

 

If the power line is not clean, maybe adding some electrolitic/tantalum capacitors might help.

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As the regulator used is a LDO one (with 0,2V Vdo,max), the best solution IMHO would be replacing the voltage supervisor with one resetting the chip when voltage drops below 3,7V ~ 3,6V (depending on the battery used). This way the battery will not continue draining when discharged. But of course, the most economic way is cutting a trace or removing the voltage supervisor.

 

Nice hack!

 

Yeah,

it woul've been great if TI decided to use a 3V3 supervisor after the LDO, and not a 5V one on the USB / battery side.

They propably had a reason to do it that way, good engineering practice maybe. But it is not that hackable as it could be ;)

 

I've actually go a 3S (11.1V) battery to power some stepper drivers and intend to "steal" 3.7V from the connector used for balance charging. I figure as the Launchpad will be drawing minimal current compared to the motors that this should be OK.

This should work fine, unless you pick the wrong balancer port and put 8V4 in it instead of 4V2 ;)

The current draw of the launchpad is minimal compared to the current draw of the steppers, so there shouldn't be any unbalancing happening.

You should however add some kind of software voltage supervisor to switch the steppers off if the voltage drops below a treshold.

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what if i have to use an external power through the VBUS (in GPIO vesid 3.3v) and also use the usb port for debugging. should i remove the jumper named R30 and supply 5v to VBUS. or i cant use both simultaneously

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