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LAUNCHXL-F28069M: Powering the LaunchPad with an External Source

Andrew Wenaus
Intellectual 675 points
Part Number: LAUNCHXL-F28069M

Hello!

I'd just like to confirm my understanding about powering the launchpad using a battery and a regulator.

We have a 12v Lead-Acid Battery that will be stepped down to 5v using an L7805 regulator. We've found the documentation to be a little vague, and we are terrified about frying out microcontroller with only 2 weeks until our project is due.

We will be using 5v to power the launchpad. Referencing the User Guide, we figure we must remove the jumpers on JP1 and JP2, and then apply the 5v to J5 Pin 41, as shown below.

We also had a question about limiting current. If we apply a 5 volt potential, doesn't the internal circuitry take care of the current via ohms law? Are we crazy?

  • 0
    Guru 30330 points
    Andrew,

    The LAUNCHXL-F28069M requires 3.3 V for MCU. This can be supplied to J9.

    J4 and J5 allow for power isolation of the second BoosterPack site. You can provide 5 V to the location that you mention, but will still require 3.3 V for the MCU.

    You would still require some limitation on Current for cases where there are other issues. the MCU will only consume as much power as its activity requires (see the F28069M datasheet for Current consumption), but if there is a current spike or short on a pin you will want some way to protect the circuit. It looks like your L7805C 5V regulator has it's own limit of 1A, this is plenty, but as I mentioned before, you will still need a 3.3 V regulator for the MCU.

    Regards,
    Mark
  • 0 in reply to Mark Labbato
    Intellectual 675 points

    Awesome! Thanks Mark!

    Just a quick follow-up question. So I provide the 3.3v to J9, do I have to remove any of the jumpers? After testing, it seems like I have to remove JP1 JP2 and JP3, is this correct?

    Also, am I able to power an external chip (HC06) using the launchpad (it requires 3.3v)? Or do I just have to power that with other methods?

  • 0 in reply to Andrew Wenaus
    Guru 30330 points
    Andrew,

    If you supply 3.3 V externally, you should ensure that JP1, JP2, and JP3 are removed as well. Especially if you are using the debug probe this is how you achieve power isolation.

    You can power external boards through J9, or through the BoosterPack connectors.