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LAUNCHXL-F28379D: Clarifications on Powering LaunchPad Using an External Supply

Adam DePinto
Prodigy 10 points
Part Number: LAUNCHXL-F28379D

Tool/software:

Hi everyone,

 

I am currently using the F28379D LaunchPad for a university Capstone project and would like to power it using an external supply (i.e. without the USB connection). I have been reading the provided User Guide to determine how this should be done and wanted to ask some questions to ensure my understanding is correct.

 

1) Does the LaunchPad require only +3.3 V externally to be powered in standalone mode, or does it require both +3.3V and +5 V? Reading through a similar post on E2E has lead me to believe that while the +3.3 V is required to power the LaunchPad, the +5 V power rail simply allows the user to route +5 V to a different device using the LaunchPad.

 

2) To supply +3.3 V externally to the LaunchPad, I would follow Configuration 2 from Table 1 of the User Guide. This voltage needs to be routed to header J10, which has 3 pins: 1 for +3.3 V, and 2 for GND. According to the schematic provided in the user guide, both ground pins are shorted together. Would it suffice to connect only 1 of the GND pins to the supply ground, or should both J10 GND pins be connected?

 

3) Suppose I have powered the LaunchPad with a +3.3 V external supply using J10. I now want to provide the LaunchPad with +5 V. To do this, it would be preferable to use Configuration 2 from Table 2 of the User Guide, where +5 V is provided through the on-board step-up regulator (which boosts the supplied +3.3 V to +5 V). In this configuration, can JP6 then be used to provide +5 V externally to a different device?

 

4) To reiterate, I am using Configuration 2 from Table 1 (to power the Launchpad with +3.3 V) and Configuration 2 from Table 2 (to supply +5 V to the LaunchPad as a means of powering other devices). I have observed that JP1, JP2, and JP3 should be left open using these configurations. In this case, is it required that I remove the jumpers from JP1, JP2, and JP3 if I am supplying the LaunchPad with an external +3.3 V? Generally, is there anything that needs to be done with jumpers JP1 through JP5 to ensure there are no issues when powering the LaunchPad without the USB connector?

Any confirmations would be greatly appreciated!

  • 0
    TI__Mastermind 45166 points

    Hi,

    1. Yes, this works. +5V is required for the ADC voltage reference, so it will be needed if using the ADC / analog peripherals at all.
    2. Correct and 1 ground is fine. Really any 3.3V / GND headers on the F2837x target side of the board could be used.
    3. Yes you can do that if you're not providing 5V externally as well. Note there will be a current limit the on-board 3.3V --> 5V boost can provide to external devices.
    4. Note (3) above about current limit. JP1-3 should be removed if wanting to isolate the USB side of the board from the f2837x target side. JP4 / 5 can stay populated to connect power to the bottom boosterpack site..

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    Prodigy 10 points

    Hi Kevin,

    Thank you for your response, that resolved quite a few of my issues! This past week, I was successful in powering the LaunchPad using an external supply, and everything seems to be in working order. Now that I have a better understanding of how to connect and power the board, I was hoping to follow up with 2 additional questions:

    1) When powering the LaunchPad, I used the following configuration:

    • External +3.3 V supplied to the LaunchPad via J10
    • Jumpers JP1, JP2, and JP3 removed to isolate the USB side from the target side
    • Jumpers JP4, JP5, and JP6 connected

    Once powered, I began measuring the voltage on some of the header pins using a voltmeter. Specifically, I found:

    • +3.245 V measured on header pins J1_1 and J5_1
    • +5.04 V measured on header pins J3_1 and J7_1, and on pin J16

    Since I measured +5 V from J16 (as well as from the two header pins), it would make sense that I can use this pin to route +5 V to power a different device, keeping in mind the current limits you mentioned previously. Is this true?

    2) Before powering the LaunchPad, I first flashed a blinking LED program to the board. Then, once the board was powered in standalone mode, the firmware appeared to execute without any issues (i.e. the LED began to blink on and off).

    It appears I already have an answer to this question, but just to make sure – is there a particular boot mode that the LaunchPad should use when operating the board in standalone mode? When powering the board, I did not change the boot mode from its default – I believe this is Emulation Boot mode? – and the firmware seemed to execute just fine. Going forward, is there a recommended boot mode that should be used when powering the LaunchPad without the USB, or is the default setting okay?

    Apologies if these are basic questions. Thank you again for your help!

  • 0 in reply to Adam DePinto
    TI__Mastermind 45166 points

    Hi,

    Adam DePinto said:
    Since I measured +5 V from J16 (as well as from the two header pins), it would make sense that I can use this pin to route +5 V to power a different device, keeping in mind the current limits you mentioned previously. Is this true?

    Yes. If boltage goes below 5V once powering another device / board then you're likely hitting the current limit.

    Adam DePinto said:
    Going forward, is there a recommended boot mode that should be used when powering the LaunchPad without the USB, or is the default setting okay?

    If wanting standalone operation you can use flash boot mode by setting the appropriate boot mode pin settings..

    Best,

    Kevin