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[FAQ] MSP-EXP432E401Y: 3V Supply Not available via Target USB only debug USB

David Dudley
Expert 1210 points
Part Number: MSP-EXP432E401Y
Other Parts Discussed in Thread: TPS2052

I'm trying to figure out how the power is generated on this board, and it seems to me that there's something missing on the schematic set.

Let's say that I want to power the unit from the Target USB connector.

I put a jumper on JP1, pins 3,4.

On page 2, it seems that if I do that, I'm connecting TARGET_VBUS -> VBUS.  From the schematics I've gotten, seems that is going to short pin 6 to pin 2 on U4, therefore rendering it useless for channel 2.  Pin 7 will provide +5 to the BoosterPack connectors.

Where in these schematics is the +3V3 generated for the board?  I see lots of connections for it, but they all seem to be loads, not supplies.

  • 0
    TI__Guru 57351 points
    You are correct. The only local source for +3V3 on this board would be when shorted to XDS_VCC on J101.

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Expert 1210 points

    So, if I plug this card into the USB port to use it, what powers the board?  Looks to me like the processor chip requires 3.3V, so where does it come from???

  • 0 in reply to David Dudley
    Expert 1210 points
    Does that mean that you can't run this card using only the HOST USB interface? You have to have the XDS110 plugged in in order to power it? Note 2 in relation to the JP1 jumper seems to indicate that you jump pins 3-4, but if that's done, it seems that +5 would be supplied to the 3.3V bus.
  • 0 in reply to David Dudley
    TI__Guru 57351 points
    If you jumper pins 3-4 this means that VBUS_Target and VBUS are shorted together (IN and OUT2 of TPS2052). It would seem (I have not confirmed) that you could possibly take the 5V output (OUT1 of TPS2052) and wire from J13 to XDS_VBUS on J101 pin4 and then the regulator on the XDS110 would provide the 3V. You could also jumper pins 3 and 5 on JP1, shorting VBUS_Target to DEBUG_VBUS again with the idea of using the regulator on the XDS110.

    e2e.ti.com/.../2771985

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Expert 1210 points
    I think that explains what I was wondering.

    Basically, the board doesn't generate the 3.3V power if you don't use the regulator on the XDS110 portion of the device.

    I was wondering if I could reduce the size of the device by cutting off the XDS110 portion of the board (which I had incorrectly assumed only contained the XDS110 portion of the card, since it wasn't going to be used in the final development device.

    Two things eventually prevent that.
    1. The RESET button is on the XDS110 portion of the card (not actually a preventative issue, I can jumper/wire the reset to a remote button, which I need anyway).
    2. The board cannot power itself without using IC101, which is on the far side of the XDS110 portion of the device.

    I could still use the card if I build a simple boosterpack that provides a 5v to 3.3v regulator, however.

    Hate to say it, but this seems like kind of an omission, as it renders the card unusable unless the XDS110 portion of the card is powered. What it means to me is that I can't develop my application, and then switch to the USB port on the HOST side, as the XDS portion is where the power comes from.

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