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MicroZed power, USB and backplane?

rdb98789

Hello, we have created a MicroZed carrier card that provides the 5V power source through the expansion connectors. However, we like to plug in the USB cable sometimes to see the serial printout. Some questions:

1) Is there any issue in having both supplies connected at once? So USB cable connected as well as the 5V regulator on our carrier card?

2) Is there any way to disable getting powered via USB? I'd like to test some power cycle reboot stuff while watching the USB UART data, but I need a true power cycle (including the carrier card components which is not powered by USB). Any recommendations?

  • 0

    I believe that Avnet always powers the USB to Uart chip from the USB cable.   That means you can power cycle the board without interrupting the serial connection.

    You must be powering the MicroZed from the carrier board by connecting 5V to the VIN_HDR pins.  VIN_HDR goes through a diode to make VIN which drives all the regulators.  The problem is that VBUS from the USB uart also goes through a diode (D4) to VIN.  If you turn off VIN_HDR the board will continue to run from the USB VBUS.

    I don't see a way to do what you want without removing D4.

    Please post your final decision.

  • 0

    I do see now in the Microzed schematic notes they have a "USB Self powered, no backfeed" option, but requires some hardware mods. So JT7 pins 2-3 gets a zero ohm resistor as opposed to the default 2-1, populate D10 and D11, do not populate R97 and R98. But you're saying that even with that, the Microzed would still power up and boot via USB power because D4 is installed? So do all of the above, plus remove D4, and now it's only able to be powered from the VIN_HDR, and USB-UART will still function?

    Or could I do all the above, skip D4 removing D4, but instead cut the 5V wire out of the USB cable?

  • 0 in reply to rdb98789

    I think you want to keep the usb-uart chip powered by VBUS on the usb cable. Othewise, you have to reconnect the serial termal application after every power cycle and you cannot see what happens at power up time.

    As I read the schematic, removing D4 is the only way to isolate VBUS from VIN.

  • 0

    Hallo,

    danke für Ihre Fragen bezüglich des MicroZed-Boards und der Stromversorgung über USB. Hier sind einige Antworten auf Ihre Fragen:

    1. Es sollte keine Probleme geben, wenn sowohl die USB-Verbindung als auch die Stromversorgung über den 5V-Regler auf Ihrem Trägerboard gleichzeitig aktiv sind. Das MicroZed-Board sollte in der Lage sein, automatisch zwischen den beiden Stromquellen zu schalten, ohne negative Auswirkungen auf die Funktion zu haben.

    2. Um die Stromversorgung über USB zu deaktivieren, könnte eine Möglichkeit sein, einen Jumper oder einen Schalter zwischen dem USB-Anschluss und dem 5V-Regler auf Ihrem Trägerboard einzubauen. Dadurch könnten Sie die Stromversorgung manuell steuern und bei Bedarf die USB-Stromversorgung trennen, während Sie den UART-Datenverkehr überwachen.

    Ich hoffe, diese Informationen helfen Ihnen weiter. Wenn Sie weitere Fragen haben, stehe ich gerne zur Verfügung.