G120 and Cobra power selection priority?


I’m currently developing a custom board and intend to use G120 module, looking at the Cobra II schematics, without actually owning one I’m not exactly sure about few things:

  1. Can the board be powered only through USB-Client connector, or does it require external power input?
  2. Can both USB(5V) and External(12V) be plugged in at the same time? Which takes priority?
  3. Do I need a power multiplexer or a similar circuit when designing my custom board with G120??


  1. You can use usb for power
  2. Yes. The power jack takes priority
  3. No. All you need is regulated 3.3V

Welcome to the community.

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Welcome to the forum:

  1. yes
  2. you can connect both. The 12V is used 1st
  3. We also made a G120 custom board, and we simply copied the Cobra II circuit at 1st
    Later we made a galvanic decoupling using a DC/DC converter and a special chip for USB.
    By this we added a jumper, so we can disable powering via USB.
    This comes in handy if the boards draws a lot of power, which USB can not supply.
    If 12V is removed, then board goes of instead of trying to get enough power from USB.
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Gus, really, can’t you give us at least half an hour to get helpful community members :snooty:

@ Reinhard Ostermeier - not sure I understand what you need.

He was just saying that you answered the question too fast, not allowing the community to answer. a compliment by scolding.

@ Mike - Yep, that was my Intention :slight_smile:

Thank you :slight_smile:

Ok, thanks for that

I have another question, the crystal on the Cobra is 32kHz, is that a correct value, also is it really required??

I’m having a problem finding a solderable package for that value.

@ Darko - I use this http://uk.rs-online.com/web/p/crystal-units/2261443/

@ Darko - The G120’s main processor datasheet does not indicate that a 32k crystal is necessary for normal operation of the processor. However, it will be needed if you want to utilize the RTC feature of the G120.

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