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G120 and Cobra power selection priority?


#1

Hi,

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??

Thanks!


#2
  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.


#3

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.

#4

Gus, really, can’t you give us at least half an hour to get helpful community members :snooty:


#5

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


#6

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


#7

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


#8

Thank you :slight_smile:


#9

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.


#10

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


#11

@ 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.