FRDM-K64 J3, Pins 4, 8. Power in or out?

[haroldharrison]

I've been mating my daughter board to the FRDM-K64 and supplying power via J3, Pins 4, 8 for normal operation.  However, when loading code via the USB port, there is an implied conflict with the power derived from the USB.  Does the PWR Switch function prevent any conflict? Or does it not really matter?

[kerryzhou]

Hi Harold Harrison,

      J3 Pin 4,8 in the FRDM-K64 is the P3V3, it the power out pin, this P3V3 is from the the USB5v conversion, just like this:

    If you add yourself daughter board, and have conflict when you connect the USB port,  Did you own board still have other power? If not, I think this problem may caused by the low current driver.

The power driver ability is not enough, you need to use other power supply instead of USB port. Because the USB port power driver have limited.

Wish it helps you!

If you still have question, please contact with me~

Have a great day,
Jingjing

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[haroldharrison]

Jingjing,

I completely missed that those alternate supply inputs that fed the big regulator included both USB ports.  Therefore D11 protects that regulator when I feed 3.3 from J3.  There was never an issue of enough supply current when both supplies were running, just didn't like the idea of forcing two supplies nose to nose.  My daughterboard supply didn't seem to care.

Thank you for the response,

Harold

[kerryzhou · Accepted solution]

OK, Now did you still have any other question?

Have a great day,
Jingjing

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