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USB Power for the ADSP-BF547

Question asked by spflanze on Mar 8, 2012
Latest reply on Mar 13, 2012 by hajimow

I am using the BF548 EZ Kit as a reference design for a BF547 based system I am designing. On page 118 of

 

http://www.analog.com/static/imported-files/eval_kit_manuals/BF548_EZKIT_Ref.Man_REV1.3.pdf


what is the point of the jumper at pins 1 & 3 at JP11? The manual indicates elsewhere there should be a jumper connecting both 1&3 and 2&4. But for there to be any significant current from pin 1 its voltage would have to be about 2.5 V. This is the 5V from 5V_USB supply minus the 2.2 V zener voltage of D3 and minus the .3V forward bias of D7. So with both jumpers in place all the current would be from pin 2 because pin 2 has a source at 3.3V.

 

I need to know if the voltage source at pin 1 is really needed before I design this in.

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