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+5V on USBi ( EVAL-ADUSB2Z ) is only 4.3V

Question asked by ThomasDKjensen on Sep 15, 2017
Latest reply on Sep 16, 2017 by KJBob

When using the USBi board to program the DSP (ADAU1701) I have noticed that the +5V voltage is only 4.31V when connected to a DSP, and 4.47V when left unconnected. My circuit draws approx 60mA.

 

This gives me a hard time, as my voltage monitoring circuit kicks in at 4.36V and resets the entire circuit. 

 

This also gives me another issue - the +3.3V i create from the 5V, is only +3V, so I don't like to lower the voltage monitoring bar - while I would like to be able to power the system with the USBi as the only connection.

 

I have looked at the schematic for the USBi and the Q1 transistor has 5.00V on Emitter, 3.66V on the Base and 4.31V on the Collector which goes out to the board.

 

I tried two different USBi's and they measure the same. Is there a failure in the USBi or why is the +5V not 5V?

 

 

Best regards

Thomas

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