Microcontroller and digital IC logic levels

rtarbell · 1st July 2006, 11:47 PM

I am working on a pcb board design used for digital volume control. All of my digital parts (microcontrollers, IC AND gates) are powered from a 7805 1.5A voltage regulator. The output voltage of the regulator is ~4.95V.

When I was testing my board, I noticed that some of the logic "hi" states at the inputs of the AND gates were actually ~5.5V, sometimes even a little higher. How is this possible, considering the AND gates are powered from a 4.95V source?

poobah · 2nd July 2006, 12:08 AM

Do you have any higher supply voltages on the boards?

If so, it sounds like the protection diodes are active and you might have some excess current flowing.

davidsrsb · 3rd July 2006, 03:20 AM

Or an uncalibrated scope probe.

poobah · 3rd July 2006, 03:29 AM

Dave... did you ever get your AM503B working?

1st July 2006, 11:47 PM	#1
rtarbell diyAudio Member Join Date: Sep 2005	Microcontroller and digital IC logic levels I am working on a pcb board design used for digital volume control. All of my digital parts (microcontrollers, IC AND gates) are powered from a 7805 1.5A voltage regulator. The output voltage of the regulator is ~4.95V. When I was testing my board, I noticed that some of the logic "hi" states at the inputs of the AND gates were actually ~5.5V, sometimes even a little higher. How is this possible, considering the AND gates are powered from a 4.95V source?

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2nd July 2006, 12:08 AM	#2
poobah diyAudio Member Join Date: Nov 2005	Do you have any higher supply voltages on the boards? If so, it sounds like the protection diodes are active and you might have some excess current flowing.

3rd July 2006, 03:20 AM	#3
davidsrsb diyAudio Member Join Date: Dec 2005 Location: Kuala Lumpur	Or an uncalibrated scope probe.

3rd July 2006, 03:29 AM	#4
poobah diyAudio Member Join Date: Nov 2005	Dave... did you ever get your AM503B working?

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