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What is AVCC and AGND

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Antenna (^.^)

Member level 3
Jul 6, 2015
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I noticed on my microcontroller there is two VCCs (VCC, AVCC) and two Grounds (GND, AGND).
Currently I have only connected up VCC and GND.
What is AVCC and AGND, and where do they connect to?

AVCC is Analog VCC and AGND is Analog GND. These connect to the ADC circuit of the MCU. If your MCU is a 5V type then connect AVCC to +5V and AGND to ground.

so I connect both VCC and the AVCC to +5V and both GND and AGND to ground?
What if I am not using the ADC part of the micrcontroller, can I leave it AVCC and AGND unconnected?


I'm sure the datasheets say how to handle AVcc and AGnd.

While some supply noise is no problem for the digital part of a microcontroller, it may harm the quality of ADC conversions.
Therefore one should use some "clean" supply for the ADC. Often it is recommended to use a RC or LC filter in AVcc.


I guess you are asking about the AVR processor (ATtiny87) used in this project

As a first step, you should review the datasheet thoroughly which already answers part of your questions.
VCC - 0.3V < AVCC < Vcc + 0.3V, however, AVCC should always be within 4.5 - 5.5V

In a brief, AGND will be always shorted to GND, AVCC either shorted to VCC, or filtered by a LC or ferrite bead+C lowpass in critical analog applications.
If you want understand the operation with an intuitive comparison, the noises due to digital switching at the GND net is like a sea that can be deeply affected by storms in the far ocean producing high waves, whereas the AGND is like a bay protected by a narrow entrance, having a small variation in the mean amplitude of the waves; although both references may be even electrically connected, exhibit a different ability to deal with disturbances.

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