What is AVCC and AGND

[Antenna (^.^)]

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?

 

[pic.programmer]

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.

 

[Antenna (^.^)]

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?

 

[KlausST]

Hi,

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.

Klaus

 

[pic.programmer]

Read these links.

It tells about using inductor and capacitor to get clean supply for ADC.

https://www.avrfreaks.net/forum/aref-agnd-avcc-avrmega

https://electronics.stackexchange.c...ega8-why-do-vcc-and-avcc-have-to-be-connected

 

[FvM]

I guess you are asking about the AVR processor (ATtiny87) used in this project https://www.edaboard.com/threads/342948/

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.

 

[andre_luis]

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.