AVdd and AVss in microcontroller

[Murugesh_89]

Hi,
Some micro controller have
1. Vdd and Vss for logic and i/o pins
2. AVdd and AVss for analog modules

Why is it so?

Shall i connect AVdd as same as Vdd.

or

Should i need to add any other component to AVdd to separate it from Vdd.

Thanks,
Murugesh

 

[lucbra]

Read the datasheet of that particular microcontroller.
Analog voltage supply will at least need proper decoupling to minimize noise. Voltage levels can be different for analog and digital (downto 1.2V in some cases). Only the datasheet can tell you how to connect.

 

[doraemon]

Hello

Why is it so?

If you connect both to the same power, then the sharp edges of the digital circuitry
will have an influence on the power supply. One transition from 0 to 1 or the opposite
takes some energy. In a digital circuit, everytime the clock raises or falls, many things
happen at the same time, and therefore it induces some noise on the whole circuit.
If you are using an ADC, then its output will be influenced by this noise.
The idea therefore is to separate the power supplies, usually with LC circuits.

Note that it's also possible to separate the grounds, and link them at a single point.

Dora.

 

[kiiid]

If you don't have separate power supplies for the analog and digital circuits, in the majority of the cases you can just connect AVdd to Vdd through a low (10-20 Ohm) resistor. If your power supply is noisy or with high ripples, and you are using the analog parts of the microcontroller, a more sophisticated filtering might be needed. In other isolated cases the IC manufacturer presents different requirements so it never huts to check with the datasheet.

 

[lucbra]

... it never hurts to check with the datasheet.

Always check the datasheet

 

[Murugesh_89]

The idea therefore is to separate the power supplies, usually with LC circuits.
Dora.

What value of L and C is proper for this operation. I am using PIC uc with 5V supply.

In data sheet it is given that AVdd is Positive supply for analog modules. Also AVDD Analog Supply Voltage Min: VDD – 0.3 and Max: VDD + 0.3 V.

 

[doraemon]

Hello!

What value of L and C is proper for this operation. I am using PIC uc with 5V supply.

In data sheet it is given that AVdd is Positive supply for analog modules. Also AVDD Analog Supply Voltage Min: VDD – 0.3 and Max: VDD + 0.3 V.

The only thing I can reply is : it depends.
It depends on what you do. In some cases, you can just wire everrything together and it will work well enough.
And in some other cases, if you want for instance 20 bit or more ADC conversion, then 100µ might be too small.
Or not. Your question is like what is the diameter required for a wire to lift a stone.

Dora.