Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

AVdd and AVss in microcontroller

Status
Not open for further replies.

Murugesh_89

Full Member level 5
Joined
Nov 23, 2012
Messages
266
Helped
7
Reputation
12
Reaction score
6
Trophy points
1,298
Location
India
Activity points
3,267
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

Advanced Member level 2
Joined
Oct 30, 2003
Messages
512
Helped
73
Reputation
146
Reaction score
63
Trophy points
1,308
Location
Belgium
Activity points
3,251
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

Super Moderator
Staff member
Joined
Jun 21, 2009
Messages
1,165
Helped
284
Reputation
576
Reaction score
274
Trophy points
1,363
Location
Japan
Activity points
11,806
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

Newbie level 4
Joined
Jul 10, 2007
Messages
6
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,312
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.
 

Murugesh_89

Full Member level 5
Joined
Nov 23, 2012
Messages
266
Helped
7
Reputation
12
Reaction score
6
Trophy points
1,298
Location
India
Activity points
3,267
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

Super Moderator
Staff member
Joined
Jun 21, 2009
Messages
1,165
Helped
284
Reputation
576
Reaction score
274
Trophy points
1,363
Location
Japan
Activity points
11,806
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.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top