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Ingo U
Ingo U, Software Engineer
Category: Programming
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Experience:  Over 25 years experience in software development. Expert in Microsoft .Net, C#, C++, VB, SQL
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I have a question about analog devices......With AD7302 analog

Customer Question

I have a question about analog devices......With AD7302 analog device........what is the min/max analog values?...isn't it +2.7V and +5.5V
Submitted: 3 years ago.
Category: Programming
Expert:  Ingo U replied 3 years ago.
Not quite - it can operate with a power supply voltage of +2.7 to +5.5V. The analog output voltage can swing rail-to-rail, meaning it can go from 0 to whatever supply voltage is being used.
Regards,
Ingo U
Customer: replied 3 years ago.
so how would I go about to calculate the step size for this device?

Step Size = (Vref+ - Vref-)/256....so how to I determine what the min/max analog voltage range is?

Expert:  Ingo U replied 3 years ago.
Your step size, normally, will be the supply voltage (2.7 to 5.5) divided by 256. The part has an optional REFIN input where you can supply your own reference voltage, in which case the step size becomes 2*Vref/256.

Here's the data sheet for details:

http://www.analog.com/static/imported-files/data_sheets/AD7302.pdf

Page 9 explains...

Ingo
Customer: replied 3 years ago.
I appreciate your help....Ive been staring it this datasheet for a while now and I just can't get it...for an additional $20 bonus can you just help me solve this that way I can get a better undretsanding....would Vref be 3.3v? = 2*3.3v/256
Expert:  Ingo U replied 3 years ago.
Let's use Vdd (no subscripts here, sorry) to designate the supplied voltage, on pin 15. You can use any voltage between 2.7 and 5.5 for this.
Also, let's say we ignore the optional REFIN input.
When you do that, the DAC reference input defaults to Vdd / 2.
So then, the output voltage from the DAC is 2 x Vdd / 2 * (N/256), where N is the 8-bit digital value (0 - 255) to be converted to analog.
Hence, the max output is

Vdd * (255/256)

and the min output is

Vdd * (0/256), i.e. zero

Each increment in the 8-bit number raises the output voltage by Vdd/256.

Keep in mind that Vdd is allowed to be in a range of your choice, so the actual numbers depend on your circuit design, i.e. your choice of voltage supplied on pin 15.

Does that help?
Customer: replied 3 years ago.
lol....not really this is the only problem that I was having trouble with and this part of an assignment i was working on....With this particular data sheet, I am just having a hard time understanding it....
Customer: replied 3 years ago.
still needs help!!!
Expert:  Ingo U replied 3 years ago.
Can you post the actual assignment so I can get some more context?

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