Can I use the voltage generated by the DAC as a constant voltage source?

[Ken Inoue]

Posted on September 15, 2017 at 08:10

Thank you for your patronage. 

I am planning to make 1.2V of the picture below with DAC. Is there any problem? I am a beginner, so I care whether this kind of thing is allowed.

[Mathias Zviedris]

Posted on September 15, 2017 at 08:55

If R2 and R1 are high enough, so that the maximum current of the DAC will not be reached then i see no problem. The amplifier has normaly a very high input impedance, so that you will not get any current problem with it. 

But you have to think about, if the switching noise from the DAC is okay for you. The 1.2V will not be perfect straight.

Best Regards,

Mathias

[Ken Inoue]

Posted on September 16, 2017 at 12:14

Dear Mr./Ms. Mathias Zviedris

Thank you for your reply. I calculated the current flowing through R2. Its value was 0.1 mA. 

Is the switching noise from the DAC so large?

From a beginner like me, I think that there is almost no switching noise.

If you were in my position, do you agree to make 1.2 V with DAC? Or should I make 1.2 V in a different way?

Best Regards,

Ken Inoue

[Mathias Zviedris]

Posted on September 16, 2017 at 14:25

 I calculated the current flowing through R2. Its value was 0.1 mA. 

This value shouldnt be a problem for the DAC.

Is the switching noise from the DAC so large?

It depends on what is 'large' for your application. In my applications i dont recognize it. But its there.

If you were in my position, do you agree to make 1.2 V with DAC? Or should I make 1.2 V in a different way?

I would suggest, that you read the application note AN4566 and build with this info your own opinion.

You have to think about, that the DAC output also depends on the Vref voltage ---> Look in the AN4566.

If you have no high requirements why dont you use an external voltage devider ?

[Dave Jones]

Posted on September 17, 2017 at 22:42

Using a precision voltage reference would only use 3 parts. The reference, a resistor, and a capacitor. It's extremely accurate, stable over time, and clean. But it does add cost.