1
\$\begingroup\$

I have a couple of questions regarding using a precision voltage reference on a DAC - AD7545A.

I am trying to fix an existing circuit that uses AD584 to provide a 5V DAC (AD745A) to provide an Analog Output between 0 to 5V using a circuit design similar to this figure 4 on the AD7545A datasheet.

And then it is stepped up (amplified to 0 - 12V) with a high current opamp OPA548 to drive a load.

Now, my question is can I use AD7545A to provide the 0 - 12 V output without going through an extra space? I will have to replace the AD711 in the figure with OPA548 to drive the load, and also I will need a precision voltage reference that can provide a 12 V reference to the DAC. AD584 has only 4 programmable outputs - 10,7.5,5 and 2.5. What would be a good replacement.

Well, and the second question is, that in case I have to use the existing circuit, the application notes I found on the AD584 datasheet shows it giving a -10V reference to DAC using the configuration of figure 16.

I would like to give it a +ve 5 V reference instead. Is it as easy as as just connecting the +5V pin to the Vdd of the DAC, providing the 15V Vin to 584 and grounding the common?

Sorry, I tried posting the figures here, but as a new user I cannot post pictures yet.

\$\endgroup\$
1
\$\begingroup\$

As for supplying AD7545A with higher voltage, that should be alright. Don't forget level shifters for your digital inputs, though.

As for the reference voltage - you need an independent 12V voltage source to set the required output voltage range of the DAC. Not sure how to do this with AD584 - I don't see any obvious way. You could perhaps use two of them but they have to refer to ground (not Vdd).

\$\endgroup\$
  • \$\begingroup\$ what do you mean by level shifters for my digital inputs? If you mean that my analog voltage will not be the same for the same binary value, then I got it. But if you are trying to warn me about something else, please explain. Yeah there is no way I can use AD584. I was looking for a replacement. Do you know of any? \$\endgroup\$ – Ender Wiggins Nov 8 '10 at 20:53
  • \$\begingroup\$ Yes, that's what I meant by level shifters at inputs. Normally I would generate the reference voltage with a basic 1.2V (or any other for that matter) reference and an opamp, but that would bring you back to the starting point regarding the part count. Maybe something like TL1431 would be good enough? \$\endgroup\$ – Andrzej Nov 9 '10 at 2:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.