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Category: Hardware

Questions for a fool

I wanted to just reach out to the analogue devices community for a bit of assistance. Im working with a AD5761 DAC and I am trying to give it appropriate bipolar voltages. Looking over the data sheet I see that I can use the ADP5070 in conjunction with a few other ICs to produce a bipolar voltage of -11v and +11v. The real question is do I really need +21v and -13v if I plan to only use +-10v? Its my first year in college and im not exactly a pro with PCB design so I also had some questions on the total power consumption as it wasn't entirely clear in the datasheet when I reviewed it. I have about 20 of my AD5761s I need to power and im not sure how many ADP5070s I might need which Is why I am asking for their total power consumption.

Anything helps, even insults on my intellect as I plan to be a good electrical engineer someday.

Parents
• Hi,

Yes, if you are interested in all the output ranges of the DAC, then you'll need to follow that indication that says (page 29 of the DS) "The AD5761/AD5721 must be powered by the following three supplies to provide any of the eight output voltage ranges available on the DAC: VDD = +21 V, VSS = −11 V, and DVCC = +5 V."

There is an output range that it goes from 0 to +20V, then you'll need +21V for having a 1V headroom.

Regards

• Hi,

Yes, if you are interested in all the output ranges of the DAC, then you'll need to follow that indication that says (page 29 of the DS) "The AD5761/AD5721 must be powered by the following three supplies to provide any of the eight output voltage ranges available on the DAC: VDD = +21 V, VSS = −11 V, and DVCC = +5 V."

There is an output range that it goes from 0 to +20V, then you'll need +21V for having a 1V headroom.

Regards

Children
• Right, which makes complete sense. But I also had a question regarding the current being drawn at that load of +21V and -11V. As I was given the unloaded current draw of Idd and Iss being 6.5mA and 3mA. How could I calculate the current that could be received? What would the current draw be under load?

• The only thing I could find was the short circuit current maximum which was around 25mA, although I assume this would be the absolute maximum current output for a short period of time. But I just cant seem to figure out the optimal current coming from Vout. I see the requirements for Iss and Idd in the same area you specified but it never talks about the current under load.

I am thinking the answer is clear but I just don't have the toolset yet to understand

A. The question I am asking
B. How to find the solution within the data sheet

• For DAC power consumption under load, that depends on the output voltage since the output current will depend on the load unless it is a current sink/source device.

As the first approximation, the DAC will dissipate the current of the load times the delta voltage of the supply minus the output voltage. This value will be added to the power consumption with no load, this value is in the DS.

• Thanks! That helps a ton with my understanding of this chip but it shows that I really fail to understand analog voltages and fundamental principles of electronics. Which is pretty sad...

• No worries. We are here to learn and help.