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Hi everyone,
I was looking for a solution to test multiple DC regulated rails (from 0.8V to 4V) using a current output DAC. The current output would essentially serve as a variable current load to these regulated rails.
Are there any programmable 12-bit+ multi-channel DACs that can sink / source currents from 1uA - 1 mA? Looking for a settling time (when switching between currents) to be around or less than 1us.
Potential DACs I found were DAC8814 and DAC8803 but datasheet mentioned Iout low of 1.6mA which would not work.
Thanks for your help!
Best,
Nik
Hi Kevin,
Thanks for your support! This means that If I connect the Iout to Vdc (say 4V), then my total current would be I = Vdc - Vref / R correct? If so, unfortunately I'd need something that I can sink directly to ground.
I'm essentially looking for something that can mimic an electronic load, a current source to ground, to the rails of a DC regulator. My goal is to characterize the DC regulator with different load conditions (Iload) and I was wondering if any DAC solution can mimic the load to ground, on the regulated output rails.
Maybe below picture will help!
Nik,
Page 16 of the DAC8814 datasheet illustrates a simplified diagram of the internal R-2R ladder. If you were to connect either your 4V or 3.3V sources to the VREFX pin of the DAC and GND to IOUTX you would effectively have your voltage source, a variable resistance, and GND in series. As you change the codes of the DAC, you would change the equivalent input impedance seen by your voltage sources.
So, the exact current value would be dependent on both the voltage source and the equivalent impedance of the DAC ladder, which I do not think is what you want. You need a constant current sink so you can characterize the voltage response of your sources.
We have a circuit cookbook for a programmable low-side current sink which should get you where you want to be. You can view that here: www.ti.com/.../slaa868.pdf
Hi Kevin,
Thanks for the note!
I was looking a pairing a DAC80508 with a OPA388 and NTA7002N to accomplish this. I'm attaching a simulation of this below.
I have multiple rails on the regulator however the rail I'm simulating in the attached schematic is a 4V rail referenced to 3V. The Vin is simulating the DAC input with using a gain of x2 5V fullscale output.
Would you be able to advise if you see any issues with this schematic? Do I need Rfb, Riso and Cf for this?
Thanks!