Controlling an Op Amp with a DAC on Isolated Grounds

Thread Starter

FreddieTheRobot

Joined Oct 3, 2019
2
Hello!

First post here, surely not the last.
I was wondering if anyone had experience driving an op amp using a Digital to analog converter that is on an isolated ground from the op amp?
See the schematic below.

Untitled.png

My device takes in 48V DC, uses an isolated DC/DC converter to bring it down to 12VDC then again dropped to 5VDC. (I am using a PYBE20-Q48-S12 as the main DC/DC converter)
As shown above, the Op Amp is using the 48VDC input as its supply(VOLTAGE_IN), and as a result is tied to the 48V's ground(DGND_48V); while the DAC is powered via 5VDC it receives from a linear regulator connected to the the isolated DC/DC 12V output, so it is tied to the isolated ground at the output of the DC/DC. (DGND)

I'm afraid that if there are any offsets between the two isolated grounds, the device will have issues with precision. Would this be the case?
Is there anything I can do to make sure there is a static offset, or no offset at all?

Thanks,

JM
 

Sensacell

Joined Jun 19, 2012
2,544
As long as everything shares a common ground- no problem.

You may have noise issues relating to the CURRENTS flowing in your common ground, but that is the case regardless of your power setup.
 

Thread Starter

FreddieTheRobot

Joined Oct 3, 2019
2
As long as everything shares a common ground- no problem.
So I have been looking into that. Even though my DC/DC is "isolated" I still need to place a single point between the DC/DC input and output ground? At the input, it is called GND on the datasheet, but at the output, it is called 0V.
 
it is called GND on the datasheet, but at the output, it is called 0V.
The 0V point is a reference and GND is ground. When laying the circuit out, the 0V reference should not carry any current.

e.g. you have a high current ground and a reference ground. They are kept separate and both are tied together at one point,

On e reason to use a current output is when your controlling a piece of equipment that requires a 0-5V signal. A resistor is placed at the equipment. The reference of the equipment is one end of the resistor.

It sometimes doesn't work for power supplies because the +output is the 0V reference for the power supply. That application requires an isolated source.
 
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