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OPA548 used to create virtual ground connection between product and test equipment, or is there a better choice?

James Dozet
Prodigy 20 points
Other Parts Discussed in Thread: OPA548, TLE2426

I have a DAQ in the test equipment which must remain within ~11V of test inputs.  The test equipment ground and the product ground are connected via a cable, but if I connect them directly to the AI Ground of my DAQ, differential readings will be impaired (due to load imbalance).  I want to generate a virtual ground for the AI Ground from the Product ground.  I am using OPA548's to create a High Current amplifier already in my Test Equipment.  Is the OPA548 suitable for use as generating the Virtual Ground input for my DAQ?

 

My greatest concern is that all my power is Single Ended, positive suppies only, and how effective will the Virtual ground be if the output is nominally at V-, or 0v in this case?  What will negative noise due, for instance?

  • 0
    TI__Guru* 93105 points

    Hello James,

    Operational amplifiers are often used to create a virtual ground - a voltage midway between ground and the positive supply level. This is usually accomplished by using two equal resistors connected as a voltage divider between the supply levels, followed by an operational amplifier connected as a unity-gain buffer amplifier. Its output being the virtual ground point. 

    The OPA548 can be configured in this manner. It is a high-current op-amp and can sink and source a current up to 5 Amperes peak. The closed-loop output impedance will be low at DC and low frequencies, but will increase as the open-loop gain decreases with increased frequency. Often, a capacitor is added at the amplifier output to the system ground. Its purpose is to provide a low impedance path to the system ground, needed for higher frequencies. Adding a capacitor to a unit-gain buffer can lead to instability and must be assessed before making that addition.

    If you don't need all the output current that the OPA548 can supply, TI has a precision virtual ground product - the TLE2426. You can read about it here:

    http://www.ti.com.cn/cn/lit/ds/symlink/tle2426.pdf

    Regards, Thomas

    PA - Linear Applications Engineering