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Single Supply OPA350 Rail to Rail Operation

Voltage Multiplier
Prodigy 110 points
Other Parts Discussed in Thread: OPA350, TINA-TI

Hello,


I am designing power electronics converter in which I will measure the DC capacitor voltage. As an isolated voltage sensor, I will use ACPL-C87X from Avago. This IC needs a post amplifier to combine its differential output into single ended signal with a difference amplifier. The IC suggest usage of OPA327 but I will use OPA350 because I assume it is superior.

The point is I want to use single supply for cost reasons.
When I search the net, I found that some people shift the referance point to Vdd/2 to resemble the structure with split supply case in which references previosly were at GND potential. Furthermore, inputs of the amplifier are AC coupled by caps.

Considering my both inputs to the difference amplifier is positive and their difference is never negative and so output voltage, do I need such things? I am measuring DC cap voltage which is unipolar (DC and 50Hz swing - maybe 10 or 20 percent at worse). I think I dont need such extra precaution. I believe what I just need to is to connect GND to negative supply pin of opamp.

The suggested application schematic can viewed in Figure 19 of the ACPL-C87X datasheet and input signal variation (Vout+ and Vout-) of the amplifier is shown in Figure 13 at the same document.

Also, I wonder the offset voltage and other undesired effects when I design the circuit as I described.

Lastly, I will use the opamp output  signal to feed the ADC of F28377D of TI. So how should I feed this signal to the DSP? An RC filter? What values?

Thank you!

  • 0
    Prodigy 10 points

    I think you can do it as you suggest, fully single ended. As long as the instantaneous current through the sense resistor is always greater than zero. When the inputs to the differential amplifier are zero, Vout will try to go to the same voltage as GND2 (in Figure 19 of the Avago data sheet). Since the opamp only goes to a few 10s of mV above, that would be an error. But as long as the current always flow one way through R2, it should work.  You could try it in TINA-TI and see for yourself.

    I can't answer about the ADC.