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OPA2673: Odd Circuit Output

Part Number: OPA2673
Other Parts Discussed in Thread: TINA-TI

Hi,

I have the attached circuit built onto a PCB.

It is essentially intended to take a 5V sine wave input of varying frequency, and outputs a differential waveform which applies power over a ~27R load, with a small amount of filtering.

The circuit successfully simulated using the pSpice model provided on the product page, (simulated within altium). 

However in reality it appears to output a wave with a tiny amplitude and large DC offset.

Can anyone make any suggestion why I am seeing the results shown on the oscilloscope screenshot, rather than those shown in the simulation?

And what may be done to resolve this issue?

Thus far all I can glean is that my setup of A1/A0 may not be ideal.

(Doesn't seem to drive above 2V as intended. Though does to exceed the absolute maximum of Vee+5, which could be the problem).

How should the bias pins be driven, if a negative supply of under -3V is used?

(If A1/A0 is referenced from GND and requires at minimum 2V for logic 1).

(Scope Screenshot Ch1 - RF_1X | CH2 - COIL_1X_P | CH3 - COIL_1X_N  | CH4 - A0/A1)

Thanks, Andrew

  • Hello Andrew,

    I am looking into this behavior for you.  Could you send your Altium simulation file or other simulation so I can attempt to replicate the issue?

    Additionally, we have an older thread which provides an alternative way to do A0/A1 control.  It may be useful in your debugging:

    https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/955636/opa2673-sequence

    Best,

    Alec

  • Hi Alec, 

    Thank you for the response and link to the thread. Please see (hopefully) the simulation file attached.

    I will be progressing the debugging today, so will report back with any findings that may help.

    Many thanks, Andrew

    4846.OPA2673.SchDoc

  • Hello Andrew,

    I am still working on your circuit and analysis.  However, I thought it would be helpful to share my two TINA-TI SPICE simulation files.  I would suggest acquiring TINA-TI and using the two circuits I provide to investigate if your design truly functions as you intended.  The first file is a copy of the OPA2673 TINA Reference Design file, setup to be able to output a sine signal and has working enable/disable.  You set A0 & A1 to 0V to operate at Full Bias, and set the values to 2V to disable the part.

    The second file is a working version of your schematic; this includes the MOSFET for disable, as well as a switchable path for A0/A1 BIAS to just use a DC source.  It would appear from the TINA-TI simulation that the circuit is not behaving as intended.

    I hope this helps you understand what I am seeing, and helps towards the resolution of your design.

    opa2673_ref_design.TSC

    a0a1_bias_issue.TSC

    Best,

    Alec 

  • Hi Alec,

    Thanks for responses and simulation files. Certainly helped more than the model I had in Altium.

    In the end it didn't seem to be an issue with the enable, i suspect it was more that I was supplying the IC from imbalanced voltage supplies... (+7V / -5V).

    I've ended up going single supply (+12V), introducing a DC offset, and using a blocking cap on the output. Which seems to now work within the parameters of what I need at least! 

    Thanks for the assistance,

    Andrew

  • Hello Andrew,

    I am glad to hear the positive update from you.  Asymmetric and unbalanced supplies do create oddities from time to time; please reconnect or ask more questions if you run into future issues.

    Take care!

    Best,

    Alec