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OPA1632: Modulation of differential output using OPA1632D

Mehdi AYADI
Prodigy 10 points
Part Number: OPA1632

Hello,

I'm using a MCU to generate a sine-wave (as single ended signal) that is amplified and changed to differential signal with a OPA1632D.

The enable pin of the OPA1632D is used as a modulation input pin.

The circuit works correctly except when the OPA1632D stays inactive for several seconds.

On first image, you can see sine-wave generation (RED) and modulated signal (BLUE). Also you can see request message and on the right of image, the answer of the device.

On second image, you can see that the beginning of the request has been truncated so no answer from the device.

I also tested the signal that attacks the Enable pin of the OPA to check if any dysfonction, but the Enable signal is also correct.

On the datasheet the delay on the Enable signal is 2 us, but the OPA takes too much time to start, I don't know why.

FYI, when I keep sending request continuously there is no problem, only when the circuit is on hold for several seconds.

Please, what can I do to avoid this misfunctionning.

Thank you

Normal SignalTruncated Signal

  • 0
    TI__Genius 16691 points

    Hello Medhi,

    Could you please share your circuit schematic and description of how you are modulating the OPA1632 via the Enable pin? I cannot provide a detailed response without seeing how the circuit is implemented.

    If possible, could you also explain why a shutdown function is being used for modulation? The shutdown functionality is designed for power savings when the device is not in use; it may not behave predictably when used to modulate an output. Is there explicit need for the OPA1632 to be modulating the signal? Could this modulation occur prior to the OPA1632 and be merely amplified by the audio amplifier? It may still be the case the OPA1632 can be sufficient in this application, but I would need to review your schematic with voltage levels and signal timings.

    The shutdown/enable function does not place the output signal at high impedance, and the enable pin itself is looking for a voltage threshold to turn on/off. The datasheet discusses the functionality in Section 7.4.1. If you are providing a signal greater than 2V away from the negative rail on the enable pin, you will turn on the device. Similarly, if the pin is floating, the device has an internal pull-up resistor to turn on the device.

    You may find your circuit design is not properly utilizing the shutdown function; this could be the cause of the perceived turn-on delay. Without the schematic and a bit of time, I cannot say for certain what is the cause.

    Please provide the information you can so I can continue to help with this behavior.

    Best,
    Alec

  • 0
    TI__Genius 16691 points

    Hello Medhi,

    After checking with my team, the HSAMPs product line does not recommend using the OPA1632 to modulate your signals.  When an op-amp has a power down or shutdown feature, this is for power savings (low quiescent current).  These disable features are not intended to be used in modulation or have constant signals at the inputs (and/or outputs) when disabled.

    Please redefine your design and circuit to use a different method or device for modulation, and keep the OPA1632 as an amplifier (and single-ended to differential) only. 

    Best,

    Alec