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OPA567: Negative Output Voltage

Hirotsugu Kobayashi
Mastermind 8485 points
Part Number: OPA567

Hi, team.

If OPA567 is used with dual power supplies, a negative voltage will appear during the first swing.

Is there a way to reduce this?

  • 0
    TI__Guru* 93105 points

    Kobayashi-san,

    That output behavior seems odd. Would it be possible for you to provide your OPA567 circuit schematic and details of the output load? Please include the supply V+/V- supply information.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Mastermind 8485 points

    Hi, thomas.

    The output is no load, +3.5V and -1.5V are applied.

    This circuit buffers external pulses.

    Best Regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Guru* 93105 points

    Kobayashi-san,

    The "OUT" trace captured with the DSO is at the IOUT (TP3) point in the circuit, or directly at the OPA567 VO_2, or VO_3 pins? Would it be possible for you to remove C933, 4.7 uF, and retest the circuit to see if that unexpected first negative-going pulse still occurs?

    Are there any high capacitance power supply decoupling capacitors used such as the 47 uF capacitors shown in Figure 1 of the OPA567 datasheet?

    Regards, Thomas

    Precision Amplifiers Applications Engineering 

  • 0 in reply to Thomas Kuehl
    Mastermind 8485 points

    Hi, Thomas.

    OUT is the waveform at TP3. C933 is not mounted.

    The data sheet shows a negative voltage once when used with dual power supplies. Is this IC characteristic?

    Best Regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Guru* 93105 points

    Kobayashi-san,

    The datasheet Typical Characteristics graphs are specified with TA = +25°C, VS = +5V, unless otherwise noted. However, with the output pulse going negative, about -1.5 V (1 V/div scale) for a portion of the Enable 10 Ω graph, that result suggests the setup used a +/-2.5 V supply. Unfortunately, we don't have any documentation that provides the specific set up information used for the Typical Characteristics graphs.

    Since the graphs are provided in the datasheet the results are obtained from real OPA567devices, which supports the transient behaviors are device behaviors. The actual transient characteristics may be different from one application to another. As the datasheet states "Examples of output behavior during disabled and enabled conditions with various load impedances are shown in the typical characteristics section. Please note that this behavior is a function of board layout, load impedances, and bypass strategies. For sensitive loads, the use of a low-pass filter or other protection strategy is recommended." So the setup likely influences the transient behavior of the OPA567.

    Regards, Thomas

    Precision Amplifiers Applications Engineering