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OPA207: in high gain application

Part Number: OPA207

Hello,

The OPA207 datasheet describes that it can replace from OP-177.

Certainly, the electrical characteristics has the same or higher performance,  

however, I have one concern.

In ADI OP177 datasheet, it is written that as below.

The OP177’s combination of outstanding specifications
insure accurate performance in high closed-loop gain applications.

On the other hand, in TI OPA207 datasheet we can see as below.

OPA207 is stable in unity gain and provide excellent
dynamic behavior over a wide range of load
conditions.

I'm going to try to replace from OP177 to OPA207 in a load cell application, the gain is about 100.

Is it not recommended ? Or do you have any other recommended part?

Thanks,

Hiro

  • Sato-san,

    Regarding the statements, "The OP177’s combination of outstanding specifications insure accurate performance in high closed-loop gain applications" and "OPA207 is stable in unity gain and provide excellent dynamic behavior over a wide range of load conditions" are primarily marketing descriptions and one really needs to refer to their electrical specifications in relation to the application.

    In a high gain application the closed-loop gain (Acl) accuracy is directly related to the open-loop gain (Aol) of the op amp, at the frequency of interest. Basically, the higher the op amp Aol, the more accurate the Acl will be.

    The OP177 Aol is specified as the LARGE SIGNAL VOLTAGE GAIN, AVO, RL ≥ 2 kΩ, VO = ±10 V, (F Grade) 5000 V/mV (134 dB) Min, 12,000 V/mV (141.5 dB) Typ, and (G Grade) 2000 V/mV (126 dB) Min, 6000 V/mV (135.6 dB) Typ. The OPA207 AOL Open-loop voltage gain is specified with (V–) + 200 mV < VO < (V+) – 200 mV, RL = 2 kΩ, as 120 Min, 140 dB Typ.

    In either case the Aol is extremely high and the differences between them will have an almost indistinguishable effect on the Acl accuracy. However, the Aol numbers themselves only tell part of the story. The other part is the output voltage Vo, over which the Aol is specified. Note that the OP177 Aol is specified with an output voltage swing that extends to +/-5 V from the supply rails. By comparison the OPA207 the output swing is specified at +/-0.2 V of the supply rails. The latter is a much more rigorous requirement to meet because Aol degrades as the output swing approaches the supply rails. The OP177 output swing is limited to about 2 to 3 V of the supply rails so a direct Aol comparison to the OPA207 cannot be made at +/-0.2 V.

    You mention, "Certainly, the electrical characteristics has the same or higher performance..." That is correct, and note that the OPA207 achieves the high levels of performance using less than a quarter of the operating current used by the OP177. Additionally, the OPA207 has significantly higher bandwidth and slew rate compared to the OP177.

    The OPA207 makes an excellent, modern replacement for the OP177.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Hello Thomas-san,

    Thank you for your quick and detailed replying, this is very helpful for us.

    Thank you very much.

    Hiro