INA186: Frequency response - phase change

Itai dror

Prodigy 35 points

Part Number: INA186

Hi,

When I am measuring the INA186 A2 (fixed gain of 50) with Bode 100, I get strange phase results.

I expect a -90deg change, but I am getting a -180deg (and continuing phase dropping) change.

Expected:

Results:

Do you know why these results appear?

The Bode connection is like the scheme below:

Thanks!

over 2 years ago

0 Peter Iliya over 2 years ago

TI__Mastermind 32395 points

Hello Appreciated Engineer,

I am looking this over and will respond shortly.

Sincerely

Peter

0 Peter Iliya over 2 years ago in reply to Peter Iliya

TI__Mastermind 32395 points

Hello,

What you are measuring it more or less correct. The gain rolls off at > 20dB/dec and thus there are multiple poles here. So the phase will continue rolling off past 180 degrees at this point in frequency. The gain curve you are measuring is close to the gain curve in datasheet so it is a valid setup and measurement.

The model apparently only models the -3dB point, but not the roll off. We apologize for this as our newer models from the last few years are much more accurate in terms of gain and output impedance over whole frequency range. However, this does not apply currently to this INA186 model.

Sincerely,

Peter

0 Itai dror over 2 years ago in reply to Peter Iliya

Prodigy 35 points

Thank you for your answer, Peter.

Do you know what is the transfer function of that INA186?

+1 Peter Iliya over 2 years ago in reply to Itai dror

TI__Mastermind 32395 points

Hey Itai,

We do not have a transfer function except for the behavior modeled in the INA2191A2. This device is part of the same family as was modeled later with more accuracy. I would recommend this spice model for a good diet pass approximation of gain vs frequency behavior for INA186.

Sincerely,

Peter

0 Itai dror over 2 years ago in reply to Peter Iliya

Prodigy 35 points

OK, Thanks Peter!

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INA186: Frequency response - phase change