Tina-TI Spice model for OPA836: too much noise

David Watt85209

Other Parts Discussed in Thread: TINA-TI, OPA836

I would like to know if the noise is modeled incorrectly in the OPA836 Tina-TI Spice model. While the OPA836 datasheet, Figure 16, has voltage noise of around 4-5 nV/sqrt(Hz), stable from 1 to 10 MHz, an input noise analysis of a simple voltage follower based on OPA836 in Tina-TI has the input-referred voltage noise at 5 nV/sqrt(Hz) at 1 MHz, then rapidly rising to about 25 nV/sqrt(Hz) at 10 MHz, and it continues to rise dramatically beyond that. Can a TI app engineer explain what is going on? I can provide the TSC file with the voltage follower. I'm including the plot of voltage noise density vs. frequency..

Sincerely,

David Watt

over 13 years ago

0 Jim Karki over 13 years ago

TI__Expert 4115 points

David,

There appears to be an error in the model. A real part wiil perform as shown in the data sheet. I will move your inquiry to the Analog eLab for further support.

0 JC Zhu over 13 years ago in reply to Jim Karki

TI__Mastermind 37790 points

Hi David,

Would you please post the TSC file if it's OK?

Thanks,
JC

0 David Watt85209 over 13 years ago in reply to JC Zhu

Prodigy 30 points

Yes, I can post the simple voltage follower. I'm new to the forum and don't know how to post, though. When I tried the paper clip icon and selected the TSC file, it says the file type is invalid.

David

0 JC Zhu over 13 years ago in reply to David Watt85209

TI__Mastermind 37790 points

David,

I am not very sure where you saw that paper clip icon (I've seen it before). For me there're three tabs on the replay message page, "Compose" (which is active since I am typing), "Options" and "Preview".

If I click "Options" there's a button for adding attachment. Do you have the same thing?

THanks,
JC

0 David Watt85209 over 13 years ago in reply to JC Zhu

Prodigy 30 points

Thanks - I did try to post it.

David

opa836_vfollow.TSC

0 Flora Carreto over 13 years ago in reply to David Watt85209

TI__Intellectual 2510 points

David,

The OPA836 model was done in such a way to represent the bandwidth for different gain settings, the slew rate for gain of 2 and Vo=2Vpp, the quiescent current and most of the DC parameters. The input-referred voltage noise is accurate from f=10Hz up to 1MHz. The OPA836 is only valid for Vcc=5V.

Best regards,

Flora

0 Neil Albaugh over 13 years ago in reply to Flora Carreto

Genius 5430 points

"The input-referred voltage noise is accurate from f=10Hz up to 1MHz. "

Good grief, for an op amp with a GBW of 110MHz, having an important parameter like noise not being anywhere correct above 1MHz is totally unacceptable. How can anyone rely on a TI device model when this slipshod stuff is provided for a new product?

I wouls suggest that TI hire some professional modelling engineers instead of having their macromodels written by amateurs.

0 Jim Karki over 13 years ago in reply to Neil Albaugh

TI__Expert 4115 points

David and Neil,

The modeling team is investigating how to increase the bandwidth of the noise in the OPA836 model. It may take some time to get it right. In the mean time, please refer to the data sheet.

0 Neil Albaugh over 13 years ago in reply to Jim Karki

Genius 5430 points

Thanks, Jim.

Having accurate models is really important. You know the old saying...GIGO.

0 Flora Carreto over 13 years ago in reply to Jim Karki

TI__Intellectual 2510 points

David and Neil,

The input-referred voltage noise was adjusted up to the frequency range given in the OPA836 data sheet.

Please see the attached TINA circuit, the noise was modified in order to meet the data sheet.

Best regards,

Flora

OPA836_Vn.zip

0 Neil Albaugh over 13 years ago in reply to Flora Carreto

Genius 5430 points

Thank you, Flora.

I have re-drawn the circuit with a reasonable sense of esthetics on the graphics and I have included the results of a DC, AC, Transient, and Noise analysis.

Note that I have done this as a TINA .tsc file rather than a ZIP file, which is a PITA.

OPA836.TSC

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Tina-TI Spice model for OPA836: too much noise