TINA / Spice: OPA847 PSpice Simulation

Wilfrid Rem

Other Parts Discussed in Thread: TINA-TI, OPA847, TLV9002, TLV9062

Tool/software: TINA-TI or Spice Models

Hi, I have a little problem with OPA847. I would like to have the gain and frequency response of my circuit, I get different results than what is shown on an article. I need help please

over 5 years ago

0 Bala Ravi over 5 years ago

TI__Expert 6625 points

Hi Wilfrid,

Based on the information provided, I see that you're trying to build an inverting attenuator circuit. The RC filter makes this circuit AC coupled. So at DC it's just an open circuit. At AC you should expect a gain of 20log(5/10) = -6dB. Did you get this? If you can share your bode plot and a link to the article above, I should be able to further assist you.

Best Regards,

Bala Ravi

0 Wilfrid Rem over 5 years ago in reply to Bala Ravi

Prodigy 65 points

Here is what I got and I think it's correct

0 Wilfrid Rem over 5 years ago in reply to Wilfrid Rem

Prodigy 65 points

Here's what I got and I don't think it's right

0 Wilfrid Rem over 5 years ago in reply to Wilfrid Rem

Prodigy 65 points

kpubs.org/.../articleMain.kpubs

0 Wilfrid Rem over 5 years ago in reply to Bala Ravi

Prodigy 65 points

Thank you very much
kpubs.org/.../articleMain.kpubs

0 kai klaas69 over 5 years ago in reply to Wilfrid Rem

Guru 140200 points

Hi Wilfrid,

this must be a mistake. The OPA847 is stable only for gains >= 12.

Kai

0 Bala Ravi over 5 years ago in reply to kai klaas69

TI__Expert 6625 points

Hi Wilfrid,

Kai is right. OPA847 is only stable for gains >= 12. You can find this information on the datasheet. So your bode plot is wrong. If you're just trying to simulate, you can try using TLV9002 or TLV9062 TINA models. Based on your setup a correct bode plot would look like this:

Also a correction to what I said earlier, at AC the capacitor would be short, making the gain = 20log(5/20) = -12dB.

Best Regards,

Bala Ravi

0 Wilfrid Rem over 5 years ago in reply to Bala Ravi

Prodigy 65 points

Hi Bala Ravi,
thanks for the help. I would like to know if you read the article. I'm just looking to realize common-mode choke of active radio interference filter . I'd like to know why we're using an OPamp? thank you in advance pending a reply from you by

0 Bala Ravi over 5 years ago in reply to Wilfrid Rem

TI__Expert 6625 points

Hi Wilfrid,
I did not completely read the article. But, from a quick view the sensing circuit senses the noise and the op-amp circuit generates the cancellation voltage to cancel the noise. Another advantage of using an op-amp is having a high input impedance and a low output impedance . I hope this helps!

Best Regards,
Bala Ravi

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TINA / Spice: OPA847 PSpice Simulation