LMV321: Output waveform

Shuji Ishiwata

Part Number: LMV321
Other Parts Discussed in Thread: TINA-TI

Hi All,

I have a question about the LMV321.

I found a device with different output waveforms in the same inverting circuit.
I understand that (1) is the correct output waveform.
I think waveform (2) is not the correct operating waveform, is my understanding correct?

The output waveform in TINA-TI was the same as in (1).

Best Regards,
Ishiwata

over 1 year ago

0 kai klaas69 over 1 year ago

Guru 140200 points

Hi Ishiwata,

hard to answer withput seeing the schematic and knowing all the details about the circuit and input signals. But it looks like the right scope plot shows the OPAmp with the output signal driven into hard saturation. Or by other words, in the right scope plot the output signal is clipping, while in the left scope everything seems to be ok.

Can you give more details?

Kai

0 Gerasimos Madalvanos over 1 year ago in reply to kai klaas69

TI__Mastermind 29006 points

Hey Ishiwata-san,

Could you provide the schematic of the inverting circuit? Additionally, this may be related to the PCN of the LMV321, where there were significant changes to the device, one of which is the addition of slew-boost. I've included a copy of the PCN that is made publicly available by Mouser.

https://www.mouser.com/PCN/Texas_Instruments_PCN20191122000_20191125165030264.pdf

Best,
Jerry

0 Shuji Ishiwata over 1 year ago in reply to Gerasimos Madalvanos

Mastermind 6655 points

Hi Jerry-san, and Kai-san,

Thanks for the reply.
I appreciate your response, it is very helpful.

A simplified circuit diagram can be found here. It is a simple inverting circuit.

I have an additional question: there is no mention of through-boost in the PCN. Has any functionality been added?
Is the waveform in (2) operating normally?

Best Regards,
Ishiwata

0 Caro Walter over 1 year ago in reply to Shuji Ishiwata

TI__Mastermind 19607 points

Hello Ishiwata-san,

The PCN says that there was a change in design:

All the best,
Carolina

0 Gerasimos Madalvanos over 1 year ago in reply to Caro Walter

TI__Mastermind 29006 points

Ishiwata-san,

Yes, this is the expected output behavior.

Best,
Jerry

0 Shuji Ishiwata over 1 year ago in reply to Gerasimos Madalvanos

Mastermind 6655 points

Hi Jerry-san, and Carolina-san,

Thank you for your answer.

I could not understand that slew-boost was added with only the description of PCN design change.

I understand it to be the expected output behavior.
What kind of function is slew-boost added by design change?
Do peripheral circuit conditions affect the output waveform?

Best Regards,
Ishiwata

0 Gerasimos Madalvanos over 1 year ago in reply to Shuji Ishiwata

TI__Mastermind 29006 points

Hello Ishiwata-san,

While all the changes are not listed in the PCN, the PCN does describe a change in design. Part of that design change was the addition of slew boost.

Here is an FAQ that helps with the understanding of slew boost.

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1055566/faq-why-does-the-slew-rate-in-my-application-not-match-the-op-amp-s-data-sheet'

The peripheral circuit does affect the output waveform, as slew boost is affected by the input voltage differential (Vid). Larger Vid will mean that slew boost is active, while a smaller Vid will not turn on slew boost.

Best,
Jerry

0 kai klaas69 over 1 year ago in reply to Shuji Ishiwata

Guru 140200 points

Hi Ishiwata,

slew-boost can make issues sometimes with bipolar OPAmps drawing very little supply currents. A bipolar OPAmp drawing very little supply current is usually slow and is not able to provide a high slew rate. An added slew-boost can speed up the OPAmp to some degree but this speed-up often works in a limited range and can result in a weird or at least unexpected behaviour. You may find this thread useful:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/999779/opa991-opa991-is-not-meeting-its-slew-rate-specification

You always have to pay a price, if you require from an OPAmp mutually exclusive characeristics...

Kai

0 Shuji Ishiwata over 1 year ago in reply to kai klaas69

Mastermind 6655 points

Hi Jerry-san, and Kai-san,

Thank you for your support.

I checked the PCN document again, and there was an addition and description of the FAB site.
・Is there a slew boost function presence or absence for different FAB sites?
・Do the characteristics of BCB and LBC9 differ depending on the process?

I would like to confirm whether the design has been changed on all FAB sites.

Best Regards,
Ishiwata

0 Gerasimos Madalvanos over 1 year ago in reply to Shuji Ishiwata

TI__Mastermind 29006 points

Ishiwata-san,

The slew boost absent in different fab sites. This will be present in the LBC9 process, the design is not changed across all FAB sites.

Best,
Jerry

0 Shuji Ishiwata over 1 year ago in reply to Gerasimos Madalvanos

Mastermind 6655 points

Hi Jerry-san,

Thank you for your reply.

I understand that LBC9 process redesigned, BCB not redesigned.
And I understood that there are identical devices with different characteristics.

Best Regards,
Ishiwata

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LMV321: Output waveform