THS4524: Differential Input voltage

Ryan Stephen

Part Number: THS4524
Other Parts Discussed in Thread: THS4551, THS4521

Hi I am seeing a possible issue with a design using the THS4524, perhaps somebody could assist?

The attached image shows the op amp topology, it is differential configuration with a gain of 0.5, 1.25V common mode. I expect an output dynamic range between ~0.1V to ~2.49V. The inputs are measuring across a 250R and voltage range of 0 to 5V. My issue is i am not seeing the full output dynamic range, something instead like 0.65V to 1.8V.

According to the datasheet it states:

Slightly confused by this?

I tried modelling this in TINA and the results were also confusing as i think the model isnt using the common mode input but the skewed output seems to conform with the datasheet:

Is this op amp suitable for this application? If not is there an alternate?

Thanks

over 3 years ago

0 Michael Steffes over 3 years ago

Guru 48395 points

Hey Ryan,

You changed your ckt in TINA, can you attach that file?

0 Ryan Stephen over 3 years ago in reply to Michael Steffes

Prodigy 30 points

TI-SPICE-SIM OpAmpTHS4524.TSCPlease see att. Thanks

0 Michael Steffes over 3 years ago in reply to Ryan Stephen

Guru 48395 points

You might have your feedback connections crossed, the V+ output needs to go to the V- input and vice versa - for the caps

0 Ryan Stephen over 3 years ago in reply to Michael Steffes

Prodigy 30 points

Thank you, this fixed it somewhat but i still think the model isnt right

0 Michael Steffes over 3 years ago in reply to Ryan Stephen

Guru 48395 points

Yea, it does look like the output headroom going low is too high in the model, here I put a -1V supply on the negative supply and it seems to work - you might try the THS4551 model in this, much newer and improved version over the single of this part, Here I added the -1V supply and probed on the negative side that had been stuck at 0.88V.

0 Sima Jalaleddine over 3 years ago in reply to Ryan Stephen

TI__Mastermind 26845 points

Hello Ryan and Michael,

Thank you for bringing this issue to our attention. There were previous model errors in regards with single vs split supply in reference to Vocm. These were fixed with recent model update for THS4521 which is the single channel version of the THS4524. This update did not seem to follow through for the rest of the THS452x. I will work with out model and web team to follow through with these changes.

I would suggest using the THS4521 model in the meantime since they share the same parameters. Also, here are part 1-3 on FDA attenuators that would be useful to guide for overall amplifier stability at lower than 1V/V gains.

Thank you,

Sima

0 Michael Steffes over 3 years ago in reply to Sima Jalaleddine

Guru 48395 points

Hey Ryan, another more up to date attenuator discussion is something I put into the THS4551 datasheet, I think that section is simply called "Designing Attenuators' Karki's articles were done at the dawn of time (FDA wise) whereas the THS4551 has the benefits of quite a bit more development after those.

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THS4524: Differential Input voltage