THS3215: Error in equation 2, page 32

Michael Steffes

Other Parts Discussed in Thread: THS3215, THS3217, TIDA-060002

art Number: THS3215

I was commenting on an old ADI app note, MT-019 Figure 3, this classic ckt is slightly off in that the impedance looking into the inverting side has an active component with a complementary DAC input.

https://www.analog.com/media/en/training-seminars/tutorials/MT-019.pdf

I noticed that the equation for alphathat I put into this section got flipped over - should have been R2/(R1+R2). This error is likely in the THS3217 data sheet as well.

To go ahead and test this result, I stepped through the sims in the attached file - this effect is definitely there often giving a mismatched load to the DAC. small effect usually, but easy to fix also.

3554.Testing MT019 diff to single for input impedance.docx

over 3 years ago

0 Hasan Babiker31 over 3 years ago

TI__Genius 15555 points

Thanks for the heads up Michael. Just to confirm, I believe the issue is only regarding to equation 2 in the datasheet.. the R1/(R1+R2) term still seems to be correct in equations 6 & 7. The following calculations after this mistake also seem to be correct as 2/3 is used rather than the wrong alpha term.

Best,

Hasan Babiker

0 Michael Steffes over 3 years ago in reply to Hasan Babiker31

Guru 47485 points

That is correct Hasan, the R1/(R1+R2) is correct for the Vref input side. And yes, that 2/3 term is correct up in Eq 3, which is how I knew Eq 2 had gotten wrong. 2/3 only makes sense (and it does work) if Eq. 2 is R2/(R2+R1)

0 Beverly Aue over 3 years ago in reply to Hasan Babiker31

Prodigy 90 points

Thanks for all of the information and correction. Does anyone know how I can get the design files listed in Section 4 of the TIDA-060002 document? Is the reference board available for purchase?

0 Hasan Babiker31 over 3 years ago in reply to Beverly Aue

TI__Genius 15555 points

Hello Beverly,

Looking into this, will respond in your previous thread.

Best,

Hasan Babiker

0 Beverly Aue over 3 years ago in reply to Hasan Babiker31

Prodigy 90 points

I found all of the design files including .PDFs of drill/fabrication and all of the Gerbers for the Reference board. Still looking for .PDFs for the Evaluation Module.

0 Beverly Aue over 3 years ago in reply to Hasan Babiker31

Prodigy 90 points

Thank you for sending the .PDFs I requested. One last request. Can you send me a link to the Gerber files for the Evaluation Module. I can look at those with a Gerber editor if necessary in case the .PDFs are not sufficient.

0 Beverly Aue over 3 years ago in reply to Hasan Babiker31

Prodigy 90 points

Nevermind. I have the Gerbers for the Evaluation Module. I think I have everything I need now. Thanks for your help!

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THS3215: Error in equation 2, page 32