AM26C31: Output characteristics very different between AM26C31IPWR and AM26C31IN package?

Mike Huisman

Part Number: AM26C31

Hi,

So a while back I posted a question regarding your differential line drivers and if it would be possible to achieve a close to rail to rail output voltage when no termination was present on the outputs. Specifically talking about the AM26C31I chip. So you confirmed (Bobby) that this would not be an issue and that we would be able to get close to rail to rail, see my earlier post:

https://www.ti.com/lit/ds/symlink/am26c31.pdf?ts=1771246411611&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FAM26C31%252Fpart-details%252FAM26C31IPWR

I confirmed this by testing with the AM26C31IN package:

So I confidently paced them into our design but with a different package: AM26C31IPWR . However the output characteristics are completely different. The output voltage with the same load now only reaches ~3.6V...

Which is not sufficient for what we are trying to do. Could you possibly provide support and why this could be? Is it true that the internals of these chips are different between the packages?

See our schematic:

These signals go directly into the UCC21710QDWRQ gate drivers. But around the same output when there is no load attached (so best case scenario).

6 months ago

0 Michael Ikwuyum 6 months ago

TI__Guru* 77812 points

Hi Mike,

Today is a holiday. Please give some time for some feedback, thanks.

Best Regards,

Michael.

0 Mike Huisman 6 months ago in reply to Michael Ikwuyum

Prodigy 40 points

Hi Michael, thanks for the heads up. Enjoy your holiday! I hope to hear from you soon.

0 Michael Ikwuyum 6 months ago in reply to Mike Huisman

TI__Guru* 77812 points

Hi Mike,

Thank you.

Our device expert would be able to follow up as soon as possible and thanks for your patience.

Best Regards,

Michael.

0 Ethan Sempsrott 6 months ago in reply to Mike Huisman

TI__Mastermind 28382 points

Hi Mike,

The internals are the same between packages. So the behavior you are seeing is not expected.

Can you send images of the top markings of both transceivers? I want to verify them internally in our system just to make sure everything lines up.

Best,

Ethan

0 Mike Huisman 6 months ago in reply to Ethan Sempsrott

Prodigy 40 points

Hi Ethan Sempsrott ,

I added the pictures here, thanks for the support. Helps us out a lot.

I also ran some tests with the same wire setup on the TSSOP as I have done with the through hole package with the same results (to ensure it's no board issue). The TSSOP only seems to reach up the 3.6-3.8V maximum compared to what I am measuring with the through hole IC.

+1 Ethan Sempsrott 6 months ago in reply to Mike Huisman

TI__Mastermind 28382 points

Hi Mike,

I verified both of those devices in our system, and everything looks good.

The particular AM26C31IN material you have is slightly newer than the AM26C31IPWR material. Because of this, the AM26C31IN happens to have an updated die with better performance as your testing has revealed.

Please note that the ~3.6V differential voltage is still the expected performance. RS-422 requires a 2V difference across a 100 Ohm load, which we still meet in either case. We do not specify the max voltage:

However, the latest AM26C31IPWR material should match the PDIP package performance you are seeing.

I recommend getting some new, free samples of AM26C31IPWR so you can verify this yourself in your system (click the "Add sample to cart" button):

https://www.ti.com/product/AM26C31/part-details/AM26C31IPWR?source=ooq&login-check=true

Best,

Ethan

0 Mike Huisman 5 months ago in reply to Ethan Sempsrott

Prodigy 40 points

Hi Ethan,

I forgot to reply but thanks for your response. Unfortunately that won't work for us as we cannot guarantee / determine in mass production that the boards will always contain the updated die. But at least it clears things up, thanks.

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AM26C31: Output characteristics very different between AM26C31IPWR and AM26C31IN package?