SN65C3232: Was there any change in technical specification from D to DR suffix?

Hi Nancy,

So this is a bit of a tricky question. 

There are two potential variants of the SN65C3232DR floating around. They have different dies. The original SN65C3232DR shared a die with the SN65C3232D - but the same time we discontinued the SN65C3232D we introduced a redesign of the SN65C3232DR - if you have the newer device (which is more likely - since it should have been on the market for almost 2 years now)  the die is different - but it was designed to be as similar as possible, but it uses a different fabrication process now. 

The datasheet highlights this in the revision section - we added new specifications that weren't in the original datasheet. Mainly ESD and Thermal Impedance Values the other changes were more to help with understanding the device operation - and wouldn't change operation. 

The big caveat we didn't have this information spec'd on the older device (ESD and thermal values) but that doesn't mean that they didn't have a value - we just didn't specify it. So there could be changes there that aren't captured because they are new specifications - however it is very unlikely that this caused problems because the ESD is not worse on the new device (we didn't really change ESD design for this part) and the thermal parameters would potentially cause some edge case failures if you are running the device in its most extreme operating conditions - but even then its still unlikely to cause issues.

The other caveat - is that we don't specify a lot of parameters on our RS-232 devices (a lot of RS-232 devices TI and elsewhere are limited in what they specify - mainly just covering the standard reqs for RS-232) - so it is possible for a device parameter that we did not specify to change and for us to be unaware and it could cause problems. However in the last two years for this device that hasn't really been an issue. 

So ultimately - the change should not result in application failure in the vast majority of applications - but they aren't exact matches. 

What kind of failure are you seeing? 

Is it a comms failure or is the device being damaged?  I.e. can you TX or RX from one device or is there no communication at all. Also have the signal lines been probed to check for communication? 

If possible - could you share a schematic snippet of the RS-232 bus - I don't need to see the whole system - but the RS-232 connections would be helpful to ensure that the standard is being followed. I understand if you can't share it - but it would be very helpful if you could.

Also could you please take a picture of the top of the IC so I can see the part markings and trace it in our system to ensure you have a legitimate device. 

Please let me know!

Best,

Parker Dodson. 

Hi Parker,

Thank you so much for your thorough information.  I can upload a schematic in next few days.  In the meantime, these are the Lot Trace Code that we are having problem with; 97A6NDM(dc. 1929), 33C355K(dc. 2311), & 37A780K(dc. 2327) - photos attached.  It is hard to believe all these three lots have same problem.  Thanks again for your great help!

Hi Nancy,

IC: 97A6NDM - This part is in our system; so I believe it should be a legitimate device.

IC: 33C355K - This part is in our system; so I believe it should also be legitimate.

IC: 37A780K - This part is in our system; so it also looks legitimate.

So what is a bit confusing is that the old die is in 97A6NDM (same die as the older "D" Device) and the new die is in the other two. So I am not sure if the issue is actually due to the die change.

Please let me know when you are able to get a schematic and also oscilloscope shots from the bus itself would be very helpful to see if the signals seem off as that could help me isolate a potential issue - but since the issue is affecting multiple variants of the die - I am a bit skeptical of the die change. 

Best,

Parker Dodson 

Hi Parker,

Thank you for the assurance we have the legimate devices.  Our customer sent us the following schematics and also oscilloscope shots.  

Thank you so much for your support!!

I have one more...

Thanks again.

Nancy

Hi Nancy,

Thanks for all the additional information.

TO clarify on the scope shots:

1. The top is what you expect and the bottom the issue - is this correct?

2. What is the green and what is the yellow line represent? 

If I am correct about 1 - the only real difference I see is that the bottom could be occurring a bit slower - but the waveforms themselves doesn't really look too concerning. 

How long is the distance between modules - and do you know if its a cable or a trace? 

On the schematic point of view - there is one or potentially 2 issues

a) DIN should not be left floating - if unused tie the pin to VCC or GND (it can cause DOUT to oscillate which could cause emissions and SI issues)

b)  It looks like the caps are polarized on the charge pump in your system - usually we use ceramic caps and not polarized here. I don't think it should be too problematic - as I think they are connected correctly - but I would be a bit worried on the C1, C2 cap as we don't spec the voltage waveform here so there could be situations where C1- or C2- is larger than C1+ or C2+ with respect to ground which could cause issues on the caps. Also ceramics are usually smaller so they take up less space too - if you switch to ceramic 16V rated are usually good for RS-232 charge pumps. 

I have bolded the questions I have for you - essentially if I am reading the scope shot that your provided correctly - it looks like it could be a delay issue maybe but I want confirmation. Also if you do have the length of the bus between nodes that would be helpful as well. I do see some less than ideal setups in the schematic - but unless I am misinterpreting the scope shots I don't think those issues are causing the largest issues - but ideally would still be remedied. 

Best,

Parker Dodson

Hi Parker,

My apology for delay in responding.  It took some time for my customer to prepare the slides per your comments.  As you may have guessed I am not an expert in this matter; therefore, I can only relay the message as best possible as I can.  Thanks in advance for your understanding.

I will add additional slides on this forum, but I do have the original slide in .ppt   (I will just add 3 new slides)

If you can provide me with your email address, I can forward the ppt file for better visual quality.

Thank you!

Sincerely,

Nancy Kim