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DAC5578: DAC latches wrong I2C address

Emanuel Zimmermann
Prodigy 30 points
Part Number: DAC5578
Other Parts Discussed in Thread: DAC121C081, , DAC43608

Hello,

I was guided to this forum by Jejomar Ildefonso from TI customer support. Here I found the following thread that might be related in some kind to our issue:

DAC121C081: I2C Addressing Question by Adam Daluga

Though we are not operating our two DACs on different potentials, we also see address select pins that are read high instead of floating. Also the above thread was taken offline so I could not see a conclusion on this. Here's how our story goes:

We are using two DAC5578 in one of our designs along with several other I2C bus slaves. The assigned addresses are 0x4E and 0x4F. A certain number of DAC's latches a wrong I2C address only in a limited range of board temperatures. For all failing DAC's the temperature range where the issue occurs is between about 18°C and 26°C. Outside this range (tested temperatures from -20°C to +85°C) the address is set correct. The issue seems to be related to the individual physical IC, since swapping a failing and a good DAC also swaps the occurrence of the issue to the other address on the bus. All observed occurrences turn 0x4E to address 0x49 and 0x4F to 0x4B. So the floating address input pin seems to be interpreted as high instead of floating!
What can cause this behavior?

Many thanks for your support,

Emanuel

  • 0
    TI__Genius 14220 points

    Hi Emanuel,

    Welcome to E2E and thank you for your query. We have seen these issues with some of our old parts with tri-state input option, especially for the I2C address. These inputs have internal weak pull-up and pull-down resistors and they probably go out of accuracy at different temperature ranges. 

    We recommend using stronger (5k to 10k) external pull-up and pull-down resistors with low-temperature co-efficient. This is a suggestion if you cannot avoid the float options for the address pins. 

    We are sorry for the trouble with the tri-state option. Hope the suggestion works for you.

    Regards,

    Uttam Sahu

    Applications Engineer, Precision DAC

  • 0 in reply to Uttam Sahu
    Prodigy 30 points

    Hello Uttam Sahu

    Many thanks for the quick reply!

    I want to better understand the issue first. You mentioned that there are probably different temperature ranges this issue can occur.

    So the 18°C to 26°C range we have seen could change depending i.e. the production lot of the DAC?

    Also, can the issue show up during lifetime even when it didn't exist initially?

    For us it is not a quick and easy fix to add external pullup/down resistors. Space is tight in this area and the floating pin is floating in the best meaning of the word - so no extra pad to solder the resistors on and a QFN package hardly exposing the solder joint! We most likely will require a respin of the board to try your solution.

    May we have overlooked it in the datasheet, but is this issue mentioned somewhere or does an errata exist?

    Thanks and best regards,

    Emanuel

  • 0 in reply to Emanuel Zimmermann
    TI__Genius 14220 points

    Hi Emanuel,

    Sorry for the trouble. I can understand your situation. The floating option is mainly an extra option to increase the number of I2C addresses, but it reduces the error margins by two. I understand that this is not explicitly mentioned in the datasheet, but the floating input is prone to error in applications that are noise-sensitive and that involve temperature drift.

    The digital timings and floating levels are not production-tested on our devices. This issue was mainly reported by the customers and not captured in the datasheets yet. At this moment, this error is listed only with the E2E logs on specific product pages on the  "training and support" tab.

    It is possible that the error may reproduce differently with different lots due to process variation. our new parts don't include the floating option due to the reduced error margin. 

    I know it may require a board respin or rework from your side. However, is it possible for you to test the external pull-up and pull-down or to switch to our new family of the DAC: DAC43608?

    Regards,

    Uttam

  • 0 in reply to Uttam Sahu
    Prodigy 30 points

    Hi Uttam,

    Thanks for the reply.

    The increased number of I2C addresses is exactly what we need in this application. So the suggested alternative is no solution for us, we will have to try the external pullup/down approach. Anyway, we will have to go for a redesign of the board. But it seems that we will not be able to cover potential issues with units already in the field!

    Again, thanks for your support. I think this case can be viewed as closed.

    Regards,

    Emanuel