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TCA9406: VCCA>VCCB due to an error of mine: how can i solve with minimal intervention?

Francesco Cavalieri
Prodigy 250 points
Part Number: TCA9406

I did erroneously design this chip in, on just received very expensive and complex prototype boards, so that VccA is powered at 3.3V and VccB at 1.8V.  

I now need fixing those boards with as little noticeable  intervention as possible.

The easier way i see is soldering the chip 180° rotated, than rearranging only GND and OE connections. 

But doing that way SDA and SCL lines are swapped with respect to pin names of TCA9406.

As far as i know this should not be a problem, both lines expect the same electrical behaviour in I2C standard.

Q1: So why did TI name these pins definitely? is there anything else inside it's logic forbidding or geopardizing this functional pin swap? the datasheet doesn't mention any as far as i can see.

Q2: Is there (, for magic!,) any known alternate part coming in R-PDSO-G8 package with same pinout but able to perform I2C 400 Khz level translation from 3.3V on side A to 1.8V on side B? 

Thanks

Francesco

  • 0
    TI__Mastermind 48195 points

    Hi Francesco,

    I'm sorry to hear about the mix-up. Your initial solution of flipping the device looks like a good solution.

    Q1: So why did TI name these pins definitely? is there anything else inside it's logic forbidding or geopardizing this functional pin swap? the datasheet doesn't mention any as far as i can see.
    The SDA and SCL channels are electrically identical in this device. Either pin combination can be used for SDA or SCL I2C signals. I believe the pins are labeled to clearly describe their use as I2C pins as other naming conventions may cause more confusion. 

    Q2: Is there (, for magic!,) any known alternate part coming in R-PDSO-G8 package with same pinout but able to perform I2C 400 Khz level translation from 3.3V on side A to 1.8V on side B?
    Unfortunately we don't have an alternative device with this swapped pinout. I believe the 180 degree rotation will be the best solution if swapping the GND and OE connections is possible. 

    Let me know if you have any other questions. Please share what solution you end up using.
    Regards,
    Eric

  • 0 in reply to Eric Schott1
    Prodigy 250 points

    Thanks Eric!   I'll try flipping the chip, am quite sure it will work perfectly.

    In a few days the boards will be at mine for hw debug: as soon as power section will be working i'll confirm everything's ok with I2C and this mod. . Should i face any problem, will  obviously report everything here.

    Don't know wether i'd better close this post (at the moment it seems the case) or wait until the end of story.  ..?

    Bye,

    F.

    PS: if only EN pin had been negative logic!!  (eventually with an internal pullup to VccA):  the chip would be perfectly reversible!. And i guess other situations may exist (apart mistakes like mine) where this could show useful .. 

  • 0 in reply to Francesco Cavalieri
    TI__Mastermind 48195 points

    Hi Francesco,

    Sounds good. This thread will automatically lock after 30 days, but until that point you can continue to add to it. If it does lock, you can link to this thread in a new one or use the "Ask a related question" button. 

    I'm looking forward to hear about this solution. I agree it would be nice if the chip was even more reversible. Unfortunately pinouts are often subject to industry standards for pin-to-pin compatibility so it's tricky to change. I wouldn't be surprised if we see more and more reversible pinouts in newer simple devices. 

    Regards,
    Eric

  • 0 in reply to Eric Schott1
    Prodigy 250 points

    Hi, i finally tried the boards with the TCA9406 traslators reversed and consequently swapped SDA/SCL lines.

    It worked perfectly during some hours of communications between about ten different peripherals and two different, independent masters creating asynchronous telegrams with continuous hardware conflictsv that never hanged any of connected devices.

    Thank you for supporting!

    Bye

    Francesco