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ISO1044: Isolated Design Dilemma :)

Nicholas Ipri1
Prodigy 210 points

Part Number: ISO1044
Other Parts Discussed in Thread: ISOW1044,

I am designing a small asset tracking device that includes 2 isolated CAN busses. 

I do not have the room on the board for 2 ISOW1044 chips

I could use 2 ISO1044 chips however I dont have the room for an isolated power supply module / external isolation transformer, etc.

I am looking at the possibility of using 2 ISO1044s with a single additional non-isolated power supply e.g. a fixed 5v buck mode supply, for powereing only the CAN side of the 1044's. Although the supply will not be truly isolated as through a transformer, it will be powered by the asset and, as mentioned, it will only power the CAN side of the transceivers. OTOH, the grounds will have to come together at that supply so I will not have ground isolation.

Any suggestions on how to create an isolated supply with very limited board space? or will isolating the CAN bus signals alone be sufficient?

 

 

  • 0
    TI__Genius 15630 points

    Hi Nicholas,

    Thanks for reaching out.

    Apologies but your requirements are not very clear here - do you need isolation at all? 

    Can you please provide a concept block diagram for us to review - showcasing the different grounds and your current plan with 5V buck converter on CAN side.

    We are not able to understand your limitation with respect to supply and how it is coming in between your isolation requirements, if you have it on Side2(CAN side) of the ISO1044.

    A block diagram as asked would help clear things for us.

    Regards
    Varun.

  • 0 in reply to Varun Kumar
    Prodigy 210 points
    Varun Kumar said:
    do you need isolation at all? 

    Don't have a block diagram yet however... our primary application is in "automotive type" equipment, that is, where everything is referenced to a single ground e.g. negative side of the battery (or perhaps positive side in some cases) so I shouldn't have different grounds to worry about. So, isolation likely isn't strictly necessary. I'm primarily concerned about this product being used in corner cases where different grounds >>might<< be an issue so I am simply trying to design the most robust system that I can... although board real-estate is a huge issue as is power consumption... also,  I am finding out that the DC/DC converter topologies use more power than our budget allows. 

    My "compromise" plan was basically to use the ISO1044 to isolate the CANH and CANL signals and use a separate power supply just to power the CAN side of the interface. That power supply would have to be on the same ground as the rest of the system however, so too with GND2 of the ISO1044... which kind of defeats the purpose of isolation anyway.  

  • 0 in reply to Nicholas Ipri1
    TI__Genius 15630 points

    Hi Nicholas,

    Thanks for clarifying.

    Well, in the case of no isolation requirement, you're in the right direction.

    Your proposed approach of using 2 ISO1044 with a separatee 5V supply is the best way to save PCB space - We do not see any red flags here.

    The ISO1044 can work both in Isolated as well as non-isolated condition in the exact same way.

    Regards
    Varun