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Does Isolated can transceiver (ISO1050) need isolated supply?

stevenh
Guru 20045 points
Other Parts Discussed in Thread: ISO1050, SN65HVD1050

Hello,

I am taking over the design from another engineer who has left the company.

The design contains an isolated CAN transceiver (part number ISO1050) connected to a uC and and external port on the PCB.  

The design currently has GND1 and GND2 connected to the same ground, VCC1 connected to 3.3V and VCC2 connected to 5V.

Isn't it incorrect to have the two grounds connected together?  I am thinking that the 5V should be isolated with its own ground.  Is that correct and why is it correct?

What's interesting is that the board does have isolated 5V 150mA supply having its own isolated ground, but it wasn't used for the CAN transceiver.  it was used for a RS232 transceiver that sinks a maximum of 15mA to 20mA.  I am thinking about using the isolated 5V for both the RS232 and the isolated CAN transceivers.  I don't think there should be much of an issue since the total current would be 93mA (  73mA max for CAN and 20mA for RS322)? What do  you think?

Thanks,
Stephen

  • 0
    TI__Guru 55815 points

    Hi Stephen,


    ISO1050 (Isolated CAN) is generally chosen in place of SN65HVD1050 (Non-Isolated CAN) to primarily provide isolation between system and the external CAN bus. Hence both the grounds shouldn't be connected to each other, though the device would still work fine.

    Regarding your other question of using power supply of RS-232, I am assuming your RS-232 device is a non-isolated RS-232. If this is true, the device should only have one VCC and the GND of this device would be shared with the uC. If the device is isolated RS-232, then I wouldn't recommend connecting the same supply to both RS-232 bus and CAN bus. Any disturbance in one could get coupled and interfere with the other.



    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Guru 20045 points

    Thanks.

    Stephen