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ISO1042: Isolated AN Transiever

kalana de silva
Prodigy 140 points
Part Number: ISO1042

Tool/software:

Hi,

I am using the ISO1042QDWVQ1 in my design, and I am a bit confused about how to implement this isolated part.

One side of the transceiver connects to my DC-DC MCU (which will act as a slave), while the signals come from the Inverter MCU (which will act as the master).

  1. Please refer to the attached schematic. Does the CAN_GND here need to connect to the other board and the transceiver on the Inverter MCU (master transceiver)?

  2. CANH and CANL will operate at 5V since the transceiver is powered by 5V as per the datasheet. However, the maximum voltage for my STM32 pins is 3.3V. Is there a TI IC available that can interface between the transceiver's CANH/CANL and the MCU to convert the signals to 3.3V?

  3. Or should I be using 4 transceivers to communicate between my 2 STM32 microcontrollers ? 
    (Each MSC gets 2 transceivers, one to send signal and to receive signal) 

  • +1
    TI__Mastermind 29265 points

    Hello Kalana, 

    Thank you for reaching out. The above schematic loos correct. Please remember to include decoupling capacitors on VCC1 and VCC2.  

    1. The CAN physical layer is a differential protocol, and a common ground is not needed between transceivers. The only wires needed are CANH and CANL.
      1. Come cables initially include a cable shield for increased EMC performance.
      2. However, this is normally not connected to the CAN GND. 
    2. CANH and CANL are not meant to be directly connected to an MCU. Another transceiver is needed on the receiving board to convert the differential CANH-CANL signal to single ended Rx for the MCU.
      1. I think the confusion is that the CAN side is meant for the off-board communication and not the logic side (TXD and RXD). Pins 1-4 are meant to be connected closely to an MCU on the same board since these are the sensitive single-ended signals.
      2. The CAN bus is meant to handle the noisy off-board environment 
    3. CAN bus is bidirectional protocol. Therefore only 2 transceivers are needed (one for each board/MCU). You won't need 4 transceivers for transmit and receive.

    Best,
    Andrew