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ISOW7841: 3.3V to 5 V isolating Power creation

Part Number: ISOW7841
Other Parts Discussed in Thread: TCAN1042HG, TCAN337,

Hi,

Good Day. I have a customer who is working with ISOW7841. Please see below his query for your reference. Thank you very much.

For a CAN application using TCAN1042HG we do need a 5 V Power Supply on the isolated side.
Primary Side of ISOW7841 is supplied with 3.3V.
PCB is ready - system is working.
Now we discovered a tiny little line in the manual that this operation mode "is not recommended".
Question: Our system so far works fine with the "not recommended" settings. What problems will we have to face ?
For a re-design we consider the TCAN337, but this device is not as protected on the CAN bus-side as the TCAN1042HG.
Please explain the situation and potential issues coming up under which conditions ( i.e. temperature, current drawn )

Section 9.4 Device Functional Modes of ISOW7841 is the one that customer is talking about not recommended.

Best Regards,

Ray Vincent

  • Hi Ray,

    Thanks for reaching out.

    3.3V to 5V conversion is a boost-mode operation where the input current requirement is going to be significantly higher than the output current drawn. Due to this, the device is not going to output similar currents as it would in all other 3 modes with a combination of 3.3V and 5V. Due to this, 3.3V to 5V boost operation is supported with a limited output current of 40mA as against 130mA in 5V to 5V mode.

    The ISOW7841 datasheet is going to be updated to indicate that 3.3V to 5V boost operation is support but with only 40mA guaranteed output current. This update has already been done for ISOW7841A-Q1, please refer to ISOW7841A-Q1 datasheet for more details on this mode.

    40mA current support is across temperature and across units. Under typical operating conditions on a typical unit, the device could work at higher loads but at worst-case temperatures on worst-case units, it might not support more than 40mA. Hence, we only recommend using ISOW7841 with upto 40mA of output current for 3.3V to 5V voltage configuration.

    5V CAN transceivers require much higher current than 40mA and hence ISOW7841 might not work with CAN transceivers in this voltage configuration. We recommend you to do one of the following address this challenge,

    1. Use 5V to 5V conversion to support CAN transceiver interface.
    2. If 5V isn't available, use a low-cost non-isolated boost converter to boost 3.3V to 5V before supplying it to ISOW7841.
    3. Use 3.3V to 3.3V conversion and choose a 3.3V CAN transceiver.
      1. Please reach out to Interface Forum for a recommendation of 3.3V CAN transceiver that is similar in performance to TCAN1042HG

    Let me know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao