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ISOW7741: What is your design suggestions to reduce radiating emission in our design concept?

Part Number: ISOW7741

We are building a compact device where it needs to log the CAN bus data. We have chosen the TACN1042 CAN transceiver and ISOW7741 digital isolator. Since the solution needs to be compact and cost-effective we wanted to have an option on our board where we can skip populating ISOW7741 when we do not need it. In ordered to achieve this goal we have 2 options with us. One to extend traces below the ISOW7741 IC or take a traces bottom side of the PCB through the via holes and keep it available to mount jumpers (0E) to establish the direct path between CAN transceiver and MCU(Microcontroller unit). I have read all the design guidelines from the ISOW7741 datasheet and it is quite challenging to achieve in our system. Can you please give us your view on our design concept? 

There is one more question about the efficiency of the power conversion in ISOW7741. The datasheet says it requires 5V - 600mA current to get a full 5V 110mA output. What is the efficiency of this integrated power converter of ISOW7741?

Looking forward to your valuable feedback and answer.

Thanks,

Ravi

  • Hi Ravi,

    Thanks for your interest in ISOW7741 and for going through the guidelines in datasheet.

    Regarding the method to choose for leaving provision to bypass ISOW7741 when it is not needed, using 0Ω resistors should keep the solution compact compared to using berg headers and jumpers. I am assuming the isolation requirement is only to reduce the ground potential difference and there is no stringent isolation working voltage rqeuirement. If this is the case, then you can have traces run right underneath ISOW7741 on the same layer as device while making sure the 0Ω resistor footprints provide some spacing to maintain isolation. This allows you to mount either the ISOW7741 or the 0Ω resistors while avoiding the need for vias.

    While following the above approach, you should be able to follow other PCB layout guidelines mentioned in datasheet for optimum radiated emissions results. If you do need to meet some minimum working voltage and isolation requirements, then let me know. In such a case, it can be challenging to leave a provision for bypassing ISOW7741.

    There is one more question about the efficiency of the power conversion in ISOW7741. The datasheet says it requires 5V - 600mA current to get a full 5V 110mA output. What is the efficiency of this integrated power converter of ISOW7741?

    The 600mA current referred here is for meeting the peak current requirements and not an average or a steady state current. If the power supply can support required average current while still supporting 600mA peak current then the average current rating of input power supply can be lower. If there is sufficient input decoupling capacitor at VDD pin then the current rating can be further lowered. The efficiency of device is 45% typical, as stated in the datasheet. Thanks.


    Regards,
    Koteshwar Rao

  • Hi Mr. Koteshwar Rao,

    Thanks for your quick response. 

    The power distribution unit in our design can only provide 4.4V. I'm aware that the operating voltage for 5V operation is 4.5 - 5.5V. Still, I want to explore 4.4V for 5V operation. What is your opinion on this experiment?. If this won't work do you recommend the TPS613222ADBVR boost converter option we have chosen? 

    Regards,

    Ravi

  • Hi Ravi,

    Thanks for sharing additional details related to the requirements. ISOW7741 will not be able to support 4.4V, although, the device might operate at room temperature we do not guarantee device operation across temperature and across units. Hence, it is best make other change to arrange 5V to ISOW7741.

    Yes, using a boost converter to boost up the voltage should be one good option. TPS613222 does sound like a good option to boost up the voltage, you might still want to post a question on Power Management Forum asking for the right device for your requirement. This way, you will get the right device recommendation from the right folks. Thanks.


    Regards,
    Koteshwar Rao