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ISOW7821: Step down recommendation and short circuit maximum current

Adrian Ymeraj
Expert 3820 points

Part Number: ISOW7821
Other Parts Discussed in Thread: TPS560200, TL331

Hello team,

my customer is planning to use the ISOW7821 in their new design but are struggling to find a good step down converter that could provide the 5V to the ISOW7821.

Do you have any recommendation? Maybe you have already seen some of the most popular buck used in combo with this device. As a first choice we are thinking of using the TPS560200 but if you have any suggestion, please let me know. If not, I'll try to ask on the power  management forum starting from the specs required by the ISOW.

Also, the ISOW7821 is protected against short-circuit at the output but the maximum DC current is not shown: for 5V -> 5V application I find in the DS an indication of a typical DC current of 137mA (but not exactly the maximum).
         I ask you if there is a maximum current data or if it is more appropriate for me to have a limitation on the primary (Vcc side of ISOW7821); in case I thought of using a TL331 comparator with input shunt, hysteresis and output driving the Enable of the TPS560200.

Please let me know what you think or if you have any suggestions.

Thank you and best regards,

Adrian

  • 0
    TI__Intellectual 2325 points

    Hi Adrian,

    • Do you have a block diagram or the larger requirements of the end-equipment? That will help us narrow down the requirements for the supply buck. My starting suggestion would be to choose one with low output ripple, either directly from the part itself, or through appropriate LC values.
    • For the maximum DC current topic:
      • You are correct that the current limit spec is right now spec'd as a typical value of 137mA
      • This will have a finite spread around typical, so I would also consider having a limit on the primary side supply as you indicated [you can choose the current limit of the buck appropriately here]
      • To help with the above bullet, there is a guidance provided in the form of a max value specified in Section 7.8 [Safety limiting values]. This needs to be taken care of at the system level, so if you chose a supply with the right limit, it will help here.
      • For completeness, we also need to know what the end application needs. what is the typical operating load current desired? Note that in 7.10, we document the worst case minimum current that the ISOW can still deliver externally to a load, which is ~130mA.

    Once the requirements are clear, checking with the power management forum can also help you get additional feedback.

    Regards,

    Abhi

  • 0 in reply to Abhi Aarey
    TI__Intellectual 2325 points

    Hi Adrian,

    Any follow-up thoughts on the above? Or did you decide to go with the TPS560200...?

    Regards,

    Abhi

  • 0 in reply to Abhi Aarey
    TI__Expert 3820 points

    Hi Abhi,

    sorry but I'm still waiting for a feedback from the customer. I'll update you in case anything changes for sure.

    Thanks again for checking in!

    Best regards,

    Adrian

  • 0 in reply to Adrian Ymeraj
    TI__Genius 17100 points

    Hi Adrian,

    Please let us know our customer's thoughts! If there is no response soon, this thread will be closed, however you may reopen it or ask a new/related question using the red and yellow buttons in the top right corner of this window.


    Thank you,
    Manuel Chavez