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TIDA-00012: About load current

tsuyoshi tokumoto
Expert 2630 points
Part Number: TIDA-00012
Other Parts Discussed in Thread: ISO1176, ISO3086, ISO1050, TPS55010

Hello team,

 I am considering a RS485 circuit by using a ISO3086 instead of the ISO1176 besed on the TIDA-0012.
  *The ISO1050 is not used.

 Please let me ask you a question about TIDA-0012.

 Q1) When the ISO3086(1Mbps) is used instead of ISO1176 without ISO1050 on the TIDA-0012, 
        could you please tell me how much current can be supplied at 3.3V(Primary side)?
   
        I am concerned that the voltage of 3.3V falls below 3.15V or the voltage of
        5V(Secondary side) falls below 4.5V when a high current flows,
        because there is the possibility that the 3.3V is used for other circuit.

 
Sincerely,
Tsuyoshi Tokumoto

  • 0
    TI__Intellectual 1210 points

    Dear Tsuyoshi Tokumoto,

    thank you for using the E2E forum!

    If I get you correct you want to know the maximum current that is flowing into the supply pins of the device.

    These values are specified in the section 6.10 in the datasheet:


    These are the specified values under no bus load.

    The typical values under load can be found in the datasheet section 6.14:
    For 1Mbps that would be:
    about 50mA Ivcc2, 6mA Ivcc1 with load
    and 12 mA Ivcc2, 6mA Ivcc1 with no load



    Please let me know if you have further questions.

    Best Regards,
    Matthias

  • 0 in reply to Mat1980
    Expert 2630 points

    Dear Matthias-san,

      Thank you very much for your prompt reply.
      I am sorry I didn't explain it clearly enough.

      My customer is considering a isolated RS485 circuit now.
      Currently,there is a non-isolated back converter(5V to 3.3V) before the isolation circuit.
       If it is possible to design an isolated power supply in the form of
       taking in the back converter by using tps55010,it will be a proposal that is
       beneficial to customer.

       From the above,I want to use the 3.3V as a power source for other external circuits.
       Is it possible to supply approximately 100mA from 3.3 V to the external circuits?
          *Please see the attached file.

    simplified schematic.xlsx

         Please lend your expertise.

    Thank you and best regards,
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    Expert 2630 points
    Dear Matthias-san,

    I'm sorry,there was typo on previous post.
    　　back ⇒ buck

    Thank you and best regards,
    Tsuyoshi Tokumoto
  • 0 in reply to tsuyoshi tokumoto
    TI__Intellectual 1210 points
    Dear Tsuyoshi-san,

    thank you for your clarifications. I now better understand your question.

    What will be the input voltage on the VIN of the TPS55010? Is there a tolerance on VIN we need to take into account?

    As mentioned above the ISO3086 needs typical 50mA on the secondary side in normal opperation at the speed you specified.
    However the maximum output short circuit current is 200mA, so it will get close to the .

    I also reached out to our isolated DCDC experts to help out and give their opinion on the power requirements.

    Best Regards,
    Matthias
  • 0 in reply to Mat1980
    Expert 2630 points
    Dear Matthias-san,

    Thank you very much for your prompt reply.
    The range of Vin is 4.75V to 5.25V.

    Thank you and best regards,
    Tsuyoshi Tokumoto
  • 0 in reply to tsuyoshi tokumoto
    TI__Mastermind 35115 points

    Hi Tokumoto-san,

    I support the TPS55010 and have taken a look at this. I do not see any issue with having 100 mA primary load and 50 mA secondary load in this design. Adding to the primary primary load current just introduces a DC offset in the transformer current and this design is very far away from the peak current limit of the TPS55010. This design could potentially support as much as 1 A of load current on the primary side.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Expert 2630 points

    Hi Anthony-san,

      Thank you very much for your prompt reply.
      Your comment is very helpful for me!

      I will propose TPS55010(Fly-Buck topology) to my customer.


    Thank you and best regards,
    Tsuyoshi Tokumoto