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ISOW1412: Short circuit protection

Shotaro Sakai
Expert 3980 points

Part Number: ISOW1412

Hello team,

For short circuit protection, datasheet mentions as below. What's the difference? Is it just typ or max/min value?

Best regards,

Shotaro

  • 0
    TI__Guru 57485 points

    Hi Shotaro-san,

    Thanks for reaching out.
    As you already stated, 250mA is the max current limit value while 180mA is a typical value. I hope that clarifies, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Expert 3980 points

    Hello Rao-san,

    Thank you for the comment. I understood.

    I have an addental question regarding the value of Idd when short circuit occurs.

    If short circuit happens, Ios value is 180mA(typ). In this case, Idd value from primary DC/DC is increased up to 180mA / 46%=544mA?

    Best regards,

    Shotaro

  • 0 in reply to Shotaro Sakai
    TI__Guru 57485 points

    Hi Shotaro-san,

    Your understanding is correct. During the short-circuit condition, the driver current is typically going to be about 180mA and the IDD current will correspondingly going to higher based on the efficiency. When MODE = HIGH, IDD will be about 544mA as the input voltage and output voltage are the same. When MODE = LOW, the input voltage and output voltage are going to be different and efficiency should be used with input and output power values to get the input current estimated.

    i.e., POUT = 3.3V * 180mA; PIN = 5V * IDD; Efficiency = 46%
    Rearranging, IDD = POUT / (Efficiency * VDD) = 258mA

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


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 10 points

    Hello Koteshwar Rao,

    shouldn't efficiency be better than 46% if MODE=HIGH (VDD=5V --> VISOOUT=5V)?

    The datasheet states short-circuit output current only for VISOOUT=3.3V, what could be expected for VISOOUT=5V?

    How do you get 544mA?

    Regards,

    Thomas

  • 0 in reply to Thomas
    TI__Guru 57485 points

    Hi Thomas,

    Welcome to TI E2E Forum!

    Thomas said:
    shouldn't efficiency be better than 46% if MODE=HIGH (VDD=5V --> VISOOUT=5V)?

    The typical efficiency of ISOW1412 for output voltages of both 3.3V and 5V is 46%.

    Thomas said:
    The datasheet states short-circuit output current only for VISOOUT=3.3V, what could be expected for VISOOUT=5V?

    The short-circuit output current is the same for VISOOUT = 5V as well, i.e., 180mA typical.

    Thomas said:
    How do you get 544mA?

    Sorry, I didn't calculate the input current for 3.3V to 3.3V voltage configuration, I just used the value 544mA from previous post (see below). But I see now that the calculated value is incorrect. The actual input current is going to be 391mA (=180mA / 0.46). Apologies for not double checking this.

    Shotaro Sakai said:
    If short circuit happens, Ios value is 180mA(typ). In this case, Idd value from primary DC/DC is increased up to 180mA / 46%=544mA?

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


    Regards,
    Koteshwar Rao