• Resolved

ISO7241C: Is the default status of INB high if I leave it floating?

Part Number: ISO7241C

Hi,

I am designing my circuit with ISO7241C. I want pass OSS signal from external MCU to TPS2388 device and the OSS pin is internally pulled down to GND. When I use ISO7241 to pass this signal, I found that if I left the INB open(without pull up or pull down resistor), the INB is high. Is the internal circuit of ISO7241 make that pin high? If I want the default status of OSS is low without any MCU controlled, should I add a pull down resistor? Thanks. 

Best regards,

Penny

 

  • Hi Penny,

    Yes this is correct, the internal circuit of ISO7241 is designed so that the output default state is HIGH.

    I can think of 2 solutions based on your use case.
    1) Use the alternative part ISO7341FC (Basic Isolation) or ISO7741F (Reinforced Isolation). Both theses parts are designed so that all the channels will have default LOW state.

    2) If all channels except the one used for OSS needs to be default HIGH and only OSS needs to be default LOW.
    In this case, continue with the same part (ISO7241C) but add a pull down resistor at the input of the channels used for OSS (INB in schematic).

    Hope this is helpful. Let me know if anything requires additional clarification.

    Regards,
    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Got you, Thanks.

    Best regards,
    Penny