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ISO1212: Max value for R_SENSE resistance

Genius 15690 points
Part Number: ISO1212

Hello

What is the maximum resistance value for R_SENSE? Is 562 ohm maximum?
Because SLLC457 excel sheet says that R_SENSE must be less than 562.
I mean what is the minimum current that ISO1212 can control?

Regards,
Oba

  • Oba,

    The recommended max is 562 to achieve the 2.25mA needed for type 1 and 3 systems. 562ohm is just a more common value close to 560ohm and it's than a 1% difference. 562ohms is considered the max allowable Rsense else you choke out the ISO1212. 

    Respectfully,

    Lucas

  • Hello Lucas,

    Thanks for your reply.
    My customer is considering to put the status LEDs on the field side and I'm discussing how to realize it.
    Then if putting LED in parallel like the below, I'm just wonder using this LED current as a part of sink current and removing ISO1212 sink current instead.
    In this case, I just wanted to understand the minimum current that ISO1212 can control.
    I understand 562ohm is the max for Type 1 and 3, but  is it the maximum as ISO1212 device in any cases?

    Regards,
    Oba

  • Oba,

    Yes the max in any case is still 562ohm. The LED wouldn't be taking any current away from the ISO1212 assuming that the supply can provide current for both. What is the reason that the customer wants to put the LED on the field side rather than the output side like in Figure 26 of the datasheet?

    Respectfully,

    Lucas