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ISO1212EVM: how to calculate the power consumption of Rthr

Cindy Chang
Intellectual 2475 points
Part Number: ISO1212EVM
Other Parts Discussed in Thread: ISO1212,

Hi,

We found that the Rthr you used for ISO1212 EVM is 0.25W and is AEC-Q200 Grade 1.

Why you need to use 0.25W resistor in this case?

Is there any calculation to let us know the power dissipation of Rthr?

Thank you.

Best Regards,

Cindy

  • 0
    TI__Mastermind 49445 points

    Hi Cindy,

    ISO1212EVM uses RSENSE and RTHR values of 562Ω and 1kΩ, respectively. These values make the inputs meet IEC 61131-2 Type 3 specifications.

    Power dissipation under normal operating conditions is going to be very small and it doesn't require any high wattage resistor. The EVMs are designed also to meet the most common EMC requirements on digital inputs, especially the surge test. RTHR is chosen to be a MELF resistor with 0.25W wattage to meet such EMC requirement as stated in ISO1212 datasheet section 9.2.1.1.

    Regards,
    Koteshwar Rao