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ISO1212: Diode threshold and resistor power rating

Francisco Fernandez
Prodigy 130 points
Part Number: ISO1212

Hi

1. If we chose: Rsense (560ohms), Rthreshold (1K) and Rshunt(100K). Which resistor size would you recommend for Rthreshold and Rshunt? We would like to know so we can properly choose the power rating of the resistors.

2. How is ISO1212 handling voltage transients above the 60VDC limit?

3. If we use the Zener diode approach, how do we calculate the Rthreshold value? The threshold calculator doesnt consider this approach. Wich would be the high threshold voltage and low threshold voltage with a 1K threshold resistor and a 30VDC TVS? We are interested of using this part number with the lowests input VDC voltage

Thanks

  • 0
    TI__Mastermind 26765 points

    Hello Francisco,

    Thanks for reaching out. 

    1. The answer depends on your application. In general, the device application should not exceed 1070mW (6.8 Safety Limiting Values). I would reccomend sizing the resistors to handle at least 1W. For more information on selecting Rsense, Rthr and Rshunt, please see How to Design Isolated Comparators for ±48V, 110V and 240V DC and AC Detection (Rev. A)
    2. I assume this is for the Vinx and Vsensex pins. Voltages applied to these pins above 60V may cause damage to the device. In general, please see the table 6.1 for the Absolute maximum values rated for the device. 
    3. Using a diode approach, a 30VDC TVS diode will clamp the voltage at 30V. When using the calculator, I would recommend letting the "module input voltage value" be the Vclamp of the TVS diode. The calculator also has a recommended set of values for this use case.
      1.  
      2. If I have misunderstood something, please let me know. 

    I hope this helps. 

    Best,
    Andrew