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ISO1212: A resistor divider before Rthr to increase Vin_max capacity

Prodigy 70 points

Replies: 4

Views: 158

Part Number: ISO1212

Hi,

I have used ISO1212 for my design of voltage monitoring. 

Input range of Voltage Vin is 19V to 58V. So the threshold for Vin can be set to around 17~18V. 

With Rthr of 2900ohm, we can set threshold to around 17V. But With this the max allowable votlage at Vin is 65V considering drop across Rthr. So when The surge is applied I will not be able to find the TVS with clamp voltage between 58V to 65V. 

So I thought of using Rshunt and bring the threshold down to around 12V~13V so that I can push Vmax to around 85V. But with this configuration, I need Rthr of around 1k and Rshunt of 2.9k which shall increse the losses in 1k resistor at 58V Vin. 

So As an alternate I thought of using external divider before Rthr of 1K to reduce the voltage at Rthr. But here, If i use hight value resitors like 10k or 40k range keeping the ratio match so that i get threshold of around 12V, I am not able to get the output at 19V input. Attached is simulation of same for reference. 

Please suggest solution.Input_V_Monitoring_Using_Divider.TSC

  • Ankit,

    What is the voltage of your system ? (Vdd1 from the simulation) Rtht and Rshunt would already form a voltage divider. What about adding a capacitor (Cin from the datasheet)? In your simulation file, is R3 serving a purpose? Is your question primarily surrounding R1, R11, and R4? 

    Respectfully,

    Lucas

  • In reply to Lucas Schulte9:

    Hi Ankit,

    Please let us know if the post above is helpful and whether assistance is still required with your ISO1212 system.


    Thank you for your time,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Ankit,

    This thread will be closed now. For continued assistance, please feel free to create a new thread or ask a related question using the red and yellow buttons in the top right corner of this window.


    Best,
    Manuel Chavez

  • In reply to Manuel Chavez:

    Hi Chavez,

    Sorry for delayed response. 

    I think the variation of Threshold from Component to component due to process is the limiting factor here. As I need a very tight Threshold. So for the purpose i am using TL431 with an optocoupler to get the tight threshold at higher input voltage. 

    For lower voltage input, I have got recommendation from Local TI representative that I can divide Rthr in two seperate resistors and connect TVS of 100V clamp between two. Which will help to reduce the effect of surge voltage.

    This was helpful. 

    Thank you

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