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ISO1212: Insulation Characteristics Curves

Mehran Mehranito
Prodigy 20 points
Part Number: ISO1212

Hello everyone,

I would like to know how can I use the Insulation Characteristics Curves which is mentioned in part 6.11 of the datasheet of the ISO1212?

In the isolated side, the supply of the chip is 3.3V.

In non isolated the input can go up to 60V.

How can I consider the values on this curve in my design and what is the purpose of the curve generally?

Best regards,
Mehran

  • 0
    TI__Guru 52980 points

    Hi Mehran,

    Welcome to TI E2E Forum!

    The curves that you see in Section 6.11 of ISO1212 datasheet are the thermal derating curves for the safety limiting values provided in Section 6.8. These parameters are safety & fault tolerant related and do not directly relate to normal operation of device.

    For normal operation of device, you do not need to consider these values and curves, the device is going to meet all datasheet electrical and switching performances with the recommended schematic and component values.

    The safety limiting values provided in Section 6.8 (also plotted on Section 6.11) are for additional safety of isolation barrier when there is a fault in the system. The isolation barrier of ISO1212 has very good isolation ratings where the device can support working voltage of 566V DC which can be applied across the barrier for its life (>>40 years) and the device still stays intact. Though the isolation barrier is very strong for high voltage, it can still be damaged by unintended system faults. For example, VCC1 supports a max voltage of 5.5V but when 10V or higher is applied to this pin, it can create a short between VCC1 & GND1 and can permanently damage the device. If the current into device is not limited externally under such situations, it can produce enough heat in device that could exceed device junction temperature ratings (TJ = 150C) and melt down the isolation barrier thereby leading to secondary system failures.

    If such system faults are expected and the sources of those failures are not current limited, then you can use the table in Section 6.8 and the curves in Section 6.11 as guidance for currents and power to be limited on to the fault sources. Limiting these currents will make sure the isolation barrier stays intact even under such local failure conditions. Failure to limit current and power will lead to compromise of isolation barrier under such fault conditions.

    The failure conditions are described in detail in the below white paper.
    www.ti.com/lit/slyy081

    The below article talks about safety limiting values in detail and how to implement those in a system.
    https://www.planetanalog.com/signal-chain-basics-154-understand-and-apply-safety-limiting-values-for-digital-isolators/#

    Please note that, these suggestions are optional and help to make the system fault tolerant. These maybe useful if your application needs to meet functional safety requirements.

    Regards,
    Koteshwar Rao