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ISO7840: Behavior when overvoltage is applied

user777540
Expert 1020 points
Part Number: ISO7840
Other Parts Discussed in Thread: ISOW7840,

Hello,

Understanding failure modes in isolators (jajy037) states that EOS damage is limited to high-powered dies.


When using with GND1 and GND2 connected, is the other VCCpin or OUTpin affected when 150V is applied to the INpin or VISOpin?

best regard,

Goto

  • 0
    TI__Mastermind 49345 points

    Hi Goto-san,

    Thanks for reaching out.

    I see that you have referred to VISO pin, ISO7840 doesn't have any pin named as VISO. I am assuming that you are referring to ISOW7840. Either ways, the below explanation is applicable to both ISO7840 and ISOW7840.

    When there is EOS damage, like the document jajy037 states, the damage would be limited to the die where EOS has been applied. This assumes that the EOS voltage is removed immediately after the device damage. If the voltage is not removed, then the EOS voltage can continue forcing high current into device thereby heating it up. If the temperature of the device goes above the maximum rating (150C) then the overall device can get damaged, including the die that is not applied with any EOS voltage.

    Hence, it is important to make sure the EOS stress is not continuous and if it is continuous, then the current into device can be limited according to the specifications provided as "Safety Limiting Values" in datasheet. Such current limits make sure the device temperature is not exceeding above its rated value (150C). This is applicable irrespective of whether GND1 and GND2 are connected together or isolated.

    I also see that you have mentioned an EOS of 150V, this seems like quite high compared to device absolute maximum ratings. Hence, sufficient current limiting is needed to make sure the current into device is not exceeding safety limiting values. Thanks.


    Regards,
    Koteshwar Rao