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ISO7741: ISO7741 internal structure, safety limiting values

Marin Babic
Prodigy 60 points
Part Number: ISO7741
Other Parts Discussed in Thread: ISO7841,

1. In TI app. note "Understanding failure modes in isolators" is described ISO7841, with internal structure consisting of two dies, thus providing reinforced protection.
Does ISO7741 have same internal structure consisting of two dies, for reinforced protection? (Does perhaps "double protection" term which would better describe two-die structure, rather than reinforced protection, if each die provides basic isolation?)
2. In ISO7741, there is table "Safety Limiting Values". If case of some fault state on board, e.g. short to ground when pin current (supply or I/O) is bigger than rated safety current, is it possible that I/O isolation simultaneously fails (on both dies)? Can this scenario be compared with "Fault mode 2" from mentioned app. note?

Best regards,

M.Babic

  • 0
    TI__Guru 55885 points

    Hi Marin,

    I can help you with my inputs to your questions, please find below my response.

    1. Yes, ISO7741 has the same internal structure as ISO7841 consisting of two die each containing one ISO cap and together supporting reinforced isolation. The major difference between ISO7841 and ISO7741 is that the latter has slightly lower isolation specs and marginally lower CMTI performance.
    The terms double protection/insulation and reinforced insulation are generally referred by different standards. In general, double insulation basically comprises of basic insulation and supplementary insulation. Whereas reinforced insulation is single insulation that provides the same degree of protection equivalent to double insulation.

    2. The safety limiting values mentioned in the datasheet are relevant for Failure Mode 2 as defined in the white paper titled "Understanding failure modes in isolators". Under Failure Mode 2, a TI reinforced isolator will still maintain basic isolation provided the safety limiting values given in datasheet are not exceeded. If the safety limiting values are exceeded then the exceeded currents raise the temperature of die to very high levels leading to thermal damage of the isolation cap that was providing basic isolation under Failure Mode 2. Hence limiting current to less than the safety limiting values either in the power supply or in the circuit is necessary for better fault protection of the isolated system.

    Thanks.

    Regards,
    Koteshwar Rao