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ISO6442: Is it possible to achieve a "default output state low" behavior by using a 10k ohm pull down on the IN pin?

Adam Torma
Mastermind 45780 points

Part Number: ISO6442

e2e, 

The ISO6442 and ISO6442F differ in the internal pull-down and pull-up circuits, respectively.

Is it possible to achieve a “default output state low” behavior by using a 10 kohm pull down on the IN pin of the ISO6442? 

image.png

 

Thank you,

Adam

  • 0
    TI__Mastermind 20600 points

    In theory sort of.  For loss of input signal the stronger pull down would work to force the input low over the integrated weaker pull up, but it creates a resistor divider at the input and will always burn current through the integrated and external pull up/down paths.  However, if the input side loses power, the output side will still have an integrated default output high (for the device without F suffix), so externally adding a pull down only partially changes the system default behavior. 

    Why not use the F or non F version with the desired default state integrated into the device to match system requirements? 

    If functional safety is required, by adding the external path and current paths it will complicate the system FuSa analysis, increase the system FIT and add new failure modes from the added external components.