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ISO7740: there is a high level pulse when the output is enabled.

Part Number: ISO7740


First, the output is disabled, the input is low, and then the output is enabled, but the pulse waveform shown in the figure above will appear.

The main reason is that it is not clear why the low level is input, and there is a high level pulse when the output is enabled?

Do you need to use the default low level, ISO7740F?


Elsa Duan

  • Hi Elsa:

    Thanks for posting your question on E2E.

    ISO7740 (without suffix 'F') is a device with default outputs HIGH. When the EN2 is driven from LOW to HIGH, the outputs will go to their default HIGH state for a brief period of time until the device internal circuits are fully powered. Once the internal circuits are fully powered, the outputs will follow the input logic states. This is what's observed on your scope plot.

    ISO7740F (with suffix 'F') has default LOW outputs. You will not see this output behavior if ISO7740F device is used. However, please note that you may need to use pull-down resistors at the outputs to maintain output LOW when EN2 is driven LOW. EN2=LOW will make the device outputs HI-Z.