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ADUM7442 minimum input frequency

The datasheet for ADUM7442 has the following statement:

"If the decoder receives no internal pulses of more than approximately 5 μs, the input side is assumed to be unpowered or nonfunctional, in which case the isolator output is forced to a default high state by the watchdog timer circuit."

Does this mean a) that if a logic transition is not registered within 5 us, the chip goes output high implying an effective minimum frequency of 200 KHz OR does this mean that b) if the internal DC correctness circuit stops working for some unspecified reason for more than 5 us that the output goes high but that under normal DC input conditions, the DC state can be held indefinitely.

Kind regards,

Bret Bronner

  • Hi Bret, 

    The ADuM7442 is an edge encoded architecture. It will sends a pulse with every incoming edge the input detects. In addition, there is essentially a keep-alive pulse being sent. If the input detects no change of input state, it will send a pulse indicating the dc state of the input and also that the input side is still powered. If the receiving side does not detect any pulses for several us, it will interpret that the input side is unpowered, and go to the default output state. The circuitry is active whenever the input side of the device is powered. And yes, a DC input state can be held indefinitely.