IL710 digital isolator series


I am trying to power the input side of a IL710 digital isolator with the input signal while the output side would stay powered on.

While the input side it unpowered and the output side is powered what would be the default state of the output signal?

There was not any available info about this scenario in the IL710 datasheet.

I’m specifically looking for a part that would have a default low output in this scenario, if this part does not fit that criteria could you point me towards similar part that would have a default low output and is readily available for order.


Welcome to the Digi-Key TechForum jessie.i.cziotka.
For the digital isolators, they act like a switch. When you power the input, it will allow power to flow through the output.
Without power going to the input side of the circuit, then power will not flow through the output side of the circuit.

Hi jessie.i.cziotka,

I am not certain whether the default state of the outputs are defined when the input side Vdd1 is unpowered, but on page 8 of the datasheet it states the following:

Signal Status on Start-Up and Shut Down
To minimize power dissipation, input signals are differentiated and
then latched on the output side of the isolation barrier to reconstruct
the signal. This could result in an ambiguous output state
depending on power up, shutdown and power loss sequencing.
Therefore, the designer should consider including an initialization
signal in the start-up circuit. Initialization consists of toggling the
input either high then low, or low then high.

This implies to me that it is undefined under the condition you describe. I’ll see if I can find a similar device which clearly defines the default state under conditions of no power on input supply.

Do you have any specific requirements for isolation, data rate, power supply, transient immunity, etc.? Also, how much current can you supply on the digital input pin?

Scenarios like this would appear well-adapted to the use of a logic-output optoisolator. These are a flavor of the common LED-input opto that provide a buffered, logic-compatible signal at the output, as opposed to a plain transistor or SCR output.

The more modern/complex digital isolation devices are typically designed to have power on both sides, and aren’t really designed or characterized for the sort of operation I understand to be described. While the logic-output opto devices don’t have the same sort of top-end speed capabilities as digital isolators, they do have the advantage of being quite common, with good potential for multiple sources of supply. If a high data rate is required, products that provide an isolated power supply (such as ADI’s IsoPower products) might be an option.

Hi jessie.i.cziotka,

I found some isolators that have defined outputs with unpowered input side, some with default High and some with default Low outputs.

Logic Low output when input unpowered:

The following have default High outputs when the input is unpowered. Not ideal, but this could be solved by feeding the output into an inverting circuit.

Logic High output when input unpowered: