ADCMP350 Vcc=0 V+>0

I have to supply rails: an adapter AC/DC and one USB. They are ORed together through diodes. I want to support 5V adapters (if it is connected the USB power is turned off) so if the voltage is greater than 4.5V on the adapter side I disable the USB power through a switch. ADCMP350 is powered from the USB side but the input is tied to the adapter side. However there might be a situation where the USB is not connected but the adapter is. In this case the device is not powered however the input is driven (high resistance - resistor divider).

I have the following question: what happens if ADCMP350 comparator is not supplied but there is some voltage through a resistor divider in its non-inverting input? Will be the output determined? Can I damage the device in this way?

According to the datasheet in normal conditions the input voltage can be much more greater than the supply but I don't know if it is true when the power is off.

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  • Thank you.

    Unfortunately the adapter voltage can be greater than 5V (<26V) so it is not possible to connect there as Vcc,max is 5.5V. (I use high input range Switching PSU) The output of this comparator is connected (with pullup) to another IC's input (logic).

    I think I will put a FET to the upper side of the resistor divider and I turn it off when USB power is not available.

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  • Thank you.

    Unfortunately the adapter voltage can be greater than 5V (<26V) so it is not possible to connect there as Vcc,max is 5.5V. (I use high input range Switching PSU) The output of this comparator is connected (with pullup) to another IC's input (logic).

    I think I will put a FET to the upper side of the resistor divider and I turn it off when USB power is not available.

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