Described is an apparatus which comprises: an input for providing a first voltage signal; a level translator, coupled to the input, to translate the first voltage signal to a second input voltage, the second input voltage having a voltage level higher than a voltage level of the first voltage signal; and an open loop reference core coupled to the level translator, the open loop reference core to receive the second input voltage and to generate an output indicating whether the first voltage signal is above or below a reference level.