Patent ID: 7872518

Claim:
A protection circuit for protecting a first voltage domain, the first voltage domain being coupled to a second voltage domain via a series transistor, wherein a conductor of the first voltage domain is connected to a source terminal of the series transistor and a conductor of the second voltage domain is connected to a sink terminal of the series transistor, the circuit comprising: a reference circuit configured to provide a reference signal; a voltage shift resistor connected to the conductor of the second voltage domain; a current provider configured to provide a regulated current flowing through the voltage shift resistor based on the reference signal, wherein the current provider is configured to regulate the regulated current such that a desired voltage difference across the voltage shift resistor is determined by the reference signal; a detection circuit being configured to compare a voltage at a first detection circuit input with a voltage at a second detection circuit input to obtain a comparison result signal, wherein the first detection circuit input is coupled to the conductor of the first voltage domain, wherein the voltage shift resistor is coupled between the second voltage domain and the second detection circuit input, such that the voltage at the second detection circuit input differs from a voltage of the second voltage domain by the desired voltage difference, and wherein the detection circuit is configured to provide the comparison result signal, such that the comparison result signal indicates, whether the voltage difference between a voltage of the second voltage domain and the voltage of the first voltage domain is below the desired voltage difference; and a series transistor regulation circuit coupled to the detection circuit to receive the comparison result signal and configured to adapt a voltage applied to a control terminal of the series transistor, such that a load path resistance of the series transistor is increased in case that the comparison result signal indicates that the voltage difference between the voltage of the second voltage domain and a voltage of the first voltage domain is below the desired voltage difference.