Current sense circuit with adaptive common mode voltage adjust and associated method thereof

A switching circuit having an input port and an output port, wherein the output port is configured to provide a switcher output voltage, the switching circuit comprising:

• a switch, coupled between the input port and the output port, and the switch is configured to be turned ON and turned OFF to regulate the switcher output voltage;
• a sensing resistor, having a positive terminal and a negative terminal, wherein the positive terminal is coupled to the switch, and the negative terminal is coupled to the output port, a target current flows through the sensing resistor from the positive terminal to the negative terminal;
• and
• a current sense circuit, having a first input port, a second input port and an output port, wherein the first input port is coupled to the positive terminal of the sensing resistor, the second input port is coupled to the negative terminal of the sensing resistor, and the current sense circuit is configured to amplify a differential voltage across the sensing resistor and provide an output voltage at the output port of the current sense circuit in response to the target current, wherein the first input port and the second input port of the current sense circuit has a common mode voltage with respect to a reference ground, and wherein the current sense circuit is configured to adaptively adjust the common mode voltage based on the switcher output voltage;
• wherein
• when the switcher output voltage is lower than a minimum common mode voltage, the current sense circuit is configured to lift the common mode voltage by generating a first adjusting current to the first input port of the current sense circuit and generating a second adjusting current to the second input port of the current sense circuit.

A method for sensing a target current flowing through a sensing resistor, wherein the sensing resistor has a positive terminal and a negative terminal, the method comprising:

• sensing a differential voltage across the sensing resistor by a first operational amplifier, the first operational amplifier having a first input terminal coupled to the positive terminal of the sensing resistor, a second input terminal coupled to the negative terminal of the sensing resistor, and an output terminal, wherein the first input terminal and the second input terminal of the first operational amplifier has a common mode voltage with respect to a reference ground;
• coupling a first transistor to the first operational amplifier, the first transistor having a control terminal, a first terminal and a second terminal, wherein the control terminal is coupled to the output terminal of the first operational amplifier, and the first terminal is coupled to the first input terminal of the first operational amplifier;
• providing an output voltage at the second terminal of the first transistor in response to the target current;
• and
• adaptively adjusting the common mode voltage when a voltage at the negative terminal of the sensing resistor is lower than a minimum common mode voltage, wherein the minimum common mode voltage varies with the differential voltage across the sensing resistor.