Measuring the On-Resistance of a Transistor Load Path

A method, comprising:

• applying a control signal to a control terminal of a transistor to switch the transistor into an on-state such that the transistor carries a load current,
• amplifying by a first factor a voltage drop across a load-path of the transistor while the load current is carried through the transistor, yielding a first measurement value,
• digitizing the first measurement value, yielding a first digital value,
• feeding a test current into the load-path of the transistor, such that the test current and the load current are combined;
• amplifying by the first factor a voltage drop across the load-path of the transistor while the combined load and test currents are carried by the transistor, yielding a second measurement value;
• digitizing the second measurement value, yielding a second digital value,
• determining a difference between the first digital value and the second digital value;
• and
• determining a quotient of the difference and a digital representation of the test current.

An apparatus, comprising:

• a measurement device coupled to a transistor and configured to measure a voltage drop across a load-path of the transistor and to generate a measurement signal representing the voltage drop;
• a switchable current source configured to provide a test current to the load-path of the transistor such that the test current and the load current are combined, the current source being switchable on and off in response to a control signal;
• and
• an evaluation device configured to generate the control signal, to store a first instance of the measurement signal representing a measurement of the voltage drop taken by the measurement device while the current source is switched off, and to determine an on-resistance of the load-path of the transistor from the test current, a second instance of the measurement signal representing a measurement of the voltage drop taken by the measurement device while the current course is switched on, and the stored first instance of the measurement signal.

An apparatus, comprising:

• a semiconductor integrated circuit chip, comprising:
• a first chip pin;
• a second chip pin;
• a third chip pin;
• a first amplifier having a first input and a second input, the first input of the first amplifier coupled to the first chip pin;
• a first resistor coupled between the first and second inputs of the amplifier;
• a second resistor switchably coupled between the first resistor and the second chip pin;
• and
• a second amplifier having a first input coupled to the second chip pin and a second input coupled to the third chip pin.