Current sensor with extended voltage range

1. A current sense circuit comprising:

a copy transistor of a first type having a gate terminal configured to be coupled to a gate terminal of an output transistor of the first type, and a drain terminal coupled to an input terminal, the drain terminal of the copy transistor configured to be coupled to a drain terminal of the output transistor;

a first transistor of the first type having a current path coupled to a current path of the copy transistor;

an error amplifier having a non-inverting input terminal coupled to a source terminal of the copy transistor, an inverting input terminal configured to be coupled to a source terminal of the output transistor, an output terminal coupled to a gate terminal of the first transistor, a positive power supply terminal coupled to the input terminal and a negative power supply terminal coupled to a reference supply terminal; and

a current-to-voltage converter having an input coupled to the current path of the copy transistor.

2. The current sense circuit of claim 1 , wherein the current-to-voltage converter is configured to sense a copy current flowing through the current path of the first transistor, and to generate a sense voltage based on the copy current.

3. The current sense circuit of claim 1 , further comprising the output transistor, wherein the gate terminal of the output transistor is coupled to the gate terminal of the copy transistor.

4. The current sense circuit of claim 3 , wherein the output transistor is a power metal-oxide-semiconductor field-effect transistor (MOSFET).

5. The current sense circuit of claim 3 , wherein the first type is n-type.

6. The current sense circuit of claim 3 , further comprising a load coupled to the source terminal of the output transistor.

7. The current sense circuit of claim 1 , wherein the current-to-voltage converter comprises:

a cascode transistor having a current path coupled between the current path of the copy transistor and the current path of the first transistor;

a second copy transistor having a gate terminal coupled to the gate terminal of the first transistor;

a third transistor having a current path coupled to a current path of the second copy transistor;

a second error amplifier having a first input terminal coupled to a source terminal of the third transistor, a second input terminal coupled to a source terminal of the cascode transistor and an output terminal coupled to a gate terminal of the third transistor; and

a current mirror coupled to the third transistor.

8. The current sense circuit of claim 7 , wherein the current mirror is configured to copy a current flowing through the second copy transistor into a sense current.

9. The current sense circuit of claim 7 , further comprising a resistor coupled to the current mirror and an output voltage terminal.

10. The current sense circuit of claim 9 , wherein the resistor is configured to generate a sense voltage at the output voltage terminal based on a sense current flowing through the current mirror.

11. The current sense circuit of claim 7 , further comprising a voltage generator coupled to a gate terminal of the cascode transistor.

12. The current sense circuit of claim 7 , wherein the copy transistor and the cascode transistor are high-voltage transistors, and wherein the first transistor, the second copy transistor and the third transistor are low-voltage transistors.

13. The current sense circuit of claim 12 , wherein low-voltage transistors are transistors implemented with 3 V devices and wherein high voltage transistors are transistors implemented with 16 V devices.

14. A method of sensing current, the method comprising:

providing an output current to a load with an output transistor of a first type having a drain terminal coupled to a first supply terminal, and a source terminal coupled to the load;

copying the output current into a first copy current by keeping a voltage of a source terminal of a copy transistor of the first type equal to a voltage of the source terminal of the output transistor, wherein the copy transistor has a drain terminal coupled to the drain terminal of the output transistor and a gate terminal coupled to a gate terminal of the output transistor;

copying the first copy current into a second copy current by keeping a voltage of a drain terminal of a second copy transistor equal to a voltage of a drain terminal of a first transistor of the first type, wherein the first transistor comprises a current path coupled to a current path of the copy transistor and a gate terminal coupled to a gate terminal of the second copy transistor;

copying the second copy current into a sense current; and

generating a sense voltage based on the sense current.

15. The method of claim 14 , wherein the first type is n-type.

16. The method of claim 14 , further comprising:

providing a first voltage to a cascode transistor having a current path coupled between the current path of the first transistor and the current path of the copy transistor.

17. The method of claim 16 , wherein copying the second copy current into the sense current comprises copying the second copy current into the sense current using a current mirror coupled to a second supply terminal.

18. The method of claim 17 , further comprising:

receiving 12 V at the first supply terminal; and

receiving 3.3 V at the second supply terminal, wherein the first voltage is equal to 1.2 V.

19. An electronic fuse circuit comprising:

a power metal-oxide-semiconductor field-effect transistor (MOSFET) of a first type having a drain terminal coupled to an input terminal and a source terminal configured to be coupled to a load;

a gate driver circuit coupled to a gate terminal of the power MOSFET;

a current sensor circuit coupled to the power MOSFET; and

a controller coupled to the gate driver circuit and further coupled to the current sensor circuit, wherein the current sensor circuit comprises:

a copy transistor of the first type having a gate terminal coupled to a gate terminal of the power MOSFET, and a drain terminal coupled to the input terminal and to the drain terminal of the power MOSFET;

a first transistor of the first type having a current path coupled to a current path of the copy transistor;

an error amplifier having a non-inverting input terminal coupled to the source terminal of the copy transistor, an inverting input terminal coupled to the source terminal of the power MOSFET, an output terminal coupled to a gate terminal of the first transistor, a positive power supply terminal coupled to the input terminal and a negative power supply terminal coupled to a reference supply terminal; and

a current-to-voltage converter configured to:

sense a copy current flowing through the current path of the first transistor, and

generate a sense voltage based on the copy current.

20. The electronic fuse circuit of claim 19 , wherein the first type is n-type.

21. The electronic fuse circuit of claim 19 , further comprising an over-current protection circuit coupled to the current sensor circuit and to the gate driver circuit, wherein the over-current protection circuit is configured to clamp an output current flowing through a current path of the power MOSFET to a predetermined value.

22. The current sense circuit of claim 19 , wherein the current-to-voltage converter comprises:

a cascode transistor having a current path coupled between the current path of the copy transistor and the current path of the first transistor;

a second copy transistor having a gate terminal coupled to the gate terminal of the first transistor;

a third transistor having a current path coupled to a current path of the second copy transistor;

a second error amplifier having a first input terminal coupled to a source terminal of the third transistor, a second input terminal coupled to a source terminal of the cascode transistor and an output terminal coupled to a gate terminal of the third transistor; and

a current mirror configured to copy a current flowing through the second copy transistor into a sense current.

23. The current sense circuit of claim 22 , wherein the copy transistor and the cascode transistor are high-voltage transistors, and wherein the first transistor, the second copy transistor and the third transistor are low-voltage transistors.