Method and apparatus for current limitation in voltage regulators
A circuit for limiting a power current from a power-controlling pass device, the power-controlling pass device being coupled to a supply voltage, comprises the following. A sense device is coupled to the supply voltage with the sense device being configured to draw a sense current that is proportional to the power current. A current mirror is coupled to the sense device and the supply voltage through a low impedance node, the current mirror being configured to draw a mirror current through the low impedance node that is relative to the sense current. A limiting device is coupled to the supply voltage, the power-controlling pass device, and the low impedance node, the limiting device being configured to limit the power current according to a voltage difference between the low impedance node and the supply voltage.
1. A circuit for limiting a power current from a power-controlling pass device, the power-controlling pass device coupled to a supply voltage, comprising:
a sense device coupled to the supply voltage, the sense device configured to draw a sense current that is proportional to the power current;
a current mirror coupled to the sense device and coupled to the supply voltage, the current mirror configured to draw a mirror current that is relative to the sense current;
a resistor coupled to the supply voltage and to the current mirror, the resistor configured to carry the mirror current and generate a resistor voltage potential; and
a limiting device coupled to the supply voltage, the power-controlling pass device, and to the resistor, the limiting device configured to limit the power current according to the resistor voltage potential.
2. The circuit of claim 1 , wherein the sense device is smaller than the power-controlling pass device.
3. The circuit of claim 2 , wherein the proportion of the sense current to the power current is the same as the proportion of the size of the sense device to the size of the power-controlling pass device.
4. The circuit of claim 3 , wherein the limiting device, the sense device and the power-controlling pass device are MOS transistors.
5. The circuit of claim 1 , wherein the sense device is further coupled to the power-controlling pass device and to the limiting device, the limiting device configured to limit the sense current according to the resistor voltage potential.
6. The circuit of claim 1 , wherein the mirror current is approximately the same as the sense current.
7. The circuit of claim 1 , further comprising an amplifier coupled to the sense device, the power-controlling pass device, and the limiting device, the amplifier having a saturation voltage.
8. The circuit of claim 7 , further configured to function in three states, normal operation, overcurrent operation, and short circuit operation, normal operation occurring while the amplifier operates below its saturation voltage.
9. The circuit of claim 8 , wherein the sense device, the power-controlling pass device, and the limiting device are MOS transistors, wherein the amplifier is coupled to the gate of the power-controlling pass device.
10. The circuit of claim 9 , further configured to respond to overcurrent operation, which occurs when the amplifier reaches its saturation voltage and the power current increases, by clamping voltage at the gate of the power-controlling pass device using the limiting device.
11. The circuit of claim 10 , further configured to respond to overcurrent operation with the limiting device in saturation.
12. The circuit of claim 9 , further configured to respond to short circuit operation, which occurs when the power-controlling pass device operates in saturation, by having the power-controlling pass device drop the power current to approximately zero.
13. A circuit for limiting a power current from a power-controlling pass device coupled to a supply voltage, the circuit comprising:
a sense device coupled to the supply voltage, the sense device configured to draw a sense current that is proportional to the power current;
a current mirror coupled to the sense device and coupled to the supply voltage through a low impedance node, the current mirror configured to draw a mirror current through the low impedance node that is relative to the sense current; and
a limiting device coupled to the supply voltage, the power-controlling pass device, and the low impedance node, the limiting device configured to limit the power current according to a voltage difference between the low impedance node and the supply voltage.
14. The circuit of claim 13 , wherein the sense device is smaller than the power-controlling pass device.
15. The circuit of claim 14 , wherein the proportion of the sense current to the power current is the same as the proportion of the size of the sense device to the size of the power-controlling pass device.
16. The circuit of claim 15 , wherein the limiting device, the sense device and the power-controlling pass device are MOS transistors.
17. The circuit of claim 13 , wherein the sense device is further coupled to the power-controlling pass device and to the limiting device, the limiting device configured to limit the sense current according to the voltage difference between the low impedance node and the supply voltage.
18. The circuit of claim 13 , wherein the mirror current is approximately the same as the sense current.
19. The circuit of claim 13 , further comprising an amplifier coupled to the sense device, the power-controlling pass device, and the limiting device, the amplifier having a saturation voltage and configured to limit the power current.
20. The circuit of claim 19 , further configured to function in three states, normal operation, overcurrent operation, and short circuit operation, normal operation occurring while the amplifier operates below its saturation voltage.
21. The circuit of claim 20 , wherein the sense device, the power-controlling pass device, and the limiting device are MOS transistors, wherein the amplifier is coupled to the gate of the power-controlling pass device.
22. The circuit of claim 21 , further configured to respond to overcurrent operation, which occurs when the amplifier reaches its saturation voltage and the power current increases, by clamping voltage at the gate of the power-controlling pass device using the limiting device.
23. The circuit of claim 22 , further configured to respond to overcurrent operation by operating the limiting device in saturation.
24. The circuit of claim 21 , further configured to respond to short circuit operation, which occurs when the power-controlling pass device operates in saturation.
25. A method for limiting a power current from a power-controlling pass device coupled to a supply voltage, the method comprising:
generating a voltage potential between the supply voltage and a low impedance node; and
limiting the power current with a limiting device based on the voltage potential.
26. The method of claim 25 , further comprising:
sensing the power current with a sense device coupled to the power-controlling pass device.
27. The method of claim 26 , further comprising:
drawing a sense current with the sense device, the sense current proportional to the power current.
28. The method of claim 27 , wherein the sense device is smaller than the power-controlling pass device and the sense current has the same proportion to the power current as the sense device has to the power-controlling pass device.
29. The method of claim 27 , further comprising:
drawing a mirror current with a current minor coupled to the sense device, the mirror current relative to the sense current.
30. The method of claim 29 , wherein the mirror current is approximately equal to the sense current.
31. The method of claim 29 , further comprising:
drawing the mirror current through the low impedance node.