System and method for current sensing

A current sensing system, comprising:

• a power transistor having a source coupled to a voltage source for providing a current through the power transistor, and a drain coupled to a load;
• a sensing transistor having a source coupled to the voltage source, and a gate coupled to ground;
• an amplifier having an inverting input coupled to a drain of said sensing transistor and to an output of the amplifier, the amplifier configured to provide a output sensed current having a scaled proportion to the current through the power transistor;
• a third transistor having a source coupled to the voltage source and a drain coupled to a non-inverting input terminal of the amplifier;
• a fourth transistor coupled between the load and the amplifier, the fourth transistor being configured for coupling the amplifier to receive at least some portion of a voltage across the power transistor;
• a driver and timing circuit configured for control of the amplifier, the driver and timing circuit being coupled to a gate of the power transistor and a gate of the fourth transistor, and configured for monitoring the voltage at the drain of the power transistor to determine whether to permit the fourth transistor to provide the at least some portion of the voltage across the power transistor to the amplifier.

A current sensing system, comprising:

• a power transistor having a source coupled to a voltage source for providing a current through the power transistor, and a drain coupled to a load;
• a sensing transistor having a source coupled to the voltage source, and a gate coupled to ground
• an amplifier having an inverting input coupled to a drain of said sensing transistor and to an output of the amplifier, the amplifier configured to provide a output sensed current having a scaled proportion to the current through the power transistor;
• a third transistor having a source coupled to the voltage source and a drain coupled to a non-inverting input terminal of the amplifier;
• a fourth transistor having a source coupled to the drain of the power transistor and a drain coupled to the non-inverting input terminal of the amplifier, the fourth transistor being configured for decoupling the amplifier from receiving a voltage at the drain of the power transistor;
• a driver circuit configured for control of the amplifier, the driver circuit being coupled to a gate of the power transistor;
• and
• a timing logic device for controlling operation of the third transistor and the fourth transistor and being coupled to gates of the third transistor and the fourth transistor and configured for monitoring the voltage at the drain of the power transistor to determine whether to permit the fourth transistor to provide the voltage at the drain of the power transistor to the amplifier.

A current sensing system, comprising:

• a first switch having first, second, and third terminals, wherein the first terminal is coupled to an input voltage and the second terminal is coupled to a driver for control of the first switch, and the third terminal is coupled to a load device;
• a second switch having fourth, fifth, and sixth terminals, wherein the fourth terminal is coupled to the input voltage, the fifth terminal is coupled to ground, and wherein a resistance of the second switch is a proportion of a resistance of the first switch;
• an amplifier having inverting and non-inverting inputs and an amplifier output, wherein the inverting input is coupled to the sixth terminal and the amplifier output;
• and
• a divider circuit comprising a third transistor and a fourth transistor, wherein the third transistor and fourth transistor comprise resistive elements, the third transistor having a source coupled to the input voltage, a gate coupled to ground, and a drain coupled to the non-inverting input of the amplifier, and the fourth transistor having a source coupled to the drain of the third transistor, a gate coupled to the driver for control of the fourth transistor, and a drain coupled to the load device, and wherein the divider circuit is configured for dividing down a voltage across the first switch to facilitate scaling down of a current passing through the first switch being sensed at the output of the amplifier.

A method for sensing current, comprising the steps of:

• driving a first switch to provide a first current;
• mirroring the first current via a second switch coupled to the first switch thereby providing a second current, wherein the second current is a ratio of the first current and the first and second switches are fabricated using substantially the same process;
• dividing the second current via a divider circuit in order to further scale the second current into a third current, wherein the third current is a ratio of the second current;
• and
• detecting the voltage across the first switch via an amplifier, wherein the amplifier provides an output voltage that is proportional to the voltage across the first switch.

A method for sensing current comprising the steps of:

• driving a first switch to provide a current through the first switch to create a voltage across the first switch;
• scaling down the voltage across the first switch and providing the scaled down voltage to an input of an amplifier;
• forcing a voltage across a second switch to be equal to the scaled down voltage of the first switch, the second switch being coupled to another input of the amplifier and an output of the amplifier;
• and
• providing an output sensed current at the output of the amplifier representing a known proportion to the current through the first switch.

A method for fabricating a current sensing system, comprising the steps of:

• fabricating first and second switches on an integrated circuit using substantially the same process, wherein the integrated circuit is configured to:
• drive the first switch to provide a first current;
• mirror the first current via the second switch coupled to the first switch thereby providing a second current, wherein the second current is a ratio of the first current;
• divide the second current via a resistor divider in order to further scale the second current into a third current, wherein the third current is a ratio of the second current;
• and
• detect the voltage across the first switch via an amplifier, wherein the amplifier provides an output voltage that is proportional to the voltage across the first switch.

A current sensing system, comprising:

• a first switch coupled to first and second resistive elements, where the first and second resistive elements scale the current output from the first switch;
• a second switch coupled to the first switch for mirroring the current output from the first switch;
• and
• an amplifier coupled between the first and second resistive elements and the second switch for sensing current, wherein the amplifier includes:
• a third switch coupled to the inverting input of the amplifier;
• a fourth switch coupled to the non-inverting input of the amplifier, wherein the third and fourth switches share a common gate and the fourth switch is diode connected;
• a fifth switch coupled to the third switch and the non-inverting input of the amplifier;
• a first current source coupled to the third and fifth switches;
• a second current source coupled to the fourth switch;
• and
• an output to the amplifier for providing an output voltage.

A current sensing system, comprising:

• a first switch having first, second, and third terminals, wherein the first terminal is coupled to an input voltage and the second terminal is coupled to a driver;
• a second switch having fourth, fifth, and sixth terminals, wherein the fourth terminal is coupled to the input voltage, the fifth terminal is coupled to an amplifier, and the third terminal is coupled to ground, and wherein the current through the second switch is a scaled current through the first switch;
• the amplifier having inverting and non-inverting inputs and an amplifier output, wherein the inverting input is coupled to the fifth terminal and the amplifier output, and wherein the amplifier includes:
• a third switch coupled to the inverting input of the amplifier;
• a fourth switch coupled to the non-inverting input of the amplifier, wherein the third and fourth switches share a common gate and the fourth switch is diode connected;
• a fifth switch coupled to the third switch and the non-inverting input of the amplifier;
• a first current source coupled to the third and fifth switches;
• a second current source coupled to the fourth switch;
• and
• an output to the amplifier for providing an output voltage;
• and
• a divider circuit coupled between the third terminal and the non-inverting input of the amplifier for scaling the current through the first switch.

A current sensing system, comprising:

• a power transistor having a source coupled to a voltage source for providing a current through the power transistor, and a drain coupled to a load;
• a sensing transistor having a source coupled to the voltage source, and a gate coupled to ground;
• an amplifier having an inverting input coupled to a drain of said sensing transistor and to an output of the amplifier, the amplifier configured to provide a output sensed current having a scaled proportion to the current through the power transistor;
• a third transistor having a source coupled to the voltage source and a drain coupled to a non-inverting input terminal of the amplifier;
• a fourth transistor coupled between the load and the amplifier, the fourth transistor being configured for decoupling the amplifier from receiving a voltage at the drain of the power transistor;
• a driver and timing circuit configured for control of the amplifier, the driver and timing circuit being coupled to a gate of the power transistor and a gate of the fourth transistor, and configured for monitoring the voltage at the drain of the power transistor to determine whether to permit the fourth transistor to provide the voltage at the drain of the power transistor to the amplifier.