Patent ID: 8085026

Claim:
A current sense amplifier for sensing current through a main switch device of a converter, wherein the main switch device has a current path coupled between an input node and a phase node and has a control input coupled to a control node, said current sense amplifier comprising: first and second matching switch devices comprising scaled down versions of the main switch device, each said first and second switch device having a control input coupled to the control node, wherein said first switch device has a current path for coupling between the input node and a first node, and wherein said second switch device has a current path for coupling between the phase node and a second node; an amplifier control circuit having a current path coupled between said first node and a third node, said amplifier control circuit having an input; a bias circuit having a current path coupled between said second node and a fourth node and having an output coupled to said input of said amplifier control circuit; a current generator circuit coupled to said third and fourth nodes which develops a constant first current through said amplifier control circuit and which develops a constant second current through said bias circuit, wherein said second current is about twice said first current; and a sense circuit having a current path coupled between said first node and ground and having a control input coupled to said third node, wherein said sense circuit develops a sense voltage indicative of current through the current path of the main switch device.