Undercurrent sense arrangement and method
AssigneeNXP B.V.
InventorBrendan Kelly
Life of this patent
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Abstract
An on-state low current detector uses a transistor with main (32) and sense (34) cells. Feedback circuit (36) acts to keep the voltage across main cells (32) at a substantially constant target value when the load current falls below a level that generates the target voltage value in the main cells. The target voltage value is sufficiently high to ensure that the voltages of low current detection comparator (18) are readily measurable.
Claims7
A power semiconductor device, comprising:
- an output transistor having main cells and sense cells
- a control input connected to the main and sense cells and
- main and sense cell controlled outputs
- an output terminal connected to one of the main cell controlled
- outputs for connection to a load
- a feedback circuit for measuring the voltage across the main cell controlled outputs of the output transistor and controlling the voltage on the control input to increase the voltage across the main cell controlled outputs if the magnitude of the voltage across the controlled outputs falls below a predetermined value;
- a reference current supply feeding a reference current through the sense cell controlled outputs;
- and a comparator arranged to compare the voltages across the main cell outputs and the sense cell outputs and to output a low-current signal when the magnitude of the voltage across the main cell outputs falls below that across the sense cell outputs
A method of operating a semiconductor device, the device including an output transistor having main cells and sense cells and a control input connected to the main and sense cells and main and sense cell controlled outputs the method including:
- driving the main and the sense cells in common;
- driving a load from one of the main cell controlled outputs feeding a reference current through the sense cell controlled outputs
- measuring the voltage across the main cell controlled outputs and controlling the voltage on the control input to increase the voltage across the main cell controlled outputs if the magnitude of the voltage across the main cell controlled outputs (4, 6) falls below a predetermined value;
- and
- comparing the voltages across the main cell controlled outputs and the sense cell controlled outputs and outputting a low-current
- signal when the magnitude of the voltage across the main cell controlled outputs falls below that across the sense cell controlled outputs.
Dependencies are inferred from the claim text.