Inrush current control method using a dual current limit power switch
First Claim
1. A circuit comprising:
- a switch;
a first comparator coupled to the switch for comparing an input of the switch to an output of the switch;
a current limit reference circuit coupled to the first comparator for providing a current reference that has a first reference level when a ratio of the output to the input is less than a fixed ratio, and a second reference level when the ratio of the output voltage to the input voltage is greater than the fixed ratio;
a second comparator coupled to the current limit reference circuit for comparing the current reference to a current level in the switch; and
a driver circuit coupled between the second comparator and a control node of the switch.
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Accused Products
Abstract
A current limit circuit regulates the current flow through a power switch 90 by measuring the current through the switch 90 and comparing it to a reference voltage VREF that represents the limit current. When the current through the power switch 90 is greater than the limit current, the current in the power switch 90 is pulled lower by a driver circuit 92 which controls the power switch 90. By using a current limit reference voltage that has two levels, the power switch 90 has two current limit thresholds. Using a comparator 94 to compare the input voltage of the power switch 90 to the output voltage of the power switch 90, an output signal is generated to control the current limit threshold. When the input voltage and output voltage has a large differential voltage, a lower current limit threshold voltage is selected. When the input voltage and output voltage has a small differential voltage, an upper limit threshold voltage is selected.
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Citations
16 Claims
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1. A circuit comprising:
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a switch;
a first comparator coupled to the switch for comparing an input of the switch to an output of the switch;
a current limit reference circuit coupled to the first comparator for providing a current reference that has a first reference level when a ratio of the output to the input is less than a fixed ratio, and a second reference level when the ratio of the output voltage to the input voltage is greater than the fixed ratio;
a second comparator coupled to the current limit reference circuit for comparing the current reference to a current level in the switch; and
a driver circuit coupled between the second comparator and a control node of the switch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A dual current limit power switch device comprising:
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a power switch having an input node, an output node, and a control node;
a driver coupled to the control node;
a first comparator having an output coupled to the driver and a first input coupled to a current detection node at the input node of the power switch;
a current limit reference circuit having an output coupled to a second input of the first comparator, and having a first input coupled to a first reference voltage node and a second input coupled to a second reference voltage node; and
a second comparator having a first input coupled to the output node of the power switch and a second input coupled to the input node of the power switch through a resistor divider, wherein the current limit reference circuit selects between the first and second reference voltages in response to the second comparator. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A method for driving a power switch comprising:
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comparing an input voltage to an output voltage of the power switch;
generating a current limit reference that has a first signal level when a ratio of the output voltage to the input voltage is less than a fixed ratio, and a second signal level when the ratio of the output voltage to the input voltage is greater than the fixed ratio;
comparing the current limit reference to a current level in the power switch; and
reducing the current level in the power switch when the current level is greater than the current limit reference.
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Specification