Symmetric sample and hold over-current sensing method and apparatus
AssigneeTexas Instruments Incorporated
InventorsJin-Biao Huang, Joseph M. Khayat, Fei Ma
Life of this patent
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Abstract
An over-current condition is detected in a synchronous DC-DC converter by sampling and holding a measured load current value. The load current is sampled while a low-side transistor is ON and then held when the low-side transistor is OFF. The held value is compared to a threshold value while the low-side transistor is OFF. The comparison occurs during the portion of the cycle when the low-side transistor is OFF so that a comparator has sufficient time in which to detect the over-current condition, even in high duty cycle applications.
Claims18
An apparatus for converting a first voltage input at an input node to a second voltage that is output at an output node, the apparatus comprising:
- a first switch that is coupled to the input node;
- a second switch that is coupled to the first switch;
- an inductor that is coupled to a node between the first and second switches and that is coupled to the output node;
- and
- a controller including:
- a pulse width modulation (PWM) logic that is coupled to the first and the second switches and that generates actuation signals for the first and second switches;
- a sample-and-hold circuit that is coupled to the node between the first and second switches and that is coupled to the PWM logic, wherein the sample-and-hold circuit receives the actuation signals for the first and second switches;
- and
- a comparator that is coupled to the sample-and-hold circuit and that is coupled to the PWM logic, wherein the comparator compares an output from the sample-and-hold circuit to a predetermined threshold to determine whether the apparatus has reached an over-current condition, and wherein the comparator outputs an over-current signal to the PWM if the over-current condition has been reached.
A controller for a DC-DC converter, the controller comprising:
- a pulse width modulation (PWM) logic that receives a clock signal and generates actuation signals;
- a sample-and-hold circuit that receives the actuation signals and that receives an inductor current value, wherein the sample-and-hold circuit is adapted to store and to output the inductor current value;
- and
- a comparator that receives the inductor current value from the sample-and-hold circuit, that compares the inductor current value to a predetermined threshold to determine whether the converter has reached an over-current condition, and that outputs an over-current signal to the PWM logic if the over-current condition has been reached.
A method for operating a DC-DC converter having a high-side transistor and a low-side transistor, the method comprising the steps of:
- actuating the low-side transistor;
- sampling an inductor current value while the low-side transistor is actuated;
- comparing the sampled inductor current value to a predetermined threshold to determine whether the converter has reached an over-current condition;
- indicating the over-current condition to PWM logic when reached;
- and
- adjusting the ON times for at least one of the high-side and low-side transistors in response to the over-current condition.
Dependencies are inferred from the claim text.