Thermistor Linearizes Current Limit
Recent advances in the design of step-down DC-DC converters have eliminated the current-sense resistor by substituting the drop across the low-side MOSFET (synchronous rectifier) instead. This topology saves the cost and space of a sense resistor, and also provides a modest boost in efficiency. One compromise imposed by the new approach, however, is a current-limit value dominated by the MOSFET’s on-resistance, which is highly temperature dependent. Fortunately, the new DC-DC converters provide a pin that allows adjustment of the current-limit threshold. By changing this threshold according to temperature, you can temperature-compensate the circuit’s output-current limit.
In this application note, a resistive network that includes a thermistor is used to temperature-compensate the current-limit input (ILIM) of a DC-DC converter.
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