PSoC® 3 and PSoC 5LP Boost Inductor Current Rating - KBA80957

Version 1
    Version: *A


    Question: What should be the minimum current rating for the inductor which can be used for the PSoC 3 or PSoC 5LP boost circuit?



    The DC current rating of the inductor should be greater than or equal to 700mA. The inductor peak current can go up to a maximum of 700 mA during start-up. So, if you use an inductor with a lesser current rating, the boost converter may not start properly.

    During startup or transient operation (when the output voltage changes), the load capacitor acts like a short circuit and will draw as much current as the converter can deliver. There are current limiting provisions inside the boost converter that prevent the current from growing unbounded. The effective current limit is under 700mA. So, if you use an underrated inductor the boost converter may not start properly. The reason is that the inductor becomes saturated and ceases to behave as an inductor, dissipating energy in it and hence, not transferring the energy effectively.

    The boost converter can give a maximum load current of 75mA. Even if the load is small, the inductor must be capable of delivering peak currents. This is because transient loads will pull the output below the narrow regulation window provided by minimum PWM signals, requiring occasional full current (maximum duty cycle) pulses to restore the voltage to target value.

    Thus the inductor always needs to be rated for full current.

    Note: The maximum ratio of the output voltage to the input voltage of the boost can be 4.