Alternatively, applications are known that are configured to allow a situation in which negative current (reverse current) is applied to the low-side transistor. In this case, when such a reverse current that flows through the low-side transistor becomes very large, this leads to a problem of heat generation or the like. Furthermore, if the high-side transistor or the low-side transistor is switched on and off in a state in which a large reverse current flows through the inductor, this induces a large voltage oscillation in the voltage at the LX pin or other voltages, which is an undesired situation. In order to solve such a problem, a Negative Current Protection (NCP) function is implemented on a control circuit employed in such an application that allows reverse current.

The common point between the zero current detection and the negative current detection is that the current that flows through the low-side transistor is compared with a threshold value of zero or a negative value.

FIG. 8A and FIG. 8B are circuit diagrams each showing a low-side current detection circuit. The monitoring of the current flowing through the low-side transistor ML does not require as severe a precision as the overcurrent detection and the peak current detection. Accordingly, in an example, only the first circuit block BLK1 is provided with a low-side current detection circuit 170_1. In contrast, the second block BLK2 is provided with no low-side current detection circuit. FIG. 8A shows a state in the first mode, and FIG. 8B shows a state in the second mode.