1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device in which the malfunction of a motor drive circuit due to a parasitic effect is prevented.
2. Description of the Related Art
Conventional three-phase motor drivers have three parallel-connected transistors (Tr1-Tr2, Tr3-Tr4, and Tr5-Tr6) each connected in series between direct-current power supplies VCC and GND. Output terminals taken from between Tr1-Tr2, Tr3-Tr4, and Tr5-Tr6 are connected to a motor M. Thus, normal/back electromotive force is generated as the motor rotates/stops. It is proposed in the art to provide a structure in which a protective diode is connected between the collector and the emitter of the transistors to dissipate the electromotive force to a fixed potential, thereby protecting the interior of an IC including the series transistors (for example, refer to Patent Document: JP-A-6-104459, pp. 13-14, FIGS. 16-17).
Also a conventional normal/reverse rotation control circuit of a DC motor is disclosed (for example, refer to Nonpatent Document: Hirobumi Miura; “Mechatronics,” Ohmsha, Ltd., pp. 204-205
In the conventional semiconductor integrated circuit devices, for example, during ON to OFF transition of a driver device, backward electromotive force (hereinafter, referred to as back electromotive force) is generated from a motor. Thus a negative potential is applied to the collector region of the driver device for driving the motor by the back electromotive force. Accordingly, free carriers (electrons) are generated from a PN junction between the emitter region and the base region of a parasitic transistor constructed of a driver device, a substrate, and a control device. The free carriers (electrons) flow from an island region having the driver device to the other island regions via the substrate. Particularly, when the free carriers (electrons) flow into the control device for controlling the driver device, the control device fails to function normally. This causes the driver device which should be in OFF action to make ON action to send an incorrect signal, thus interfering with the normal operation of the motor.