Motor driving device

In a motor driving device, an IC chip of a drive circuit for driving a motor is die-bonded to one island of a leadframe, and a diode chip of a protection diode for preventing the drive circuit from being destroyed when supplied power is connected to the IC chip with reverse polarities is die-bonded to another island of the leadframe. The supplied-power pad of the IC chip is wire-bonded to the second island, which serves as the cathode electrode of the diode chip.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor driving device.

2. Description of the Prior Art

Motor driving devices are known that are provided with a drive circuit for driving a motor and a protection diode for preventing the drive circuit from being destroyed when a power source is connected thereto with reverse polarities. FIG. 2 shows an example of a circuit configuration of an output stage of a pre-drive circuit 1 for a two-phase half-wave fan motor. A MOS-type field-effect transistor (or bipolar transistor) 100 an a resistor 200 are connected in series between a supplied-power terminal T 1 and a ground terminal T 2 . A node between the transistor 100 and the resistor 200 is connected to an output terminal T 3 .

In actual use, to the output terminal T 3 , the base of an NPN-type power transistor 3 is connected through resistor 6 . The transistor 3 has its emitter grounded, and has its collector connected to one end of a coil 4 of a fan motor. The other end of the coil 4 is connected to a cathode of a diode 5 . An anode of the diode 5 is connected to a supplied voltage V cc .

With a motor driving device provided with the pre-drive circuit 1 as described above, there is a risk of a power source being connected thereto with reverse polarities, for example, as a result of improper insertion of a connector. Therefore, to prevent destruction, resulting from reverse connection of a power source, of the circuit elements, such as the MOS transistor 100 , constituting the pre-drive circuit 1 , it has been customary to connect to the supplied-power terminal T 1 of the pre-drive circuit 1 the cathode of a protection diode 2 of which the anode is connected to a terminal (not shown) to which the supplied power is supplied.

Here, the current that flows into the base of the transistor 3 to drive the motor is supplied directly from the power source, and therefore the protection diode 2 needs to have a high current capacity. In general, however, it is difficult to obtain a satisfactorily high current capacity with a diode formed within an IC (integrated circuit). For this reason, usually, in FIG. 2 , whereas the pre-drive circuit 1 is formed as a one-chip IC, the protection diode 2 is connected externally to the IC. As a result, conventional motor driving devices provided with a pre-drive circuit and a protection diode has the disadvantage of requiring an unduly large mounting area and also requiring an extra assembly step.

The same problem is addressed by Japanese Patent Application Laid-Open No. H7-130927, which proposes, as a solution, mounting a MOS transistor and a diode on a single island. However, this is possible only with a single MOS transistor; that is, with a common IC, which is not formed on a single substrate together with a diode, it is impossible to mount the IC and the diode on a single island.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a motor driving device that, despite being provided with a drive circuit for driving a motor and a protection diode, requires a reduced mounting area and a reduced number of assembly steps.

To achieve the above object, according to the present invention, a motor driving device is provided with: an IC chip incorporating a circuit for driving a motor; a diode chip provided in a power-supply path through which electric power is supplied to the IC chip; a leadframe having a first island on which the IC chip is mounted and a second island on which the diode chip is mounted; a wire connecting together a supplied-power island provided on the IC chip and the second island; and a package incorporating the leadframe, the IC chip, and the diode chip.

This structure eliminates the need to connect a protection diode externally. Moreover, this structure makes it possible to obtain not only a higher current capacity but also a higher peak inverse voltage in the protection diode than when it is formed within an IC.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing in detail the structure inside a package 40 of a motor driving device embodying the invention. A leadframe 30 has a first island I 1 , a second island I 2 , eight inner leads L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , L 7 and L 8 , and three support bars S 1 , S 2 and S 3 .

The first island I 1 is supported by the support bars S 1 and S 2 , and the second island I 2 is supported by the support bar S 3 . The inner leads L 1 , L 2 , L 3 , L 4 , L 5 , L 6 , L 7 , and L 8 are so formed as to extend out of the package, and are used as terminals. The first island I 1 is down-set at portions A and B of the support bars S 1 and S 2 .

An IC chip 10 of a drive circuit for driving a motor is die-bonded to the first island I 1 of the leadframe 30 . A diode chip 20 of a protection diode is die-bonded to the second island I 2 , so that the second island I 2 serves as the cathode electrode of the diode chip 20 . The IC chip 10 is, for example, an IC chip of a pre-drive circuit 1 for a two-phase half-wave fan motor that has a circuit configuration as shown in FIG. 2 .

On the top surface of the IC chip 10 , eight bonding pads P 1 , P 2 , P 3 , P 4 , P 5 , P 6 , P 7 , and P 8 are formed. Of these bonding pads, the supplied-power pad P 1 , i.e. the one connected to the power-supply line within the IC chip 10 , is wire-bonded to the second island I 2 (i.e. the cathode electrode of the diode chip 20 ).

The other pads P 2 , P 3 , P 4 , P 5 , P 6 , P 7 and P 8 are connected to the inner leads L 2 , L 3 , L 4 , L 5 , L 6 , L 7 and L 8 respectively. A bonding pad P that serves as an anode electrode of the diode chip 20 is wire-bonded to the inner lead L 1 .

As described above, the motor driving device of this embodiment incorporates a drive circuit for driving a motor and a protection diode as separate chips. This eliminates the need to connect a protection diode externally. This in turn makes it possible to reduce the mounting area required and also reduce the number of assembly steps required.

Moreover, it is possible to make the current capacity of a protection diode higher than when it is formed within an IC of a drive circuit. As a result, it is possible to supply a larger amount of current as a motor-driving current, and also make the peak inverse voltage of the protection diode higher. Thus, it is possible to enhance the function of preventing destruction of the circuit.

As described above, according to the present invention, a motor driving device incorporates a drive circuit for driving a motor and a protection diode as separate chips. This eliminates a need to connect the protection diode externally. Thus, it is possible to reduce a the mounting area required and also reduce the number of assembly steps required.

Moreover, it is possible to make the current capacity of the protection diode higher than when it is formed within an IC. As a result, it is possible to supply a larger amount of current as a motor-driving current, and also make the peak inverse voltage of the protection diode higher. Thus, it is possible to enhance the function of preventing destruction of the circuit.