The configuration of an output circuit in a semiconductor device drive circuit varies depending on an element or a circuit to be connected downstream of the output circuit. Commonly, such an output circuit connected with a gate-voltage-controlled semiconductor switching element disposed downstream thereof is a circuit that controls the gate voltage by supplying a current to the gate of the semiconductor switching element. The value of the current supplied to the gate is adjusted according to switching characteristics of the semiconductor switching element and is determined for each product category of semiconductor device drive circuits.
The method for determining the current value for each product category differs depending on the circuit configuration of the semiconductor device drive circuit. The output current capability of a circuit from which a transistor outputs a current can be adjusted by adjustments to the size of the transistor. The “output current capability” indicates the maximum value of the current that can be output by the transistor, and more specifically indicates the value of the current which the transistor can supply to the semiconductor switching element when the maximum possible voltage between the source and the drain of the transistor is applied, or typically, when the voltage equivalent to the supply voltage of the semiconductor device drive circuit is applied between the source and the drain.
The size of the transistor is commonly adjusted with consideration given to the general versatility of the semiconductor device drive circuit. Specifically, a plurality of transistors are disposed on the output terminal side in the semiconductor device drive circuit, and the drains of all or some of the transistors are connected to the output terminal through aluminum wires. The number of transistors to be electrically connected to the output terminal can be adjusted by changing the aluminum wire pattern. Thus, the overall transistor size can be adjusted without changing the size of the individual transistor. This configuration can foster the general versatility of the semiconductor device drive circuit. Specifically, unlike the development of tailor-made products in different categories based on different output current capabilities, this method requires a shorter time of work and allows cost reduction. According to this method, however, a mask pattern for each aluminum wire pattern needs to be newly produced at some cost in time and money.
To meet the requirement on reduced output current capability, the overall transistor size associated with the driving of the semiconductor switching element is reduced according to the method above. The area in which a surge voltage input from the output terminal is absorbed decreases with decreasing transistor size, so that an inadequate surge resistance may be provided.
Products having different aluminum wire patterns should fall into different product categories for the inventory control. Allowing commonality of some portions among semiconductor device drive circuits brings about almost no advantage in the inventory control. Problems which arise in the inventory control are as follows.
Semiconductor device drive circuits are normally manufactured in lots. For example, about 25 wafers are used per lot. This means that a relatively large number of products are manufactured in order to meet the immediate demand for a small number of products per category. Consequently, surplus stocks need to be controlled. In the manufacturing of products in ten different categories based on different aluminum wire patterns, the process of producing as many as 250 wafers in total is necessary to meet the immediate demand for a small amount of outgoing shipments.
A method for adjusting the output current capability with no change in the mask pattern is necessary as a workaround to the above-mentioned problems. Disclosed in Japanese Patent Application Laid-Open No. 05-308272 (1993) is a technique for trimming an integrated circuit (IC) drive circuit, which is currently manufactured or has already been manufactured, such that the drive circuit in active use can reach the optimal driving capability. Specifically, fuses are cut off with a laser beam to perform trimming Disclosed in Japanese Patent Application Laid-Open No. 2008-92663 is a technique for controlling the current value at the time of switching by adjustments to the gate resistance based on the detection results on the gate voltage of the semiconductor switching element.
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