1. Field
This is related to a semiconductor device having a function, for limiting (cutting) the power supply of an internal circuit.
2. Description of the Related Art
Inclusion of a function of partially limiting (cutting) the power supply of an internal circuit, namely, a so-called power gating function, in large-scale integrated circuits (LSIs) to decrease the power consumption is becoming the mainstream. On the other hand, LSIs have a plurality of test circuits for use in a test of the LSIs. More specifically, the LSIs have circuits, such as an input/output test circuit that performs fault diagnosis of data writing/reading circuits and an accelerated test circuit that performs an accelerated test on internal circuits of the LSIs.
An input/output test circuit includes a circuit that serially couples, in series like a chain, flip flops related to writing and reading of an LSI and a control circuit that receives control signals and test data from outside of the LSI and controls the state of the test (see, for example, Japanese Laid-open Patent Publication No. 2003-98223). In addition, an accelerated test circuit includes a circuit that applies an accelerated test voltage to an internal circuit and a control circuit that receives control signals from outside of an LSI and controls the state of the test (see, for example, Japanese Laid-open Patent Publication No. 10-21699).
A test of an LSI having a control circuit that performs a power gating operation and a control circuit that controls the state of the test has to be carried out while allowing the control circuits to operate in cooperation with each other. However, sending a control signal for permitting the cooperation between the control circuits to an LSI from a testing equipment residing outside of the LSI requires an expensive testing equipment having an advanced function, which thus increases the cost for the test.
Nevertheless, when the expensive testing equipment that generates a control signal for permitting the cooperation between control circuits does not employed and the control circuit that performs the power gating operation and the control circuit that controls the state of the test do not operate in cooperation with each other, the following disadvantages may occur. At the time of an accelerated test, application of a sufficient level of stress, which is carried out by applying a predetermined voltage level to an internal circuit, is not achieved because the power gating function is not cancelled. Additionally, at the time of an input/output test, test data is not transferred since an unexpected power gating operation is activated. As a result, the accelerated test or the input/output test may be undesirably prevented.