JPH01214779A - Input-voltage detecting circuit - Google Patents

Abstract

PURPOSE:To prevent erroneous operations during the operation of an IC and to reduce current consumption, by performing transition into an operating mode by the input of a negative voltage, and to prevent the operations of two transistors when the input voltage is at a reference potential. CONSTITUTION:Transistors (Tr)Q1 and Q2 are provided in a semiconductor integrated circuit. The base of the TrQ1 and the emitter of the TrQ2 are connected to reference potential points. An input terminal is connected to the emitter of the TrQ1 through a resistor R3. The emitter of the TrQ1 is connected to the base of the TrQ2 through a resistor R4. The base of the TrQ2 is connected to the reference potential through a resistor R5. Control outputs are obtained from the collectors of the Trs Q1 and Q2. Even if a slight difference occurs in a power source voltage with respect to a peripheral circuit during the operation of an IC, an erroneous operation does not occur and transition into a test mode does not occur. When the input voltage is equal to the reference potential, the two Trs Q1 and Q2 are not operated. Therefore a current does not flow. When a standby mode is set during the operating mode of the semiconductor integrated circuit, the current consumption can be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an input voltage detection circuit that detects a control voltage for switching the operating mode of an IC, and particularly to a test for preparing an IC for a test to determine the quality of the IC. Control transition to mode.

[Conventional technology]

Conventionally, in order to perform this type of control, there is a technique of shifting to a test mode when a voltage exceeding the power supply voltage, which is not applied during normal operation, is applied to an external terminal originally provided for controlling the operation mode.

[Problem that the invention seeks to solve]

The above-described conventional technique of shifting to the test mode using a voltage exceeding the power supply voltage has the following drawback in that the mode shifts to the test mode during actual operation.

In other words, if the power supply voltages of a first IC equipped with a test mode and a second IC that provides a control voltage to the first IC are supplied from different power supplies, the power supply voltage to the first IC is higher than that of the second IC. When the power supply voltage of the second IC increases and a high level control voltage is applied from the second IC to the first IC, a voltage higher than the power supply of the first IC is applied to the input terminal of the first IC. Therefore, there is a drawback that the first IC malfunctions and enters the test mode.

[Differences between the invention and the prior art]

In contrast to the conventional technique for transitioning to the test mode described above, the present invention performs the control voltage for the test mode at a negative voltage lower than the reference potential point, and furthermore, when the input voltage is at the reference potential, no current flows. It has an original content.

[Means for solving problems]

The input voltage detection circuit of the present invention detects the base-emitter voltage of each transistor by a third resistor R8, a fourth resistor R4,
and a fifth resistor R6, and includes a first transistor Q and a second transistor Q2 that do not operate when the input voltage is at the reference potential.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a resistor R3 is connected to the input terminal VIN. The other end of resistor R3 is connected to the emitter of transistor Q1 and resistor R4. The other end of resistor R4 is connected to the base of transistor Q2 and resistor R6.

The other end of the resistor R6 is connected to a reference potential point. The base of the transistor Q1 is connected to a reference potential point, and the collector of the transistor Q1 is connected to a power supply via an output terminal A and a resistor R1.

Also, the emitter of transistor Q2 is connected to the reference potential point, and the collector of transistor Q2 is connected to output terminal B.
and is connected to a power supply via a resistor R3.

Here, assume that the voltage of the power supply Vcc is in the range of 4.5 to 5.5V, and furthermore, each transistor does not operate if the base-emitter voltage is less than 0.5V, and operates when it becomes 0.8V or more. shall be. Further, 70% or more of the power supply voltage is treated as an old gh level signal, and 30% or less of the power supply voltage is treated as a low level signal.

Now, considering the circuit shown in FIG. 1, when a signal at the old GH level is input to the input terminal VIN, the transistor Q1 does not operate. At this time, the transistor Q operates as follows: If >0.254, the voltage between base R1+R*+Rs and emitter becomes 0.8V or more.

Next, considering the case where a low level signal is input to the input terminal v1N, the transistor Q1 does not operate and the transistor Q2 also does not operate, that is, if -1 and =->0.303, the base R
s+R*+R* ・It does not operate because the emitter voltage is less than 0.5V.

Also, the input terminal v! , if the following equation is satisfied and VIN' of a voltage lower than the reference voltage is input, the transistor Q1 operates and the transistor Q2 does not operate.

By the way, if we consider the relationship between transistor operation and output, if transistor Q1 operates, if resistor R1 is set to a large value, the voltage at output terminal A will be at a low level, and transistor Q1 will not operate. In this case, the voltage at the output terminal A becomes the old gh level. Further, when the transistor Q2 operates, the voltage at the output terminal B becomes the Low level by setting the resistor R2 to a large value, and when the transistor Q2 does not operate, the voltage at the output terminal B becomes the old gh level.

As explained above, by setting the resistance values of the resistors Rs, R4, and Rs and the values of v, , and ' to satisfy the formulas ■, ■, and ■, the voltage at the output terminals A and B relative to the input voltage can be can be made as shown in FIG.

By the method shown in FIG. 3, the input voltage v1 can be detected by the output terminals A and B.

If the transition to the operating mode is performed by inputting a negative voltage as in the present invention, even if there is a slight difference in the power supply voltage with the surrounding circuits while the IC is operating, the IC will malfunction and transition to the test mode. There's nothing to do. In addition, the input voltage v1N is Low
In the case of level, no current flows in the circuit.

FIG. 2 shows another input voltage detection circuit according to the present invention. Compared to the example shown in FIG. 1, the only difference is that the first and second diodes D+ and Dz are connected between the emitter of the third transistor and the reference potential point, and the other configurations are the same. It becomes.

Figure 2 is 1. By adding the second diode, the magnitude of the reverse bias between the base and emitter of the third transistor Q is increased to the magnitude of the first. This is an example in which the third transistor Q is protected by preventing the forward voltage from exceeding the forward voltage of the second diode DIPD2.

〔Effect of the invention〕

As explained above, according to the present invention, even if there is a slight difference in power supply voltage with surrounding circuits during operation of an IC, malfunction will occur.
There is no transition to the test mode, and if the input voltage is at the reference potential, the two transistors are not operated, so no current flows, so if the semiconductor integrated circuit is set to standby mode, the current consumption It has the advantage of being able to be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the input voltage detection circuit according to the present invention, and FIG. 2 is a circuit diagram of another embodiment of the input voltage detection circuit according to the present invention. In the figure, Vcc is the power supply, VfN is the input signal, A,
B, C, D are output terminals, R1~R1゜ are resistors, Q1~
Q represents a transistor, and Dl and D2 represent diodes. FIG. 3 shows the output terminal A for input voltage according to the present invention;
The voltage level scheme of B is shown. In the figure, the negative voltage needs to satisfy formula (2). Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] The semiconductor integrated circuit includes first and second transistors, the base of the first transistor and the emitter of the second transistor are connected to a reference potential point, and the second The emitter of the first transistor is further connected to the base of the second transistor via a fourth resistor, and the base of the second transistor is connected to the base of the second transistor via a fifth resistor. An input voltage detection circuit characterized in that the input voltage detection circuit is connected to a reference potential and obtains a control output from the collectors of the first and second transistors.