JPH04339415A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To easily investigate the factor of a malfunction due to the abnormal voltage input from an external part in a semiconductor integrated circuit. CONSTITUTION:When the voltage higher than a power terminal 52 is inputted to a general purpose terminal 51, the voltage of a joint A becomes the voltage lower than inputted to the general purpose terminal 51 and higher than the voltage of power terminals 52 and 53. When the voltage of the joint A and the voltage of a power terminal 53 are inputted to a comparator 4 and the voltage of the joint A is higher than the voltage of the power terminal 53, a comparing output signal (l) is outputted and stored through a writing circuit 6 to an EEPROM circuit 7. When the voltage lower than the potential of a ground point is inputted to the general purpose terminal 51, the voltage of the joint A becomes the voltage higher than the voltage inputted to the general purpose terminal 51 and lower than the voltage of the ground point. When the voltage of the joint A and the voltage of the ground point are inputted to a comparator 5 and the voltage of the joint A is lower than the voltage of the ground point, a comparing output signal (2) is outputted, and stored through the writing circuit 6 to the EEPROM circuit 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor integrated circuits.

0002

2. Description of the Related Art Semiconductor integrated circuits generally have the problem that latch-up occurs due to noise and the like, resulting in destruction of internal circuits. For this reason, protection circuits are provided at general-purpose terminals of semiconductor integrated circuits to prevent damage to the internal circuits. What is shown in FIG. 2 is this general purpose terminal. Note that in FIG. 2, internal circuits and the like are not shown at all because they are not particularly necessary for the purpose of explanation. As shown in FIG. 2, as a protection circuit for the semiconductor integrated circuit 8, diodes 9 and 10 are provided which are connected in series between the power supply terminal 55 and the ground point with respect to the general-purpose terminal 54. A general-purpose terminal 54 is connected to the connection point (node A) between both diodes.

In FIG. 2, when a voltage higher than the power supply voltage applied to the power supply terminal 55 is input to the general-purpose terminal 54, the diode 9 becomes forward biased, and the voltage from the general-purpose terminal 54 to the node A and the diode 9 is Through the power terminal 55
Current flows into the power supply via. At this time, the voltage at node A is determined by (node voltage)={(voltage at general-purpose terminal 54)-(voltage at power supply terminal 55)}×{R1/(R1+R2)}+(voltage at power supply terminal 55).

Therefore, it is possible to lower the voltage applied to the internal circuit than the voltage input to the general-purpose terminal 54, making latch-up less likely to occur. Similarly, even when a voltage lower than the potential of the ground point is input to the general-purpose terminal 54, the diode 10 becomes forward biased, so that the voltage applied to the internal circuit is reduced to the voltage input to the general-purpose terminal 54. This makes it possible to make it higher than the current value, making it difficult for latch-up to occur.

[0005]

[Problems to be Solved by the Invention] In the conventional semiconductor integrated circuit described above, in a protection circuit formed by a pair of diodes provided corresponding to a general-purpose terminal, a current flows due to forward bias of the diode. Due to this, carriers are injected into the substrate or well of the semiconductor integrated circuit, and the potential of the substrate or well near these diodes fluctuates, causing malfunctions in the holding circuits included in the internal circuits. There is a drawback that it is difficult to investigate the cause of the malfunction.

[0006]

[Means for Solving the Problems] A semiconductor integrated circuit of the present invention includes, as an input circuit corresponding to a general-purpose terminal, a first diode whose cathode side is connected to a power supply terminal and whose anode side is connected to the general-purpose terminal; side is connected to the general purpose terminal,
A voltage (1) is obtained by comparing the voltage (1) of the second diode whose anode side is connected to the grounding point, the voltage (1) of the power supply terminal, and the voltage (2) of the connection point of the first and second diodes. ＞
a first comparator that outputs a first comparison output signal corresponding to the voltage (2), a voltage (2) at the connection point of the first and second diodes, and a voltage (3) at the ground point; a first comparator that compares and outputs a second comparison output signal corresponding to voltage (2)<voltage (3);
and a storage circuit that stores the first and second comparison output signals output from the second comparator.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing a portion of a protection circuit in an embodiment of the present invention, and internal circuits and the like are omitted and not shown. As shown in FIG. 1, the input circuit corresponding to the general-purpose terminal of this embodiment includes diodes 2 and 3 corresponding to the general-purpose terminal 51 and power supply terminals 52 and 53.
, comparators 4 and 5, write circuit 6, and EE
It is configured to include a PROM circuit 7.

In FIG. 1, when a voltage higher than that of the power supply terminal 52 is input to the general-purpose terminal 51, the diode 2 becomes forward biased, and the voltage at the node A is applied to the general-purpose terminal 51.
However, the voltage is higher than the voltage at power supply terminals 52 and 53. The voltage at node A and the voltage at power supply terminal 53 are input to comparator 4, but comparator 4 outputs a comparison output between the two as a signal only when the voltage at node A is higher than the voltage at power supply terminal 53. (1), therefore, in the above state, the comparator 4 outputs
A signal (1) indicating that the voltage at node A is higher than the voltage at power supply terminal 53 is output and input to write circuit 6;
The information of the signal (1) is stored in the EEPROM circuit 7 via the write circuit 6.

Furthermore, when a voltage lower than the potential of the ground point is input to the general-purpose terminal 51, the diode 3 becomes forward biased, and the voltage at the node A becomes higher than the voltage input to the general-purpose terminal 51. However, the voltage is lower than the voltage at the ground point. These voltages at the node A and the voltage at the ground point are input to the comparator 5, but the comparator 5
It has the function of outputting the comparison output of both as signal (2) only when the voltage at node A is lower than the voltage at the ground point. Therefore, in the above state, comparator 5 A signal (2) indicating that the voltage at A is lower than the voltage at the ground point is output and input to the write circuit 6, and the information of the signal (2) is stored in the EEPROM circuit 7 via the write circuit 6. be done.

[0011] Therefore, by going through the above operations,
If some kind of malfunction occurs in the semiconductor integrated circuit 1, by reading the data contents stored in the EEPROM circuit 7, it can be determined whether the cause of the malfunction is latch-up due to an abnormal voltage from the outside. It can be easily determined whether or not.

0012

[Effects of the Invention] As explained above, the present invention makes it possible to easily determine the cause of malfunction by recording the progress of latch-up that occurs in response to abnormal voltage input to a general-purpose terminal. There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1, 10 Semiconductor integrated circuit 2, 3, 9, 10 Diode 4, 5 Comparator 6 Write circuit 7 EEPROM circuit

Claims (1)

[Claims] [Claim 1] As an input circuit corresponding to a general-purpose terminal,
a first diode whose cathode side is connected to the power supply terminal and whose anode side is connected to the general-purpose terminal; a second diode whose cathode side is connected to the general-purpose terminal and whose anode side is connected to the ground point; Comparing the voltage (1) with the voltage (2) at the connection point of the first and second diodes,
a first comparator that outputs a first comparison output signal corresponding to voltage (1)>voltage (2);
A first comparison output signal that compares the voltage (2) at the connection point of the diode with the voltage (3) at the ground point and outputs a second comparison output signal corresponding to voltage (2) < voltage (3). a comparator, and a storage circuit that stores first and second comparison output signals output from the first and second comparators;
A semiconductor integrated circuit characterized by comprising: