JPH04170063A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To improve the breakdown withstanding voltage of a semiconductor integrated circuit having a static protection circuit by a method wherein a MOS transistor having a threshold voltage whose absolute value is larger than the power supply voltage of an internal circuit and which is smaller than the breakdown voltage of the diode of the internal circuit is included. CONSTITUTION:A source terminal 4 is connected to a power supply potential point, a drain terminal is connected to an outer terminal 1, a gate terminal is connected to an input terminal and, further, a MOS transistor having a threshold voltage whose absolute value is larger than the power supply voltage of an internal circuit 9 and which is smaller than the breakdown voltage of the diode 6 of the internal circuit 9 is included. Therefore, when an excessive surge voltage exceeding the power supply voltage is applied by the outer terminal 1 which can be inserted and extracted in a live state, a voltage equal to the threshold voltage of the MOS transistor 2 is applied to the gate terminal of the MOS transistor 2 having the threshold voltage whose absolute value is larger than the power supply voltage of the source terminal 4 and, at the same time, the MOS transistor 2 is turned on and an electric energy is discharged from the drain terminal to the power supply terminal 4. With this constitution, an electronic energy applied to the input buffer element 6 is suppressed and the breakdown voltage can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor integrated circuit, and more particularly to an electrostatic protection circuit for external terminals that can be hot-swappable.

[Conventional technology]

Conventionally, as shown in FIG. 5, a static electricity protection circuit for an external terminal of a semiconductor integrated circuit normally protects an internal circuit 9 from which an input buffer 6 is an input using, for example, a diffusion diode 7.8 and a resistor element 5. It constitutes a power protection circuit.

However, in order to enable hot-line insertion and removal, when the power is turned off, there must be no current path for the signal that is at the ``H'' level if the positive power source is supplied from the outside, or is at the ``L'' level if the negative power source is supplied from the outside. As shown in FIGS. 3 and 4, an electrostatic protection circuit was configured without a diffusion diode connected to the power supply potential side (that is, connected to the power supply terminal 4).

[Problem to be solved by the invention]

The above-mentioned conventional semiconductor integrated circuit with an electrostatic protection circuit for hot-swappable external terminals differs from a normal electrostatic protection circuit in that there is no current path to the power supply potential side, so the absolute value does not change from the outside to the external terminal. When an excessive surge voltage exceeding the power supply voltage is applied, the diffusion diode mainly connected to the ground potential side breaks down and electrical energy is released to the substrate.

At this time, the breakdown voltage is generally as high as 15V or more, and therefore, electrical energy is likely to be applied to the elements in the manual buffer, causing the elements of the input buffer to be destroyed, so it is necessary to increase the breakdown voltage. The disadvantage was that it was difficult.

[Means to solve the problem]

The semiconductor integrated circuit device of the present invention provides an electrostatic protection circuit having an external terminal connected to an input end of an internal circuit via a series resistor and connected to one end of a diode characteristic element whose other end is grounded. A semiconductor accumulation circuit including a source terminal connected to a power supply potential point, a drain terminal connected to the external terminal, a gate terminal connected to the input terminal, and an internal circuit whose absolute value is larger than the power supply voltage of the internal circuit. The circuit includes a MOS transistor having a threshold voltage designed to be smaller than the breakdown voltage of a diode in the circuit.

〔Example〕

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

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

1 is an external terminal for an input buffer connected to the bonding pad, 4 is a power supply terminal to which a power supply voltage 5 is supplied, 5 is a resistance element, 6 is an input buffer, and 2 is a gate It is an N-channel transistor whose threshold voltage V↑IOV is adjusted to be higher than the power supply voltage 5V and lower than the breakdown voltage 15V of the diode composed of the drain and substrate by controlling the thickness of the insulating film directly under the polysilicon and channel doping. The train terminal is connected directly, the gate terminal is connected to an external terminal via a resistor 5, and the source terminal is connected to a power supply terminal. Further, 3 is a diode with a breakdown voltage of 15V, which is composed of the drain of the N-channel transistor 2 and the substrate.

The oxide film thickness of a normal transistor is 0.015 .mu.m, but here, by setting it to 0.17 .mu.m, a transistor having a threshold voltage (T) of about 10V can be obtained.

Next, to explain the operation of the circuit, in the operating state where 5V is supplied to the power supply terminal 4, even if a signal with a logic amplitude of 0 to 5 is input to the external terminal, the N-channel transistor 2 will have a voltage of 10V between the gate and the substrate. Even in the off state of the chip where the power supply terminal 4 is short-circuited to the ground potential 0■, the N-channel transistor 2 will not turn on and the external terminal 1 can be hot-switched. .

Furthermore, when an excessive surge voltage exceeding the power supply voltage 5.5 is applied to the external terminal 1, when the surge voltage exceeds 10V, the N-channel transistor 2 is turned on and electrical energy begins to be released to the power supply terminal side.

This can reduce the electrical energy applied to the elements of the input buffer 6 faster than discharging electrical energy to the substrate due to the breakdown of the diode 3.

Furthermore, when an excessively negative surge voltage is applied to the external terminal 1, the diode 3 becomes forward-directed and easily releases electrical energy to the substrate, as in the conventional case.

FIG. 2 is a circuit diagram of a second embodiment of the present invention in which external terminals are hot-swappable using a negative power source.

11 is a power supply terminal to which a power supply voltage of -5V is supplied;
is the absolute value of the power supply voltage, which is 10V, which is greater than the absolute value of the power supply voltage, which is 5■
10 is a P-channel transistor tuned to P
This is a diode with a breakdown voltage of 15V, which is composed of the drain of the channel transistor 9 and the substrate. The circuit operating characteristics are similar to those described in the first embodiment.

〔Effect of the invention〕

As explained above, in the semiconductor cumulative circuit of the present invention, when an excessive surge voltage whose absolute value exceeds the power supply voltage is applied to the hot-swappable external terminal, the source terminal is connected to the power supply terminal and the When a voltage equal to the threshold voltage is applied to the gate terminal of the M○S transistor, which has a threshold value larger in absolute value than the leakage voltage, the MOS transistor is turned on, and electrical energy is released from the drain terminal to the power supply terminal.

This has the effect of reducing the electrical energy applied to the elements of the input buffer and increasing the breakdown voltage.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, FIG. 2 is a circuit diagram of a second embodiment of the present invention, and FIGS. 3 and 4 are conventional hot-swappable semiconductor integrated circuits. FIG. 5 is a circuit diagram of another example of a conventional semiconductor integrated circuit. 1... Pad connection external terminal, 2.9... MOS) transistor (high Vt), 3.10... Diode connection M
OS transistor, 4.11...power supply terminal, 7°8.
...Diffusion diode, 9...Internal circuit.

Claims (1)

[Claims] In a semiconductor integrated circuit including an electrostatic protection circuit having an external terminal connected to an input terminal of an internal circuit via a series resistor and connected to one end of a diode characteristic element whose other end is grounded, the source terminal is connected to a power supply potential point, a drain terminal is connected to the external terminal, a gate terminal is connected to the input terminal, and the absolute value is larger than the power supply voltage of the internal circuit and smaller than the breakdown voltage of the diode of the internal circuit. A semiconductor integrated circuit comprising a MOS transistor having a designed threshold voltage.