JPH0812921B2 - Semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a sense terminal for detecting current.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor device of this type,
For example, as shown in FIG. 2, a power MOSFET 10 including a double diffusion type MOS transistor (DMOS) is known. In this type of power MOSFET 10, DMOS1 and DMOS2 sharing a drain terminal D and a gate terminal G are formed in the same semiconductor substrate, the source of DMOS1 is the source terminal S, and the source of DMOS2 is the sense terminal SE for current detection. DMOS1 and D
Since the MOS 2 divides the current flowing from the drain terminal D according to the cell ratio, the current flowing to the source terminal S side can be detected from the current flowing to the sense terminal SE side.

Therefore, this type of power MOSFET 10
As illustrated in FIG. 2, the load RL is applied to the source terminal S.
By connecting a resistor R1 for current detection to the sense terminal SE, respectively.
It is used to detect the load current flowing through L and control the load current.

In FIG. 2, the source terminal S and the sense terminal SE are held at the same potential by the negative feedback operation of the operational amplifier OP1, so that the current flowing through the resistor R1 corresponds to the load current flowing through the load RL. In the control circuit 14, based on the voltage across the resistor R1, the DMOS1 and DMO are supplied via the gate drive circuit 12.
The load current control circuit that controls the load current by controlling the operation state of S2 is shown.

[0005]

In the conventional power MOSFET, a Zener diode is provided between the gate terminal and the source terminal of the power MOSFET in order to prevent the element from being destroyed by the overvoltage applied to the gate terminal. When an overvoltage is applied, the gate terminal voltage is limited by energizing the source side via a Zener diode.

However, in the case of the power MOSFET 10 having the sense terminal SE as described above, if the Zener diode Z11 is provided only between the gate terminal G and the source terminal S as shown in FIG. D on the side
There is a problem that the MOS2 cannot be protected. In order to solve this problem, as shown in FIG. 3B, the Zener diode Z is provided between the gate terminal G and the source terminal S and between the gate terminal G and the sense terminal SE, respectively.
Although it is conceivable to connect 11 and Z12, in this case, if the Zener diodes Z11 and Z12 are simply connected, a current may flow into the sense terminal SE and the load current may not be detected well.

That is, for example, the Zener diode Z1
When the same zener diodes having the breakdown voltages VZ11 and VZ12 are used for 1 and Z12, a current flows from the gate terminal G to the sense terminal SE due to variations in the zener diodes and the like, and a source current (that is, a load current) flows to the sense terminal SE side. A current larger than the current determined by the cell ratio may flow, and the load current may not be accurately detected.

In view of the above, the present invention has been made in order to enable protection of the element in such a semiconductor device with a sense terminal without affecting the current detected by the sense terminal.

[0009]

That is, according to the present invention, which has been made to achieve the above object, a first semiconductor element and a second semiconductor element which share a drain terminal and a gate terminal are formed in the same semiconductor substrate. In a semiconductor device in which the source of the first semiconductor element is a source terminal and the source of the second semiconductor element is a sense terminal for current detection, a voltage between the terminals is a predetermined breakdown voltage between the gate terminal and the source terminal. A first Zener diode that conducts when the above conditions are provided is provided, and between the gate terminal and the sense terminal,
It is characterized in that a second Zener diode is provided, which becomes conductive when the voltage between the terminals becomes at least a predetermined breakdown voltage higher than the breakdown voltage of the first Zener diode.

[0010]

As described above, in the semiconductor device of the present invention, the first Zener diode is provided between the gate terminal and the source terminal, and the breakdown voltage is higher than that of the first Zener diode between the gate terminal and the sense terminal. Big second
A Zener diode is provided.

Therefore, according to the semiconductor device of the present invention, when an overvoltage is applied to the gate terminal, most of the current flowing from the gate terminal flows through the first Zener diode to the source terminal, which is detected by the sense terminal. It is possible to protect the first and second semiconductor elements without affecting the current.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an electric circuit diagram showing a configuration of a semiconductor device of an embodiment including an N-type channel double diffusion type MOS transistor.

In the figure, DMOS1 and DMOS2
Are formed in the same semiconductor substrate in the same manufacturing process, sharing the drain terminal D. The cell ratio of DMOS1 and DMOS2 is set to 3000 to 4000: 1, and the current flowing from the drain terminal D is shunted according to the cell ratio. Also DMOS1 and D
The gates of the MOS2 are both connected to the gate terminal G, and are turned on when a high level signal is input to the gate terminal G. On the other hand, the source of the DMOS 1 is the source terminal S and the source of the DMOS 2 is the sense terminal SE. As described above, the load current flowing to the source terminal S side can be detected from the current flowing to the sense terminal SE side. There is.

Further, in this embodiment, the Zener diode Z1 is connected between the gate terminal G and the source terminal S, and the Zener diode Z2 is connected between the gate terminal G and the sense terminal SE. These Zener diodes Z1 and Z2
Are formed of well-known Poly-Si diodes on the same substrate as DMOS1 and DMOS2, and their breakdown voltages VZ1 and VZ2 reduce the number of cells constituting the Zener diode Z1 by one less than the Zener diode Z2. Therefore, VZ1 = VZ2-VF (however, VF
Is the forward voltage of the cell).

Therefore, in the semiconductor device of this embodiment, the breakdown voltage VZ1, of the Zener diodes Z1, Z2 is
VZ2 becomes VZ1 <VZ2, and most of the current flowing from the gate terminal G when the overvoltage is applied to the gate terminal G due to noise, static electricity, etc.
Flow to the source terminal S via the DMO, without affecting the detection current by the sense terminal SE,
It is possible to protect S1 and DMOS2.

The present invention is not limited to the above embodiment, but can be modified as shown below. That is, in the above embodiment, the N-type channel double diffusion type MOS transistor has been described as an example.
The present invention can be applied to both an OS transistor and an insulated gate bipolar transistor.

Further, in the above embodiment, the Zener diodes Z1 and Z2 as the first Zener diode and the second Zener diode are provided on the same substrate as the DMOS1 and DMOS2 as the first semiconductor element and the second semiconductor element, respectively.
Although the Zener diodes Z1 and Z2 are formed by the olly-Si diode, they may be connected from the outside between the terminals. In addition, each Zener diode
Any element that can be clamped to a constant voltage can be used.

In the above embodiment, the number of cells forming the Zener diode Z1 is smaller than that of the Zener diode Z2 by one so that the breakdown voltages VZ1 and VZ2 of the diodes Z1 and Z2 are VZ1 <VZ2. However, this is because the Zener diodes Z1 and Z2 can be formed on the same semiconductor substrate in the same process, so that the characteristics of each cell can be made equal, and if VZ1 <VZ2 can be set, the number of cells and the like are appropriately set. do it. Further, it is possible to set VZ1 <VZ2 by using Zener diodes having different characteristics.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a semiconductor device of an example.

FIG. 2 is an electric circuit diagram showing a circuit configuration of a load current control circuit using a semiconductor device.

FIG. 3 is an electric circuit diagram showing a configuration of a conventional semiconductor device.

[Explanation of symbols]

1, 2 ... DMOS 10 ... Power MOSFET D
... Drain terminal G ... Gate terminal S ... Source terminal SE ... Sense terminal Z1, Z2 ... Zener diode

Claims (1)

[Claims] 1. A first semiconductor element and a second semiconductor element sharing a drain terminal and a gate terminal are formed in the same semiconductor substrate, and the source of the first semiconductor element is a source terminal and the source of the second semiconductor element is a current. In a semiconductor device serving as a sense terminal for detection, a first Zener diode is provided between the gate terminal and the source terminal to conduct when a voltage between the terminals becomes equal to or higher than a predetermined breakdown voltage, and the gate terminal is provided. A second zener diode is provided between the sense terminal and the sense terminal to conduct when a voltage between the terminals is at least a predetermined breakdown voltage higher than the breakdown voltage of the first zener diode. .