JP3094564B2 - 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, and more particularly to a power field effect transistor (hereinafter, referred to as an FET) provided with a current detection circuit.

[0002]

2. Description of the Related Art In recent years, ICs incorporating an output circuit for driving a load with a power MOSFET have been increasing. In the output circuit using the power MOSFET, the power MO
A current detection circuit is required to detect an overcurrent flowing through the SFET and protect the load. Therefore, an example of a power MOSFET having a current detection transistor will be described below with reference to FIGS. First, in the equivalent circuit (1) shown in FIG. 4, (Qa) is a current detecting MOSFET,
(Qb) is a power MOSFET, (Ra) is a detection resistor, and (Rz) is a load. The above MOSFET (Qa)
(Qb) constitutes a current mirror circuit. Specifically, a bias voltage is applied by connecting the gates in common, and a power supply voltage (Vdd) is applied by connecting the drains in common. Is connected to a detection resistor (Ra).

In the circuit (1), the MOSFET (Q
a) When the area ratio of (Qb) is set to 1: N, each MOS
Source currents of FETs (Qa) (Qb) (Ia) (Ib)
Becomes Ia: Ib = 1: N, and the detection resistance (Ra)
, The voltage (Va) across the detection resistor (Ra) is reduced by the source current (I
b) That is, since the voltage (Va) is proportional to the load current,
, The load current (Ib) is detected. Here, as shown in FIG. 5, when the circuit (1) is incorporated into a rectangular semiconductor substrate (2), a MOSFET is used.
A MOSFET (Qbx) similar to that of (Qa) is used as a basic unit cell, and N units thereof are assembled at a predetermined pitch along the periphery of the substrate to form a large-capacity power MOSFET (Qb) and to make the current uniform. MOS in the approximate center
An FET (Qa) is incorporated.

[0004]

The problem to be solved is that the equivalent circuit (1) has a MOSFET (Qa).
(Qb) configures an ideal current mirror circuit when the respective drain-source voltages match, while
Since the detection resistor (Ra) is connected to the source of the MOSFET (Qa), the drain-source voltage is increased by the MOSFET.
It is lower than T (Qb), so that it is difficult to form an ideal current mirror circuit, and the detection accuracy and sensitivity are lowered.

[0005]

According to the present invention, there is provided a large-scale MOS transistor having a plurality of MOS field-effect transistor groups each having a single-conductivity-type semiconductor substrate as a common drain and having a plurality of sources and gates formed on the surface thereof. A power field effect transistor having a capacity, and a collector formed by selectively diffusing other conductivity type impurities in a ring in a part thereof based on the semiconductor substrate and forming a collector by selectively diffusing other conductivity type impurities in the ring. And a detection resistor is connected to the collector or the emitter, and the drain and the emitter of the field effect transistor are connected. When the voltage drop due to the substrate resistance becomes higher than the voltage between the base and the emitter, the transistor becomes conductive. And a lateral bipolar transistor for current detection for detecting a collector current. In the above-described semiconductor device in which a detection resistor is connected to the collector, a bias voltage substantially equal to the voltage between the base and the emitter is added between the emitter and the back electrode of the bipolar transistor, and the collector is connected directly or through the detection resistor. It is grounded.

[0006]

According to the above technical means, when the voltage drop due to the substrate resistance becomes higher than the base-emitter voltage and the lateral bipolar transistor for current detection is turned on, the collector current is detected by the detection resistor.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. First, in FIG. 1, (3) is a rectangular semiconductor substrate, (Qbx)... Are MOSFETs, and (Qc) is a lateral bipolar transistor for current detection. The semiconductor substrate (3) is of an N-type, and has a MOSFET (Q
bx) as the common drain (D) and the base (B) of the bipolar transistor (Qc). MOSFET (Q
bx) is conventionally the same, the drain (D) and comprising a semiconductor substrate (3) sequentially P-type and N + type impurity, and selectively diffused
It forms the Gate (G) and source (S), N number of MOSFET (QBX) ... the element group consisting of formed along the periphery of the substrate surface large MOSFET Power
(Qb). The lateral bipolar transistor (Qc) for current detection uses the substrate (3) as a base (B), and FIG.
As shown in FIG. 5, a collector (C) is formed by selectively diffusing P + -type impurities in a ring shape in order to increase current injection efficiency, and a P + -type impurity is selectively diffused in a circular shape into a ring to form an emitter (E). ) Is formed at the center of the substrate as in the prior art, in order to make the current uniform. Then, a detection resistor (Ra) is connected to the collector (C) inside or outside the substrate, and the detection resistor (R) is connected.
a), the collector (C) is connected to the source (S), and the back electrode (4) serving as the drain (D) and the emitter (E) are directly connected or the base-emitter voltage (Vb
Connect via a bias voltage (Vo) approximately equal to e).

FIG. 3A shows an equivalent circuit of the semiconductor device (5). The drain (D) of the MOSFET (Qb) is connected to the base (B) of the bipolar transistor (Qc). The drain (D) and the emitter (E) are connected directly via a substrate resistance (Rd) or via a bias voltage (Vo). In addition, the collector (C) is connected to the source (S) via the detection resistor (Ra).

The operation of the present invention based on the above configuration will now be described. First, a current (Id) flows from the drain (D) of high potential (Vdd) to the source (S) via the substrate resistance (Rd), and a voltage drop generated at both ends of the substrate resistance (Rd) is a voltage between the base and the emitter. When the voltage exceeds (Vbe), the bipolar transistor (Qc) becomes conductive and the collector current (Ia) flows. Therefore, a voltage (Va) generated at both ends of the detection resistor (Ra) is detected to extract an overcurrent signal. At this time, when the drain (D) and the emitter (E) are connected together with the substrate resistance (Rd) via the bias voltage (Vo), the bipolar transistor (Qc) conducts even with a small current (Id), and the detection sensitivity is reduced. improves.

FIG. 3B shows another embodiment of the present invention.
(C) Referring to each equivalent circuit shown in (d), first, the equivalent circuit in FIG. 3 (b) is a bipolar transistor (Q
The collector (C) of (c) is grounded instead of being connected to the source (S) via the detection resistor (Ra). This causes an amplifying action and reduces a small current (Id) to a large detection voltage (Va). And the detection sensitivity is improved as described above. The equivalent circuits shown in FIGS. 3C and 3D are shown in FIG.
In (a) and (b), the detection resistors (Ra) connected to the collector (C) are connected to the emitter (E), respectively, and the collector side or the emitter side may be selectively connected as appropriate according to the load circuit. .

[0011]

According to the present invention, in a power MOSFET having a bipolar transistor for current detection, when a bias voltage is applied to the emitter of the transistor or when the collector is grounded via a detection resistor, the bipolar transistor Current detection sensitivity is improved.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a main part of an embodiment of a semiconductor device according to the present invention.

FIG. 2 is a plan view showing an embodiment of a semiconductor device according to the present invention.

FIG. 3A is an equivalent circuit diagram of the semiconductor device shown in FIG. (B), (c) and (d) are equivalent circuit diagrams showing another embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram illustrating an example of a conventional semiconductor device.

FIG. 5 is a plan view showing an example of a conventional semiconductor device.

[Explanation of symbols]

 3 Semiconductor substrate Qbx MOSFET Qc Current detecting lateral bipolar transistor 4

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/06 311 H01L 29/78

Claims (3)

(57) [Claims] 1. A large-capacity power field-effect transistor comprising a similar group of MOS-type field-effect transistors in which a semiconductor substrate of one conductivity type is used as a common drain and a number of sources and gates are formed on the surface thereof. Forming a collector by selectively diffusing other conductivity type impurities in a ring on a part of the surface of the drain area based on the semiconductor substrate to form a collector, and selectively diffusing other conductivity type impurities in the ring to form an emitter; In addition, a detecting resistor is connected to the collector or the emitter, and the drain and the emitter of the field effect transistor are connected to each other. And a current detecting lateral bipolar transistor. 2. The semiconductor device according to claim 1, wherein a detection resistor is connected to a collector of the bipolar transistor.
A semiconductor device wherein a bias voltage substantially equal to a base-emitter voltage is applied between an emitter and a back electrode. 3. The semiconductor device according to claim 1, wherein the collector of the bipolar transistor is grounded directly or via a detection resistor.