JP3239052B2 - Semiconductor integrated circuit - 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 integrated circuit having a current detecting function, and more particularly to a semiconductor integrated circuit that can be suitably used for a switching power supply that operates as overcurrent protection or a current mode type.

[0002]

2. Description of the Related Art In recent years, an output element such as a power transistor and a resistor for detecting a current flowing through the power transistor and the like are integrated and formed in a semiconductor integrated circuit, and the number of components connected to the outside is reduced. Have been. FIG.
1 shows a schematic configuration of a current mode control type step-up switching power supply circuit. A coil 1 is inserted in series with the input voltage Vin, and a current is supplied to a load resistor 3 via a diode 2. A capacitor 4 is connected in parallel to the load resistor 3. The voltage supplied to the load resistor 3 is controlled by a semiconductor integrated circuit (hereinafter abbreviated as “IC”) 5. The power transistor 6 in the IC 5
A current detection resistor 7, a current amplifier 8, an error amplifier 9, a comparator 10, and the like are formed. The error amplifier 9 detects the voltage at the midpoint between the voltage dividing resistors 11 and 12 connected in series between both ends of the load resistor 3. In IC5,
Further, an oscillator 13 and a drive circuit 14 are included, and perform switching control of the power transistor 6.

FIG. 8 shows operation waveforms of the step-up switching power supply circuit shown in FIG. As shown in FIG.
Generates a Set signal at every W cycle of OSC of, for example, 20 μs. The drive circuit 14 starts the oscillator 1 at time t1.
When the Set signal is given from 3, the power transistor 6 is turned on. Power transistor 6 is ON
In this state, the voltage between the collector and the emitter of the power transistor 6 decreases to the saturation voltage, and the collector voltage Vc almost drops to the potential of the ground GND as shown in FIG. When the power transistor 6 is ON, the emitter current IE is equal to the input voltage Vin and the saturation voltage Vsa of the power transistor 6, as shown in FIG.
It increases according to the slope obtained by dividing the difference from t by the value of the inductance L of the coil 1. During this time, electromagnetic energy is stored in the coil 1 by the current flowing through the coil 1. When the power transistor 6 is turned off at time t2 and the collector current flowing through the power transistor 6 is cut off, the electromagnetic energy stored in the coil 1 is equal to the current ID flowing through the load resistor 3 and the capacitor 4 via the diode 2. Is supplied as shown in (D). That is,
The load resistor 3 has a capacitor 4 between time t1 and t2.
At the time t2
Until time t3 when the next Set signal rises, the current flowing through the diode 2 is supplied to the load resistor 3 and the capacitor 4 is charged.

[0004] As shown in (E), the output from the current amplifier 8 changes corresponding to the emitter current IE shown in (C). The output of the current amplifier 8 is a comparator 10
Is compared with the output level Le from the error amplifier 9, and at time t2 when the output level Le from the error amplifier 9 is exceeded, the comparator 10 outputs a Reset as shown in FIG.
A signal is derived. The drive circuit 14 turns off the power transistor 6 when the Reset signal from the comparator 10 rises.

The output of the error amplifier 9 becomes higher as the output voltage V0 across the load resistor 3 becomes lower than a set value,
It becomes lower as V0 becomes higher than the set value. That is,
When the output voltage V0 decreases, the output voltage from the error amplifier 9 increases. Therefore, the power transistor 6 keeps on until the output of the current amplifier 8 increases. As a result, the amount of electromagnetic energy stored in the coil 1 increases, and a feedback mechanism that increases the output voltage V0 is formed. When the output voltage V0 is higher than the set value, the reverse operation is performed. The reference voltage in the error amplifier 9 is Vre
f, where the resistance values of the voltage dividing resistors 11 and 12 are R1 and R2, the output voltage V0 is expressed by the following first equation.

[0006]

(Equation 1)

[0007] A limiter circuit is provided in the error amplifier 9, and overcurrent protection can be performed by limiting the upper limit of the current flowing through the power transistor 6.

FIG. 9 is an electric circuit diagram in a case where, for example, 60 power transistors 16 for low power are connected in parallel as the output transistor 15 instead of the power transistor 6 of FIG. An emitter diffused resistor 17 is connected in series to the emitter of each power transistor 16. One of the emitter diffusion resistors 17 corresponds to the current detection resistor 7 in FIG. The emitter diffusion resistor 17 as a current detection resistor has a resistance value of about 10Ω, and its temperature coefficient is about 2000 ppm / ° C.
The current amplifier 8 detects the voltage drop of the current detection resistor 7 and amplifies it by about 10 times.

[0009]

In the switching power supply circuit as shown in FIG. 7, the current detection resistor 7 is formed by the emitter diffusion resistor 17. The accuracy of this resistance value is ±
Since the temperature coefficient is as large as 20% and the temperature coefficient is 2000 ppm / ° C., the overcurrent detection level greatly varies. When the resistance value fluctuates to a smaller value, the power transistor 16 is not protected until the current flowing through the power transistor 16 increases, so that a large power transistor 16 having a large current capacity is required. Further, when, for example, 60 power transistors 16 are connected in parallel as one output transistor 15, no problem occurs if the emitter current IE of each power transistor 16 flows evenly, but actually, the temperature distribution Does not flow evenly due to a change in the data, and this also increases the error.

An object of the present invention is to provide a semiconductor integrated circuit capable of accurately detecting a current in the semiconductor integrated circuit and performing a highly reliable operation by the detected current.

[0011]

SUMMARY OF THE INVENTION The present invention provides an output element which operates as a switching element of a switching power supply circuit, and a metal wiring in which a current to be detected flows and a current detection section is provided in a path of a current flowing through the output element. And the said
An error in which a voltage obtained by dividing the output voltage of the output element is input
An amplifier, voltage limiting means for generating a limiting voltage that changes the temperature of the output from the error amplifier at the same level as the temperature characteristic of the electrical resistance of the metal wiring, and limiting by the limiting voltage from the voltage limiting means. A comparator for comparing the output voltage with a voltage obtained by amplifying a voltage drop in a current detection section of the metal wiring, and controlling an output of the output element based on an output of the comparator to switch the output element. And a drive means for driving. According to the present invention, a current detection section in which a current to be detected flows is provided in the metal wiring section, and a voltage obtained by dividing the output voltage of the output element is input.
In response to the output from the power amplifier, the voltage limiting means generates a limited voltage that changes in temperature at the same level as the temperature characteristic of the electrical resistance value of the metal wiring, and the voltage limited by the limited voltage and the voltage drop in the current detection section The comparator is compared with the amplified voltage. Although the electric resistance value of the metal wiring greatly varies depending on the temperature change, the temperature compensation is performed with the limited voltage, so that the influence of the temperature change can be suppressed. Since the current is accurately detected, the comparator can perform a highly accurate and highly reliable comparison operation. Since the current detection is performed at the metal wiring portion, there is no need to perform diffusion for forming the detection resistor, and the metal wiring can be used effectively.

Further, according to the present invention, since the current detection section is provided in the path of the current flowing through the output element, control relating to the operation of the output element can be performed accurately.

Further, according to the present invention, since the drive means switches and controls the output element of the switching power supply circuit based on the output of the comparator, a highly reliable switching power supply circuit can be easily constructed. .

Further, the drive means of the present invention is characterized in that the drive means performs overcurrent protection of the output element. According to the present invention, the overcurrent protection of the output element of the switching power supply circuit can be effectively performed by the drive means, and a highly reliable switching power supply circuit can be realized.

[0015]

Further, the output element according to the present invention comprises a plurality of output elements connected in parallel, and the current detection section is provided commonly to the entire output element. According to the present invention, since a plurality of output elements are connected in parallel,
Heat loss per one output element can be reduced. Since the current detection section is provided in the metal wiring, a common connection state can be easily realized for all of the plurality of output elements.

Further, the output elements of the present invention form a plurality of groups each of which is connected in parallel, and the current detection section is provided for a preselected group of output elements. And According to the present invention, since the current detection section is provided on the metal wiring, the accuracy can be improved, and even when the current detection section is provided for a partial output element group, accurate control of the entire output element can be performed. Can be. Further, the present invention provides a power transistor operating as a switching element, a metal wiring provided with a current detection section for detecting an emitter current of the power transistor, a current amplifier for amplifying a voltage drop in the current detection section of the metal wiring. An error amplifier to which a voltage obtained by dividing the output voltage of the power transistor is input, and a limit voltage that changes the temperature of the output from the error amplifier at the same level as the temperature characteristic of the electric resistance value of the metal wiring. and voltage limiting means for, comparator and, the power to control the output of the power transistor based on an output of said comparator for comparing the output of the current amplifier and the output of the error amplifier that is voltage limited by the voltage limiting means Drive means for switchingly driving the transistor. A semiconductor integrated circuit which is characterized in that the overcurrent protection Njisuta. According to the present invention, the output current of the power transistor operating as a switching element is amplified by a current amplifier as a voltage drop in a current detection section provided on a low-loss metal wiring. The output voltage of the power transistor is divided and input to the error amplifier, and the output from the error amplifier is compensated for by a temperature change at the same level as the temperature characteristic of the electrical resistance of the metal wiring. And a voltage limit is performed. The comparator compares the output with the output of the current amplifier, and the drive means performs switching driving of the power transistor based on the output of the comparator to perform overcurrent protection. Even if a low-loss metal wiring is used as the detection resistor, highly accurate detection independent of temperature is possible.

[0018]

FIG. 1 shows a configuration of a step-up switching regulator by a control system according to an embodiment of the present invention. A coil 21, a diode 22, and a load resistor 23 are connected in series, and a capacitor 24
3 are connected in parallel. The connection point between the coil 21 and the anode of the diode 22 is connected to the collector of the power transistor 26 in the IC 25. The IC 25 includes a current detection resistor 27 connected to the emitter side of the power transistor 26. Further, a current amplifier 28 for detecting a voltage drop between both ends of the current detection resistor 27, an error amplifier 29 for detecting a voltage corresponding to a voltage between both ends of the load resistor 23, a current amplifier 28 and an error amplifier 29
Is also included. The voltage between both ends of the load resistor 23 is determined by the voltage dividing resistor 3 connected in series.
1, 32. The detection voltage obtained from the connection point between the voltage dividing resistors 31 and 32 is input to the error amplifier 29. The IC 25 also includes an oscillator 33 and a drive circuit 34.

In the error amplifier 29, a comparator 35 to which the input voltage from the voltage dividing resistors 31 and 32 is input to the inverting input side, a reference voltage source 36 for applying the reference voltage Vref to the non-inverting input side of the comparator 35, and a comparator A voltage limiting circuit 37 provided on the output side of the power supply 35 is included. The drive circuit 34 includes an RS flip-flop 38 and a driver 39. The reset input R of the RS flip-flop 38 has a reset
A signal is input. A clock signal from the oscillator 33 is input to a set input S of the RS flip-flop 38 as a Set signal. The operation of the IC 25 is the same as the operation of the IC 5 shown in FIG. However, the point that the current detection resistor 27 is formed using the metal wiring of the IC 25 is different from the diffusion resistor used in the IC 5.

In the switching power supply circuit of FIG. 1, the inductance L of the coil 21 is, for example, 100 μH, the capacitance C of the capacitor 4 is 470 μF, the gain of the comparator 35 in the error amplifier is 100 times, 40 dB, and the gain of the current amplifier 28 is 10 times. Is 20 dB. The current IL flowing through the coil 21 is switched according to the switching state of the power transistor 26, whether it becomes the current IE flowing through the power transistor 26 or the current ID flowing through the diode 22.

FIG. 2 shows the configuration of the power transistor 26 of FIG. In the present embodiment, 240 power transistors 41 each having a small capacity are integrated, and an emitter diffusion resistor 42 is inserted in each emitter, and the power transistors 26 are operated in parallel as a whole. The emitter diffusion resistance 42 of each power transistor 41 is approximately 1
It has a resistance value of 0Ω and enhances the uniformity of the emitter current IE flowing through each power transistor 41. The greater the number of the power transistors 41, the higher the homogeneity, and the more difficult it is for the switching current to concentrate on a part and to be destroyed.

The current detection resistor 27 is inserted after the emitter current of each power transistor 41 has joined.
It is formed in a part of a portion for performing metal wiring as a semiconductor integrated circuit. Since the entire emitter current IE of the power transistor 41 is directly detected, the detection accuracy can be improved. The resistance value of the metal wiring is 50 mΩ.
And the variation is ± 10%, which can be made smaller than ± 20% in the case of forming as an emitter diffusion region, so that the detection accuracy can be further improved. However, since metal wiring uses, for example, aluminum (Al), the temperature coefficient of resistance is about 39.
It is about 00 ppm / ° C., which is larger than about 2000 ppm / ° C. in the case of the emitter diffusion resistance. In order to improve this, in the present embodiment, the voltage limiting circuit 37 is provided with a temperature characteristic, and the temperature characteristic of the limited voltage can be adjusted according to the resistance temperature characteristic of the metal wiring.

FIG. 3 shows the configuration of the voltage limiting circuit 37 of FIG. The PNP transistor 52 through which the collector current I1 of the NPN transistor 51 flows
A current mirror circuit is formed in a pair with 3. Current I
2 flows through the collector side of the PNP transistor 53 where P2 flows.
The base of NP transistor 54 is connected. A positive constant voltage Vs = 2.3 V is applied to the voltage limiting circuit 37, and a voltage V obtained by dividing the constant voltage Vs by the resistors 55 and 56 is applied.
1 is applied to the base of NPN transistor 51. N
A resistor 57 is connected between the emitter of the PN transistor 51 and the ground GND. A resistor 58 is connected between a common connection point between the collector of the PNP transistor 53 and the base of the PNP transistor 54 and the ground GND.
The resistance values of the resistors 55, 56, 57, 58 are R11, R1
2, R13 and R14. One example of the resistance value is R11 =
30 kΩ, R12 = 16 kΩ, R13 = 1 kΩ, R14
= 10 kΩ.

Assuming that the limiting voltage of the voltage limiting circuit 37 is Vl, this Vl is the temperature characteristic 39 of the current detecting resistor 27.
If the temperature changes at the same level as 00 ppm / ° C., the fluctuation of the detected current value due to the temperature change can be offset. Assuming that Vl = 2 V, a rise of 7.8 mV per 1 ° C. is required to have a temperature characteristic of +3900 ppm / ° C. Assuming that the base-emitter voltages of the transistors 51 and 54 are VBE1 and VBE4, Vl is represented by the following second equation.

[0025]

(Equation 2)

That is, P constituting the current mirror circuit
Collector currents I1, I2 of NP transistors 52, 53
Is equal, and the base-emitter voltages of the respective transistors 51, 52, 53, 54 can be regarded as equal to VBE. The temperature characteristic of the emitter voltage Vl is expressed by the following third equation.

[0027]

(Equation 3)

The temperature characteristic of VBE is -2 mV because it is a silicon transistor. Therefore, the ratio between R14 and R13 is 4.9 as shown in the fourth equation.

[0029]

(Equation 4)

That is, if R14 / R13 = 4.9, the temperature characteristic of Vl when Vl = 2V is +390.
0 ppm / ° C., which can be matched with the temperature characteristics when the metal wiring is used as the resistor, and the fluctuation due to the temperature can be offset. If the ratio of R14 / R13 is reduced, the positive temperature characteristic of Vl is reduced, and the overcurrent detection level is also slightly negative. If the temperature characteristic becomes smaller than the temperature characteristic of the metal wiring, it is detected as an overcurrent quickly. Thus, the temperature characteristic of the overcurrent detection level can be adjusted by the ratio of R14 / R13. Therefore, the problem that a metal wiring is used for the current detection resistor 27 and its temperature coefficient is large is solved.

FIG. 4 shows a circuit arrangement on the chip surface of the IC 25, and FIG. 5 shows a cross section taken along the line VV of FIG. For convenience of illustration, the number of small transistors is 4
As shown. The power transistor 26 is connected to the field 60
The base diffusion region 61, the emitter diffusion region 62, and the collector diffusion region 63 are provided therein. The base contact 6 is provided in the base diffusion region 61.
4 and 65 are provided, emitter contacts 66 and 67 are provided in the emitter diffusion region 62, and a collector contact 68 is provided in the collector diffusion region 63. I
A metal wiring indicated by a virtual line is provided on the surface of C25. A base wiring 71 is connected to the base contacts 64 and 65, an emitter wiring 72 is connected to the emitter contacts 66 and 67, and a collector wiring 73 is connected to the collector contact 68. The emitter wiring 72 is GN
It is formed to extend to the D pad 74, and a current detection section 75 is provided in the middle. In order to measure the voltage drop in the current detection section 75, detection lines 76 and 77 are formed, and the input to the current amplifier 28 shown in FIG. 1 is led.

As shown in FIG. 5, the field 60 contains P
It is formed as an island on the buried N ⁺ layer 81 of the mold substrate 80. The chip surface except for the base contacts 64 and 65, the emitter contacts 66 and 67, and the collector contact 68 is protected by the oxide film 82. An isolation diffusion layer 83 is provided around the field 60.

FIG. 6 shows a configuration of a current detection resistor 84 and an output transistor 85 according to another embodiment of the present invention. The output transistor 85 is formed by connecting, for example, 48 small power transistors 41 as shown in FIG. 2 in parallel. An emitter diffusion resistor 42 is connected to the emitter of each power transistor 41 to make the operating current uniform. Thus, each of the 48 power transistors 4
Five output transistors 85 each having 1 connected in parallel are connected in parallel, and the operation as one power transistor 86 is performed by 240 power transistors 41 as a whole. The equivalent emitter of the output transistor 85 has
The current detection resistors 84 formed on the metal wiring are connected to each other, and one of them, that is, one out of five, is detected as a representative output current. The current detection resistor 84 can be formed with high accuracy, and furthermore, each output transistor 85
And 5 less than the conventional one
Since the detection is performed by one of the components, the current detection accuracy can be improved as compared with the conventional case.

In the above embodiment, the case where a bipolar transistor is used as the power transistor has been described. However, the same control can be performed with another output element such as a MOS transistor. In addition, although the output current of the switching transistor of the step-up switching power supply circuit is detected, other types of switching power supply circuits, semiconductor integrated circuits including current output elements such as semiconductor integrated circuits for linear stabilized power supplies, or By similarly performing temperature compensation on a semiconductor integrated circuit that needs to detect current, current detection using metal wiring can be performed.

[0035]

As described above, according to the present invention, since the current detection section is provided using the metal wiring in the semiconductor integrated circuit, the current detection section is formed as compared with the case where the current detection section is formed using the diffusion region. The current can be detected with high accuracy. Since the resistance temperature characteristic of the metal wiring is temperature-compensated, the reliability of operation as a semiconductor integrated circuit can be improved.

Further, according to the present invention, since the current flowing through the output element in the semiconductor integrated circuit can be detected with high accuracy, the semiconductor integrated circuit can be used with high reliability.

Further, according to the present invention, since the drive circuit switches the output element of the switching power supply circuit based on the output of the comparator using the temperature-compensated limit voltage, the switching power supply circuit can be operated in a highly reliable state. Can be operated.

Further, according to the present invention, overcurrent protection of the output element can be performed with high reliability.

Further, according to the present invention, the output voltage when the switching power supply circuit is operated in the current mode type can be stabilized with high reliability and with high accuracy.

Further, according to the present invention, the output element can be constituted by a plurality of parallel connections, the current as a whole can be detected with high accuracy, and a highly reliable operation can be performed.

Further, according to the present invention, the entire output current can be accurately controlled based on the output current of a partial group of a plurality of output elements. Further according to the invention,
Current detection is performed using a low-loss metal wiring, and the effect of a change in the resistance value of the metal wiring is temperature-compensated, so that high-precision current detection can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the voltage limiting circuit of FIG.

FIG. 3 is an electric circuit diagram in which the power transistor 26 of FIG. 1 is constituted by a plurality of power transistors.

FIG. 4 is a circuit layout diagram of a chip surface when the power transistor 26 of FIG. 1 is constituted by a plurality of power transistors.

FIG. 5 is a cross-sectional view taken along the line VV of FIG. 4;

FIG. 6 is a partial electric circuit diagram showing a configuration of a power transistor and a current detection resistor according to another embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic electrical configuration of a conventional switching power supply circuit.

FIG. 8 is a time chart illustrating an operation of the switching power supply circuit of FIG. 7;

9 is an electric circuit diagram in a case where the power transistor of FIG. 7 and a small-capacity power transistor are connected in parallel.

[Explanation of symbols]

 Reference Signs List 21 coil 22 diode 23 load resistor 24 capacitor 25 IC 26, 41, 86 power transistor 27, 84 current detection resistor 28 current amplifier 29 error amplifier 30 comparator 31, 32 voltage dividing resistor 33 oscillator 35 comparator 36 reference voltage source 37 voltage limiting circuit 51 NPN transistor 52,53,54 PNP transistor 55-58 Resistance 60 Field 75 Current detection section

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-3-186909 (JP, A) JP-A-2-256275 (JP, A) JP-A-6-102292 (JP, A) JP-A-6-102292 188641 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 3/155 H01L 27/04

Claims (5)

(57) [Claims] An output element that operates as a switching element of a switching power supply circuit, a metal wiring in which a current to be detected flows, and a current detection section is provided in a path of a current flowing through the output element, and an output voltage of the output element Input voltage divided
Limits and Raanpu, the output from the error amplifier, a voltage limiting means for generating the limit voltage to temperature change at the same level as the temperature characteristics of the electric resistance of the metal wire, by limiting voltage from said voltage limiting means A comparator that compares the output voltage with a voltage obtained by amplifying a voltage drop in a current detection section of the metal wiring, controlling an output of the output element based on an output of the comparator, and switching the output element. A semiconductor integrated circuit, comprising: a driving unit for driving. 2. The semiconductor integrated circuit according to claim 1, wherein said drive means performs overcurrent protection of said output element. 3. The semiconductor according to claim 1, wherein the output element comprises a plurality of elements connected in parallel, and the current detection section is provided in common for the entire output element. Integrated circuit. 4. The output element forms a plurality of groups consisting of a plurality of elements connected in parallel, and the current detection section is provided for a preselected group of output elements. The semiconductor integrated circuit according to claim 1. 5. A power transistor operating as a switching element, a metal wiring provided with a current detection section for detecting an emitter current of the power transistor, and a current amplifier for amplifying a voltage drop in the current detection section of the metal wiring. An error amplifier to which a voltage obtained by dividing the output voltage of the power transistor is input; and a limit voltage that changes the temperature of the output from the error amplifier at the same level as the temperature characteristic of the electric resistance value of the metal wiring. A voltage limiting means for comparing the output of the error amplifier, the voltage of which is limited by the voltage control means, with the output of the current amplifier; and controlling the output of the power transistor based on the output of the comparator to control the power. Drive means for switchingly driving a transistor; A semiconductor integrated circuit for performing overcurrent protection of a transistor.