JP2007084057A - Air bag device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air bag device capable of accomplishing reduction of cost by efficiently assembling IC for communication in a processing circuit for outputting a signal for air bag deployment. <P>SOLUTION: The air bag device is provided with a first processing circuit (3) for determining collision of a vehicle based on an output of a G sensor (1); and a second processing circuit (21) for outputting an air bag deployment signal based on an output of a circuit (3). On the second processing circuit (21), a communication means for controlling information communication between the first processing circuit (3) and external electronic control devices (200, 300); a first power source means (7) for producing a drive voltage of the first and second processing circuits based on an external power source (10) voltage and having a backup power source means (11); a second power source means (23) for producing a drive voltage of the communication means (22) based on the output of the first power source means (7); a power source control means (24) for detecting reduction of the external power source voltage and stopping provision of power from the second power source means to the communication are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an airbag apparatus for deploying an airbag in the event of a vehicle collision to protect the safety of an occupant, and in particular, communication means for configuring an information network with other electronic control apparatuses in the vehicle. The present invention relates to an airbag device provided.

  A controller area network (hereinafter referred to as CAN) is a serial bus system standardized for vehicles for exchanging information and data between a plurality of electronic control units (hereinafter referred to as ECUs). A CAN driver for controlling CAN communication is usually provided as an independent IC, which is used as an independent component in an ECU such as an airbag. However, the CAN driver IC itself is expensive, which is a major factor in increasing the cost of the ECU. For this reason, it is desirable to reduce the cost of the ECU by eliminating the need for an independent CAN driver IC by incorporating the CAN driver together with other electronic units in the ECU into one integrated circuit to configure the ASIC.

  The CAN driver IC is disclosed in, for example, Patent Document 1, and the incorporation of the CAN driver in the ASIC is disclosed in, for example, Patent Document 2.

  FIG. 1 shows a configuration of a conventional airbag ECU incorporating a CAN driver. The airbag ECU 100 is a microcomputer (hereinafter referred to as a microcomputer) that determines a collision state in a software manner based on outputs from a main G sensor (acceleration sensor) 1 that detects a vehicle collision, a G sensor 2 for safing, and a main G sensor 1. , Main microcomputer) 3, microcomputer (hereinafter referred to as sub-microcomputer) 4 that performs a collision determination for safing based on the output of the safing G sensor 2, a collision determination signal from the main microcomputer 3 and the sub-microcomputer 4 Output circuit 5 (5a, 5b,..., 5n) for outputting an ignition signal of the airbag based on the safing determination signal. The output circuit 5 outputs a driving signal to the airbag 6 (6a, 6b... 6n) mounted on the vehicle. Although not shown, each airbag 6 includes a squib that explodes when energized to deploy the airbag and a switching transistor that controls the supply of power to the squib. Power is supplied to the squib by the system power supply circuit 7. The output circuit 5 is connected to the base of the switching transistor. Therefore, when the output circuit 5 outputs an ignition signal, the switching transistor is turned on and power is supplied to the squib.

  Usually, the output circuit 5 is incorporated in one IC as an ASIC 8 together with a power circuit (hereinafter referred to as a system power circuit) 7 that forms a voltage necessary for driving each component in the airbag ECU from an external power source. Yes.

  The system power supply circuit 7 is supplied with electric power by being connected to the in-vehicle battery 10 via the ignition switch 9, and forms a voltage necessary for driving the output circuit, the main microcomputer, the sub microcomputer, and the like. Further, the system power supply circuit 7 is connected to a capacitor 11 serving as a backup power supply. When power is supplied from the in-vehicle battery 10, the capacitor 11 is charged, and the ignition switch 9 is turned off to turn off the in-vehicle battery 10. When the power supply from is stopped, power is supplied to the system power supply circuit 7.

  The airbag ECU 100 needs to operate normally and deploy the airbag even when the ignition switch 9 is turned off, for example, due to a vehicle collision, and power is no longer supplied from the in-vehicle battery 10 to the system power supply circuit 7. In such a case, the backup power supply is provided to provide necessary power for the entire system.

  The airbag ECU 100 further includes an input circuit 12, and inputs outputs from the other acceleration sensors 13 and 14 provided outside the ECU 100 to the main microcomputer 3 and the sub-microcomputer 4. The acceleration sensor 13 is, for example, a front-side collision front sensor that is provided at the front side portion of the vehicle body and detects a collision from the front direction. The acceleration sensor 14 is provided at the side portion of the vehicle body and is a side collision satellite that detects a collision from the side surface. It is a sensor.

  The airbag ECU 100 further includes a CAN driver 15 for performing CAN communication between the main microcomputer 3 and other external ECUs such as an electronic fuel injection (hereinafter referred to as EFI) ECU 200 and a door ECU 300. The CAN driver 15 is provided as a single IC. As described above, since the airbag ECU 100 needs to operate normally even when the external power supply is cut off, the airbag ECU 100 has a backup power supply, but the CAN driver 15 seems to be cut off. No longer need to be active. Therefore, if the power source of the CAN driver 15 and the system power source are shared, the CAN driver 15 continues to draw current consumption from the backup power source of the airbag when the external power source is shut off. When the backup power source is consumed by the CAN driver 15, it is necessary to configure the backup power source with a capacitor having a large capacity, which adversely affects the miniaturization of the airbag ECU 100 and increases the cost.

  Therefore, in the airbag ECU 100, a power source for the CAN driver 15 is provided on a separate path from the system power source circuit 7, and the power supply to the CAN driver 15 is also stopped when the ignition switch 9 is off. Yes. Reference numeral 16 denotes a power supply circuit (CAN driver power supply circuit) for providing drive power to the CAN driver 15, and a commercially available power supply IC is used.

JP-A-10-105309 JP 2004-286029 A

  As described above, in the conventional airbag device, it is necessary to provide a power source for communication means such as a CAN driver on a separate path from the system power source because of the necessity of a backup power source. Therefore, in order to incorporate the communication means in the processing circuit that outputs the signal for deploying the airbag, it is necessary to provide a separate power circuit connected to the external power source through a different path from the system power circuit. The overall structure becomes complicated, and a large chip area is required to realize this. As a result, there is a problem that even if the communication means, which has conventionally been constituted by an independent IC, is incorporated in the processing circuit and the communication IC is omitted, it is not possible to expect a significant cost reduction as an airbag device. To do.

  The present invention has been made with respect to such a point, and provides an airbag apparatus capable of realizing a large cost reduction by efficiently incorporating a communication IC into a processing circuit that outputs a signal for deploying an airbag. This is the issue.

  In order to solve the above problems, an airbag device of the present invention includes a first processing circuit that determines a vehicle collision based on an output from a sensor for detecting a vehicle collision, and a first processing circuit In an airbag apparatus including a second processing circuit that outputs a signal for deploying an airbag based on an output, the second processing circuit includes a first processing circuit and another electronic control device outside the airbag apparatus. A communication means for controlling information communication between the first power supply means and a first power supply means for generating a voltage for driving the first and second processing circuits based on the external power supply voltage, and backup when the external power supply voltage drops A first power supply means including a backup power supply means for supplying a voltage; a second power supply means for supplying a drive voltage to the communication means based on an output of the first power supply means; and detecting a decrease in the external power supply voltage Then Providing a power supply control means for stopping the provision of the driving voltage from the power supply means to the communication means.

  In the airbag apparatus configured as described above, in the second processing circuit, when the power supply control means detects a decrease in the external power supply voltage, the supply of the drive voltage from the second power supply means to the communication means is stopped. For this reason, even if the backup power supply operates and supplies power to the second processing circuit due to the voltage drop of the external power supply, the power supply to the communication means is cut off, and the communication means does not waste backup power. Therefore, the drive voltage for the communication means can be formed by the second power supply means based on the output of the first power supply means, and the circuit configuration of the second power supply means can be simplified accordingly. The circuit configuration of the entire power supply circuit is simplified, and the communication means can be incorporated in the second processing circuit with a small chip area. As a result, it is possible to provide an airbag device with a low manufacturing cost.

  The external power source is an in-vehicle battery connected via an ignition switch. Further, the second processing circuit is composed of one ASIC. Further, the communication means is a CAN driver that controls the controller area network. The first processing circuit is constituted by a microcomputer.

  Further, the first power supply means of the second processing circuit further includes voltage monitoring means for monitoring an input voltage from the external power supply, and the power supply control means has a monitor value in the voltage monitoring means that is a predetermined value or less. In this case, the second power supply unit is brought into a stopped state. As a result, even if the backup power supply is activated due to a voltage drop of the external power supply, the second power supply means does not operate, and therefore consumption of the backup power by the communication means is prevented.

  Further, the first power supply means in the second processing circuit has a case where the output of the first power supply means falls below a predetermined value, specifically, below the driving voltage of the first and / or second processing circuit. The power supply control means includes a reduced voltage detection means for outputting a reset signal, and the power supply control means turns off the second power supply means by the input of the reset signal. As a result, when the output of the first power supply means falls below the output level necessary for driving the first and / or second processing circuit, the communication means is activated and the first processing circuit malfunctions. Is prevented from being transmitted to an external electronic control device.

  When the first processing circuit is constituted by a microcomputer, the second processing circuit further includes a microcomputer runaway detection circuit, and the power supply control means receives the runaway detection circuit output to receive the second runout circuit. Turn off the power supply means. As a result, when the microcomputer runs away, the communication means is stopped to ensure communication reliability.

  The second processing circuit further includes a thermal shutdown circuit that detects abnormal heat generation of the communication means. The power supply control means turns off the second power supply circuit upon receipt of the abnormality detection signal of the thermal shutdown circuit. Further, the second power supply means in the second processing circuit includes a reduced voltage detection circuit that detects that the output voltage has become a predetermined value or less, and turns off the communication means by the output of the reduced voltage detection circuit. Thereby, the reliability of communication by the communication means is ensured. The thermal shutdown information is transmitted to the microcomputer via the power supply control means. Thereby, the microcomputer knows that the communication means has stopped driving due to the thermal shutdown.

  The first power supply means in the second processing circuit includes a booster circuit that boosts the input voltage from the external power supply, and the backup power supply means generates a backup voltage based on the booster circuit output. The second processing circuit includes a step-down circuit after the booster circuit in the first power supply unit, and the second power supply unit generates a voltage for the communication unit based on the output of the step-down circuit. As a result, the second power supply means can be configured by a low power circuit, so that the circuit configuration is simplified and the chip area for realizing the entire power supply circuit is reduced.

  With the above configuration, in the airbag device of the present invention, the power supply for the communication means can be configured on the same path as the power supply for the system, so the configuration of the power supply means for the communication means can be simplified. Therefore, even if the communication means is incorporated in the second processing circuit, the processing circuit is not complicated and the chip area is not increased. Therefore, a highly reliable airbag device can be obtained at low cost.

  FIG. 2 is a block diagram showing a configuration of the airbag ECU 20 according to the embodiment of the present invention. In the following drawings, the same reference numerals as those shown in FIG. 1 indicate the same or similar components.

  As shown in FIG. 2, in the airbag ECU 20 of the present embodiment, a CAN circuit 25 is incorporated in the ASIC 21. The CAN system circuit 25 includes a CAN driver 22, a CAN power supply circuit 23, and a power supply control unit 24 as communication means. Note that a conventional CAN driver, which is a single IC, has a thermal shutdown circuit. Therefore, the CAN circuit 25 has a thermal shutdown circuit 26 as well, which will be described later with reference to FIG. .

  Similar to the ASIC 8 in FIG. 1, the ASIC 21 further includes an output circuit 5 (5 a, 5 b... 5 n) for air bag ignition and a system power circuit 7. FIG. 3 is a diagram showing the relationship between the output circuit 5 and the airbag 6, and in particular, the output circuit 5 a and the airbag 6 a are representatively shown. However, other output circuits and airbags have the same configuration. is doing. The airbag 6a has a switching transistor 60 and a squib 61 connected in series between the power source B (vehicle battery 10) and the ground, and the output circuit 6a is connected to the base of the switching transistor 60 via a resistor 62. The output is configured to be input. Therefore, when the output circuit 5a outputs the ignition signal of the airbag, the transistor 60 is turned on and a current flows through the squib 61. The squib 61 is heated and explodes by this current, and the airbag 6a is deployed.

  In FIG. 2, the CAN power supply circuit 23 includes a 5V circuit, and generates a 5V voltage for driving the CAN driver 22 based on the intermediate output of the system power supply circuit 7. The power supply control unit 24 has a function of performing on / off control of the CAN power supply circuit 23 according to the state of the external power supply. Therefore, for example, when the battery is dropped from the vehicle body due to a vehicle collision or the like and power is not supplied to the airbag ECU 20 via the ignition switch 9, this is detected and the power supply circuit 23 for CAN is turned off. Consumption of backup power in the CAN driver 22 is prevented. The CAN driver originally notifies other ECUs of the collision. During an actual collision, a collision signal is transmitted to the airbag microcomputer on a separate line from this communication. Therefore, even if the power of the CAN driver is cut off, the communication of the collision signal is not cut off.

  FIG. 4 is a diagram showing details of the ASIC 21 in the airbag ECU 20 of FIG. 2, and particularly shows detailed structures of the CAN system circuit 25 and the system power supply circuit 7. As shown in the figure, the system power supply circuit 7 includes an ignition voltage (hereinafter referred to as IG voltage) monitor circuit 71, a booster circuit 72, a step-down circuit 73, and a 5V circuit 74. The IG voltage monitor circuit 71 is connected to the IG input terminal 30 of the airbag ECU 20, and the IG input terminal 30 is connected to the in-vehicle battery 10 via the ignition switch 9. The input side of the booster circuit 72 is connected to the IG input terminal 30. The backup power supply 11 is connected between the step-up circuit 72 and the step-down circuit 73.

  The IG voltage of, for example, 12V input to the airbag ECU 20 via the IG input terminal 30 is boosted to 23V by the booster circuit 72 in order to efficiently charge the backup power supply 11, and then, for example, to 7V by the step-down circuit 73. The voltage is stepped down and provided to the 5V circuit 74. The 5V circuit 74 generates a system voltage for driving the ASIC 21, the microcomputer 3, etc., and includes a reduced voltage reset circuit, and outputs a reset signal to prevent malfunction of the microcomputer 3 when a reduced voltage occurs. To do.

  The ASIC 21 also includes an output circuit 5 for airbag ignition, a runaway detection circuit 31 of the main microcomputer 3, and a serial communication circuit 32 that controls communication between the main microcomputer 3 and the ASIC 21. In the output circuit 5, the current supplied to the squib (not shown) for deploying the airbag 6 is supplied via a path different from the system power supply circuit 7.

  4, only the ASIC 21, the CAN system circuit 25, the backup power supply 11 and the main microcomputer 3 are shown in the airbag ECU 20. Other circuits shown in FIG. Etc. are omitted.

  The CAN system circuit 25 includes a thermal shutdown circuit 26 in addition to the above-described CAN driver 22, CAN power supply circuit 23, and power supply control unit 24 including a digital circuit. The power supply control unit 24 includes a CAN power supply control circuit 27, a CAN driver mode control circuit 28, and an input logic circuit 29. The CAN power supply control circuit 27 receives the monitor output (voltage drop detection signal) of the IG voltage monitor circuit 71, the reset signal from the voltage drop detection circuit included in the 5V circuit 74, and the reset signal from the runaway detection circuit 31. A signal for turning off the CAN power supply circuit 23 is output based on one of the signals.

  The CAN power supply circuit 23 creates a drive voltage for the CAN driver 22 based on the 7V output of the step-down circuit 73 in the system power supply circuit 7. The CAN power supply circuit 23 includes a 5V circuit similar to the 5V circuit 74 included in the system power supply circuit 7 and a reduced voltage detection circuit. The reset signal output from the reduced voltage detection circuit is input to the CAN driver 22 via the CAN driver mode control circuit 28 and the input logic circuit 29.

  As described above, the CAN power supply circuit 23 creates the drive voltage of the CAN driver 22 based on the 7V output of the step-down circuit 73 in the system power supply circuit 7. This is due to the following reason. For example, when the CAN power supply circuit 23 is connected between the booster circuit 72 and the step-down circuit 73 and the drive voltage 5V of the CAN driver 22 is created based on the 23V output of the booster circuit 72, the difference between 23V and 5V, 18V is applied to the CAN power supply circuit 23, which causes a large power loss. As a result, the CAN power supply circuit 23 cannot be built in the ASIC 21. Even when the CAN power supply circuit 23 is connected to the input side (16V) of the booster circuit 72, the difference between 16V and 5V, 11V is applied to the CAN power supply circuit 23, and a large power loss occurs here. Therefore, in the present embodiment, it is most preferable to connect the CAN power supply circuit 23 to the output side of the step-down circuit 73.

  The CAN driver mode control circuit 28 transmits a standby mode setting signal, a normal mode setting signal, and a receive mode setting signal to the CAN driver 22 in response to various commands input from the microcomputer 3 via the serial communication circuit 32. To do. The input logic circuit 29 outputs a standby mode setting signal to the CAN driver 22 when a standby mode setting signal is output from the CAN driver mode control circuit 28 or a power supply reset signal is output from the CAN power supply circuit 23. . Further, when the CAN driver mode control circuit 28 outputs a normal mode setting signal and the power supply reset signal is not output from the CAN power supply circuit 23, the normal mode setting signal is output to the CAN driver 22. Further, when the CAN driver mode control circuit 28 outputs a receive mode setting signal and no power supply reset signal is output from the CAN power supply circuit 23, the CAN driver mode control circuit 28 outputs a receive mode setting signal to the CAN driver 22.

  The thermal shutdown circuit 26 detects the abnormal heat generation of the CAN driver 22 and outputs a thermal shutdown (TSD) signal to the CAN driver mode control circuit 28. The CAN driver mode control circuit 28 transmits TSD information to the main microcomputer 3 via the CAN power supply control circuit 27 and the serial communication circuit 32. When receiving the TSD information, the CAN power supply control circuit 27 outputs a power supply off signal to the CAN power supply circuit 23 to turn off the CAN power supply circuit 23. By receiving the TSD information, the main microcomputer 3 knows that the CAN driver 22 is in a thermal shutdown state, and can use the information for control in the airbag EC 20 or communication control.

  Below, the control function of the CAN power supply in ASIC21 is shown collectively.

  (1) The IG voltage monitor circuit 71 monitors the reduced voltage of the external input power supply. When the input voltage becomes a predetermined value or less, the CAN power supply circuit 23 turns off the CAN power supply circuit 23 and the CAN driver 22 Stop driving.

  (2) When a reduced voltage is detected in the 5V circuit 74 of the system power supply circuit 7, a power supply reset signal is output to the CAN power supply control circuit 27 to turn off the CAN power supply circuit 23 and supply power to the CAN driver 22. Stop.

  (3) When the microcomputer runaway detection circuit 31 detects the microcomputer runaway, the microcomputer 3 is reset. Therefore, a runaway detection signal is output to the CAN power supply control circuit 27, the CAN power supply circuit 23 is turned off, and the CAN driver 22 is turned off. Stop driving.

  (4) When the voltage generated in the CAN power supply circuit 23 falls below a predetermined value, the CAN power supply circuit 23 outputs a power supply reset signal and sets the CAN driver 22 to the standby mode via the input logic circuit 29. . This is to prevent the CAN driver 22 from being able to guarantee communication due to a voltage drop of the CAN power supply.

  (5) The main microcomputer 3 monitors the output of the IG voltage monitor circuit 71. If it is determined by this monitor that the CAN driver 22 in the ASIC 20 is in a startable state, a CAN command is sent from the microcomputer 3 to the CAN driver mode control circuit. The CAN driver 22 is set to the normal mode.

  (6) When the microcomputer 3 sets the ASIC 21 to the initialization mode, an initialization command is output to the CAN driver mode control circuit 28 to set the CAN driver 22 to the standby mode.

  (7) The thermal shutdown circuit 26 transmits information related to the thermal shutdown of the CAN driver 22 to the main microcomputer 3 via the CAN driver mode control circuit 28 and the serial communication circuit 32. The main microcomputer 3 uses the information for control of other electronic devices in the airbag ECU 20 and communication control.

  FIG. 5 is a diagram showing an example of a detailed structure of the ASIC 21 shown in FIG. Correspondence between each component in this figure and the constituent members in FIG. 4 is indicated by a region indicated by a dotted line and a reference numeral attached to the region. Note that a backup capacitor is connected to the tip of Vback, which is the output of the booster circuit 72, but is omitted in this figure. The CAN power supply circuit 23 generates a voltage for driving the CAN driver 22 on the basis of the output voltage Vcc that is made lower than the IG voltage by the step-down circuit 73. Therefore, the input of the CAN power supply circuit 23 is reduced in power, and when incorporated in the ASIC 20, the CAN power supply circuit 23 can be realized with a small chip area. Thus, since the conventional CAN driver is an independent IC, if the power supply of the airbag ASIC and the power supply of the CAN driver are shared, the current consumption is continuously drawn from the backup power supply of the airbag when the IG / OFF is established. For this reason, wasteful power consumption occurs even in the case of IG / OFF, but in this embodiment, in the case of IG / OFF, the CAN power supply can be turned off, so that wasteful power can be suppressed.

The block diagram which shows the structure of the conventional airbag ECU. The block diagram which shows the structure of airbag ECU concerning one Embodiment of this invention. The figure which shows the relationship between the output circuit shown in FIG. 2, and an airbag. The block diagram which shows the structure of ASIC shown in FIG. The block diagram which shows the detailed structure of ASIC shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main G sensor 2 G sensor for safing 3 Main microcomputer 4 Sub microcomputer 5 (5a, 5b ... 5n) Output circuit 6 (6a, 6b ... 6n) Air bag 7 Power supply circuit for system 9 Ignition switch 10 In-vehicle Battery 20 Airbag ECU
21 ASIC
22 CAN Driver 23 CAN Power Supply Circuit 24 Power Supply Control Unit 25 CAN System Circuit

Claims (16)

A first processing circuit that determines a vehicle collision based on an output from a sensor for detecting a vehicle collision, and a second that outputs a signal for airbag deployment based on the output from the first processing circuit. In the airbag apparatus provided with the processing circuit of
The second processing circuit further includes:
Communication means for controlling information communication between the first processing circuit and another electronic control device outside the airbag device;
First power supply means for generating a voltage for driving the first and second processing circuits based on an external power supply voltage, comprising backup power supply means for supplying a backup voltage when the external power supply voltage drops. 1 power supply means;
Second power supply means for supplying a drive voltage to the communication means based on the output of the first power supply means;
An airbag apparatus comprising: power supply control means for detecting a drop in the external power supply voltage and stopping the supply of drive voltage from the second power supply means to the communication means.   2. The airbag device according to claim 1, wherein the external power source is an in-vehicle battery connected via an ignition switch.   3. The airbag device according to claim 1, wherein the second processing circuit includes one ASIC. 4.   4. The airbag device according to claim 1, wherein the first power supply unit of the second processing circuit further includes a voltage monitoring unit that monitors an input voltage from the external power supply. 5. The power supply control means puts the second power supply means in a stopped state when the monitored value in the voltage monitoring means becomes a predetermined value or less.   5. The airbag device according to claim 1, further comprising: processing an output from a second sensor for detecting a collision of a vehicle different from the sensor; An air bag apparatus comprising a third processing circuit for transmitting to the second processing circuit.   The airbag apparatus according to any one of claims 1 to 5, wherein the first power supply means in the second processing circuit is configured such that when the output of the first power supply means falls below a predetermined value, An airbag apparatus comprising: a reduced voltage detecting means for outputting a reset signal to the power supply control means, wherein the power supply control means turns off the second power supply means by the input of the reset signal.   The airbag apparatus according to any one of claims 1 to 6, wherein the first processing circuit includes a microcomputer.   8. The airbag apparatus according to claim 7, wherein the second processing circuit further includes a runaway detection circuit of the microcomputer, and the power supply control means receives the output from the runaway detection circuit. An airbag device characterized in that the power supply means is turned off.   9. The airbag apparatus according to claim 7, wherein the second processing circuit further includes a thermal shutdown circuit for detecting abnormal heat generation of the communication unit and stopping driving of the communication unit. An air bag device is characterized.   10. The airbag device according to claim 9, wherein the power supply control means in the second processing circuit turns off the second power supply circuit upon receipt of an abnormality detection signal of the thermal shutdown circuit. Air bag device.   11. The airbag apparatus according to claim 9, wherein the second processing circuit further includes a serial communication circuit that communicates with the microcomputer, and outputs the thermal shutdown circuit via the serial communication circuit. 11. An airbag device, wherein the airbag device is transmitted to a computer.   12. The airbag apparatus according to claim 11, wherein the microcomputer has a function of monitoring an output of the voltage monitoring unit in the first power supply unit of the second processing circuit, and the microcomputer performs the monitoring by the monitor. When the communication means determines that it is in a communicable state, the airbag device transmits an activation command for the communication means to the serial communication circuit.   13. The airbag apparatus according to claim 1, wherein the second power supply means in the second processing circuit detects that the output voltage has become a predetermined value or less. An airbag device comprising a circuit, wherein the communication means is turned off by an output of the reduced voltage detection circuit.   14. The airbag apparatus according to claim 1, wherein the first power supply means in the second processing circuit includes a booster circuit that boosts an input voltage from the external power supply. The airbag device according to claim 1, wherein the power supply means generates a backup voltage based on the booster circuit output.   15. The airbag apparatus according to claim 14, wherein the second processing circuit includes a step-down circuit at a stage subsequent to the step-up circuit in the first power supply unit, and the second power supply unit is based on the output of the step-down circuit. And generating a voltage for the communication means.   16. The airbag device according to claim 1, wherein the communication means in the second processing circuit is a CAN driver that controls a controller area network.

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