Abstract:
A battery monitoring system including: plural battery cell sets; and semiconductor devices, wherein: each of the semiconductor devices includes a measuring section, a high side communication section that is supplied with a drive voltage in a first voltage range, and, when a semiconductor device is present at a higher position that operates at a higher operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the high side of the battery cell set measured by the semiconductor device itself, can perform communication with the high side semiconductor device, a low side communication section, and a communication level converter; the semiconductor device at the highest stage further includes a signal level determination section; and the first voltage range of the highest stage is set to a specific voltage range narrower than the first voltage range of another of the semiconductor devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-082531 filed on Mar. 30, 2012 and Japanese Patent Application No. 2013-052078 filed on Mar. 14, 2013, the disclosures of which are incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present invention is related to a battery monitoring system and a semiconductor device. 
     2. Related Art 
     High capacity, high output batteries employed in as motor drives in for example hybrid vehicles and electric vehicles generally employ a battery configured from plural serially connected batteries (battery cells). Lithium ion rechargeable batteries are employed for example as such battery cells. 
     Due to the high energy density of such battery cells, there is the concern that this energy might be instantaneously discharged such as when a problem arises that results in an internal short-circuit. In order to avoid such an occurrence, and in order to avoid abnormal states such as an overcharged state or an excessive discharge state, battery voltage monitoring of the battery cells is performed by a battery monitoring system. Examples of such battery monitoring systems include the technology disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2009-100644, JP-A No. 2010-178400, and JP-A No. 2010-281717. 
     The battery monitoring systems of JP-A No. 2009-100644, JP-A No. 2010-178400 and JP-A No. 2010-281717 are provided with plural battery monitoring semiconductor devices (ICs) that monitor each collection (battery cell set) in a configuration wherein plural serially connected battery cells are divided into collections each containing a specific number of battery cells. 
     The battery monitoring systems described above are configured such that plural the battery monitoring ICs are connected to the plural serially connected battery cells. 
     Each battery monitoring IC includes a voltage measuring section that measures battery cell battery voltage, a high side communication section that performs communication with a battery monitoring IC that monitors a higher position battery cell set, a low side communication section that performs communication with a battery monitoring IC that monitors a lower position battery cell set, and a communication level converter that converts the voltage levels of the high side communication section and the low side communication section. 
     Each battery monitoring IC operates employing a battery voltage of each of the battery cell sets to be monitored. In order to perform communication between the respective battery monitoring ICs there is a need to match the voltage levels employed for signals during communication between the respective battery monitoring ICs since the battery voltage levels of each of the battery cell sets to be monitored are different from each other. The communication level converter accordingly performs conversion between the voltage levels of the high side communication section and the low side communication section. 
     In such battery monitoring systems, for example the battery monitoring IC that monitors the lowest position battery cell set receives for example a control signal from a controller in the low side communication section, converts the voltage level in the communication level converter, and then transmits the control signal from the high side communication section to the low side communication section of the battery monitoring IC that monitors a higher position battery cell set. Each of the battery monitoring ICs accordingly receives signals in the low side communication section, performs voltage conversion in the communication level converter, and transmits signals from the high side communication section. However, there is no need to operate the communication level converter or the high side communication section of the battery monitoring IC that monitors the highest position battery cell set since there is no higher position battery monitoring IC present. 
     There is accordingly the issue that current for operating the communication level converter and the high side communication section of the highest position battery monitoring IC is wasted. 
     SUMMARY 
     The present invention is proposed in order to address the above issue, and an object thereof is to provide a battery monitoring system and a semiconductor device capable of suppressing the overall current consumption of a battery monitoring system. 
     A first aspect of the present invention provides a battery monitoring system including: 
     plural battery cell sets of a specific number plural serially connected battery cells;
         plural semiconductor devices that are each respectively provided to each of the plural battery cell sets and that each measure battery voltage of the corresponding battery cell set, wherein:       

     each of the semiconductor devices includes
         a measuring section that measures the battery voltage of the corresponding battery cell set,   a high side communication section that is supplied with a drive voltage in a first voltage range, and, when a semiconductor device is present at a higher position that operates at a higher operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the high side of the battery cell set measured by the semiconductor device itself, is capable of performing communication with the high side semiconductor device,   a low side communication section that is supplied with a drive voltage in a second voltage range, and, when a semiconductor device is present at a lower position that operates at a lower operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the low side of the battery cell set measured by the semiconductor device itself, is capable of performing communication with the low side semiconductor device, and   a communication level converter that converts in both directions between the first voltage range of the high side communication section and the second voltage range of the low side communication section, that is capable of converting a high side communication signal input from the high side communication section to a low side communication signal and outputting the converted signal to the low side communication section, and that is capable of converting a low side communication section input from the low side communication section to a high side communication section and outputting the converted signal to the high side communication section;       

     the semiconductor device at the highest stage in communication between the semiconductor devices further comprises a signal level determination section that detects the first voltage range of the high side communication section, and that determines the level of the low side communication signal that the communication level converter outputs to the low side communication section when the first voltage range is narrower than a specific voltage range; and 
     the first voltage range of the highest stage is set to a specific voltage range narrower than the first voltage range of another of the semiconductor devices. 
     A second aspect of the present invention provides a semiconductor device including: 
     a high side communication section that is supplied with a drive voltage in a first voltage range, and, when a semiconductor device is present at a higher position that operates at a higher operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the high side of the battery cell set measured by the semiconductor device itself that is one semiconductor device out of plural semiconductor devices that are each respectively provided to each of plural battery cell sets of collections of a specific number plural serially connected battery cells, is capable of performing communication with the high side semiconductor device; 
     a low side communication section that is supplied with a drive voltage in a second voltage range, and, when a semiconductor device is present at a lower position that operates at a lower operating voltage than the operating voltage of the semiconductor device itself when measuring a battery cell set on the low side of the battery cell set measured by the semiconductor device itself, is capable of performing communication with the low side semiconductor device; 
     a communication level converter that converts in both directions between the first voltage range of the high side communication section and the second voltage range of the low side communication section, that is capable of converting a high side communication signal input from the high side communication section to a low side communication signal and outputting the converted signal to the low side communication section, and that is capable of converting a low side communication section input from the low side communication section to a high side communication section and outputting the converted signal to the high side communication section; 
     a signal level determination section that detects the first voltage range of the high side communication section, and that determines the level of the low side communication signal that the communication level converter outputs to the low side communication section when the first voltage range is narrower than a specific voltage range. 
     The present invention exhibits the advantageous effect of being able to suppress the overall current consumption of a battery monitoring system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic configuration diagram illustrating an example of an outline configuration of a battery monitoring system of a present exemplary embodiment; 
         FIG. 2  is a schematic configuration diagram illustrating an example of an outline configuration related to a signal communication function of a battery monitoring IC of the present exemplary embodiment; 
         FIG. 3  is a block diagram showing an example of specific communication functions in a battery monitoring IC of the present exemplary embodiment; 
         FIG. 4  is a circuit diagram illustrating an example of a battery voltage monitoring circuit of the present exemplary embodiment; 
         FIG. 5  is a circuit diagram illustrating an example of an HV-LV converter of a communication level converter and a reception circuit section of a high side communication section of the present exemplary embodiment; 
         FIG. 6  is a circuit diagram illustrating a specific example of a current mirror circuit configured by PMOS transistors of the present exemplary embodiment; 
         FIG. 7  is a circuit diagram illustrating a specific example of a current mirror circuit configured by NMOS transistors of the present exemplary embodiment; 
         FIG. 8  is a flow chart illustrating an example of a flow of communication operation in a battery monitoring system of the present exemplary embodiment; 
         FIG. 9  is a flow chart illustrating an example of a flow of communication operation in a battery monitoring system of the present exemplary embodiment; 
         FIG. 10  is a circuit diagram illustrating another example of a power supply voltage monitoring circuit of the present exemplary embodiment; 
         FIG. 11  is a schematic configuration diagram illustrating an example of an outline configuration related to a signal communication function of a battery monitoring IC of a comparative example; and 
         FIG. 12  is a circuit diagram illustrating an example of an HV-LV converter of a communication level converter and a reception circuit section of the high side communication section of a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     Explanation follows regarding a battery monitoring system and a semiconductor device (battery monitoring IC) for battery monitoring according to a present exemplary embodiment, with reference to the drawings. 
     Explanation first follows regarding an overall schematic configuration of a battery monitoring system according to the present exemplary embodiment. An example of a schematic configuration of the battery monitoring system according to the present exemplary embodiment is illustrated in  FIG. 1 . Note that explanation follows regarding a battery monitoring system  10  for monitoring battery voltage of battery cell sets  12  each configured from plural serially connected lithium ion batteries serving as rechargeable batteries, as a specific example of the present exemplary embodiment. 
     The battery monitoring system  10  in the present exemplary embodiment includes n individual battery cell sets  12  ( 12   1  to  12   n ), battery monitoring Integrated Circuits (ICs)  20  (IC 1  to ICn) that monitor the voltage of each of the battery cell sets  12 , and a controller  14  for controlling the overall operation of the battery monitoring system  10 . 
     Each of the battery cell sets  12  is equipped with plural individual (four individual in the example in  FIG. 1 ) lithium ion rechargeable battery cells (referred to below simply as “battery cells”). 
     The controller  14  has a function of controlling the battery monitoring system  10  overall, and is configured by a microcomputer equipped with a CPU, ROM and RAM, called an MCU. In the battery monitoring ICs  20  of the present exemplary embodiment, the controller  14  is connected to a low side communication section  24  of the battery monitoring IC  20  (IC 1 ) at the lowest position, and various data (signals) are transmitted and received between the controller  14  and the battery monitoring IC  20  (IC 1 ). 
     The battery monitoring ICs  20  have the function of monitoring the battery voltage of the battery cell sets  12  they are respectively connected to, and power at a voltage VCC 1  is supplied to the battery cell set  12  at the highest position side of the battery cell sets  12  to be monitored. 
     The battery monitoring ICs  20  are each equipped with a battery voltage measuring section  22  that measures the battery voltage of each of the battery cell sets  12  to be monitored. The battery voltage measuring section  22  has the function of selecting a battery cell from the respective battery cell set  12 , outputting the battery voltage of the selected battery cell, and evening out the voltages of the battery cells. 
     In the present exemplary embodiment, instructions such as instructions related to measuring battery voltage are input from the controller  14  to the battery monitoring IC  20  (IC 1 ) at the lowest position, and then transmitted onwards in sequence to higher position battery monitoring ICs  20 . Data such as data related to measured battery voltage values is output from each of the battery monitoring ICs  20  to the controller  14 . However data from higher position battery monitoring ICs  20  is transmitted in sequence through the lower position battery monitoring ICs  20 . Note that transmission (communication) of signals is performed by serial peripheral interface (SPI) communication as a specific example in the present exemplary embodiment. 
       FIG. 2  is a schematic configuration diagram illustrating an example of an outline configuration related to a signal communication function of the battery monitoring ICs  20  according to the present exemplary embodiment.  FIG. 2  illustrates a system configuration when monitoring battery voltage of the battery cell sets  12  using two individual battery monitoring ICs  20  in the battery monitoring system  10  illustrated in  FIG. 1 . Note that although a system configured by only two individual battery monitoring ICs  20  is illustrated in order to simplify the drawings, the battery monitoring system  10  may be configured such that battery voltage monitoring of battery cell sets  12  is performed by 3 or more individual battery monitoring ICs  20 . 
     The battery monitoring ICs  20  (IC 1 , IC 2 ) are each equipped with a battery voltage measuring section  22 , a low side communication section (LV-SPI)  24 , a communication level converter (DLVL)  26 , a high side communication section (HV-SPI)  28 , a power supply voltage monitoring circuit (VMON)  30  and a regulator (REG)  32 . Note that for simplification purposes the battery voltage measuring section  22  is omitted from illustration in  FIG. 2 , since the battery voltage measuring section  22  is not directly related to explanation of the operation of the signal communication function. 
     Explanation first follows regarding configuration of the battery monitoring IC  20  (IC  1 ), with reference to  FIG. 2 . 
     The regulator  32  of the battery monitoring IC  20  (IC 1 ) has a function to generate from a power supply voltage VCC 1  (IC 1 ) supplied from the battery cell set  12  a power supply voltage VDD to act as an internal power supply. The generated power supply voltage VDD is supplied to the low side communication section  24 , the communication level converter  26 , and the power supply voltage monitoring circuit  30 . 
     The power supply voltage monitoring circuit  30  of the battery monitoring IC  20  (IC 1 ) is connected to a power supply voltage VCC 1  (IC 1 ) and a power supply voltage VCC 2  (IC  1 ), and has a function to monitor the power supply voltage VCC 1  (IC 1 ) and the power supply voltage VCC 2  (IC 1 ), and to output to the communication level converter  26  a signal INV corresponding to the potential difference between the power supply voltage VCC 1  (IC 1 ) and the power supply voltage VCC 2  (IC 1 ). 
     The operating voltage of the low side communication section  24  is the power supply voltage VDD from the regulator  32 , with GND of voltage VSS. The low side communication section  24  of the battery monitoring IC  20  (IC 1 ) is connected to the controller  14  through an SPI signal line. 
     The communication level converter  26  of the battery monitoring IC  20  (IC 1 ) is connected to the power supply voltage VCC 1  (IC 1 ), the power supply voltage VCC 2  (IC 1 ), the power supply voltage VDD, and the power supply voltage monitoring circuit  30 . In the present exemplary embodiment a digital level shifter is employed as an example of the communication level converter  26 . An SPI signal is received from the high side communication section  28  based on the level of the signal INV input from the power supply voltage monitoring circuit  30 . The voltage level of the SPI signal received from the high side communication section  28  is converted to a voltage level corresponding to the low side communication section  24  and output to the low side communication section  24 . The voltage level of the SPI signal received from the low side communication section  24  is converted to a voltage level corresponding to the high side communication section  28  and output to the high side communication section  28 . 
     The operating voltage of the high side communication section  28  of the battery monitoring IC  20  (IC 1 ) is the power supply voltage VCC 2  (IC 1 ) supplied from the battery monitoring IC  20  (IC 2 ) through the VDD terminal, with GND of the power supply voltage VCC 1  (IC 1 ) of the battery cell set  12 . The power supply voltage VCC 2  (IC 1 ) supplied to the high side communication section  28  of the battery monitoring IC  20  (IC 1 ) is the power supply voltage VDD of the battery monitoring IC  20  (IC 2 ). At the battery monitoring IC  20  (IC 1 ), VCC 2  (IC 1 )−VCC 1  (IC 2 )=the power supply voltage VDD of the battery monitoring IC  20  (IC 2 ). The high side communication section  28  of the battery monitoring IC  20  (IC 1 ) is connected to the low side communication section  24  of the battery monitoring IC  20  (IC 2 ) through the SPI signal line. 
     Explanation follows regarding a configuration of the battery monitoring IC  20  (IC 2 ), with reference to  FIG. 2 . 
     The regulator  32  of the battery monitoring IC  20  (IC 1 ) has a function to generate from a power supply voltage VCC 1  (IC 2 ) supplied from the battery cell set  12   2  a power supply voltage VDD to act as an internal power supply. The generated power supply voltage VDD is supplied to the low side communication section  24 , the communication level converter  26 , and the power supply voltage monitoring circuit  30 . 
     The power supply voltage monitoring circuit  30  of the battery monitoring IC  20  (IC 2 ) is connected to a power supply voltage VCC 1  (IC 2 ) and a power supply voltage VCC 2  (IC 2 ), and has a function to monitor the power supply voltage VCC 1  (IC 2 ) and the power supply voltage VCC 2  (IC 2 ), and to output to the communication level converter  26  a signal INV corresponding to the potential difference between the power supply voltage VCC 1  (IC 2 ) and the power supply voltage VCC 2  (IC 2 ). 
     The operating voltage of the battery monitoring IC  20  (IC 2 ) low side communication section  24  is the power supply voltage VDD from the regulator  32 , with GND of voltage VSS. The low side communication section  24  of the battery monitoring IC  20  (IC 2 ) is connected to the high side communication section  28  of the battery monitoring IC  20  (IC 1 ) through an SPI signal line. 
     The communication level converter  26  of the battery monitoring IC  20  (IC 2 ) is connected to the power supply voltage VCC 1  (IC 2 ), the power supply voltage VCC 2  (IC 2 ), the power supply voltage VDD, and the power supply voltage monitoring circuit  30 . In the present exemplary embodiment a digital level shifter is employed as an example of the communication level converter  26  as described above. The communication level converter  26  is configured substantially the same as that of the battery monitoring IC  20  (IC 1 ) described above. 
     The operating voltage of the high side communication section  28  of the battery monitoring IC  20  (IC 2 ) is the power supply voltage VCC 2  (IC 2 ), with GND of the power supply voltage VCC 1  (IC 2 ) of the battery cell set  12   2 . Since the high side communication section  28  of the battery monitoring IC  20  (IC 2 ) is not employed (is not connected to a battery monitoring IC  20  on the high side), in place of a battery monitoring IC  20  on the high side, the power supply voltage VCC 1  (IC 2 ) and the power supply voltage VCC 2  (IC 2 ) are connected together. At the battery monitoring IC  20  (IC 2 ), VCC 1  (IC 2 )=VCC 2  (IC 2 ). 
     Since the battery monitoring IC  20  (IC 2 ) is the highest position battery monitoring IC  20 , there is no need to perform communication (SPI communication) with a battery monitoring IC  20  on the high side. There is accordingly no need to operate the communication level converter  26  and the high side communication section  28 . However, since the communication level converter  26  and the high side communication section  28  are connected to the power supply voltage VCC 1  (IC 2 ) and the power supply voltage VCC 2  (IC 2 ), the communication level converter  26  and the high side communication section  28  operate unintentionally in response to a potential difference between the power supply voltage VCC 1  (IC 2 ) and the power supply voltage VCC 2  (IC 2 ). More specifically, the communication level converter  26  and the high side communication section  28  are unintentionally driven when the voltage level of VCC 2  (IC 2 )−VCC 1  (IC 2 ) exceeds the drive voltage (threshold value voltage) of an electronic component (for example a MOS transistor) configuring the communication level converter  26  and the high side communication section  28 . Note that “driving” of the communication level converter  26  in the present exemplary embodiment refers to the communication level converter  26  operating to perform SPI communication with the battery monitoring IC  20  on the high side. Moreover, “driving” of the high side communication section  28  refers to the high side communication section  28  operating to perform SPI communication. The current consumption is increased by operation of the communication level converter  26  and the high side communication section  28 . In the present exemplary embodiment VCC 1  (IC 2 )=VCC 2  (IC 2 ) such that the communication level converter  26  and the high side communication section  28  are not driven. Note that configuration may be made such that even when VCC 1  (IC 2 ) does not exactly equal VCC 2  (IC 2 ), the voltage level of VCC 2  (IC 2 )−VCC 1  (IC 2 ) is less than the operating voltages of the communication level converter  26  and the high side communication section  28 . 
     Detailed explanation follows regarding SPI communication by the battery monitoring IC  20  according to the present exemplary embodiment, with reference to the drawings.  FIG. 3  is an example of a block diagram illustrating an example of specific communication functions in the battery monitoring IC  20  illustrated in the schematic diagram of  FIG. 2 . Note that for the purpose of simplifying the drawing, parts of the configuration not relevant to the following explanation are not illustrated in  FIG. 3 . 
     The low side communication section  24  in the present exemplary embodiment includes a reception circuit section  24 R and a transmission circuit section  24 T. The communication level converter  26  is equipped with a LV-HV converter  26 LH, and a HV-LV converter  26 HL. The high side communication section  28  is equipped with a transmission circuit section  28 T and a reception circuit section  28 R. 
     The power supply voltage monitoring circuit  30  includes a function for fixing (described in detail later) an input voltage of an inverter provided to the HV-LV converter  26 HL.  FIG. 4  is a circuit diagram illustrating an example of the power supply voltage monitoring circuit  30 . 
     The power supply voltage monitoring circuit  30  of the present exemplary embodiment is equipped with a resistor R 1 , a resistor R 2 , a PMOS transistor MP 1 , an NMOS transistor MN  1 , and an inverter INV 1 . 
     One end of the resistor R 1  is connected to the power supply voltage VCC 2 , and the other end is connected to the source and bulk of the PMOS transistor MP 1 . The drain of the PMOS transistor MP 1  is connected to the drain of the NMOS transistor MN 1  and the gate is connected to the power supply voltage VCC 1 . The gate of the NMOS transistor MN 1  is fixed to a power supply and the source is connected to one end of the resistor R 2  and to the input of the inverter INV 1 . The bulk of the NMOS transistor MN 1  is connected to the voltage VSS. One end of the resistor R 2  is connected to the input of the inverter INV 1 . The other end of the resistor R 2  is connected to the voltage VSS. The power supply to the inverter INV 1  is the power supply voltage VDD, and GND is connected to voltage VSS. The output of the inverter INV 1  is connected to OUT, and the signal INV is output from the inverter INV 1 . 
     Explanation follows regarding operation of the power supply voltage monitoring circuit  30 . Note that when it is not necessary to discriminate between the battery monitoring IC  20  (IC 1 ) and the battery monitoring IC  20  (IC 2 ) when referring to the power supply voltage VCC 1  (IC 1 , IC 2 ) and the power supply voltage VCC 2  (IC 1 , IC 2 ), the symbols (IC 1 , IC 2 ) are omitted and reference is made to power supply voltage VCC 1  and power supply voltage VCC 2  respectively. 
     Explanation first follows regarding operation in a case when VCC 2 −VCC 1 =VDD (in the battery monitoring IC  20  (IC 1 )). The PMOS transistor MP 1  is in an ON state due to the potential difference between the power supply voltage VCC 2  and the power supply voltage VCC  1 . The gate of the NMOS transistor MN 1  is fixed to the power supply, and the NMOS transistor MN 1  is always in an ON state. Current accordingly flows in the resistor R 1  and the resistor R 2 . A voltage is accordingly generated across the resistor R 2  due to the current flow in the resistor R 2 . The input of the inverter INV 1  is accordingly at H level, and a detection signal (INV signal) is output at L level. Hence when VCC 2 −VCC 1 =VDD, the detection signal (INV signal) of the power supply voltage monitoring circuit  30  is at L level. 
     Explanation follows regarding operation when VCC 1 =VCC 2  (in the battery monitoring IC  20  (IC 2 )). The PMOS transistor MP 1  is in an OFF state since there is no potential difference between the power supply voltage VCC 1  and the power supply voltage VCC 2 . Since current does not flow in the resistor R 1 , current also does not flow in the resistor R 2 . The input of the inverter INV 1  is accordingly at L level, and the output detection signal (INV signal) is at H level. 
     In the communication level converter  26 , the input of an inverter INV 3  of the HV-LV converter  26 HL is fixed according to the level of the INV signal. Detailed explanation follows of such operation, with reference to the drawings.  FIG. 5  is a circuit diagram illustrating an example in the present exemplary embodiment of the HV-LV converter  26 HL of the communication level converter  26  and the reception circuit section  28 R of the high side communication section  28 . 
     The reception circuit section  28 R is equipped with a current mirror circuit PCM 1 , a current mirror circuit PCM 2 , an inverter INV 2 , a constant current source I 1  and a constant current source  12 . The HV-LV converter  26 HL is equipped with a current mirror circuit PCM 3 , a current mirror circuit NCM 1 , a current mirror circuit NCM 2 , an inverter INV 3  and a switching element SW. 
     The current mirror circuit PCM 1 , the current mirror circuit PCM 2  and the current mirror circuit PCM 3  are current mirror circuits configured by PMOS transistors. A specific example of these current mirror circuits is illustrated in  FIG. 6 . The current mirror circuit NCM 1  and the current mirror circuit NCM 2  are current mirror circuits configured by NMOS transistors. A specific example of these current mirror circuits is illustrated in  FIG. 7 . 
     In the reception circuit section  28 R, the input of the current mirror circuit PCM 1  is connected to a constant current source and the output is connected to the current mirror circuit NCM 1  of the HV-LV converter  26 HL. The input of the current mirror circuit PCM 2  is connected to a constant current source and the output is connected to a current mirror circuit NCM 2  of a HV-LV converter  26 HL. 
     In the HV-LV converter  26 HL, the input of the current mirror circuit NCM 1  is connected to the output of the current mirror circuit PCM 1  and the output is connected to the input of the current mirror circuit PCM 3 . The input of the current mirror circuit NCM 2  is connected to the output of the current mirror circuit PCM 2  and the output is connected to the output of the current mirror circuit PCM 3 . The output of the current mirror circuit PCM 3  is also connected to the input of the inverter INV 3 . The switching element SW is ON/OFF controlled according to the level of the signal INV input from the power supply voltage monitoring circuit  30 . The switching element SW is in an OFF state when the signal INV is at L level, and the switching element SW is in an ON state when the signal INV is at H level. A signal LV_SP 1  is output from the inverter INV 3 . 
     The SPI signal input from the battery monitoring IC  20  on the high side is input from the SPI signal terminal of the reception circuit section  28 R. When the SPI signal is at L level, the input of the current mirror circuit PCM 1  is connected to the constant current source I 1  and the input of the current mirror circuit PCM 2  is connected to the constant current source  12 . On the other hand, when the SPI signal is at H level, the input of the current mirror circuit PCM 1  is connected to the constant current source  12 , and the input of the current mirror circuit PCM 2  is connected to the constant current source I 1 . 
     Explanation follows regarding operation of the HV-LV converter  26 HL and the reception circuit section  28 R when VCC 2 −VCC 1 =VDD (in the battery monitoring IC  20  (IC 1 )). Note that in such cases the INV signal is at L level, and the switching element SW is in an OFF state. 
     Explanation follows regarding an example when the SPI signal line is at L level. The input current of the current mirror circuit PCM 1  is the current I 1  and the output current is also current I 1 . The input current of the current mirror circuit PCM 2  is current I 2  and the output current is also current I 2 . 
     The input current of the current mirror circuit NCM 1  is current I 1  and therefore the output current is also current I 1 . The input current of the current mirror circuit NCM 2  is current I 2  and therefore the output current is also current I 2 . In the current mirror circuit PCM 3 , when current I 1  is much greater than current I 2 , the output current also attempts to be current I 1  according to the input current I 1 , however the output current by the current mirror circuit NCM 2  is current I 2 , and so I 1 =I 2 . In such cases, the input voltage of the inverter INV 3  is power supply voltage VDD. However when I 1  is much less than current I 2 , the input voltage of the inverter INV 3  is voltage VSS. 
     Explanation follows regarding operation of the HV-LV converter  26 HL and the reception circuit section  28 R when VCC 2 =VCC 1  (in the battery monitoring IC  20  (IC 2 )). Note that in such cases the INV signal is at H level and the switching element SW is in an ON state. The input voltage of the input to the inverter INV 3  is 0V (VSS) due to the ON state of the switching element SW. The input voltage of the inverter INV 3  is accordingly fixed, and shoot-through current does not flow. 
     As a comparative example, explanation follows regarding configuration and operation of an HV-LV converter of a communication level converter and a reception circuit section of a high side communication section of a battery monitoring system when a communication level converter is not provided to the battery monitoring IC. A schematic diagram of an example of an outline configuration of a battery monitoring system  100  of a comparative example is illustrated in  FIG. 11 . As illustrated in  FIG. 11 , the battery monitoring system  100  of the comparative example is equipped with a controller  114  and two individual battery monitoring ICs  120  (IC 1 , IC 2 ). The battery monitoring ICs  120  of the comparative example are not equipped with the power supply voltage monitoring circuit  30  provided to the battery monitoring IC 20  of the present exemplary embodiment, however they are otherwise configured substantially similarly. 
       FIG. 12  is a circuit diagram of an example of a HV-LV converter  126 HL of a communication level converter and a reception circuit section  128 R of a higher voltage communication section in the comparative example. As illustrated in  FIG. 12 , the configuration of the reception circuit section  128 R of the comparative example is a configuration substantially the same as the reception circuit section  28 R of the present exemplary embodiment. On the other hand, as illustrated in  FIG. 12 , the HV-LV converter  126 HL of the comparative example is not equipped with the switching element SW provided to the HV-LV converter  26 HL of the present exemplary embodiment. The input of the inverter INV 3  is only connected to the output of a current mirror circuit PCM 3  (the output of the current mirror circuit NCM 2 ). 
     Operation of the HV-LV converter  126 HL and the reception circuit section  128 R when VCC 2 −VCC 1 =VDD (when VCC 2  (IC 1 )−VCC 1  (IC 2 )=VDD in the battery monitoring IC  120  (IC 1 )) is substantially the same as the operation of the HV-LV converter  26 HL and the reception circuit section  28 R described above for the present exemplary embodiment, and so further explanation thereof will be omitted. 
     Further, operation of the HV-LV converter  126 HL and the reception circuit section  128 R when VCC 1 =VCC 2  (when VCC 1  (IC 2 )=VCC 2  (IC 2 ) in the battery monitoring IC 120  (IC 2 )) differs from the operation described above for the HV-LV converter  26 HL and the reception circuit section  28 R. Since a high side communication section  128  does not operate, the output current of the current mirror circuit PCM 1  and the current mirror circuit PCM 2  of the reception circuit section  128 R is zero. The output currents of the current mirror circuit NCM 1 , the current mirror circuit NCM 2  and the current mirror circuit PCM 2  are accordingly also zero. Since the output currents of the current mirror circuit PCM 3  and the current mirror circuit NCM 2  are both zero, the input voltage of the inverter INV 3  is indeterminate, and shoot-through current flows in the circuit of the inverter INV 3 . The current consumption accordingly increases. The shoot-through current stops flowing when the input voltage of the inverter INV 3  settles to either L level or H level, due for example to leak current. However time is required (as a specific example about 10 to 20 seconds) until the level of the input voltage settles down and the shoot-through current stabilizes, namely until the shoot-through current settles down to a desirable current value or lower. Note that since the current consumption is unstable, sometimes a problem arises of the current consumption increasing, as described. Moreover, in the battery monitoring IC  120  (IC 2 ), since time is required until the shoot-through current settles down to a desirable current value or lower, sometimes the measurement result of the battery voltage of the highest position cell battery also fluctuates due to the influence of the shoot-through current, and as a result the measurement precision of the battery voltage of the battery cell set  12  decreases. 
     On the other hand, in the HV-LV converter  26 HL and the reception circuit section  28 R of the present exemplary embodiment as described above, when VCC 1 =VCC 2 , even when the signal from the reception circuit section  28 R to the HV-LV converter  26 HL is indeterminate, the switching element SW is in the ON state due to the H level INV signal, and the input voltage of input to the inverter INV 3  is fixed to 0V, so shoot-through current does not flow. The current consumption can accordingly be stabilized quickly, and a difference does not arise in current consumption between the battery monitoring IC  20  (IC  1 ) and the battery monitoring IC  20  (IC 2 ). Moreover, since the current consumption is stabilized quickly, the measurement precision of the battery voltage of the battery cell set  12  does not decrease. 
     Explanation follows regarding a flow of communication operations in the battery monitoring system  10  of the present exemplary embodiment when the SPI signal output from the controller  14  is transmitted (communicated) to the battery monitoring IC  20  (IC 1 ) and the battery monitoring IC  20  (IC 2 ).  FIG. 8  illustrates a flow chart of an example of flow of communication operation in the battery monitoring system  10 . As a specific example, explanation follows regarding a case in which an instruction (SPI signal) is communicated in order to run each of the battery monitoring ICs  20  when starting up the battery monitoring ICs  20  or on resumption after a power save mode (sleep mode). 
     Start up or operation resumption from power save mode is started when the controller  14  detects driving of an engine. The controller  14  outputs to the battery monitoring ICs  20  (IC 1 ) an instruction (SPI signal) to run each of the battery monitoring ICs  20 . 
     First the battery monitoring IC  20  (IC 1 ) receives the SPI signal output from the controller  14  with the reception circuit section  24 R of the low side communication section  24  (step S 100  in  FIG. 8 ). The received SPI signal is transmitted to each of the sections of the battery monitoring IC  20  (IC 1 ), such as the battery voltage measuring section  22  and a non-illustrated MCU (a logic circuit for controlling the battery monitoring IC  20  (IC 1 )), and a specific run operation is executed. 
     On the other hand, in the power supply voltage monitoring circuit  30  of the battery monitoring IC  20  (IC 1 ), the VCC 2 −VCC 1 =VDD, and therefore an INV signal is generated and output at L level (step  150  of  FIG. 8 ). In the communication level converter  26 , the input to the inverter INV 3  of the HV-LV converter  26 HL is fixed as described above by the L level INV signal (step  152  of  FIG. 8 ). 
     The SPI signal (LV_SPI signal) received by the reception circuit section  28 R is converted by the LV-HV converter  26 LH of the communication level converter  26  from the voltage level LV of the low side communication section  24  to the SPI signal (HV_SPI signal) of the voltage level HV of the high side communication section  28  (step  102  of  FIG. 8 ). Reference here to the voltage level HV of the high side communication section  28  means the voltage level of the battery monitoring IC  20  on the high side (IC 2 ) (the voltage level of the low side communication section  24  of the battery monitoring IC  20  (IC 2 )). The HV_SPI signal is transmitted from the transmission circuit section  28 T of the high side communication section  28  to the battery monitoring IC  20  (IC 2 ) (step  104  of  FIG. 8 ) 
     The SPI signal transmitted from the battery monitoring IC  20  (IC  1 ) is received by the reception circuit section  24 R of the low side communication section  24  in the battery monitoring IC  20  (IC 2 ). The received SPI signal is transmitted to each of the sections of the battery monitoring IC  20  (IC 2 ), such as the battery voltage measuring section  22  and a non-illustrated MCU (a logic circuit for controlling the battery monitoring IC  20  (IC 2 )), and a specific run operation is executed. Each of the battery monitoring ICs  20  (IC 1 , IC 2 ) of the battery monitoring system  10  is accordingly placed in a run state. 
     Note that in the battery monitoring IC  20  (IC 2 ), the LV_SPI signal in response to the received SPI signal is output from the reception circuit section  24 R to the LV-HV converter  26 LH of the communication level converter  26 , however since VCC 1 =VCC 2 , the communication level converter  26  and the high side communication section  28  do not operate. 
     In the power supply voltage monitoring circuit  30  of the battery monitoring IC  20  (IC 2 ), since VCC 1 =VCC 2 , an INV signal at H level is generated and output (step  250  of  FIG. 8 ). In the communication level converter  26 , as described above, the input of the inverter INV 3  of the HV-LV converter  26 HL is fixed by the H level INV signal, and current consumption is stabilized quickly (step  252  of  FIG. 8 ). 
     Thus, since the current consumption of the battery monitoring IC  20  (IC 1 ) and the battery monitoring IC  20  (IC 2 ) are quickly made stable, there is no reduction in measurement precision even when measuring the battery voltage of each of the battery cell sets  12  straight after instruction to run has been issued as described above. 
     Explanation follows regarding when the SPI signal from the battery monitoring IC  20  (IC 2 ) is transmitted (communicated) to the controller  14  through the battery monitoring IC  20  (IC 1 ). For such a case an example follows of when, for example, an SPI signal representing data related to battery voltage of a measured battery cell set  12  is transmitted (communicated) from the battery monitoring IC  20  (IC 2 ) to the controller  14 . A flow chart illustrating an example of flow of communication operation in the battery monitoring system  10  is illustrated in  FIG. 9 . 
     Note that in the battery monitoring IC  20  (IC 2 ), since VCC 1 =VCC 2 , the INV signal is output at H level from the power supply voltage monitoring circuit  30  to the HV-LV converter  26 HL of the communication level converter  26 . Moreover, since the VCC 1 =VCC 2 , the communication level converter  26  and the high side communication section  28  are not driven even though they are being supplied with a signal (voltage). 
     First, in the battery monitoring IC  20  (IC 2 ), a signal output from each of the sections, such as the battery voltage measuring section  22 , is transmitted through the transmission circuit section  24 T of the low side communication section  24  (step  400  of  FIG. 9 ). 
     In the battery monitoring IC  20  (IC 1 ), the SPI signal transmitted from the battery monitoring IC  20  (IC 1 ) is received by the reception circuit section  28 R of the high side communication section  28  (step  300  of  FIG. 9 ). The HV_SPI signal is output from the reception circuit section  28 R to the HV-LV converter  26 HL of the communication level converter  26 . The HV-LV converter  26 HL is driven due to the INV signal of the output of the power supply voltage monitoring circuit  30  being at L level. In the HV-LV converter  26 HL, the input HV_SPI signal is converted to an SPI signal line of voltage level for the low side communication section  24  (LV_SPI signal) and output to the low side communication section  24  (step S 302  of  FIG. 9 ). In the low side communication section  24  the SPI signal is output to the controller  14  through the transmission circuit section  24 T (step S 304  of  FIG. 9 ). 
     As explained above, the battery monitoring ICs  20  of the battery monitoring system  10  of the present exemplary embodiment are each equipped with the low side communication section  24 , the communication level converter  26 , the high side communication section  28 , and the power supply voltage monitoring circuit  30 . Since for the battery monitoring IC  20  (IC 2 ) there is no battery monitoring IC  20  present at a higher position, the power supply voltage VCC 2  that is the power supply voltage for driving and the power supply voltage VCC 1  that is GND are both at the same potential (VCC 1 =VCC 2 ), in a configuration such that the high side communication section  28  and the communication level converter  26  are not driven. The current consumption of the battery monitoring system  10  overall can accordingly be suppressed due to thereby being able to suppress the current consumption consumed by the communication level converter  26  and the high side communication section  28 . 
     Note that since there is a presumption that the high side communication section  28  and the communication level converter  26  do not operate in the battery monitoring IC  20  (IC 2 ), in order to suppress current consumption a configuration might be considered in which a semiconductor device omits provision of the high side communication section  28  and the communication level converter  26  in the battery monitoring IC  20  (IC 2 ). However, in such a case different types of battery monitoring ICs  20  would need to be manufactured, and this is not preferable from for example the cost perspective due to having to make dedicated different battery monitoring ICs  20 . 
     Moreover, in order to suppress current consumption, a configuration might be considered in which terminals are provided to each of the battery monitoring ICs  20  and individual IDs are set for the battery monitoring ICs  20  through these terminals, with the controller  14  specifying the ID of the battery monitoring IC  20  (IC 2 ) and transmitting a halt signal to the high side communication section  28  of the battery monitoring IC  20  (IC 2 ) to halt driving. However the drive voltages would differ in such a case depending on the battery monitoring IC  20 , and the battery monitoring ICs  20  would be larger due to providing each of the terminals. Moreover, since it takes time to set the individual IDs, such a configuration is not preferable as a similar problem would arise to the problem of the time required for the current consumption to stabilize, as explained for the battery monitoring system  100  of the comparative example (see  FIG. 11  and  FIG. 12 ). 
     Consequently, preferably each of the battery monitoring ICs  20  (IC 1 , IC 2 ) are configured the same as each other as in the present exemplary embodiment, and the VCC 1 =VCC 2  is set so that the high side communication section  28  and the communication level converter  26  of the battery monitoring IC  20  at the highest position are not driven. Note that the potential difference is not limited to VCC  1 =VCC 2  as described above, as long as the potential difference between the power supply voltage VCC 1  and the power supply voltage VCC 2  is less than the respective drive voltages (threshold value voltages) of the high side communication section  28  and the communication level converter  26 . 
     In the present exemplary embodiment, due to VCC 1 =VCC 2  or the potential difference between VCC 1  and VCC  2  being less than the respective drive voltages (threshold value voltages) of the high side communication section  28  and the communication level converter  26 , the signal input from the high side communication section  28  to the communication level converter  26  is sometimes indefinite, as described above. In contrast, in the present exemplary embodiment the power supply voltage monitoring circuit  30  is also provided to detect that VCC 1 =VCC 2 , or that the potential difference between VCC 1  and VCC  2  is less than the respective drive voltages (threshold value voltages) of the high side communication section  28  and the communication level converter  26 , and to output a detection signal (INV signal) to the HV-LV converter  26 HL of the communication level converter  26  when VCC 1 =VCC 2 , or the potential difference between VCC 1  and VCC  2  is less than the respective drive voltages (threshold value voltages) of the high side communication section  28  and the communication level converter  26 . In the HV-LV converter  26 HL, the input voltage of the inverter INV 3  is fixed to a specific level (0V) by the input voltage INV signal, and hence shoot-through current can be quickly suppressed from occurring. The influence of shoot-through current shoot-through current on the battery voltage measurement result can accordingly be suppressed, enabling the measurement precision of the battery voltage of the battery cell set  12  to be prevented from falling. 
     Note that the configuration of the power supply voltage monitoring circuit  30  illustrated in the above exemplary embodiment ( FIG. 4 ) is merely an example. There are no particular limitations to the configuration as long as the potential difference between the power supply voltage VCC 2  and the power supply voltage VCC 1  is detected, or more specifically as long as whether or not the potential difference exceeds the operating voltage of the communication level converter  26  and the high side communication section  28  is detected, and as long as a detection signal (INV signal) can be output at a level representing the detection result. An example of the power supply voltage monitoring circuit  30  is illustrated in  FIG. 10 . In the power supply voltage monitoring circuit  30  illustrated in  FIG. 4 , the gate of the NMOS transistor MN 1  is fixed to the power supply, however instead of this, configuration may be made in as the power supply voltage monitoring circuit  30  illustrated in  FIG. 10  such that the gate of the NMOS transistor MN 1  is input with a power down (PD) signal. The PD signal is output from a controller  29  (such as an MUC) provided in each of the battery monitoring ICs  20  to the power supply voltage monitoring circuit  30  according to the operation state of the battery monitoring IC  20 , with the PD signal expressing H level for operation mode and expressing L level at power down. In the power supply voltage monitoring circuit  30  illustrated in  FIG. 10 , VCC 2 −VCC 1 =VDD, and so the PMOS transistor MP 1  and the NMOS transistor MN 1  are in an ON state when the PD signal is H level, and current flows in the resistor R 1  and the resistor R 2 . A voltage arises when current flows in the resistor R 2 , making the input voltage to the inverter INV 1  H level and the output voltage L level. However, VCC 2 −VCC 1 =VDD, and the PMOS transistor MP 1  and the NMOS transistor MN 1  are in an OFF state when the PD signal is at L level. Current accordingly does not flow in the resistor R 1  and the resistor R 2 . The input voltage of the inverter INV 1  is accordingly at L level, and the output voltage is at H level. It is preferably to achieve a configuration such as described above in which a detection signal (INV signal) is output at a level according to the mode (operation mode/power down mode). 
     The number (number of stages) of the battery cell sets  12  and of the battery monitoring ICs  20  in the battery monitoring system  10  is not limited to those of the present exemplary embodiment. For example, the battery monitoring system  10  may be configured with multiple connected stages of 3 to 32 stages. In such multistage configurations, the highest stage battery monitoring IC  20  is configured similarly to the battery monitoring IC  20  (IC 2 ) of the present exemplary embodiment, the lowest stage battery monitoring IC  20  is configured similarly to the configuration of the battery monitoring IC  20  (IC 1 ) of the present exemplary embodiment, and the other battery monitoring ICs  20  are configured such that the low side communication section  24  of the battery monitoring IC  20  (IC 1 ) of the present exemplary embodiment is connected to the high side communication section  28  of the lower stage battery monitoring IC  20 . 
     The present exemplary embodiment is configured such that the low side communication section  24  of the lowest stage battery monitoring IC  20  (IC 1 ) is connected to the controller  14 , however there is no limitation thereto. For example, configuration may be made such that a battery monitoring IC  20  at an intermediate stage out of multistage connected battery monitoring ICs  20  is connected to the controller  14 . In such cases, since this battery monitoring IC  20  is at the highest stage when communication is performed between each of the battery monitoring ICs  20 , this battery monitoring IC  20  may be configured similarly to the battery monitoring IC  20  (IC 2 ) of the present exemplary embodiment. 
     Moreover, although the present exemplary embodiment is configured with the power supply voltage monitoring circuit  30  provided to all of the battery monitoring ICs  20  in the battery monitoring system  10 , there is no limitation thereto. For example, configuration may be made such that the power supply voltage monitoring circuit  30  is only provided to the highest position battery monitoring IC  20  (IC 2 ). Note that configuration is preferably made with the power supply voltage monitoring circuit  30  provided to all of the battery monitoring ICs  20  since this avoids having to make dedicated different battery monitoring ICs  20 . 
     Moreover, in the present exemplary embodiment explanation has been given of a case in which SPI communication is performed, however it should be understood that the method of communication is not limited to SPI communication. 
     The battery cells are also not limited to lithium ion rechargeable batteries, and other batteries may be employed. Note that lithium ion rechargeable batteries have the characteristics of obtaining a higher energy density (higher power density) compared to other rechargeable batteries, and have a high battery voltage per battery cell, a high electrical energy discharge efficiency, and also have no memory effect. Lithium ion rechargeable batteries are accordingly preferably employed in fields such as hybrid vehicles and motor driven machines. 
     Note that configuration of the battery monitoring system  10 , the controller  14 , the battery monitoring ICs  20 , the high side communication section  28 , the power supply voltage monitoring circuit  30  etc. and each of the operations explained in the above exemplary embodiment are merely examples thereof. It should be understood that various modifications are possible according to circumstances within a range not departing from the spirit of the present invention.