Abstract:
An apparatus for driving a load that may include, for instance, a semiconductor chip, comprising a first switch, and a fracture sensor. The apparatus may further include, for instance, a circuit disposed outside the semiconductor chip and comprising a second switch coupled in series with the first switch, and configured such that an on/off state of the second switch is set in accordance with a state of the fracture sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to German patent application no. 10 2006 057 042.1-31, filed Dec. 4, 2006, and hereby incorporated by reference as to its entirety. 
       BACKGROUND 
       [0002]    Motor vehicles typically include passenger protection systems such as airbags or seatbelt pretensioners. Many of these protection systems are triggered by a firing element, for example a pyrotechnic firing cap (squib), which initiates further processes for opening an airbag or for tensioning a seatbelt. Such a firing cap is usually activated by virtue of the fact that a predefined activation current/firing current is applied to it for a predefined activation period by a drive circuit. 
         [0003]    Circuit arrangements are known in which two semiconductor switches, with which the firing element is connected in series, are integrated into a common semiconductor body or semiconductor chip. During operation, a supply voltage is applied across the series circuit of the two semiconductor switches and the firing element, and the voltage gives rise to the firing current through the firing element when the two semiconductor switches are switched on. 
         [0004]    The integration of the two semiconductor switches on one semiconductor chip can lead to a situation in which, when there is a serious fault on the chip, uncontrolled activation of the passenger protection system occurs. Such a serious fault may include the fracturing of the chip, for example due to thermal or mechanical stresses. 
       SUMMARY 
       [0005]    Various aspects are described herein. For example, some aspects are directed to an apparatus for driving a load. The apparatus may include, for instance, a semiconductor chip, comprising a first switch, and a fracture sensor. The apparatus may further include, for instance, a circuit disposed outside the semiconductor chip and comprising a second switch coupled in series with the first switch, and configured such that an on/off state of the second switch is set in accordance with a state of the fracture sensor. 
         [0006]    These and other aspects will be described in more detail in connection with various illustrative embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Various illustrative embodiments are explained in more detail below with reference to figures. In this context it is to be noted that the figures serve only for illustration and that the component and circuit structures which are illustrated in the figures are not necessarily illustrated with correct dimensions and are not necessarily to scale. In the figures, unless stated otherwise, the same reference symbols designate the same elements. 
           [0008]      FIG. 1  shows an example of a circuit arrangement for driving a load which has a semiconductor body having at least one semiconductor switch which is integrated into the semiconductor body, and having a fracture sensor, and has an external protective circuit which is connected to the fracture sensor and has a further semiconductor switch. 
           [0009]      FIG. 2  shows an example of the protective circuit with a semiconductor switch which is embodied as a p-type conductive MOSFET. 
           [0010]      FIG. 3  shows another example of the protective circuit with a semiconductor switch which is embodied as a p-type conductive MOSFET. 
           [0011]      FIG. 4  shows another example of the protective circuit with a semiconductor switch which is embodied as a p-type conductive MOSFET. 
           [0012]      FIG. 5  shows another example of the protective circuit with a semiconductor switch which is embodied as an n-type conductive MOSFET. 
           [0013]      FIG. 6  shows another example of the circuit arrangement in which the at least one semiconductor switch which is integrated into the semiconductor body is driven as a function of an operating state of the fracture sensor. 
           [0014]      FIG. 7  shows an example of a driver circuit for driving the semiconductor switch which is integrated into the semiconductor body. 
           [0015]      FIG. 8  shows a further example of a driver circuit for driving the semiconductor switch which is integrated into the semiconductor body. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows an example of a circuit arrangement for driving a load  101 , which can be, for example, a firing element of a passenger protection system, such as a firing element of an airbag or of a seatbelt pretensioner. This particular circuit arrangement comprises a semiconductor body  1 , which is illustrated schematically in  FIG. 1  as a rectangular block and into which at least one semiconductor switch is integrated. In the embodiment illustrated in  FIG. 1 , a first and a second semiconductor switch  2 ,  3 , which are illustrated in the form of their electrical symbols, are integrated into the semiconductor body  1 . These semiconductor switches  2 ,  3  each have a control terminal  21 ,  31  and load paths between first load path terminals  22 ,  32  and second load path terminal  23 ,  33 . These semiconductor switches  2 ,  3  are embodied, for example, as metal-oxide-semiconductor (MOS) transistors, such as MOS field-effect transistors (MOSFETs), or insulated-gate bipolar transistors (IGBTs), which each has a gate terminal as the control terminal  21  and drain and source terminals as load path terminals. 
         [0017]    The semiconductor chip  1  is partially or fully surrounded by a housing  11  which is illustrated by dashed lines in  FIG. 1  and which has connection terminals (such as connection pins) for making contact with individual components which are integrated into the semiconductor chip  1 . Individual load terminals  22 ,  23 ,  32 ,  33  of the integrated semiconductor switches  2 ,  3  are each assigned one connection pin  24 ,  25 ,  34 ,  35  here, with the load terminals  22 ,  23 ,  24 ,  25  being connected to the respectively assigned connection pin by means of a bonding wire connection, for example. The load includes the firing element  101  and may also include, for example, a supply line  102  to the firing element  101 , can be connected via these connection pins  22 ,  23 ,  24 , in series with the load paths of the integrated semiconductor switches  2 ,  3 . With reference to  FIG. 1 , the load is, for this purpose, connected, for example, between the second load path terminal  23  of the first semiconductor switching element  2  and the first load path terminal  32  of the second semiconductor switching element  3 . 
         [0018]    The first and second integrated semiconductor switches  2 ,  3  are driven as a function of drive signals S 2 , S 3  which are generated by a control circuit  6  which is integrated into the semiconductor body  1 . This control circuit  6  is connected, for example, by means of an input terminal  63  and an associated input pin  64  to sensors, for example acceleration sensors, which provide sensor signals in accordance with which the firing element  101  is to be triggered. Driver circuits  4 ,  5  are connected between the control circuit  6  and the drive inputs  21 ,  23  of the semiconductor switches  2 ,  3 . These driver circuits are designed to convert the drive signals S 2 , S 3 , which are for example logic signals, to signals which are suitable for driving the semiconductor switches  2 ,  3 . The driver circuits  4 ,  5  are matched here to the type of the respectively used semiconductor switch. These semiconductor switches  2 ,  3  can each be semiconductor switches of the same type, for example n-channel MOSFETs or IGBTs, or complementary semiconductor switches, i.e. for example the first semiconductor switch can be a p-channel MOSFET and the second semiconductor switch can be an n-channel MOSFET, or vice-versa. 
         [0019]    A voltage supply of the circuit components which are integrated into the semiconductor body  1  is provided, for example, by a voltage supply circuit  7 , which may be connected to the individual circuit components. This voltage supply  7  is connected via supply inputs  71 ,  73  to voltage supply pins  72 ,  74  to which a supply voltage can be applied. For this purpose, one of these voltage supply pins  74  is connected to a terminal for a positive supply potential Vs, while a second of these voltage supply pins  72  is connected during operation of the circuit arrangement to a terminal for a negative supply potential or reference potential GND. 
         [0020]    The semiconductor body  1  has a fracture sensor  8  which is implemented in the illustrated example as an electrically conductive sensor line which, at least over part of its length, is mechanically coupled to a surface of the semiconductor body  1 . This line, which is referred to below as a sensor line, is composed, for example, of metal or a doped polycrystalline semiconductor material such as polysilicon. This sensor line is, for example, electrically insulated from active component areas of the semiconductor body  1 , i.e. from component areas in which doped semiconductor zones are arranged in order to implement the components which are integrated into the semiconductor body  1 . The sensor line  8  can be, in particular, part of a wiring structure which is arranged above a surface of the semiconductor body  1 . Such a wiring structure comprises for example a plurality of wiring planes or metallization planes with conductor tracks, in which case insulation layers may be arranged between the individual metallization planes. Conductor tracks in different planes can be connected to one another here by means of vertical cross connections, referred to as vias, and they serve to wire the semiconductor components which are integrated into the semiconductor body. The sensor line  8  can be implemented here as a conductor track of a metallization plane but it can also comprise a plurality of conductor track sections which are connected to one another in different metallization planes. 
         [0021]    The mechanical coupling of the sensor line  8  to the surface of the semiconductor body  1  has the effect that, when there is a fracture in the semiconductor body  1  which results in a fissure in the surface of the semiconductor body  1 , the sensor line  8  also fractures, which is evaluated in a way which will also be explained. In an arrangement of the sensor line  8  in a wiring structure above the surface of the semiconductor body  1 , there is sufficient mechanical coupling of the sensor line to the surface so that it is possible to assume that, when there is a fracture of the semiconductor body  1 , the layered configuration of the wiring structure, and thus the sensor line  8 , also fractures. When a fracture occurs in the semiconductor body, a fissure usually starts in the edge region of the semiconductor body and propagates from there into the interior of the semiconductor body. In order to be able to detect such a fissure early and to be able to monitor the semiconductor body  1  as completely as possible, the sensor line  8  can be arranged in the edge region or above the edge region of the semiconductor body  1  and can be implemented in such a way that it follows the edge of the semiconductor body over its entire length, but without being short-circuited. It is possible to make contact with the sensor line  8  at one end via a first terminal contact  81 , and at a second end facing away from the first end via a second terminal contact  82 . 
         [0022]    The circuit arrangement illustrated in  FIG. 1  also has an external protective circuit  9 , i.e. one which is arranged outside the semiconductor body  1 , with a further semiconductor switch  91  and a driver circuit  92  for the further semiconductor switch  91 . This driver circuit  92  is connected to the sensor line  8  and is designed to switch off the further semiconductor switch  91  when there is a fracture in the sensor line  8 , and thus as a function of an operating state of the sensor line  8 . 
         [0023]    The further semiconductor switch  91  is implemented, for example, as a MOS transistor and has a control terminal which is connected to the driver circuit  92 , and a load path which extends between first and second load terminals  93 ,  94 . The load path of this further semiconductor switch  91  can be connected in series with the load paths of the semiconductor switches  2 ,  3  which are integrated into the semiconductor body  1  and in series with the load  101 . In the illustrated example, the load path  93 - 94  of this further semiconductor switch  91  is connected directly in series with the first semiconductor switch  2  which is integrated into the semiconductor body  1 . 
         [0024]    The driver circuit  92  of the further semiconductor switching element  91  has a first drive input  96  which is connected via a connection pin  84  to the second connection terminal  82  of the sensor line  8 . The first terminal  81  of the sensor line  8  can be connected hereby via a further connection pin  83  to an external supply potential, for example reference potential GND. 
         [0025]    The driver circuit  92  of the protective circuit  9  may have a second drive input  95  which is connected via a drive pin  62  to a further output  61  of the control circuit  6 . In this variant, the semiconductor switching element  91  of the protective circuit is also driven via the control circuit  6 , making it possible to provide that switching on of the semiconductor switching element  91  of the protective circuit occurs together with switching on of the semiconductor switching elements  2 ,  3  which are integrated into the semiconductor body  1 . 
         [0026]    While the circuit arrangement is operating, the load paths of the semiconductor switches  2 ,  3  which are integrated into the semiconductor body  1  and of the semiconductor switching element  91  of the protective circuit  9  are connected in series with one another and in series with the firing element  101 , with the firing element in the illustrated example being connected between the two integrated semiconductor switches  2 ,  3 . This series circuit is connected between supply potential terminals, with, for example, the load terminal  93 , facing away from the semiconductor body  1 , of the semiconductor switching element  91  of the protective circuit being connected to a terminal for a positive supply potential Vb, and the second load terminal  35 , facing away from the firing element  101 , of the second semiconductor switching element  3  which is integrated into the semiconductor body  1  being connected to a terminal for negative supply potential or reference potential GND. In order to fire the firing element  101 , the control circuit  6  switches on the two integrated semiconductor switches  2 ,  3  and the semiconductor switching element  91  of the protective circuit  9  for a predefined time period, as a result of which the firing element  101  is supplied with a firing current via the series circuit of the integrated semiconductor switches  2 ,  3  and of the external semiconductor switch  91 , and can trigger. 
         [0027]    Fracturing of the semiconductor body  1  constitutes a serious fault whose occurrence makes it unlikely that satisfactory functioning of the circuit arrangement will occur thereafter. In order to prevent faulty triggering of the firing element  101  when there is such a fracture in the semiconductor body  1 , the driver circuit  92  switches off the semiconductor switching element  91  of the protective circuit  9  when there is such a fault, thus preventing, even if the integrated semiconductor switches  2 ,  3  are switched on, a firing current from flowing through the firing element  101 , and thus preventing triggering of the firing element  101 . In this circuit arrangement, fracturing of the semiconductor body  1  is detected via the sensor line  8  which has an electrically conductive path between the terminals  82 ,  83 , which path is interrupted when the semiconductor body  1  fractures. 
         [0028]    A first implementation example of the driver circuit  92  which detects an interruption in the sensor line  8  is illustrated in  FIG. 2 . Of this semiconductor body,  FIG. 2  shows only the drive pin  62 , connected to the second drive input  95  of the driver circuit, and the connection pins  83 ,  84  for the sensor line  8 . A load Z which is connected to the second load terminal  94  of the further semiconductor switching element  91  represents in  FIG. 2  the series circuit with the two semiconductor switches ( 2 ,  3  in  FIG. 1 ), which are integrated into the semiconductor body, and the firing element ( 101  in  FIG. 1 ). 
         [0029]    The semiconductor switching element  91  of the protective circuit  9  which is illustrated in  FIG. 2  may be implemented as a p-type conductive MOSFET whose source terminal forms the first load terminal which is connected to the terminal for the positive supply potential Vb during operation. In this protective circuit, the driver circuit  92  comprises a first resistor element R 1  which is connected between the gate terminal and the source terminal of the MOSFET  91 , and a semiconductor switching element T 1  which is embodied in the example as an npn bipolar transistor and has a control terminal (base terminal) and a load path (collector-emitter path). The load path of this bipolar transistor is connected to the gate terminal of the MOSFET  91  and is connected in series with the sensor line  8 . The first terminal  83 , facing away from the bipolar transistor T 1 , of the sensor line  8  is connected during operation here to a supply potential which is lower than the supply potential Vb to which the source terminal of the MOSFET  91  is connected. This supply potential which is applied to the first terminal  83  of the sensor line  8  is, for example, the reference potential GND. The base terminal of the bipolar transistor T 1  is connected via the drive pin  62  to the control circuit  6  (not illustrated in  FIG. 2 ). A further resistor element R 2  which is connected between the drive pin  62  and the base terminal is optionally present and serves as a series resistor for protecting the bipolar transistor against excessively high base currents. 
         [0030]    An illustrative method of operation of the protective circuit which is illustrated in  FIG. 2  will be explained below. The MOSFET  91  is conductive, thus permitting current to flow through the downstream load arrangement Z when its gate terminal is at an electrical potential which is lower by the value of the threshold voltage of this MOSFET  91  than the electrical potential at its source terminal  93 . This is brought about in the protective circuit  9  illustrated in  FIG. 2  if there is an electrically conductive connection between the gate terminal and the reference potential GND. This is equivalent to the bipolar transistor T 1  being switched on under the control of the control circuit  6  and at the same time the sensor line  8  being intact, i.e. not interrupted. If one of these two conditions is not met, that is to say if the sensor line  8  is interrupted or if the bipolar transistor T 1  is switched off, the gate potential of the MOSFET  91  is drawn to the value of the source potential via the first resistor element R 1 , as a result of which the MOSFET  91  switches off. In this context it is to be noted that the resistance value of the first resistor element R 1  is higher, ideally substantially higher, than the ohmic resistance of the series circuit of the bipolar transistor T 1  and of the sensor line  8  when the bipolar transistor T 1  is switched on and the sensor line  8  is intact. 
         [0031]    If semiconductor chip  1  in the explained circuit arrangement fractures and if as a result the sensor line  8  is interrupted, the MOSFET  91  of the protective circuit  9  switches off irrespective of whether the control circuit makes available a suitable drive potential for switching on the bipolar transistor T 1  and thus for switching on the MOSFET  91 . This may reliably prevent, in the event of the semiconductor chip  1  fracturing, a current from being able to flow through the load arrangement Z which is connected downstream of the semiconductor switching element  91  of the protective circuit  9 , which may reliably prevent triggering of the firing element ( 101  in  FIG. 1 ). 
         [0032]    The previously explained driving of the semiconductor switching element  91  of the protective circuit  9  via the drive pin  62  of the control circuit serves to reduce the current drain of the circuit arrangement and permits the semiconductor switching element  9  to be switched on via the control circuit  6  only when the firing element  101  is to trigger, i.e. when the two integrated semiconductor switching elements  2 ,  3  are also to be switched on by the control circuit  6 . With regard to the desired protective function of the protective circuit  9  which, in the event of an interruption of the sensor line  8 , is intended to prevent a flow of current through the downstream load arrangement Z, it is possible to dispense with driving by means of the control circuit  6  and thus with the bipolar transistor T 1 . In this example, the sensor line  8  is connected directly to the control terminal of the semiconductor switching element  9  via the second terminal of said sensor line  8 . This variant is illustrated in  FIG. 3 . 
         [0033]      FIG. 4  show a modification of the protective circuit illustrated in  FIG. 2 . In this protective circuit illustrated in  FIG. 4 , a thyristor TH 1 , instead of a bipolar transistor, is connected in series with the sensor line  8  between the gate terminal of the MOSFET  91  and the terminal for reference potential GND. An anode terminal of the thyristor is connected here to the gate terminal of the MOSFET  91 , and a cathode terminal of the thyristor TH 1  is connected to the sensor line  8 . A firing terminal of the thyristor TH 1  is connected via a series resistor R 2  to the drive pin  62  of the control circuit  6 . 
         [0034]      FIG. 5  shows a further exemplary embodiment of the protective circuit  9 . The semiconductor switching element  91  is embodied in this exemplary embodiment as an n-type conductive MOSFET whose drain terminal forms the first load terminal  93  which is connected to the positive supply potential Vb, and whose source terminal forms the second load terminal  94 . This MOSFET  91  is switched on if a drive potential which is above the potential of the source terminal  94  by at least the value of the threshold voltage of this transistor  91  is applied to the gate terminal of said MOSFET  91 . The driver circuit  92  for driving this MOSFET has, in addition to the components of the driver circuit  92  which have already been explained with reference to  FIG. 2 , an inverting circuit which is connected between the terminal  99 , which is common to the first resistor element R 1  and the bipolar transistor T 1 , and the gate terminal of the MOSFET  91 . This inverting circuit comprises in the example a further bipolar transistor T 2  which is implemented as a pnp-type bipolar transistor and which is connected between the drain terminal and the gate terminal of the MOSFET  91 , as well as a further resistor element R 3  which is connected between the gate terminal and the source terminal of the MOSFET  91 . If the input of the inverting circuit which is formed by the common node of the first resistor element and of the first bipolar transistor T 1  is approximately at reference potential when the first bipolar transistor T 1  is switched on and the sensor line  8  is intact, the further bipolar transistor T 2  is switched on, as a result of which the MOSFET  91  switches on. If the input  99  of the inverting circuit is at the positive supply potential Vb when the bipolar transistor T 1  is switched off and the sensor line  8  is interrupted, the further bipolar transistor T 2  switches off, as a result of which the gate potential of the MOSFET is drawn approximately to the value of the source potential via the further resistor R 3  so that the MOSFET  91  switches off. 
         [0035]    Of course, in the protective circuit which is illustrated in  FIG. 5 , it is also possible to dispense with the bipolar transistor T 1 , for example if only a protective function and not additional driving of the semiconductor switch  91  via the control circuit  6  is desired. In this case, in accordance with the exemplary embodiment in  FIG. 3 , the sensor line  8  may be connected directly to the circuit node  99 . 
         [0036]      FIG. 6  shows a further exemplary embodiment of the circuit arrangement. In this exemplary embodiment, the semiconductor switches  2 ,  3  which are integrated into the semiconductor chip  1  are also driven as a function of the operating state of the sensor line  8 . The driver circuits  4 ,  5  of these integrated semiconductor switches  2 ,  3  are for this purpose connected to the sensor line  8  and designed to detect an interruption in the sensor line  8  and to switch off the semiconductor switches  2 ,  3  if there is an interruption in the sensor line. 
         [0037]    A possible exemplary embodiment of a driver circuit with such functionality is explained below with reference to  FIG. 7  for the driver circuit  4  of the first integrated semiconductor switch  2 . This driver circuit  4  has a driver  41  to which the drive signal S 4 , according to which the semiconductor switch  2  is to be switched on or off, is fed and which makes available, as a function of this drive signal S 4 , a suitable drive signal for switching the semiconductor switch  2  on or off. This driver  41  can be a conventional driver suitable for driving the semiconductor switch  2 . In the circuit configuration illustrated in  FIG. 6 , the driver is to be embodied as what is referred to as a high side driver when two n-channel MOSFETs or two IGBTs are used as semiconductor switches  2 ,  3 , said high side driver making available, for the purpose of switching on the semiconductor switch, a drive potential which is higher than the positive supply potential Vb of the circuit arrangement. What is referred to as a low side driver which, for the purpose of switching on this semiconductor switch  3 , generates a drive potential which is above the reference potential GND merely by the value of the threshold voltage of the semiconductor switch  3 , is sufficient for driving the second integrated semiconductor switch  3 . 
         [0038]    The driver  41  of the driver circuit  4  has voltage supply terminals for applying a supply voltage and a switch  42  which is connected between one of the supply terminals and a terminal for supply potential Vs, said switch  42  being switched on or off as a function of the operating state of the sensor line  8 . In the illustrated example, the switch  42  is a p-conducting MOS transistor which is connected between a terminal for a positive supply potential Vs and the associated supply potential terminal of the driver circuit  41 . The load path of a bipolar transistor  43 , in the example an npn-type bipolar transistor, is connected to the gate terminal of the MOS transistor  42 , in series with the sensor line  8 . A bias voltage Vbias, which keeps the bipolar transistor  43  continuously switched on, is connected to a base terminal of this bipolar transistor  43 . A resistor element  44  is connected between the gate terminal of the MOS transistor  42  and the terminal for the positive supply potential Vs. If the sensor line  8  is intact in this circuit arrangement, the gate terminal of the MOS transistor  42  is at a potential which is lower than the positive supply potential Vs, as a result of which the MOS transistor  42  switches on. As a result, the driver  41  is supplied with a supply voltage in order to switch the semiconductor switch  2  on or off as a function of the drive signal S 4 . If the sensor line  8  is interrupted, the potential at the gate terminal of the MOS transistor  42  is drawn to the value of the positive supply potential Vs, as a result of which the MOS transistor  42  switches off and consequently interrupts a voltage supply of the driver  41 . The driver  41  is embodied here in such a way that, when a voltage supply is not present, it switches off the associated semiconductor switch  2 . This may provide that when the sensor line  8  is interrupted, i.e. when there is a fracture in the chip, the semiconductor switches  2 ,  3  which are integrated into the semiconductor chip  1  may be reliably prevented from being switched on. 
         [0039]    The concept, explained with reference to  FIG. 7 , of switching off the integrated semiconductor switches  2 ,  3  by interrupting the voltage supply of the associated driver circuits  4 ,  5  can be implemented more easily in terms of circuit technology by virtue of the fact that the supply terminal which is connected to the negative supply potential or reference potential during operation is connected to this supply potential via the sensor line  8 , which is illustrated in  FIG. 8 . A voltage supply of the driver circuit  41  is directly interrupted here when there is an interruption in the sensor line  8 . 
         [0040]    The concept, explained with reference to  FIGS. 7 and 8 , of switching off the integrated semiconductor switches  2 ,  3  by interrupting the voltage supply to the associated driver switches  4 ,  5  can also be applied (in a way not illustrated in more detail) to the driving of the semiconductor switch  91  of the protective circuit  9  by virtue of the fact that a driver circuit is provided here which is supplied with a voltage as a function of an operating state of the sensor line  8  and which switches off the semiconductor switch in the unsupplied state. 
         [0041]    In the previously explained circuit arrangements, two semiconductor switches  2 ,  3  are integrated into the semiconductor chip  2  for safety reasons, and said semiconductor switches  2 ,  3  are connected in series with the firing element  101  when the circuit arrangement is operating, and they have to both be switched on for the firing element to be fired. There is, of course, also the possibility of integrating just one semiconductor switching element into the semiconductor chip  1 , in which case the firing element  101  is to be connected either between this semiconductor switching element and reference potential GND or between this semiconductor switching element and the protective circuit  9 .