Abstract:
In a preferred embodiment, a multi-configurable output driver, including: circuit apparatus to provide driving current to an inductive load; and the circuit apparatus being configurable, without the addition or rearrangement of components, in at least two different output topographies.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to output drivers generally and, more particularly, but not by way of limitation, to a novel multi-configurable output driver which is configurable as an internal high or low side driver or as an external high or low side driver. 
     2. Background Art 
     A switched inductive load, such as may be present in pulse-width-modulated drive systems, requires the dissipation of the flyback current that is generated in the load as the magnetic field created therein collapses upon removal of the driving current. Since the driver and load may take one of a number of configurations, a specific arrangement is conventionally provided unique to any one configuration to provide for dissipation of the flyback current. Thus, each arrangement requires that a specific circuit be designed for the arrangement. It would be desirable to have a single circuit that is easily configurable to provide for dissipation of flyback current upon switching of current to an inductive load for a plurality of driver configurations. 
     Accordingly, it is a principal object of the present invention to provide a multi-configurable output driver for the dissipation of flyback current from a switched inductive load. 
     It is a further object of the present invention to provide such an output driver that is easily implemented in an output driver integrated circuit. 
     Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a multi-configurable output driver, comprising: circuit means to provide driving current to an inductive load; and said circuit means being configurable, without the addition or rearrangement of components, in at least two different output topographies. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Understanding of the present invention and the various aspects thereof will be facilitated by reference to the accompanying drawing figures, submitted for purposes of illustration only and not intended to define the scope of the invention, on which: 
     FIG. 1 is a schematic/block diagram showing the basic circuit of the present invention. 
     FIG. 2 is a schematic/block diagram showing the circuit configured as an internal low side output driver and showing the dissipation path of flyback current. 
     FIG. 3 is a schematic/block diagram showing the circuit configured as an internal high side output driver and showing the dissipation path of flyback current. 
     FIG. 4 is a schematic/block diagram showing the circuit configured as an external low side output driver and showing the dissipation path of flyback current. 
     FIG. 5 is a schematic/block diagram showing the circuit configured as an external high side output driver and showing the dissipation path of flyback current. 
     FIG. 6 is a schematic/block diagram showing the circuit configured as an external high side output driver and showing the dissipation path of flyback current during loss of battery voltage. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference should now be made to the drawing figures, on which similar or identical elements are given consistent identifying numerals throughout the various figures. 
     FIG. 1 illustrates the basic circuit of the present invention, generally indicated by the reference numeral 10, and having Drn, Sen, and Src output connections. Circuit 10 may be part of an integrated circuit (not shown). Circuit 10 includes an internal wave-shaped gate pre-drive circuit (U1) 12 having an enable input and being connected to drive an internal MOSFET (M1) 14. (U1) 12 is connected to a clamped battery voltage (U3) through a first switch (SW1) 20, if circuit 10 is configured as a low side driver, or is connected to a charge pumped voltage (U2) through SW1 20, if the circuit is operated as a high side driver. The drain of internal MOSFET 14 is connected to the Drn output and first and second zener diodes (CR1) 22 and (CR2) 24, respectively, having their anodes connected are connected in series between the gate of internal MOSFET 14 and the Drn output. The source of internal MOSFET 14 is connected to the Src output and a second switch (SW2) 26 is connected between the gate and source of the MOSFET. SW2 26 is closed, if circuit 10 is operated as an external driver, and is open, if the circuit is operated as an internal driver. A third zener diode (CR3) 28 is connected between the Drn and Sen outputs. 
     It will be understood that circuit 10 may be implemented in an integrated circuit. 
     The table on FIG. 1 indicates the positions of SW1 20 and SW2 26 for the four different configurations of circuit 10. 
     FIG. 2 illustrates circuit 10 configured as an internal low side driver driving a load 40. Here, the high side of load 40 is connected to a voltage source (Vbat), the low side of the load being connected to the Drn output of circuit 10, the Src output is connected to ground, and the Sen output is left open. SW1 20 is connected to Vbat and SW2 26 is open. 
     In operation, when (U1) 12 is enabled, it supplies Vbat to the gate of internal MOSFET 14, enhancing the MOSFET, resulting in a low Drn voltage, and causing load 40 to conduct current. When disabled, (U1) 12 will now sink &lt;1 mA of current. The current in inductive load 40 flies back through CR1 22, CR2 24, and (U1) 12 as is indicated by the broken line path on FIG. 2. CR1 22 and CR2 24 will limit the Drn voltage to about 44 VDC, preventing a drain-to-source breakdown in internal MOSFET 14. The gate of internal MOSFET 14 will go to a voltage of about 3 VDC, which is determined by the threshold voltage and transconductance of the internal MOSFET. The drain and source of internal MOSFET 14 conduct all the flyback current of load 40, less the current that flows to U1 12. 
     FIG. 3 illustrates circuit 10 configured as an internal high side output driver. Here, the high side of load 40 is connected to the Src output and the low side of the load is connected to ground. The Drn output is connected to a voltage source (Vbat) and the Sen output is left open circuited. 
     In operation, when U1 12 is enabled, it supplies pumped voltage (U2) to the gate of internal MOSFET 14, enhancing the MOSFET, resulting in high Src voltage, and causing load 40 to conduct current. When disabled, U1 12 will go low and the current in load 40 will fly back through a parasitic diode (CR4) 50 of MOSFET 14 to ground as is indicated by the broken line path on FIG. 3. The gate of MOSFET 14 will go to a voltage of 0 VDC. Thus, the source of MOSFET 14, i.e., CR4 50 will conduct all the flyback current of load 40. 
     FIG. 4 illustrates circuit 10 configured as an external low side output driver. Here, the high side of load 40 is connected to a voltage source (Vbat). The low side of load 40 is connected to the Sen output and to the drain of an external MOSFET 60. The Src output is connected to the gate of external MOSFET 60. The source of external MOSFET 60 is grounded and the Drn output is left open circuited. 
     In operation, when U1 12 is enabled, it supplies Vbat (U3) to the gate of external MOSFET 60 through closed SW2 26. This enhances external MOSFET 60, resulting in low external MOSFET drain voltage, and causing load 40 to conduct current. When disabled, U1 12 will now sink &lt;1 mA of current and CR3 28 allows the current in inductive load 40 to flyback through the internal zener diode structure of CR3 28, CR1 22, and CR2 24, and U1 12, as indicated by the broken line path on FIG. 4. The zener diode structure limits the voltage to about 45 VDC, preventing a drain-to-source breakdown in external MOSFET 60. Since SW2 26 is closed, the gate of external MOSFET 60 will go to a voltage of about 3 VDC, which is determined by the threshold voltage and transconductance of the external MOSFET. The drain and source of external MOSFET 60 conduct all the flyback current of load 40 minus the current that goes to U1 12. 
     FIG. 5 illustrates circuit 10 configured as an external high side output driver. Here, the high side of load 40 is connected to the source of external MOSFET 60 and to the Sen output and the low side of the load is connected to ground. A voltage source (Vbat) is connected to the drain of MOSFET 60 and the Src output is connected to the gate of the external MOSFET. The Drn output is left open. 
     In operation, when U1 12 is enabled, it supplies pumped voltage (Vbat+15) to the gate of external MOSFET 60 through closed SW2 26. This enhances external MOSFET 60, resulting in a high external MOSFET drain voltage, and causing load 40 to conduct current. when disabled, U1 12 and the gate of external MOSFET 60 will go to 0 VDC (since SW2 26 is closed). The source of external MOSFET 60 will go to a voltage of about -3 VDC, which is determined by the threshold voltage and transconductance of external MOSFET 60. The current in load 40 flies back through the drain and source of external MOSFET 60 as is indicated by the broken line path on FIG. 5. 
     FIG. 6 illustrates the path of flyback current in load 40 when Vbat is lost to the drain of external MOSFET 60. Here, as is indicated by the broken line path on FIG. 6, all of the flyback current in load 40 flies back through parasitic drain-to-substrate diode 50 of internal MOSFET 14 and through zener diode 28. This clamps the maximum voltage at the drain of external MOSFET 60 to about -11 VDC. Since the gate of external MOSFET 60 will go to a voltage of 0 VDC, this protects against a gate-to-source breakdown in external MOSFET 60. 
     It will thus be seen that the objects set forth above, among those elucidated in, or made apparent from, the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown on the accompanying drawing figures shall be interpreted as illustrative only and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.