Abstract:
The present invention concerns a device for controlling the operation of a power module composed of switches, each switch being composed of a plurality of power dies connected in parallel, characterized in that the device comprises, for each power die of the power module: a temperature sensor to sense the temperature of the power die, a current sensor to sense the current going through the power die, a gate interrupt circuit to interrupt the signal provided to the power die if the sensed current is higher than a predetermined current threshold, a controller to reduce the conducting time of the die if the sensed temperature of the power die is higher than the average die temperature across the power dies of at least one switch.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to a device for controlling the operation of a multi-die power module. 
       BACKGROUND ART 
       [0002]    Multi-die power modules are classically composed of several parallel connected power dies and are used for increasing the current capability over that of a single power die. 
         [0003]    For example, a three-phase converter is composed of four parallel power dies per switch, giving twenty four power dies in total. 
         [0004]    Emerging devices technologies, such as SiC (Silicon Carbide) and GaN (Gallium Nitride) Transistors, are typically realized in high current density, small power dies due to limitations of yield and cost of wafer substrate. 
         [0005]    In order to realize higher power SiC-based modules, a multitude of parallel connected SiC dies is necessary. Unlike parallel connected modules, parallel connected dies constitute a single switch that ideally commutates the same load current. 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, regardless of the type of die used, i.e. diodes or voltage-driven switch, e.g. MOSFETs (Metal Oxide Semiconductor Field Effect Transistor), characteristics exist within the dies that limit the balanced sharing of the load current both statically and dynamically. The incremental addition of each parallel die does not result in full utilization of the die, and thus, more dies are needed in parallel to achieve a given current rating, thereby increasing the overall costs and physical surface area of the power module. 
         [0007]    In addition to the electrical characteristics of the die, the physical placement of the dies within the power module also limits the reliability and utilization of the dies. One such example is the unequal thermal distribution within a module due to heating from neighbouring dies. Unless the design of the module allows for sufficient spacing between the dies, thereby increasing the physical size of the power module, the dies close to the center of the power module experience higher temperatures than the dies close to the periphery of the power module. 
         [0008]    Another geometric consideration is the dynamic performance of the parallel dies. Due to the inevitably different routing of interconnections and the placement of the dies on the substrate, the parallel dies can begin to switch at different times, causing oscillatory behaviour that can impact the maximum capability of each die. This phenomenon is especially problematic for emerging wideband gap devices where the switching times are significantly shorter compared to silicon based devices. 
         [0009]    Furthermore, localized temperature increases can occur across a set of dies due to localized degradation of the thermal interface of the die, e.g. as a result of over-stressing that set of dies. 
       Solution to Problem 
       [0010]    The present invention aims at enhancing the switching speed of multi-die switches and to increase the maximum capability of a multi-die power module by minimising die de-rating due to thermal mismatches within the module. 
         [0011]    To that end, the present invention concerns a device for controlling the operation of a power module composed of switches, each switch being composed of a plurality of power dies connected in parallel, characterized in that the device comprises, for each power die of the power module:
       a temperature sensor to sense the temperature of the power die,   a controller to reduce the conducting time of the die if the sensed temperature of the power die is higher than the average die temperature across the power dies of at least one switch.       
 
         [0014]    The present invention concerns also a method for controlling the operation of a power module composed of switches, each switch being composed of a plurality of power dies connected in parallel, characterized in that the method comprises the steps, executed for each power die of the power module of:
       sensing the temperature of the power die,   reducing the conducting time of the die if the sensed temperature of the power die is higher than the average die temperature across the power dies of at least one switch.       
 
         [0017]    Thus, the maximum capability of the multi-die power module is increased. 
         [0018]    By controlling individually each die of the multi-die power module, it is possible to overcome problems related to different routing of interconnections and the placement of the dies, unequal thermal distribution within the multi-die power module and natural dispersion of the die parameters. 
         [0019]    According to a particular feature, the device further comprises:
       a current sensor to sense the current going through the power die,   a gate interrupt circuit to gate the signal provided to the power die if the sensed current is higher than a predetermined current threshold.       
 
         [0022]    According to a particular feature, the conducting time of the power die is reduced by modifying the duty cycle of the signal provided to the power die. 
         [0023]    Thus, the losses in the power die are reduced, lowering the local die temperature. 
         [0024]    According to a particular feature, the signal is a gating signal. 
         [0025]    Thus, the device acts to modulate the activity of the dies, transparent to the host controller. 
         [0026]    According to a particular feature, the device further comprises an analogue to digital converter to convert the sensed temperature and a scaling device to scale the sensed temperature. 
         [0027]    According to a particular feature, the signal provided to each power die is provided by a respective amplifier. 
         [0028]    Thus, by providing an amplifier for each die, the gate-controller parasitic loop is reduced and allows for an increase of switching speed or a reduction of unwanted oscillations. 
         [0029]    The characteristics of the invention will emerge more clearly from a reading of the following description of example embodiments, the said description being produced with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  represents an example of a system for controlling the operation of a multi-die power module according to the present invention. 
           [0031]      FIG. 2  represents an example of an architecture of a controller of the system for controlling the operation of a multi-die power module according to the present invention. 
           [0032]      FIG. 3  represents an example of an architecture of a device for controlling the operation of a power die according to the present invention. 
           [0033]      FIG. 4  represents an example of an architecture of a signal conditioning module of the device for controlling the operation of a power die according to the present invention. 
           [0034]      FIG. 5  represents an example of an architecture of a gate interrupt circuit of the signal conditioning module. 
           [0035]      FIG. 6  represents an algorithm executed by the controller of the system for controlling the operation of a multi-die power module. 
           [0036]      FIG. 7  represents gate voltage variations generated by a device for controlling the operation of a power die according to the output of current and temperature sensing means. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0037]      FIG. 1  represents an example of a system for controlling the operation of a multi-die power module according to the present invention. 
         [0038]    The system for controlling the operation of the multi-die power module  150  uses power die feedback mechanisms like thermal information or on-state voltages or individual die voltage/current trajectory, to modulate the control electrode command for each individual die in the multi-die power module  150 . 
         [0039]    The system for controlling the operation of the multi-die power module  150  obtains, for each die, thermal information or on-state voltages or die voltage/current trajectory and controls each die according to the obtained information. 
         [0040]    The system for controlling the operation of the multi-die power module  150  comprises a plurality of devices  102  for controlling the operation of a power die  305 , one for each die. 
         [0041]    In the example of  FIG. 1 , the system for controlling the operation of the multi-die power module  150  comprises five devices  102   a  to  102   e  for controlling the operation of five power dies  305   a  to  305   e,  respectively. 
         [0042]    Each device for controlling the operation of a power die  102  uses die information and controls said die in order to increase the performance of the multi-die power module  150 , increasing then the utilization factor of each die. The architecture of a device for controlling the operation of a power die  102  is disclosed in  FIG. 2 . 
         [0043]    Each device for controlling the operation of a power die  102  includes low cost circuitry to determine various state of health characteristics, e.g. gate threshold voltages or other measurable temperature-dependent parameters to determine the junction temperature and therefore be used to provide optimal control of the die. Each device for controlling the operation of a power die  102  uses information obtained from the die to translate the obtained information to useful state of health measurements, such as the junction temperature, in order to enable a controller  104  to balance the temperatures within the parallel set of dies. The controller  104  and each device for controlling the operation of a power die  102  modulates the die activity in response to light loads in order to improve operating efficiency. 
         [0044]    Each device for controlling the operation of a power die  102  may also be removed from operation (passivation) in the event of a fault, thereby improving the fault tolerance of the entire power module  150 . 
         [0045]    In response to unequal interface degradation of the devices for controlling the operation of a power die  102 , the loading of each die can be altered to reduce the thermal strain of the affected die and then improve the overall reliability of the power module  150 . 
         [0046]    It has to be noted here that each device for controlling the operation of a power die does not require an isolated power supply. 
         [0047]    The controller is disclosed in more details in reference to  FIG. 2 . 
         [0048]      FIG. 2  represents an example of an architecture of a controller of the system for controlling the operation of a multi-die power module according to the present invention. 
         [0049]    The controller  104  has, for example, an architecture based on components connected together by a bus  201  and a processor  200  controlled by the program as disclosed in  FIG. 6 . 
         [0050]    The bus  201  links the processor  200  to a read only memory ROM  202 , a random access memory RAM  203  and an input/output interface I/O  205 . 
         [0051]    The memory  203  contains registers intended to receive variables and the instructions of the program related to the algorithm as disclosed in  FIG. 6 . 
         [0052]    The processor  200  receives and transfers information to the devices for controlling the operation of the power dies  102  through the input/output interface I/O  205 . The input output interface I/ 0   205  may be split into two interfaces, one with the host controller and one with the device for controlling the operation of a power die  102 . 
         [0053]    Through the input/output interface  205 , the controller  104  receives an activation or load command from a host controller. The controller  104  interprets this activation command and provides synchronized control over the plurality of dies. 
         [0054]    The controller  104  provides information, like for example the duty cycle, to each device for controlling the operation of a power die  102 . 
         [0055]    The read only memory  202  contains instructions of the programs related to the algorithm as disclosed in  FIG. 6 , which are transferred, when the controller  104  is powered on, to the random access memory  203 . 
         [0056]    Any and all steps of the algorithm described hereafter with regard to  FIG. 6  may be implemented in software by execution of a set of instructions or program by a programmable computing machine, such as a PC (Personal Computer), a DSP (Digital Signal Processor) or a microcontroller; or else implemented in hardware by a machine or a dedicated component, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). 
         [0057]    In other words, the controller  104  includes circuitry, or a device including circuitry, causing the controller  104  to perform the steps of the algorithm described hereafter with regard to  FIG. 6 . 
         [0058]    The controller  104  may be realized, for example, by a pre-programmed CPLD (Complex Programmable Logic Device). 
         [0059]    According to the invention, from the synchronized control pattern and from the sensed temperature value, the controller  104  generates a duty cycle which is different from the one corresponding to the synchronized control pattern if the sensed temperature is higher than a predetermined temperature threshold. 
         [0060]    For example, if the parasitic inductor  306  generates oscillatory behavior that impacts the temperature of the die  305 , the temperature sensed by the temperature sensing means  303 , converted by the ADC  310  and scaled by the voltage and/or temperature scaling device  401  is higher than the predetermined temperature threshold, the controller  104  reduces the duty cycle of the periodic signal which drives the power die in order to reduce the conduction time of the power die  305 . 
         [0061]      FIG. 3  represents an example of an architecture of a device for controlling the operation of a power die according to the present invention. 
         [0062]    Each device for controlling the operation of a power die  102  comprises temperature sensing means  303  for sensing the junction temperature of the power die  305  and/or current sensing means  304  for sensing the current going through the power die  305 . 
         [0063]    The temperature sensing means  303  may be a thermocouple or may be implemented by monitoring threshold voltages or other measurable temperature-dependent parameters to determine the junction temperature. 
         [0064]    The current sensing means  304  may be part of a die function, for example as a scaled current mirror of the drain current, or separately from a sensor, for example as a current transducer, or an estimator using known on-state voltage dependence on current. 
         [0065]    The current sensing means  304  is connected to a signal conditioning module  312 . The current amplifier  308  and the signal conditioning module  312  interrupt the voltage control to the power die  305  when the current is higher than a predetermined current threshold, for example during a short circuit event. When the current is lower than the predetermined current threshold, the current amplifier  308  and the signal conditioning module  312  amplify the current to be provided to the power die  305  according to voltage control signals provided by the controller  104 . 
         [0066]    The inductor  306  represents the parasitic inductance of the routing of interconnections between the power die  305  and the current amplifier  308 , or any coupling inter-die parasitics. 
         [0067]    The temperature sensing means  303  is connected to an analogue to digital converter  310  which provides the digital signal to the signal conditioning module  312 . 
         [0068]    The signal conditioning module  312  is disclosed in more details in reference to  FIG. 4 . 
         [0069]      FIG. 4  represents an example of an architecture of a signal conditioning module of the device for controlling the operation of a power die according to the present invention. 
         [0070]    The signal conditioning module  312  comprises a voltage and/or temperature scaling device  401  and a gate interrupt circuit  400 . The voltage and/or temperature scaling device  401  translates the feedback signal of the temperature sensing means  303  converted by the ADC to a scaled value for the controller  104 . 
         [0071]      FIG. 5  represents an example of an architecture of a gate interrupt circuit of the signal conditioning module. 
         [0072]    The gate interrupt module  400  interrupts the voltage control signals provided by the controller  104  to the current amplifier  308  in the event of an over-current event sensed from the current sensing means  304 . 
         [0073]    The current amplifier  308  receives, from the controller  104 , synchronized control pattern like the duty cycle of a periodic signal once passed the gate interrupt circuit  400  of the signal conditioning module  312 . 
         [0074]    The gate interrupt circuit  400  is composed of a means to compare  502  the sensed current from the current sensing means  304  to a limit value, which modulates the pass gate signal circuit of  403 . As an example, the means to compare  502  can be implemented by means of a comparator which modulates a switch of a pass gate signal  503 , allowing the gating signal either to be blocked or not, removing that power device from operation. 
         [0075]      FIG. 6  represents an algorithm executed by the controller of the system for controlling the operation of a multi-die power module. 
         [0076]    At step S 600 , the controller  104  receives from the host through the input/output interface  205 , an activation command. The activation command may be a duty cycle or a current to be provided by the multi-die power module  150 . 
         [0077]    At step S 602 , the controller  104  obtains for each die, information representative of the temperature of the die from each module  312 . At that step, the controller  104  calculates an average of the temperatures. 
         [0078]    At step S 603 , the controller  104  determines duty cycles corresponding to the load command and synchronizes the gating signal of each operating die. 
         [0079]    At step S 604 , the controller  104 , for each die, compares the temperature of the die to the average value determined at step  602 . If the temperature of the die is greater than the average value, the controller  104  reduces the duty cycle for the die. 
         [0080]    At step S 605 , the controller transfers to each device for controlling the operation of a power die  102 , information representative of the duty cycle. 
         [0081]    At step S 606 , the controller  104  may also inform the host controller parameter information for condition monitoring purposes or the state of health of each device. 
         [0082]      FIG. 7  represents currents variations generated by a device for controlling the operation of a power die according to the output of current and temperature sensing means. 
         [0083]    The curve noted  700  corresponds to a periodic voltage to be transmitted to the power die  305  which is provided by the current amplifier and controller  308  with a duty cycle that corresponds to the synchronized control pattern provided by the controller  104 . Instants t 1  and t 2  correspond to the switching of the current. 
         [0084]    The curve noted  701  corresponds to a periodic voltage control signal provided by the current amplifier  308  with a duty cycle that is reduced by the controller  104 . The curve  701  corresponds to an operating mode wherein the sensed temperature is higher than a target temperature, determined for the purpose of temperature equilibrium between dies. Instants t 1 ′ and t 2  correspond to the switching of the current according to the modified duty cycle. 
         [0085]    The curve noted  702 , up to instant t 3 , corresponds to a periodic voltage control signal provided by the current amplifier  308  with a duty cycle that is reduced by the controller  104 , similarly to curve  701 . The curve noted  702 , after instant t 3 , corresponds to an operating mode wherein the current amplifier  308  and signal conditioning module  312  interrupt the providing of current to the power die  305  when the current is higher than a predetermined current or a temperature threshold. 
         [0086]    Naturally, many modifications can be made to the embodiments of the invention described above without departing from the scope of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0087]    The device and method of the present invention are applicable to control for operation of multi-die power modules in many kinds of fields.