Abstract:
A multi-chip module (MCM) for power supply circuitry integrates a controller, a driver and two power MOSFETs in a single chip to shorten the signal path between the controller and the driver. When applied to a voltage regulator, the MCM shortens the feedback paths between the current sensors and the controller, so as to reduce the loss of and interference with the feedback signals, thereby improving the efficiency of the voltage regulator and simplifying the PCB traces routing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to low-voltage, high-current voltage regulator applications which use multi-channel buck converters. More specifically, the present invention relates to a multi-chip module (MCM) which combines a controller, a driver and two MOSFETs for a multi-channel buck converter to improve response performance during load transient and efficiency. 
       BACKGROUND OF THE INVENTION 
       [0002]    The circuitry of low-voltage, high-current voltage regulator applications using multi-channel buck converters has substantial area on printed circuit boards (PCBs). It is agreeable to improve the converter efficiency by reducing the power losses due to the parasitic components present in the layout path and the noise susceptible traces on the PCBs. 
         [0003]    Based on the Intel Platform Layout Requirements for CPU power supply, some stages of a multiphase voltage regulator are placed away from the PWM controller as shown in  FIG. 1 . In this partial layout of a motherboard, the voltage regulator has four channels, and in order to facilitate explanation, the southbridge chip, northbridge chip and CPU chip  18  are designated by numerals  12 ,  14  and  18  on a PCB  10 . The controller of the voltage regulator is arranged at the position  16  below the CPU chip  18 , and the four channels are distributed from the controller&#39;s position  16  to the north. More specifically, the channels  1  and  2  are located at the position  20  near and to the east of the CPU&#39;s position  18 , and the other channels  3  and  4  are located at the position  22  to the north of the CPU&#39;s position  18 . In this layout, the feedback traces from the channels  3  and  4  to the controller will go through over half of the PCB  10  and thus have quite long paths. If more channels are included in a voltage regulator, the feedback traces will go through across the entire PCB  10  and have even longer paths. 
         [0004]    MCM is an electronic package which includes several integrated circuits (ICs) placed on a common substrate and mutually isolated by insulator, and an encapsulant to encapsulate the whole module. U.S. Pat. No. 6,879,491 to Jauregui eliminates the PCB traces between one driver and two MOSFETs by integrating the driver and MOSFETs into a MCM package. However, there is no help for minimizing the signal paths between the controller and drivers of a voltage regulator. Referring to  FIG. 2  for further details, a voltage regulator includes plural MCMs  22 , each combining a driver and two MOSFETs and called a DrMOS, and a controller  24  to provide pulse width modulation signals PWM 1  to PWMN to the MCMs  22  to control the drivers in the MCMs  22  to drive the MOSFETs. Since one driver and two MOSFETs are packaged into a single chip  22 , the signal loss and interference that might otherwise occur along the signal paths therebetween are eliminated. However, for the controller  24  to obtain the feedback signals from the current sensors (CSs)  26 , two traces  28  and  30  are required for each channel to deliver the current sense signals. Consequently, a voltage regulator having N channels needs 2×N traces to deliver the current sense signals as the feedback signals to the controller  24 . As a result, the current sense signals suffer from signal loss and noise interference along the long physical paths defined by these traces  28  and  30  on the PCB. Moreover, these traces  28  and  30  may cause difficulty in traces routing between the controller  24  and current sensors  26  on the PCB. 
       SUMMARY OF THE INVENTION 
       [0005]    An object of the present invention is to provide a multi-chip module for power supply circuitry. 
         [0006]    Another object of the present invention is to shorten the PCB traces of a voltage regulator. 
         [0007]    A further object of the present invention is to improve the efficiency of a voltage regulator. 
         [0008]    Still another object of the present invention is to reduce the power loss of a voltage regulator. 
         [0009]    Yet another object of the present invention is to reduce the noise interference of a voltage regulator. 
         [0010]    According to the present invention, an MCM for power supply circuitry comprises a controller, a driver and two MOSFETs integrated in a single module to shorten the feedback paths between each of the channels and the controller, thereby reducing the signal loss and interference, and in turn improving the efficiency of the converter. 
         [0011]    Preferably, the MCM further comprises an internal current sensor to detect the channel current to provide a current sense signal to the controller. 
         [0012]    Preferably, the internal current sensor detects the current in one of the two MOSFETs to provide the current sense signal to the controller. 
         [0013]    According to the present invention, a voltage regulator comprises a plurality of channels connected in parallel between a power input and a power output, each including an MCM and an inductor connected in series between the power input and the power output. The MCM comprises a controller, a driver and two MOSFETs, and the controller provides an internal PWM signal to the driver to switch the two MOSFETs. 
         [0014]    In one embodiment of the present invention, each of the channels further comprises an external current sensor to detect the inductor current of this channel, to provide a feedback signal to the MCM of this channel. 
         [0015]    In another embodiment of the present invention, the MCM of each of the channels further comprises an internal current sensor to detect the inductor current of this channel, to provide a feedback signal to the controller of this channel. 
         [0016]    Preferably, a reference current generator is provided to supply a reference current signal to each of the MCMs to balance the inductor currents of the channels. 
         [0017]    In one embodiment of the present invention, the voltage regulator further comprises an external current sensor to detect the total current of the channels at the power output, to provide a total current signal to the reference current generator to generate the reference current signal accordingly. 
         [0018]    In another embodiment of the present invention, the reference current generator generates the reference current signal from the inductor currents of the channels. 
         [0019]    By eliminating the parasitic elements between the current sensor, the controller, and the power switches, the present invention reduces the converter loss. In addition, by placing the current sensor close to the controller, the noise along the feedback paths is reduced and the PCB traces routing is simplified. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a diagram showing the partial layout of a motherboard; 
           [0022]      FIG. 2  is a circuit diagram showing a conventional voltage regulator; 
           [0023]      FIG. 3  is a circuit diagram showing an MCM according to the present invention; 
           [0024]      FIG. 4  is a partial circuit diagram of a voltage regulator according to a first embodiment of the present invention; 
           [0025]      FIG. 5  is a partial circuit diagram of a voltage regulator according to a second embodiment of the present invention; 
           [0026]      FIG. 6  is a partial circuit diagram of a voltage regulator according to a third embodiment of the present invention; 
           [0027]      FIG. 7  is a partial circuit diagram of a voltage regulator according to a fourth embodiment of the present invention; 
           [0028]      FIG. 8  is a partial circuit diagram of a voltage regulator according to a fifth embodiment of the present invention; and 
           [0029]      FIG. 9  is a partial circuit diagram of a voltage regulator according to a sixth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]      FIG. 3  shows an embodiment according to the present invention, in which an MCM  32  combines a modulator  34 , a driver  36  and two power MOSFETs  38  and  40  in a single chip. The modulator  34  generates an internal PWM signal to the driver  36  according to an external control signal CTL to switch the MOSFETs  38  and  40 . The external control signal CTL may include a current signal, a voltage signal and others such as a reference current signal, an output voltage feedback signal, an external PWM signal, and so on, depending on the demands in practical applications. As known in the art, the modulator  34 , the driver  36  and the MOSFETs  38  and  40  are all bounded on an MCM package substrate (not shown). Based on practical circuit planning, a current sense function may be also integrated in the MCM  32 , for example, by incorporating an internal current sensor  42  shown in  FIG. 3 . In this disclosure, the term “internal” indicates “inside an MCM” while the term “external” indicates “outside an MCM”. In many applications, as shown in the MCM  44  in the lower portion of  FIG. 3 , a controller  46  represents a control circuit including a modulator and sometimes is also known as a PWM controller, and power switches  48  and  50  are MOSFETs or other switching elements. In the following description, without departing from the generality principle, the controller  46  is used to refer to a circuit which provides the internal PWM signal to the driver  36 . 
         [0031]      FIG. 4  is a partial circuit diagram of a voltage regulator according to one embodiment of the present invention, in which a plurality of channels are connected in parallel between a power input Vin and a power output Vo, each including an MCM  52  and an inductor L j  (j=1,2, . . . ,N) connected in series between the power input Vin and the power output Vo. The MCM  52  is integrated therein with a controller  46 , a driver  36  and two power MOSFETs  38  and  40 . Each channel uses an external current sensor  26  to detect the inductor current i Lj  (j=1,2, . . . ,N) to provide a feedback signal to the controller  46  of this channel. In each channel, the MCM  52  uses its own controller  46  to generate an internal PWM signal PWMj (j=1,2, . . . ,N) to its own driver  36 , to control the inductor current i Lj  of this channel. Since the controller  46  and the driver  36  are integrated in the MCM  52 , the signal path therebetween is very short. Furthermore, the controller  46  may be arranged close to the external current sensor  26  so that the feedback path is also very short. 
         [0032]      FIG. 5  is a partial circuit diagram of a voltage regulator using the MCM  44  of  FIG. 3 . In this embodiment, not using external current sensors to detect the inductor currents i L1 -i LN , the feedback signals are provided by internal current sensors  42  instead, and thus have shorter feedback path than that of  FIG. 4 . The internal current sensor  42  may detect the current in either one of the MOSFETs  38  and  40  or other signals, to generate the feedback signal related to the inductor current of its channel. 
         [0033]    In some embodiments, as shown in  FIG. 6 , the internal current sensor  56  in the MCM  54  detects the current i j  (j=1,2, . . . ,N) in the MOSFET  40  in the same MCM  54 , but not directly detects the inductor current i Lj  (j=1,2, . . . ,N) of this channel. Moreover, an external current sensor  58  detects the total current at the power output Vo to generate a total current signal i total , and a reference current generator  60  generates a reference current signal i ref  from the total current signal i total  to supply to each of the MCMs  54 . In each channel, the controller  46  generates an internal PWM signal according to the feedback signal from the internal current sensor  56  and the reference current signal i ref  from the reference current generator  60  for the driver  36 . By feeding back the reference current signal i ref  to each channel, the inductor currents i L1 -i LN  of the channels could be balanced to eliminate the non-ideal effects caused by element differences between the channels. The reference current generator  60  is placed near the power output Vo, thereby simplifying the PCB traces routing. 
         [0034]      FIG. 7  is a diagram showing an alternative embodiment, in which the signal i j  (j=1,2, . . . ,N) generated by detecting the current in the MOSFET  40  by the internal current sensor  64  to feed back to the controller  46  is also sent out to a reference current generator  66  to generate a reference current signal i ref  for the controller  46  in each MCM  62 . 
         [0035]      FIG. 8  is a diagram showing a modified embodiment from that of  FIG. 4 , in which the external current sensor  58  detects the total current, and the reference current generator  60  generates the reference current signal i ref  from the total current signal i total , to supply to the controllers  46  of the channels to balance the inductor currents i L1 -i LN  of the channels. 
         [0036]      FIG. 9  is a diagram showing a modified embodiment from that of  FIG. 8 , in which the reference current generator  66  generates the reference current signal i ref  from the inductor currents i L1 -i LN  of the channels, to supply to each MCM  68  to balance the inductor currents i L1 -i LN  of the channels. 
         [0037]    The MCM of the present intention, by integrating a controller, a driver, and two MOSFETs in a single chip, eliminates PCB traces between the controller and the driver and shortens the signal paths between the current sensors and the controller, thus reducing power loss and noise interference. Meantime, the MCM of the present intention also simplifies PCB routing. 
         [0038]    While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as set forth in the appended claims.