Abstract:
The present technology discloses a package for a synchronous rectifier module, and also discloses synchronous rectification circuits and power supply adapters. The synchronous rectification circuit co-packages the synchronous rectifier and the driver into one single package. The single package simplifies the external circuitry and reduces potential electromagnetic interferences.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of Chinese patent application No. 201020301258.2, filed on Jan. 22, 2010, the disclosure of which is incorporated herein by reference is its entirety. 
       TECHNICAL FIELD 
       [0002]    The present technology relates generally to voltage converters, and more particularly, relates to packages of a synchronous rectifier module of an isolated converter system. 
       BACKGROUND 
       [0003]    Generally speaking, two rectifying schemes are adopted in the secondary side of a fly-back converter. One is non-synchronous rectification which adopts a diode D ( FIG. 1A ). And another is synchronous rectification which rectifies the current through controlling on/off of a synchronous rectifier Q, e.g., an N-MOSFET ( FIG. 1B ). The voltage-current characteristic is plotted in  FIG. 1C , for the diode D (curve  12 ) and for the synchronous rectifier Q (curve  11 ). In practical applications, the work area of a low power fly-back power converter typically falls into the shadow area. The resistance of the synchronous rectifier Q is typically less than that of the diode D in the area because curve  11  is always above curve  12 . So, compared with a diode, a scheme with a synchronous rectifier is more preferable for lower power consumption and better efficiency. Such a scheme thus finds increasingly wide applications in equipment sensitive to efficiency such as laptop adapters, wireless equipment, LCD power management modules and so on. 
         [0004]    However, the synchronous rectifying scheme requires a synchronous rectification driver to control the rectifier Q. The synchronous rectifier under the control of the driver functions as the diode with low resistance and high efficiency. Usually, two separate packages for the synchronous rectifier and the driver are adopted with additional external components. This results in a complicated system and introduced EMI (Electro Magnetic Interference) because of the signal transmission between the different packages. Thus, a simpler system may be desirable for synchronous rectification. 
       SUMMARY 
       [0005]    In one embodiment, a package for a synchronous rectifier module comprises a first lead, a second lead, a third lead, a driver die and a synchronous rectifier die. The driver die comprises a first input contact pad, a second input contact pad, a power supply contact pad and an output contact pad. The synchronous rectifier die comprises a source region, a drain region and a gate region. And the first lead is coupled to the source region and to the first input contact pad. The second lead is coupled to the drain region and to the second input contact pad. The third lead is coupled to the power supply contact pad. 
         [0006]    In another embodiment, a synchronous rectification circuit comprises a secondary winding of a transformer, an output node configured to deliver an output signal and a synchronous rectifier module. The package of the synchronous rectifier module comprises a first lead, a second lead and a third lead. The first lead is externally coupled to the first end of the secondary winding. The second lead is externally coupled to the output node. A power supply source is coupled between the first lead and the third lead. The other end of the secondary winding is coupled to the secondary ground. In a further embodiment, the second lead is externally coupled to the secondary ground, and the other end of the secondary winding is coupled to the output node. 
         [0007]    In a yet further embodiment, a power supply adapter comprises a smart driver in a single package. The smart driver comprises a synchronous rectifier and a driver. The synchronous rectifier is coupled between the secondary winding of an isolated converter and the output of the isolated converter. The driver delivers a gate driving signal to the control end of the synchronous rectifier for controlling the switching function of the synchronous rectifier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Non-limiting and non-exhaustive embodiments are described with reference to the following drawings. The drawings are only for illustration purposes. Usually, the drawings only show part of the circuits/devices of the embodiments. These drawings are not necessarily drawn to scale. The relative sizes of elements illustrated by the drawings may differ from the relative size depicted. 
           [0009]      FIG. 1A  shows a diode D used as a non-synchronous rectifier in accordance with the prior art. 
           [0010]      FIG. 1B  shows a MOSFET Q used as a synchronous rectifier in accordance with the prior art. 
           [0011]      FIG. 1C  shows a voltage-current curve for the non-synchronous rectifier D of  FIG. 1A  and the synchronous rectifier Q of  FIG. 1B  in accordance with the prior art. 
           [0012]      FIG. 2  shows a synchronous rectification circuit according to one embodiment of the present technology. 
           [0013]      FIG. 3  shows another synchronous rectification circuit according to another embodiment of the present technology. 
           [0014]      FIG. 4  shows yet another synchronous rectification circuit comprising a synchronous rectifier module according to one embodiment of the present technology. 
           [0015]      FIG. 5A  is a plan view showing a package system of a synchronous rectifier module according to one embodiment of the present technology. 
           [0016]      FIG. 5B  is a cross-sectional view of the package system in  FIG. 5A . 
           [0017]      FIG. 6A  shows a package system of a synchronous rectifier module according to another embodiment of the present technology. 
           [0018]      FIG. 6B  is a cross-sectional view of the package system in  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The following description provides a description for certain embodiments of the technology. One skilled in the art will understand that the technology may be practiced without some of the features described herein. In some instances, well known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. In other instances, similar structures and functions that have been described in detail for other embodiments have not been described in detail for such embodiments to simplify and ease understanding. 
         [0020]      FIG. 2  shows a synchronous rectification circuit  200  according to one embodiment of the present technology. The synchronous rectification circuit  200  and other synchronous rectification circuits described below can be used in a fly-back converter system or other suitable systems. For purposes of clarity, a complete description of the fly-back converter system or other suitable systems is omitted though embodiments of the current technology may include certain components of such systems. 
         [0021]    As shown in  FIG. 2 , the synchronous rectification circuit  200  includes a synchronous rectifier module  21  to perform synchronous rectification. The synchronous rectifier module  21  comprises three external nodes including the first node V S , the second node V D  and the third node V DD . The synchronous rectification circuit  200  further comprises a secondary winding T, an output node OUT delivering output signal V OUT  for supplying a load, a secondary ground node GND, and an output capacitor C O  The output capacitor C O  is coupled between the output node OUT and the secondary ground node GND. The synchronous rectifier module  21  has the first node V S  coupled to the first end of the secondary winding T for receiving the drain-source current I SD  and has the second node V D  coupled to the output node OUT. A power supply source U S  is coupled between the first node V S  and the third node V DD  to supply the synchronous rectifier module  21 . The other end of the secondary winding T is connected to the secondary ground GND. 
         [0022]      FIG. 3  shows another synchronous rectification circuit  300  according to an embodiment of the present technology. The synchronous rectification circuit  300  is similar to the synchronous rectification circuit  200  of  FIG. 2  except that the synchronous rectifier module  31  in circuit  300  is a low-side rectifier while the synchronous rectifier module  31  in circuit  200  is a high-side rectifier. The synchronous rectifier module  31  in circuit  300  has the first node V S  coupled to the secondary ground GND, and has the second node V D  coupled to one end of the secondary winding T for receiving the drain-source current I SD , while the other end of the secondary winding T is coupled to the output node OUT. 
         [0023]      FIG. 4  shows an internal configuration of a synchronous rectifier module  41  in a synchronous rectification circuit  400  according to one embodiment of the present technology. As shown in  FIG. 4 , the synchronous rectifier module  41  comprises a synchronous rectifier  411  (Q) and a driver  412  (U 1 ) coupled to the control end of the synchronous rectifier  411  for controlling the switching action of synchronous rectifier  411 . The synchronous rectifier  411  is an N type MOSFET (Metal Oxide Semiconductor Field Effect Transistor) as shown in  FIG. 4  and the control end is its gate. Yet in other embodiments, the synchronous rectifier  411  can include other types of Field Effect Transistor devices different than that shown in  FIG. 4 . The driver  412  is coupled to receive the source-drain voltage V SD  of the rectifier  411  and controls the rectifier  411  to function as a diode. In the illustrated embodiment, the driver  412  turns on the rectifier  411  when the body diode D 0  of the rectifier  411  is forward biased and turns off the rectifier  411  when the bias on the body diode D 0  of the rectifier  411  is reversed. 
         [0024]    The first node V S  of the synchronous rectifier module  41  is coupled to the source of the synchronous rectifier  411  and to the first input of the driver  412 . The second node V D  of  41  is coupled to the drain of the rectifier  411  and to the second input of the driver  412 . And the third node V DD  of  41  is coupled to the power supply terminal of the driver  412 . A power supply source U S  is coupled between the first node V S  and the third node V DD . Furthermore, the output of the driver  412  is coupled to the gate of the synchronous rectifier  411  for providing the driving signal. With this configuration, the driver  412  automatically turns on or turns off the rectifier  411  according to the source-drain voltage V SD  of the rectifier  411 . 
         [0025]    Furthermore, the synchronous rectifier module  41  can be fabricated in a single package that co-packages the synchronous rectifier  411  and the driver  412 . The term “co-package” as used hereinafter generally refers to packaging two or more dies in a single package. As a result, the synchronous rectifier module  41  only has three external pins for nodes V S , V D  and V DD  respectively. This results in a simplified synchronous rectification system. Co-packaging of the synchronous rectifier  411  and the driver  412  shortens the signal transmission distances therebetween and thus can reduce power consumption and EMI when compared to conventional devices. 
         [0026]      FIG. 5A  shows a stacked die package  500  of the synchronous rectifier module U 2  with one die attached on another die according to one embodiment of the present technology. A stacked die package comprises two or more dies in a single package with one die arranged vertically relative to other dies. The package  500  comprises a first die  501 , a second die  502 , a first lead V S , a second lead V D  and a third lead V DD . Each lead is partially exposed to form a corresponding pin. The first lead V S , the second lead V D  and the third lead V DD  function as the first node V S , the second node V D  and the third node V DD  of the synchronous rectifier module respectively, as shown in  FIGS. 2-4 . 
         [0027]    The first die  501  and the second die  502  are stacked together. The first die  501  can be the driver die with a driver  412  ( FIG. 4 ) fabricated on a semiconductor substrate and the second die  502  can be the synchronous rectifier die with the synchronous rectifier  411  ( FIG. 4 ) fabricated on another semiconductor substrate. The synchronous rectifier die comprises the source region, the gate region and the drain region. The source region shown in  FIG. 5A  comprises multiple contact pads S pad  to assure high current carrying capability. The drain region is the opposite surface of the synchronous rectifier die and contacts the second lead V D  of the package  500  at the bottom surface of the synchronous rectifier die. 
         [0028]    The driver die  501  is attached to the surface of the synchronous rectifier die  502 . The driver die  501  comprises a first input contact pad D 1 , a second input contact pad D 2 , a power supply contact pad D 3  and an output contact pad D 4 . The first lead V S  is coupled to the source region of the synchronous rectifier die  102  and the first input contact pad D 1  of the driver die  501 , and receives source signal of the synchronous rectifier die  502 . The second lead V D  is coupled to the drain region of the synchronous rectifier die  502  and the second input contact pad D 2  of the driver die  501 , and receives the drain signal of the synchronous rectifier die  502 . The third lead V DD  is coupled to the power supply contact pad D 3  of the driver die  501 , and receives the power supply source. The output contact pad D 4  of the driver  501  is coupled to the gate region of the synchronous rectifier die  502 , such that the driver die  501  delivers gate driving signal to the synchronous rectifier die  502 . In the embodiment shown in  FIG. 5A , the driver die  101  is placed on the surface of the source region of the synchronous rectifier die  502 . 
         [0029]      FIG. 5B  illustrates a stacked die package  500 B. As shown in  FIG. 5B , the first die  501  is attached on the surface of the second die  502  and the second die  502  is attached on the surface of the lead frame structure  51  having a plurality of leads. Typically, to “couple” or “coupling” is achieved by bonding wires as the lines shown in  FIG. 5A  each having one end attached to a contact pad and the other end attached to the lead of the lead frame structure  51  though other electrical couplers (e.g., bumps, pins, etc.) may also be used in certain embodiments. 
         [0030]      FIG. 6A  shows a die-to-die package  600  according to one embodiment of the present technology. A die-to-die package comprises two or more dies arranged side by side on a substrate. In one embodiment, the die-to-die package  600  co-packages a synchronous rectifier and a driver of the synchronous rectifier module with the driver die  601  (or the first die  601 ) placed side by side with the synchronous rectifier die  602  (or the second die  602 ).  FIG. 6B  illustrates a sectional view of a die-to-die package  600 B as one example in which the first die  601  and the second die  602  are positioned side by side, with both first and second dies  601  and  602  attached to the lead frame structure  61 . For simplification, the connection relationship of the package  600  is not elaborated. The die-to-die package  600  is similar to the die-to-die package  500  except that the driver  601  is placed side by side with the synchronous rectifier die  602 , not attached on the surface of the synchronous rectifier die  602 , as in  FIG. 5A . Though the packages shown in  FIG. 5B  and  FIG. 6B  are in SOP (Small Outline Package) packages, the packages can have other forms such as DFN (Dual Flat No leads) packages in other embodiments. 
         [0031]    The multi-chip die packages  500  and/or  600  co-package the driver die  501 / 601  and the synchronous rectifier die  502 / 602  of a synchronous rectifier module in a single package. The distance of the signal transmission is substantially reduced when compared to conventional devices. Thus external circuitry for a fly-back converter system can be simplified and introduced EMI can be reduced. 
         [0032]    From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the technology is not limited except as by the appended claims.