Patent Publication Number: US-2011074383-A1

Title: Assemblies and Methods for Sensing Current Through Semiconductor Device Leads

Description:
FIELD 
     The present disclosure relates to assemblies and methods for sensing current through one or more leads of a semiconductor device. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Current sensors are commonly employed in electric circuits to measure (directly or indirectly) one or more flowing currents. For example, power converters often include current sensors to provide feedback information for use in controlling the power converter. Many current sensors include a transformer having a primary winding connected in the path of a current to be measured, and a secondary winding for providing a (typically reduced) signal indicating the level of current flowing in the current path. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     According to one aspect of the present disclosure, an assembly for sensing current through a lead of a semiconductor device includes a carrier for mounting to the lead of the semiconductor device and a current sensor supported by the carrier. The carrier includes output terminals. The current sensor has leads electrically coupled to the output terminals. The current sensor is positioned to extend around at least a portion of the lead and provide a signal to the output terminals representing current flowing in the lead when the carrier is mounted to the lead. 
     According to another aspect of the present disclosure, an assembly includes a semiconductor device having a lead, a carrier including output terminals and a non-conductive sleeve for receiving the lead of the semiconductor device, and a current sensor supported by the carrier and having leads electrically coupled to the output terminals. The current sensor is positioned to extend around the lead of the semiconductor device and provide a signal to the output terminals representing current flowing in the lead of the semiconductor device. 
     According to yet another aspect of the present disclosure, a method includes mounting a current sense assembly about a lead of a semiconductor device. 
     According to still another aspect of the present disclosure, a carrier is disclosed. The carrier is adapted to hold a current sensor in close proximity to a semiconductor device lead to sense current flowing in the lead. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a bottom perspective view of an assembly for sensing current through a semiconductor device lead according to one example embodiment of the present disclosure. 
         FIG. 2  is a top view of the assembly of  FIG. 1 . 
         FIG. 3  is a front perspective view of an integrated circuit assembly including the assembly of  FIG. 1  according to another example embodiment. 
         FIG. 4  is a side elevational view of the assembly of  FIG. 3 . 
         FIG. 5  is a front elevational view of the assembly of  FIG. 3 . 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     According to one aspect of the present disclosure, a method is provided for sensing current flow in a semiconductor device lead. The method includes mounting a current sense assembly about the lead of the semiconductor device. Additionally, the method may further include mounting the semiconductor device to a circuit board. In that event, the current sense assembly may be mounted about the lead before or after the semiconductor device is mounted to the circuit board. Further, the current sense assembly may be mounted about the lead on a same side of the circuit board as the integrated circuit or, alternatively, on an opposite side (e.g., after the integrated circuit has been mounted to the board with the lead extending through the board to the opposite side). The current sense assembly may also include an output for providing a signal representing current flowing through the semiconductor device lead. In that case, the method may further include electrically coupling the output of the current sense assembly to the circuit board. 
     In some embodiments, the current sense assembly includes a current sensor and a carrier adapted to hold the current sensor in close proximity to the semiconductor device lead to sense current flowing in the lead. The carrier may be further adapted for attachment to the lead, with the carrier supporting the current sensor on the lead. Additionally, the carrier may include a nonconductive material defining an opening. In that event, the current sense assembly may be mounted about the semiconductor device lead by inserting the lead through the carrier opening. 
     Employing the method described above may result in a number of advantages, which may include reducing the amount of circuit board space required for current sensing components, reducing the resistance and/or inductance of the current path for which current is sensed, reducing the number of solder connections, reducing noise and/or other advantages. 
     One example embodiment of a current sense assembly suitable for use in the method described above will now be described with reference to  FIGS. 1-5 . It should be understood, however, that the example embodiment is provided for illustrative purposes only, and that the method described above can be practiced with a variety of other current sense assemblies. Further, the current sense assembly described below with reference to  FIGS. 1-5  may be usable in other methods. 
     As shown in  FIG. 1 , the example embodiment of a current sense assembly  100  includes a carrier  102  for mounting to the lead of a semiconductor device and a current sensor  104  supported by the carrier  102 . The carrier  102  includes output terminals  106 ,  108 . The current sensor  104  includes leads  110 ,  112  electrically coupled to the output terminals  106 ,  108 , respectively. When the carrier  102  is mounted to the lead of a semiconductor device, the current sensor  104  is positioned to extend around at least a portion of the lead and provide a signal to the output terminals  106 ,  108  representing current flowing in the lead. 
     The carrier  102  includes an opening  114  for receiving the lead of the semiconductor device. In this particular embodiment, the current sensor  104  includes a magnetic core  116  surrounding the carrier opening  114 . As shown, the magnetic core  116  has a generally toroidal shape. Alternatively, current sensors having other core shapes may be employed. The magnetic core  116  is wrapped with a winding  118  having opposite ends (i.e., the leads  110 ,  112 ) coupled to the output terminals  106 ,  108 . In this example, the leads  110 ,  112  are routed to the output terminals  106 ,  108  through U-shaped channels  120 ,  122  extending along the top and side of the carrier  102 . 
     As shown in  FIG. 1 , the carrier  102  further includes a nonconductive sleeve  124  that defines the opening  114 . In this particular embodiment, the sleeve  124  is configured to contact and form a friction fit with the lead when the carrier  102  is mounted about the lead of the semiconductor device. The nonconductive sleeve  124  is positioned to inhibit contact between the lead and the current sensor  104  to prevent electrical shorts and/or protect the current sensor  104  and/or the lead. For example, if the current sensor includes a coated winding wire, the nonconductive sleeve may protect the wire coating from one or more edges of a metallic lead. In other embodiments, the carrier may not contact a lead of the semiconductor device, in which case the sleeve  124  may not be used. 
     The carrier  102  shown in  FIGS. 1 and 2  may be formed from a nonconductive nylon material such as DuPont Zytel 101 HSL. Alternatively, other types of nonconductive materials may be employed. Further, the entire carrier  102  (except for the output terminals  106 ,  108 ) or only portion(s) thereof may be formed from a nonconductive material. Depending on the type of material(s) employed, the carrier  102  may be formed by injection molding or any other suitable process. 
     As shown in  FIG. 2 , the carrier  102  includes slots  126 ,  128  for receiving additional leads of the semiconductor device to inhibit rotational movement of the assembly  100  relative to the semiconductor device. Other carrier embodiments may include a different number of slots, e.g., one, three, none, etc. The number of slots may depend on the number of leads included in the semiconductor device and/or whether other means are provided for inhibiting rotation of the carrier  102  relative to the lead. Alternatively, contact between a carrier and a semiconductor device may be avoided altogether. 
     Referring again to  FIG. 1 , the carrier  102  includes a plurality of tabs  130  positioned about and contacting an outer periphery of the current sensor  104 . The tabs  130  retain the current sensor  104  at least partially within a region  132  defined by the carrier  102 . In the embodiment shown, each tab  130  includes an undercut surface  134  for retaining the current sensor  104  and a ramp surface  136  for receiving and guiding the current sensor  104  into the region  132  of the carrier  102 . A different number of tabs and/or other provisions (such as fasteners, adhesives, covers, etc.) may be employed in other embodiments for securing a current sensor to a carrier. 
       FIGS. 3-5  illustrate an integrated circuit assembly  200  according to another example embodiment. The assembly  200  includes the assembly  100  of  FIGS. 1-2  mounted to a semiconductor device  202 . As shown, the semiconductor device  202  includes three leads  204 ,  206 ,  208  and a body  210 . Lead  206  is received through the magnetic core of current sensor  104  and forms a friction fit with the sleeve  124 . Leads  204 ,  208  are received in the slots  126 ,  128 , respectively, to inhibit rotational movement of the assembly  100  about the lead  206 . As shown in  FIGS. 3-5 , the assembly  200  includes a circuit board  212 . The assembly  100  and the semiconductor device  202  are positioned on the same side (i.e., the top) of the circuit board  212 . Alternatively, the current sense assembly may be positioned on a different side (i.e., the bottom) of the circuit board  212  than the semiconductor device  210 . Further, while the current sensor  104  is adapted to extend completely around the lead of a semiconductor device, it could alternatively include a slot or other provisions that permit the sensor to be positioned around at least a portion of the lead without requiring insertion of the lead through an opening. In this manner, the sensor could be positioned to extend around only a portion of the lead, on the same side of the circuit board as the body of the semiconductor device, after the semiconductor device is coupled (e.g., soldered) to the circuit board. 
     As shown, a footprint of the semiconductor device  202  is increased only minimally, while incorporating the assembly  100  for sensing current through the lead  206  of semiconductor device  202 . 
     When the lead  204  is received in the opening  114 , the magnetic core  116 , the winding  118 , and the lead  204  behave substantially as a transformer. In particular, the lead  204  functions as the primary winding of the transformer for energizing the core  116 . Thus, when current flows through the lead  204 , current is induced in winding  118 , resulting in a voltage across the output terminals  106 ,  108 . This voltage represents the current flowing in the lead  204  of the semiconductor device  202 . As shown in  FIGS. 3-5 , the output terminals  106 ,  108  of the carrier  102  are electrically coupled to the circuit board  212  for providing the voltage signal representing current flowing through the lead  206  of the semiconductor device  202 . 
     Because current is sensed through the lead  206  of the semiconductor device  202  (i.e., an inline current path), the assembly  200  reduces interconnection inductance by about 4 nH (as compared to an assembly employing a prior art current transformer. 
     As shown in  FIGS. 4-5 , the carrier includes tabs  130  to inhibit contact between the current sensor  104  and the circuit board  212 . In this example embodiment, the tabs  130  retain the current sensor between the tabs and inhibit contact between the current sensor and the circuit board. Further, the carrier  102  abuts a wider portion  214  of the lead  206  to position the carrier  102  on the lead  206  as desired (which may include inhibiting contact between the body  210  of the semiconductor device  202  and the current sensor  104 ). 
     In the example assembly  200  shown in  FIGS. 3-5 , the semiconductor device  202  is a power MOSFET with the drain lead  206  extending through the opening  124  of the current sense assembly  100 . It should be understood, however, that the teachings of this disclosure may be used with a wide variety of other semiconductor devices, including those that do not employ a through-hole packaging arrangement. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.