Patent Application
20250164529
As is known in the art, conventional magnetic field current sensors sense current in a current-carrying conductor via a magnetic field generated by the current through the conductor. The current sensor generates an output signal having a magnitude proportional to the magnetic field induced by the current through the conductor.
Example embodiments of the disclosure provide method and apparatus for a current sensor having a leadframe with at least one notch in a throat of the sensor and at least one magnetic field sensing element for concentrating magnetic field in the sensing area to increase signal on the magnetic field sensing element(s). The notches decrease the feature size in this area of the current loop for increasing the frequency at which skin effects occur. The smaller feature size provided by the notches reduces the total charge movement even when skin effects do occur. In embodiments, first and second magnetic field sensing elements positioned in relation to the respective notches enable differential sensing of the magnetic field.
In one aspect, a current sensor integrated circuit package comprises: a die having a first magnetic field sensing element; a leadframe to support the die, the leadframe having a U-shaped current conductor loop with a throat region and a first notch in the throat region of the current conductor loop; and a first magnetic field sensing element positioned in relation to the first notch.
A package can further include one or more of the following features: a second magnetic field sensing element and a second notch in the leadframe, the first magnetic field sensing element is aligned with an edge of the first notch, the first magnetic field sensing element comprises a Hall effect element, the first magnetic field sensing element comprises an MR element, the first magnetic field sensing element comprises a TMR element, a second notch in the throat region of the current conductor loop, the U-shaped current conductor loop comprises a U-shape with a bottom between first and second legs, wherein the first notch is formed in the first leg facing the throat region and the second notch is formed in the second leg facing the throat region, a first outer notch in the first leg, wherein the first notch and the first outer notch are on opposite sides of the first leg, and further including a second outer notch in the second leg, wherein the second notch and the second outer notch are on opposite sides of the second leg, the first notch and the first outer notch are symmetrical in shape, the first notch and the first outer notch are symmetrical with respect to an axis, a distance from a bottom of the first notch to a bottom of the first outer notch is a minimum width of the leadframe in the throat region, a width of the first notch is at least two times a thickness of the leadframe, the width of the first notch is less than four times a thickness of the leadframe, a distance from the bottom of the U to a beginning of the first notch is at least two times a thickness of the leadframe, the first magnetic field sensing element straddles an edge of the first notch and further including a second magnetic field sensing element that straddles an edge of the second notch, and/or the first magnetic field sensing element comprises MR sensing elements located over the leadframe.
In another aspect, a method comprises: employing a die having a first magnetic field sensing element in a current sensor integrated circuit package; supporting a leadframe with the die, the leadframe having a U-shaped current conductor loop with a throat region and a first notch in the throat region of the current conductor loop; and positioning a first magnetic field sensing element in relation to the first notch.
A method can further include one or more of the following features: a second magnetic field sensing element and a second notch in the leadframe, the first magnetic field sensing element is aligned with an edge of the first notch, the first magnetic field sensing element comprises a Hall effect element, the first magnetic field sensing element comprises an MR element, the first magnetic field sensing element comprises a TMR element, a second notch in the throat region of the current conductor loop, the U-shaped current conductor loop comprises a U-shape with a bottom between first and second legs, wherein the first notch is formed in the first leg facing the throat region and the second notch is formed in the second leg facing the throat region, a first outer notch in the first leg, wherein the first notch and the first outer notch are on opposite sides of the first leg, and further including a second outer notch in the second leg, wherein the second notch and the second outer notch are on opposite sides of the second leg, the first notch and the first outer notch are symmetrical in shape, the first notch and the first outer notch are symmetrical with respect to an axis, a distance from a bottom of the first notch to a bottom of the first outer notch is a minimum width of the leadframe in the throat region, a width of the first notch is at least two times a thickness of the leadframe, the width of the first notch is less than four times a thickness of the leadframe, a distance from the bottom of the U to a beginning of the first notch is at least two times a thickness of the leadframe, the first magnetic field sensing element straddles an edge of the first notch and further including a second magnetic field sensing element that straddles an edge of the second notch, and/or the first magnetic field sensing element comprises MR sensing elements located over the leadframe.
The foregoing features of this disclosure, as well as the disclosure itself, may be more fully understood from the following description of the drawings in which:
Bond pad 114 provides a voltage and current input, typically Vcc, to provide power to the integrated circuit 100. A ground bond pad 116 may be provided to integrated circuit 100. Input bond pad 114 is coupled to a master current supply circuit 118 that provides power to the circuitry within integrated circuit 100. Although master current supply 118 is provided as a current supply, it would be apparent that voltages may also be provided to the circuits on integrated circuit 100. A Hall effect current drive circuit 120 takes current (or voltage) from the master current supply 118 and provides a regulated current to the Hall Effect sensing elements 104a,b. The master current supply 118 also provides power to a power on reset circuit 122. The power on reset circuit monitors the power coming into the circuit 100 and provides a signal to EEPROM and control logic circuit 124. The power on reset circuit 122 and EEPROM and control logic circuit 124 are used to configure and enable the integrated circuit, including the output circuit 110.
The EEPROM and control circuit 124 provides a signal to a sensitivity control circuit 126 which provides a signal to the front end amplifier 106 to adjust the sensitivity of the front end amplifier. The adjustment may be the result of a change in the power level in the circuit 100, or as a result of a temperature change of the circuit. An example of a temperature sensor circuit may include but is not limited to a diode temperature sensor, or the use of known temperature compensation resistors.
The EEPROM and control circuit 124 provides a signal to an offset control circuit 128. The offset control circuit 128 provides a signal to the amplifier 108. The offset control circuit 128 allows the circuit 100 to adjust the offset of the amplifier 108 for changes in power or temperature (the temperature compensation circuit is not shown) or a combination of temperature and power changes. The offset control circuit 128 may also provide adjustment for other offset sources, such as a stress in the integrated circuit die.
An input lead 115 may be provided to set a threshold for a fault indication circuit 130 (i.e., provide a fault trip level). In an embodiment, the input lead 115 provides a fault voltage level. The fault indication circuit 130 can include a threshold circuit 132 and a fault comparator 134. The EEPROM and control circuit 124 provides an input to the threshold circuit 132. The threshold circuit 132 provides a signal to the fault comparator 134, which compares the output of threshold circuit 132 with the output of the front end amplifier 106 to indicate when a fault exists to the output circuit block 110. The output circuit generates a fault output at output bond pad 113. The fault output may indicate an overcurrent condition in which the current sensed in the current conductor path exceeds a fault trip level, which trip level may be provided in the form of a fault voltage level on bond pad 115. The fault allows, in one example, the user of the current sensor package to turn off the current in the primary current path in order to prevent a high current condition in an electrical circuit.
It is understood that any of the above-described processing may be implemented in hardware, firmware, software, or a combination thereof. Processing may be implemented in computer programs executed on programmable computers/machines that each includes a processor, a storage medium or other article of manufacture that is readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and one or more output devices. Program code may be applied to data entered using an input device to perform processing and to generate output information.
The current conductor loop 204, which has a generally U-shape, includes a throat region 216 about which current flows to change direction from into the throat to out of the throat. In the illustrated embodiment, the die 214 includes a first magnetic field sensing element 218 and a second magnetic field sensing element 220. The first magnetic field sending element 218 is positioned in relation to a first notch 222 in the throat region 216 of the leadframe and the second magnetic field sensing element 220 is positioned in relation to a second notch 224 in the throat region 216. In the illustrated embodiment (see
In the illustrated embodiment, the second notch 224 region of
It is understood that the width, depth, geometries, and ratios to lengths and widths of the notch and leadframe can vary to meet the needs of a particular application and achieve desired sensor performance characteristics.
In example embodiments of the sensor, a distance E (width) of the first notch IN is at least twice a distance D (depth) of the first notch to avoid current crowding in this narrowest part of the leadframe. In example embodiments, the distance E ranges from two to fourth times the distance D of the first notch.
In example embodiments, the distance E is at least two times the thickness T of the leadframe. It is understood that 8 mil and 12 mil are common leadframe thicknesses, however, any suitable leadframe thickness can be used to meet the needs of a particular application. In embodiments, distance E is between 2 and 3.5 times leadframe thickness T.
In embodiments, it may be desirable to space the notch IN from the bottom of the U where the current I changes direction so that the direction of current flow is generally parallel to an axis 260 of the throat 216 when passing by the sensing elements. In the illustrated embodiment, the notches IN, ON are spaced by distance A from surface 252. A distance H defines a distance from a bottom 262 of the U-shaped to the beginning of the inner notch IN. In embodiments, distance A enables selection of a distance from a beginning of the notch indentation to a narrowest part of the leadframe at distance F. In example embodiments, distance A is within a range of 60% to 80% of the distance F. It can be seen that distance C=D+F+G.
In embodiments, the notches are formed to achieve sensor performance characteristics (see, e.g.,
In the illustrated embodiment, the leadframe includes a taper region 270 in which the distance between the U-portions of the leadframe increases in distance approaching the throat region 216.
As shown in
In conventional notchless sensors, high speed current sensing with an integrated leadframe poses challenges for signal magnitude and signal flatness over a wide band of input frequency. Skin effects move charge within the leadframe which can change the coupling to the magnetic sensing element, and the SNR/sensitive direction of the transducer can require strange shapes of the conductor to concentrate field on the element.
In example embodiments, a current sensor includes a looped leadframe with sections necked down to concentrate magnetic field in the sensing area of the throat to increase signal on the sensing elements. Smaller feature sizes in this area increase the frequency at which skin effects occur and reduce the total charge movement even when skin effects do occur. A pair of sensing elements in the current loop allows differential sensing. In some embodiments, half etching of the leadframe where the notches are located can improve performance. In some embodiments, the leadframe can be laminated to reduce eddy effects.
As used herein, the term “magnetic field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic field sensing element can be, but is not limited to, a Hall effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall effect elements, for example, a planar Hall effect element, a vertical Hall effect element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of ‘magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, for example, a spin valve, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). The magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half-bridge or full (Wheatstone) bridge, configured for single-ended or differential sensing. Depending on the device type and other application requirements, the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb). A coil may also be used to sense magnetic fields, which may be referred to as inductive sensing. Using a coil to sense a magnetic field is more typical as the frequency of the magnetic field to be sensed increases.
As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall effect elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall effect elements tend to have axes of sensitivity parallel to a substrate.
As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or a ferromagnetic target (e.g., gear teeth) where the magnetic field sensor is used in combination with a back-biased or other magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) may be used to describe elements in the description and drawing. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the described concepts, systems, devices, structures, and techniques are not intended to be limiting in this respect. Accordingly, a coupling of elements can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. As an example of an indirect positional relationship, positioning element “A” over element “B” can include situations in which one or more intermediate elements (e.g., element “C”) is between elements “A” and elements “B” as long as the relevant characteristics and functionalities of elements “A” and “B” are not substantially changed by the intermediate element(s). Relative or positional terms including, but not limited to, the terms “upper,” “lower,” “right,” “left,” “vertical,” “horizontal, “top,” “bottom,” and derivatives of those terms relate to the described structures and methods as oriented in the drawing figures. The terms “overlying,” “atop,” “on top, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, where intervening elements such as an interface structure can be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary elements.
Also, the following definitions and abbreviations are to be used for the interpretation of the claims and the specification. The terms “comprise,” “comprises,” “comprising,” “include,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation are intended to cover a non-exclusive inclusion. For example, an apparatus, a method, a composition, a mixture, or an article, that includes a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such apparatus, method, composition, mixture, or article.
The terms “one or more” and “at least one” indicate any integer number greater than or equal to one, i.e., one, two, three, four, etc. The term “plurality” indicates any integer number greater than one. The term “connection” can include an indirect “connection” and a direct “connection”.
References in the specification to “embodiments,” “one embodiment, “an embodiment,” “an example embodiment,” “an example,” “an instance,” “an aspect,” etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may or may not include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it may affect such feature, structure, or characteristic in other embodiments whether explicitly described or not.
Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another, or a temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.
Having described exemplary embodiments of the disclosure, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may also be used. The embodiments contained herein should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.
Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.
