PATENT DOCUMENT

Publication Number: US-11237191-B2
Application Number: US-202017092158-A
Country: US
Kind Code: B2

Title: Dynamically controlled auto-ranging current sense circuit

Abstract:
Embodiments relate to sensing a current provided by a power supply circuit. The current sensing circuit includes a sense transistor for sensing the current provided by a main transistor, a driver for controlling a bias provided to the sense transistor and the main transistor, and a sense resistor for converting the sensed current to a voltage value. Moreover, the current sensing circuit includes a controller that modifies at least one of: (a) a resistance of the main transistor by adjusting the bias voltage provided by the driver, (b) a gain ratio between a load current and a sensing current by adjusting a number of individual devices that are active in the sense transistor, and (c) a resistance of the sense resistor.

Claims:
What is claimed is: 
     
       1. A current sensing circuit comprising:
 a sense transistor coupled to a main transistor that provides a load current, the sense transistor configured to generate a sensing current proportional to the load current; 
 a driver having an output terminal coupled to the sense transistor, the driver configured to generate a continuous bias voltage to bias the sense transistor and the main transistor; 
 a sense resistor coupled to the sense transistor; and 
 a controller circuit configured to generate a control signal for controlling at least one of a gain ratio of the sense transistor, a resistance of the sense resistor, and the bias voltage generated by the driver, the controller comprising:
 a counter configured to modify a value of the control signal in a first direction responsive to an output voltage of the main transistor becoming smaller than a first threshold voltage and configured to modify the value of the control signal in a second direction responsive the output voltage of the main transistor becoming larger than a second threshold voltage, the second direction opposite to the first direction. 
 
 
     
     
       2. The current sensing circuit of  claim 1 , wherein the output voltage of the main transistor is a drain-to-source voltage of the main transistor, wherein modifying the value of the control signal in the first direction comprises increasing the value of the control signal, and wherein modifying the value of the control signal in the second direction comprises decreasing the value of the control signal. 
     
     
       3. The current sensing circuit of  claim 1 , wherein the output voltage of the main transistor is a load voltage at an output terminal of the main transistor, wherein modifying the value of the control signal in the first direction comprises decreasing the value of the control signal, and wherein modifying the value of the control signal in the second direction comprises increasing the value of the control signal. 
     
     
       4. The current sensing circuit of  claim 3 , wherein the controller further comprises:
 a first comparator coupled to a first input of the counter, the first comparator configured to generate a first counter signal responsive to the output voltage of the main transistor becoming larger than the second threshold voltage; and 
 a second comparator coupled to a second input of the counter, the second comparator configured to generate a second counter signal responsive to the output voltage of the main transistor becoming smaller than the first threshold voltage. 
 
     
     
       5. The current sensing circuit of  claim 4 , wherein the counter is configured to increase the value of the control signal in response to receiving the first counter signal through the first input, and to decrease the value of the control signal in response to receiving the second counter signal through the second input. 
     
     
       6. The current sensing circuit of  claim 4 , wherein the controller circuit further comprises:
 a third comparator coupled to a third input of the counter, the third comparator configured to generate a third counter signal responsive to the output voltage of the main transistor becoming smaller than a third threshold voltage, wherein the counter is configured to reset in response to receiving the third counter signal through the third input. 
 
     
     
       7. The current sensing circuit of  claim 1 , wherein the driver comprises:
 a current source configured to provide a bias current; 
 a first driver device coupled to the current source and configured to receive the bias current; 
 a second driver device coupled to the first driver device and configured to receive at least part of the bias current; and 
 a first switch coupled to a gate of the second driver device, the first switch configured to turn on or off the second driver device to control the bias voltage according to the value of the control signal received from the controller circuit. 
 
     
     
       8. The current sensing circuit of  claim 1 , wherein the sense transistor comprises a plurality of individual devices which are selectively activated to adjust the gain ratio of the sense transistor, wherein the plurality of individual devices comprises:
 a first sensing device having a gate connected to a first bias switch and a first bypass switch, the first bias switch configured to couple the gate of the first sensing device to the driver when the first bias switch is in a closed position; and 
 a second sensing device having a gate connected to a second bias switch and a second bypass switch, the second bias switch configured to couple the gate of the second sensing device to the driver when the second bias switch is in a closed position; 
 wherein a gain ratio between the load current and sensing current is adjusted by controlling a number of bias switches that are in a closed position. 
 
     
     
       9. The current sensing circuit of  claim 1 , wherein the control signal comprises a first subset of bits for controlling the drive, a second subset of bits for controlling the sense resistor, and a third subset of bits for controlling the sense transistor. 
     
     
       10. A method for sensing a load current, comprising:
 generating, by a sense transistor, a sensing current, the sense transistor coupled to a main transistor that provides the load current, the sensing current proportional to the load current; 
 providing, by a driver, a continuous bias voltage to the sense transistor and the main transistor to control the load current; 
 generating, by a sense resistor, a sense voltage; 
 monitoring a voltage at an output voltage of the main transistor; and 
 generating a control signal for controlling at least one of a gain ratio of the sense transistor, a resistance of the sense resistor, and the bias voltage generated by the driver, wherein the control signal is generated by:
 modifying the value of the control signal in a first direction responsive to the output voltage of the main transistor becoming smaller than a first threshold voltage, and 
 modifying the value of the control signal in a second direction responsive to the output voltage of the main transistor becoming larger than a second threshold voltage, the second direction opposite to the first direction. 
 
 
     
     
       11. The method of  claim 10 , wherein the output voltage of the main transistor is a drain-to-source voltage of the main transistor, wherein modifying the value of the control signal in the first direction comprises increasing the value of the control signal, and wherein modifying the value of the control signal in the second direction comprises decreasing the value of the control signal. 
     
     
       12. The method of  claim 10 , wherein the output voltage of the main transistor is a load voltage at an output terminal of the main transistor, wherein modifying the value of the control signal in the first direction comprises decreasing the value of the control signal, and wherein modifying the value of the control signal in the second direction comprises increasing the value of the control signal. 
     
     
       13. The method of  claim 12 , further comprising:
 generating a first counter signal having an active level in response to the output voltage of the main transistor becoming larger than the second threshold voltage; and 
 generating a second counter signal having an active level in response to the output voltage of the main transistor becoming smaller than the first threshold voltage. 
 
     
     
       14. The method of  claim 13 , wherein the value of the control signal is increased in response to generating the first counter signal having the active level, wherein the value of the control signal is decreased in response to generating the second counter signal having the active level. 
     
     
       15. The method of  claim 13 , further comprising:
 generating a third counter signal having an active level in response to the output voltage of the main transistor becoming smaller than a third threshold voltage; and 
 resetting the value of the control signal in response to generating the third counter having the third counter signal having the active level. 
 
     
     
       16. The method of  claim 10 , wherein the driver comprises a current source configured to provide a bias current, a first driver device coupled to the current source and configured to receive the bias current, a second driver device coupled to the first driver device and configured to receive at least part of the bias current, and a first switch configured to turn on or off the second driver device to control the bias voltage according to a control signal received from a controller circuit, and wherein controlling the bias voltage generated by the driver comprises opening the first switch to increase the bias voltage. 
     
     
       17. The method of  claim 10 , wherein the sense transistor comprises a plurality of individual devices which are selectively activated to adjust the gain ratio of the sense transistor, wherein the plurality of individual devices comprises a first sensing device having a gate connected to a first bias switch and a first bypass switch, and a second sensing device having a gate connected to a second bias switch and a second bypass switch, wherein controlling the gain ratio of the sense transistor comprises a number of bias switches that are in a closed position. 
     
     
       18. The method of  claim 10 , wherein the control signal comprises a first subset of bits for controlling the drive, a second subset of bits for controlling the sense resistor, and a third subset of bits for controlling the sense transistor. 
     
     
       19. A controller circuit for controlling a sensing circuit, the sensing circuit for sensing an output of a main transistor, the controller circuit comprising:
 a first comparator configured to generate a first counter signal responsive to an output voltage of the main transistor becoming smaller than a first threshold voltage; 
 a second comparator configured to generate a second counter signal responsive to the output voltage of the main transistor becoming larger than a second threshold voltage; and 
 a counter having a first input coupled to an output of the first comparator and a second input coupled to an output of the second comparator, the counter configured to modify a value of a control signal in a first direction responsive receiving the first counter signal and configured to modify the value of the control signal in a second direction responsive receiving the second counter signal, the second direction opposite to the first direction, the control signal for controlling at least one of a gain ratio of a sense transistor of the sensing circuit, a resistance of a sense resistor of the sensing circuit, and a continuous bias voltage generated by a driver of the sensing circuit. 
 
     
     
       20. The controller circuit of  claim 19 , further comprising:
 a third comparator coupled to a third input of the counter, the third comparator configured to generate a third counter signal responsive to the output voltage of the main transistor becoming smaller than a third threshold voltage, wherein the counter is configured to reset in response to receiving the third counter signal through the third input.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. application Ser. No. 16/734,017, filed Jan. 3, 2020, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates a circuit for a current sense circuit and more specifically to a dynamic auto-ranging current sensing circuit. 
     2. Description of the Related Arts 
     Current sensing is used in a wide variety of application including battery life indicators, battery charger control, over current protection, circuits supervision, current and voltage regulation, ground fault detection, proportional solenoid control, etc. Current sense circuits suffer from many sources of error including mismatch between the power and sense transistors, offset and gain limit in amplifiers, process variation of sense resistors, and input referred noise at large sense ratios. For example, for high load currents, threshold voltages (VT), channel width/length ratios (W/L), and metallization mismatches between power and sense transistors become a significant source of error for current sense circuits. Moreover, for low load currents, amplifier offset and the limit in the gain of the amplifier can cause a significant error in the sensing of the load current. 
     SUMMARY 
     Embodiments relate to sensing a current provided by a power supply circuit. The current sensing circuit includes a sense transistor for sensing the current provided by a main transistor, a driver for controlling a bias provided to the sense transistor and the main transistor, and a sense resistor for converting the sensed current to a voltage value. The current sensing circuit includes a controller that modifies at least one of (a) a resistance of the main transistor by adjusting the bias voltage provided by the driver, (b) a gain ratio between a load current and a sensing current by adjusting a number of individual devices that are active in the sense transistor, and (c) a resistance of the sense resistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high-level diagram of an electronic device, according to one embodiment. 
         FIG. 2  is a circuit diagram illustrating a current sense circuit, according to one embodiment. 
         FIG. 3  is a circuit diagram, illustrating a dynamic auto-ranging current sense circuit, according to one embodiment. 
         FIG. 4  is a circuit diagram illustrating the driver of the dynamic auto-ranging current sense circuit of  FIG. 3 , according to one embodiment. 
         FIG. 5A  is a circuit diagram illustrating a dynamic current sense circuit for the dynamic auto-ranging current sense circuit of  FIG. 3 , according to one embodiment. 
         FIG. 5B  is a circuit diagram illustrating a dynamic current sense circuit for the dynamic auto-ranging current sense circuit of  FIG. 3 , according to a second embodiment. 
         FIG. 5C  is a circuit diagram illustrating a dynamic current sense circuit for the dynamic auto-ranging current sense circuit of  FIG. 3 , according to a third embodiment. 
         FIG. 5D  is a circuit diagram illustrating a digital encoder to generate the sense control signal for controlling the dynamic current sense circuit, according to one embodiment. 
         FIG. 5E  is a plan view illustrating a layout of the sense transistors and the main transistor, according to one embodiment. 
         FIG. 6  is a circuit diagram illustrating a variable sense resistor for the dynamic auto-ranging current sense circuit of  FIG. 3 , according to one embodiment. 
         FIG. 7  is a circuit diagram illustrating a controller circuit for the dynamic auto-ranging current sense circuit of  FIG. 3 , according to one embodiment. 
         FIG. 8A  is a flowchart illustrating a method for dynamically adjusting the sensitivity of the sense circuit, according to one embodiment. 
         FIG. 8B  is a flowchart illustrating a process for adjusting the sensitivity of the sense circuit when the count of the up/down counter increases, according to one embodiment. 
         FIG. 8C  is a flowchart illustrating a process for adjusting the sensitivity of the sense circuit when the count of the up/down counter decreases, according to one embodiment. 
     
    
    
     The figures depict, and the detail description describes, various non-limiting embodiments for purposes of illustration only. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the various described embodiments. However, the described embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
     Embodiments relate to a dynamically controlled auto-ranging current sensing circuit that dynamically adjusts the sensitivity based on the current level being provided to a load. The dynamically controlled auto-ranging current sensing circuit modifies a bias voltage provided by a driver to a main transistor and a sense transistor, a current gain between a load current and a sensing current, and a resistance of a sensing resistor that generates a voltage proportional to the current generated by the sense transistor. Moreover, the dynamically controlled auto-ranging current sensing circuit includes a low-resolution analog-to-digital converter (ADC) for converting the voltage generated by the sense transistor to a digital value. The digital value provided by the low-resolution ADC is adjusted based on the current gain, and the resistance of the sensing resistor to match the performance of a high-resolution ADC. 
     Exemplary Electronic Device 
     Embodiments of electronic devices, user interfaces for such devices, and associated processes for using such devices are described. In some embodiments, the device is a portable communications device, such as a mobile telephone, that also contains other functions, such as personal digital assistant (PDA) and/or music player functions. Exemplary embodiments of portable multifunction devices include, without limitation, the iPhone®, iPod Touch®, Apple Watch®, and iPad® devices from Apple Inc. of Cupertino, Calif. Other portable electronic devices, such as wearables, laptops or tablet computers, are optionally used. In some embodiments, the device is not a portable communications device, but is a desktop computer or other computing device that is not designed for portable use. In some embodiments, the disclosed electronic device may include a touch sensitive surface (e.g., a touch screen display and/or a touch pad). An example electronic device described below in conjunction with  FIG. 1  (e.g., device  100 ) may include a touch-sensitive surface for receiving user input. The electronic device may also include one or more other physical user-interface devices, such as a physical keyboard, a mouse and/or a joystick. 
     Figure ( FIG. 1  is a high-level diagram of an electronic device  100 , according to one embodiment. Device  100  may include one or more physical buttons, such as a “home” or menu button  104 . Menu button  104  is, for example, used to navigate to any application in a set of applications that are executed on device  100 . In some embodiments, menu button  104  includes a fingerprint sensor that identifies a fingerprint on menu button  104 . The fingerprint sensor may be used to determine whether a finger on menu button  104  has a fingerprint that matches a fingerprint stored for unlocking device  100 . Alternatively, in some embodiments, menu button  104  is implemented as a soft key in a graphical user interface (GUI) displayed on a touch screen. 
     In some embodiments, device  100  includes touch screen  150 , menu button  104 , push button  106  for powering the device on/off and locking the device, volume adjustment buttons  108 , Subscriber Identity Module (SIM) card slot  110 , head set jack  112 , and docking/charging external port  124 . Push button  106  may be used to turn the power on/off on the device by depressing the button and holding the button in the depressed state for a predefined time interval; to lock the device by depressing the button and releasing the button before the predefined time interval has elapsed; and/or to unlock the device or initiate an unlock process. In an alternative embodiment, device  100  also accepts verbal input for activation or deactivation of some functions through microphone  113 . The device  100  includes various components including, but not limited to, a memory (which may include one or more computer readable storage mediums), a memory controller, one or more central processing units (CPUs), a peripherals interface, an RF circuitry, an audio circuitry, speaker  111 , microphone  113 , input/output (I/O) subsystem, and other input or control devices. Device  100  may include one or more image sensors  164 , one or more proximity sensors  166 , and one or more accelerometers  168 . The device  100  may include components not shown in  FIG. 1 . 
     Device  100  is only one example of an electronic device, and device  100  may have more or fewer components than listed above, some of which may be combined into a component or have a different configuration or arrangement. The various components of device  100  listed above are embodied in hardware, software, firmware or a combination thereof, including one or more signal processing and/or application specific integrated circuits (ASICs). Device  100  may include one or more current sense circuits described herein. 
     Example Current Sense Circuit 
       FIG. 2  is a circuit diagram illustrating current sense circuit  200 , according to one embodiment. The current sense circuit  200  includes main transistor Mp  220  for driving a load current Iload to a load  250 , and a sense transistor Msense  210  for providing a sense current Isense that has an amplitude based on the load current Iload to a sense resistor Rsense  270 . The sense current Isense may be proportional to the load current Iload. The relationship between the sense current Isense and the load current Iload may be based on a size ratio between the sense transistor Msense  210  and the main transistor Mp  220 . The output of the main transistor Mp  220  may be coupled to a capacitor C  260 . 
     The current sense circuit  200  further includes a driver  230  that provides a driving voltage to the main transistor Mp  220  and the sense transistor Msense  210 . The driver  230  is coupled to the gate of the main transistor Mp  220  and the gate of the sense transistor Msense  210 . In some embodiments, the driver  230  provides a bias voltage to the gate of the main transistor Mp  220  and the gate of the sense transistor Msense  210 . In yet other embodiments, the driver  230  is a low resolution digital to analog converter (DAC) that receives a digital control signal and generates the analog voltage provided to the gate of the main transistor Mp  220  and the gate of the sense transistor Msense  210 . 
     The current sense circuit  200  additionally includes an amplifier transistor Tamp  280  that is controlled by a sense amplifier  240 . The amplifier transistor Tamp  280  is coupled between the sense transistor Msense  210  and the sense resistor Rsense  270 . The sense amplifier  240  includes a first input terminal that is coupled to an output of the main transistor Mp  220 , and a second input terminal that is coupled to an output of the sense transistor Msense  210 . The output of the sense amplifier  240  is then coupled to a gate of the amplifier transistor Tamp  280 . The sense amplifier forces the voltage at the output of the sense transistor Msense  210  to be the voltage at the output of the main transistor Mp  220 . Because the gate of the main transistor Mp  220  and the gate of the sense transistor Msense  210  are connected together, the sense amplifier  240  forces the gate-to-source voltage (Vgs) of the sense amplifier Msense  210  to be the Vgs of the main transistor Mp  220 . 
     The current sense circuit  200  further includes a digital-to-analog converter (ADC)  290  coupled to the sense resistor Rsense  270 . The ADC  290  senses the voltage at one terminal of the sense resistor Rsense  270  and converts the sensed voltage to a digital value D&lt;N high_res :1&gt;. Since the value of the sense resistor Rsense  270  is known, the amplitude of the sense current Isense can be determined by dividing the voltage Vout by the resistance Rsense  270 . Moreover, since the size ratio between the size of the main transistor Mp  220  and the size of the sense transistor Msense  210  is known, the load current Iload can be determined by multiplying the sense current Isense by this ratio. In the current sense circuit  200  of  FIG. 2 , the ADC has a high resolution to enable an accurate reading of the voltage Vout and thus, an accurate sensing of the load current Iload. 
     However, in the current sense circuit  200 , errors may be introduced during the sensing process. For instance, the voltage (Vp) at the load side is equal to:
 
 Vp=V   DD   −ΔVp , where Δ Vp=l   load ( Ron   p   +Rm   p )  (1)
 
and the voltage (Vs) at the sense side is equal to:
 
 Vs=V   DD   −ΔVs , where Δ Vs=l   sense ( Ron   s   +Rm   s )  (2)
 
where Ron p  and Ron s  are the on resistances of the main transistor Mp  220  and the sense transistor Msense  210 , and Rm p  and Rm s  are metallization resistances of the main transistor Mp  220  and the sense transistor Msense  210 .
 
     Moreover, the relationship between Vs and Vp can be expressed using the following equation:
 
 A   v ( Vp−Vs+V   off )= Vs   (3)
 
where A v  is the gain of the sense amplifier  240  and V off  is the offset of the sense amplifier  240 . Thus, substituting Vs and Vp, we obtain:
 
                       A   v     ⁡     (       V     D   ⁢   D       -     Δ   ⁢           ⁢   Vp     +     V   off       )       =       (       A   v     +   1     )     ⁢     (       V     D   ⁢   D       -     Δ   ⁢           ⁢   Vs       )               (   4   )                 Δ   ⁢           ⁢   Vs     =       Δ   ⁢           ⁢     Vp   ·       A   v         A   v     +   1           -       V   off     ·       A   v         A   v     +   1         +       V     D   ⁢   D       ·     1       A   v     +   1                   (   5   )               
Therefore:
 
                       I     s   ⁢   e   ⁢   n   ⁢   s   ⁢   e       =         I   load     ·         Ron   p     +     R   ⁢     m   p             Ron   s     +     R   ⁢     m   s           ·       A   v         A   v     +   1         +           -     V   off       +       V     d   ⁢   d       /     A   v             R   ⁢   o   ⁢     n   s       +     R   ⁢     m   s           ·       A   v         A   v     +   1             ⁢     
     ⁢           ⁢   and           (   6   )                 V     o   ⁢   u   ⁢   t       =         I   load     ·         Ron   p     +     R   ⁢     m   p             Ron   s     +     R   ⁢     m   s           ·       A   v         A   v     +   1       ·     R     s   ⁢   e   ⁢   n   ⁢   s   ⁢   e         +           -     V   off       +       V     d   ⁢   d       /     A   v             R   ⁢   o   ⁢     n   s       +     R   ⁢     m   s           ·       A   v         A   v     +   1       ·     R     s   ⁢   e   ⁢   n   ⁢   s   ⁢   e                   (   7   )               
As a result, both the sense current (Isense) and the sense voltage (Vout) are prone to errors due to a limited amount of gain of the sense amplifier  240  and an offset in the sense amplifier  240 .
 
Example Dynamic Auto-Ranging Current Sense Circuit
 
       FIG. 3  is a circuit diagram, illustrating dynamic auto-ranging current sense circuit  300 , according to one embodiment. The dynamic auto-ranging current sense circuit  300  may include, among other components, main transistor Mp  220  for driving a load current Iload to a load  250 , and a sense transistor Msense  310  for providing a sense current Isense that has an amplitude based on the load current Iload to a sense resistor Rsense  370 . The dynamic auto-ranging current sense circuit  300  further includes a driver  330  that provides a driving voltage to the main transistor Mp  220  and the sense transistor Msense  310 . The driver  330  is coupled to the gate of the main transistor Mp  220  and the gate of the sense transistor Msense  310 . Additionally, the dynamic auto-ranging current sense circuit  300  includes a low resolution ADC  380  that converts the analog voltage at the sense resistor Rsense  370  to a digital value D&lt;N low_res :1&gt;. 
     Controller  390  is a circuit that controls the driver  330 , sense transistor Msense  310 , and the sense resistor Rsense  370 . The controller  390  receives as an input the voltage at an output of the main transistor Mp  220  and generates control signals for the driver  330 , the sense transistor Msense  310 , and the sense resistor Rsense  370 . In particular, the controller  390  generates a control signal Dcontrol to control the driver  330 , a control signal Scontrol to control the sense transistor Msense  310 , and a control signal Rcontrol to control the sense resistor Rsense  370 . The controller  390  is described in more detail below in conjunction with  FIG. 7 . 
     The driver  330  provides a bias voltage Vbias to the main transistor Mp  220  and the sense transistor Msense  310 . The driver  330  receives as an input control signal Dcontrol. Moreover, the output  335  of the driver  330  is coupled to the sense transistor Msense  310  and the main transistor Mp  220 . By changing the bias voltage Vbias, the on resistance (Rdson) of the main transistor Mp  220  and the on resistance (Rdson) of the sense transistor Msense  310  is controlled. Adjusting Rdson of the main transistor Mp  220  and the sense transistor Msense  310  does not change the value of sense voltage Vout but improves sense accuracy. Increasing Rdson allows for bigger voltage drop at lower load currents and keeps the signal level high relative to offset and noise. That is, adjusting Rdson adjusts the sense voltage signal amplitude across the main transistor Mp  220  and the sense transistor Msense  310 . At larger voltage drops across the main transistor Mp  220  and the sense transistor Msense  310 , sensing is less susceptible to offset and noise. 
     In some embodiments, as the drain-to-source voltage (Vds) of the main transistor Mp  220  decreases, Rdson of the main transistor Mp  220  and Rdson of the sense transistor Msense  310  are increased. For instance, if the Vds of the main transistor Mp  220  decreases below a first threshold Vds value (VTH_LOW) (e.g., VDS_LOW=30 mV), Rdson is increased to keep Vds higher than VTH_LOW. Rdson of the main transistor Mp  220  may be increased by lowering the gate-to-source voltage (Vgs) of the main transistor Mp  220 . 
     In some embodiments, as Vds of the main transistor Mp  220  increases, Rdson of the main transistor Mp  220  and the sense transistor Msense  310  are decreased. For instance, if the Vds of the main transistor Mp  220  increases above a second threshold Vds value (VTH_HIGH) (e.g., VTH_HIGH=60 mV), Rdson is decreased to keep Vds lower than VTH_HIGH. Rdson of the main transistor Mp  220  may be decreased by increasing the Vgs of the main transistor Mp  220 . 
     In some embodiments, Vgs of the main transistor Mp  220  and the sense transistor Msense  310  provided by the driver  330  is increased or decreased in discrete steps. The driver  330  is described below in more detail in conjunction with  FIG. 4 . 
     The size of the sense transistor Msense  310  is controlled by controller  390 . In some embodiments, the size of the sense transistor Msense  310  is expressed as a ratio (W/L) between the channel width (W) and the channel length (L) of the sense transistor Msense  310 . The size of the sense transistor Msense  310  may be controlled by activating or deactivating individual sense devices that are connected in parallel. In some embodiments, each of the sense devices of the sense transistor Msense  310  have the same length. As such, an effective width of the sense transistor Msense  310  can be increased or decreased by activating or deactivating a subset of devices. By increasing or decreasing the size of the sense transistor Msense  310 , the ratio between the sense current Isense and the load current Iload (sense current ratio) can be increased or decreased. 
     In some embodiments, as the load current Iload decreases, the sense current ratio is decreased to maintain the output voltage Vout within a set range. For instance, if the load current Iload reaches a first threshold value, the sense current ratio is decreased. In some embodiments, Vds of the main transistor Mp  220  is used as a proxy to determine whether the load current Iload has reached the first threshold value. For instance, if Vds of the main transistor Mp  220  decreases below VTH_LOW, the sense ratio is decreased. Changing the sense current ratio is advantageous, among other reasons, because the dynamic range and noise performance of the dynamic auto-ranging current sense circuit  300  can be enhanced. Lower sense current ratio helps to decrease input referred noise at low current conditions. However, if the sense current ratio is lowered at high current conditions, power consumption is increased due to increased sense current. 
     In some embodiments, as the load current Iload increases, the sense current ratio is increased to maintain the output voltage Vout within the set range. For instance, if the load current Iload reaches a second threshold value, the sense current ratio is increased; and if Vds of the main transistor Mp  220  increases above VTH_HIGH, the sense current ratio is increased. The sense current ratio may be increased or decreased in discrete steps. The variable size sense transistor Msense  310  is described below in more detail in conjunction with  FIG. 5 . 
     The resistance (R) of the sense resistor Rsense  370  is controlled by the controller  390 . The sense resistor Rsense may include a resistor ladder with multiple resistors in series. The resistance of the sense resistor Rsense  370  may be controlled by selecting a node in the resistance ladder and connecting the selected node to ground. By increasing or decreasing the resistance R of the sense resistor Rsense  370 , the value of the sense voltage Vout can be increased or decreased accordingly. 
     In some embodiments, as the load current Iload decreases, the resistance R of the sense resistor Rsense  370  is increased to maintain the output voltage Vout within a set range. For instance, if the load current reaches a first threshold value, the resistance of the sense resistor Rsense  370  is increased. In some embodiments, Vds of the main transistor Mp  220  is used as a proxy to determine whether the load current Iload has reached the first threshold value. For instance, if Vds of the main transistor Mp  220  decreases below VTH_LOW, the resistance R of the sense resistor Rsense  370  is increased. Changing the resistance R of the sense resistor Rsense  370  is advantageous, among other reasons, because as the load current Iload changes, and thus the sense current Isense changes, the output voltage Vout is kept within the dynamic range of the ADC  380 , allowing the use of a low resolution ADC. 
     In some embodiments, as the load current Iload increases, the resistance R of the sense resistor Rsense  370  is decreased to maintain the output voltage Vout within the set range. For instance, if the load current reaches a second threshold value, the resistance of the sense resistor Rsense  370  is decreased. For example, if Vds of the main transistor Mp  220  increases above VTH_HIGH, the resistance R of the sense resistor Rsense  370  is decreased. The resistance R of the sense resistor Rsense  370  may be increased or decreased in discrete steps. The variable sense resistor Rsense  370  is described below in more detailed in conjunction with  FIG. 6 . 
     In some embodiments, adjusting Rdson of the main transistor Mp  220 , adjusting the resistance R of the sense resistor Rsense  370 , and adjusting the sense current ratio are performed independently. The adjustment of each of Rdson, resistance R and the sense current ratio can be associated with different current thresholds. 
     The analog-to-digital converter (ADC)  380  is coupled to the sense resistor Rsense  370  and converts the voltage Vout at the sense resistor Rsense  370  to a digital value D&lt;N low_res :1&gt;. In some embodiments, the ADC  380  has a low resolution. For instance, the resolution of ADC  380  is lower than the resolution of ADC  290  of the current sense circuit  200  of  FIG. 2 . Using a low resolution ADC reduces the area occupied by the ADC. 
       FIG. 4  is a circuit diagram illustrating the driver  330  of the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to one embodiment. The driver  330  may include, among other components, a chain of diode connected transistors  410 A through  410 N connected in series and a current source Ibias  415 . The current source Ibias  415  and the chain of diode connected transistors  410 A through  410 N are connected between a first terminal  420  and a second terminal  430 . In some embodiments, the first terminal  420  is a power supply terminal (Vdd). Moreover, the second terminal  430  may be connected to an output terminal of the main transistor Mp  220  of  FIG. 3 . The gate of each of a subset of diode connected transistors  410 A through  410 N is connected to the second terminal  430  through one of switches  4   440 B through  440 N. In the example of  FIG. 4 , the gate of the second diode connected transistor  410 B is connected to the second terminal  430  through switch  440 B, the gate of the (n−1)th diode connected transistor  410 M is connected to the second terminal  430  through switch  440 M, and the gate of the nth diode connected transistor  410 N is connected to the second terminal  430  through switch  440 N. 
     Each of the switches  440 B through  440 N is controlled by a driver control signal  450 . In some embodiments the driver control signal  450  is the control signal Dcontrol received from the controller  390 . In one embodiment, the driver control signal  450  is generated using an address decoder (not shown) based on a binary signal Dcontrol received from the controller  390 . 
     When one of the switches  440 B through  440 N is closed, a source terminal of a previous diode connected transistor  410  is connected to the second terminal, bypassing a subset of diode connected transistors  410 . For instance, if a jth switch is closed, the source of the (j−1)th diode connected transistor is connected to the second terminal  430 , bypassing the jth to nth diode connected transistors. As such, the bias current Ibias is configured to flow through the first to the (j−1)th diode connected transistors. As a result, the output voltage (Vbias) of the driver  330  is equal to the sum of the gate-to-source voltage (Vgs) of the first to the (j−1)th diode connected transistors as shown in the following equation: 
     
       
         
           
             
               
                 
                   Vbias 
                   = 
                   
                     
                       ∑ 
                       
                         k 
                         = 
                         0 
                       
                       
                         ( 
                         
                           j 
                           - 
                           1 
                         
                         ) 
                       
                     
                     ⁢ 
                     VGS_k 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     As such, the bias voltage Vbias provided by the driver  330  to the main transistor Mp  220  and the sense transistor Msense  310  is controlled by controlling the number of diode connected transistors  410  the bias current Ibias flows through. That is, for a given transistor, 
             Ibias   =       1   2     ⁢   μ   ⁢   C   ⁢   o   ⁢   x   ⁢     W   L     ⁢       (     Vgs   -   Vth     )     2             
Thus, the following equation can also be derived:
 
                   Vgs   =           2   ⁢   Ibias       μ   ⁢   C   ⁢   o   ⁢     x   ⁡     (     W   L     )             +   Vth             (   9   )               
If every diode connected transistor  410  is identical (i.e., if the channel length and width for each of the diode connected transistors  410  are equal), the value of the bias voltage Vbias would be proportional to the number of diode connected transistors that are connected in series without being bypassed by a switch  440 . As such, the gate voltage of the main transistor  220  can be changed in discrete steps equal to the gate-to-source voltage (Vgs) of a single diode connected transistor  410 . In some embodiments, the size of each the diode connected transistors  410  are selected based on a desired step. That is, if a non-uniform step is desired, diode connected transistors  410  with differing sizes may be used.
 
       FIG. 5A  is a circuit diagram illustrating the sense transistor Msense  310  for the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to one embodiment. The sense transistor Msense  310  includes a set of transistors  510 A through  510 M (Msense_0 through Msense_M) connected in parallel. Each of the transistors  510 A through  510 M are connected between a first terminal  560  and a second terminal  570 . The first terminal  560  is then connected to a first terminal of the main transistor Mp  220  and the second terminal  570  is connected to the sense amplifier  240  as shown in  FIG. 3 . The sense transistor Msense  310  further includes a set of bias switches  520 A through  520 M and a set of bypass switches  530 A through  530 M. At least each of a subset of the transistors  510  is connected to a first switch from the set of bias switches  520  and a second switch from the set of bypass switches  530 . For instance, in the example of  FIG. 5A , transistor  510 B (Msense_1) is connected to a bias switch  520 B and a bypass switch  530 B. Similarly, transistor  510 C (Msense_2) is connected to a switches  520 C and  530 C, and transistor  510 M (Msense_M) is connected to a switches  520 M and  530 M. 
     In the example of  FIG. 5A , each transistor  510  has a different size. For instance, each transistor  510  has a different channel width (W). In particular, in the example of  FIG. 5A , the size of the transistors exponentially increases with a factor of 2. That is, the first transistor  510 A (Msense_0) has a size of W/L 0 =2 0 x=1x, the second transistor  510 B (Msense_1) has a size of W/L 1 =2 1 x=2x, the third transistor  510 C (Msense_2) has a size of W/L 2 =2 2 x=4x, and the mth transistor  510 M (Msense_M) has a size of W/L M =2 M x. In some embodiments, each transistor is made of multiple devices or multiple fingers having the same size. That is, each transistor  510  is made of one or more devices or fingers having the same W/L ratio. For instance, the first transistor  510 A (Msense_0) is made of a single device having a 1x size, the second transistor  510 B (Msense_1) is made of two devices having a 1x size connected in parallel, the third transistor  510 C (Msense_2) is made of four devices having a 1x size connected in parallel, and the mth transistor  510 M (Msense_M). 
     As such, the size of the sense transistor Msense  310  can be modified by dynamically activating or deactivating one or more transistors  510 . For example, in the embodiments of  FIG. 5A , by closing a first subset of bias switches  520 , the transistors  510  corresponding to the closed bias switches  520  are activated. Moreover, by opening a second subset of bias switches  520 , the transistors  510  corresponding to the opened bias switches  520  are deactivated. As such, the activated transistors are connected together, defining the size of the sense transistor Msense  310 . 
     In some embodiments, the second set of bypass switches  530  are used to deactivate a subset of transistors  510 . That is, by closing a bypass switch  530  form the set of bypass switches, the corresponding transistor  510  is deactivated by connecting the gate of the corresponding transistor  510  to the second terminal  570 . In some embodiments the set of bias switches  520  and the set of bypass switches are controlled such that when a switch from the set of bias switches  520  is opened, the corresponding switch from the set of bypass switches  530  is closed. For example, when a switch  520 J of the set of bias switches  520  corresponding to the jth transistor  510 J is opened, the switch  530 J of the set of bypass switches  530  corresponding to the jth transistor  510 J is closed. Moreover, the set of bias switches  520  and the set of bypass switches are controlled such that when a switch from the set of bias switches  520  is closed, the corresponding switch from the set of bypass switches  530  is opened. For example, when a switch  520 J of the set of bias switches  520  corresponding to the jth transistor  510 J is closed, the switch  530 J of the set of bypass switches  530  corresponding to the jth transistor  510 J is opened switch. 
     In some embodiments, the switches  520  and  530  are made using transistors. That is, switches  520  and  530  are transistors that can be turned on to close a connection to the gate of a transistor  510  or turned off to open a connection to the gate of a transistor  510 . In some embodiments, since switches  520  and  530  are not used to drive a current, the size of the transistor used to implement switches  520  and  530  are smaller than the size of transistors  510 . 
     Each of the switches  520  and  530  is controlled by a sense control signal  550 . In some embodiments the driver control signal  450  is the control signal Scontrol received from the controller  390 . In one embodiment, the sense control signal  550  is generated using an encoder based on the control signal Scontrol received from the controller  390 .  FIG. 5D  illustrates one implementation of an encoder used to generate the sense control signal  550 . 
       FIG. 5B  is a circuit diagram illustrating the sense transistor Msense  310  for the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to a second embodiment. In the embodiment of  FIG. 5B , the first transistor  510 A (Msense_0) does not have switches and is directly connected to Vbias. As such, the first transistor  510 A cannot be deactivated. As such, the embodiment of  FIG. 5B  ensures that the minimum size of the sense transistor Msense  310  is the size of the first transistor  510 A (Msense_0). 
       FIG. 5C  is a circuit diagram illustrating the sense transistor Msense  310  for the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to a third embodiment. In the embodiment of  FIG. 5C , every transistor  510  has the same size. In other embodiments, the sense transistor Msense  310  may include a first subset of transistors  510  having a first size, and a second subset of transistors  510  having a second size. In the example of  FIG. 5C , the size of the sense transistor Msense  310  is controlled by the number of transistors  510  that are activated, and not based on which transistor  510  is activated. As such, the transistors that are activated to be used for the sense transistor Msense  310  can be rotated to account for transistor deterioration and process variation. That is, the transistors that are activated can be rotated to enable mismatches between different transistors to be distributed over time. Moreover, the activated transistors are rotated to sample different locations of the main transistor Mp  220  in terms of temperature, stress, and the like. 
     In some embodiments, to control which transistor  510  is used, a digital encoder having a scrambler is used.  FIG. 5D  is a circuit diagram illustrating a digital encoder  580  to generate the sense control signal  550  for controlling the sense transistor Msense  310 , according to one embodiment. The digital encoder  580  may be part of the sense transistor Msense  310 . Alternatively, the digital encoder  580  may be a separate module located in the signal path between the controller  390  and the sense transistor Msense  310 . The digital encoder  580  receives, from the controller  390 , the control signal Scontrol for controlling the sense transistor Msense  310 , and generates the sense control signal  550 . The digital encoder  580  may include, among other components, a thermometer encoder  590  and a scrambler  595 . 
     The thermometer encoder  590  (or unary encoder) receives a binary number n as an input and generates an output having n bits have a first value. The binary number n is the control signal Scontrol received from the controller  390 . In one embodiment, the thermometer encoder  590  receives a binary number n as an input and generates an output having n ones followed or preceded by zeros. In another embodiment, the thermometer encoder  590  receives a binary number n as an input and generates an output having n zeros followed or preceded by ones. For example, if the input has a value of 5 (i.e., 0101), the thermometer encoder  590  may generate an output having a value of 111110000000000 or 000000000011111. That is, an output having five 1s. In another embodiment, for an input value of 5 (i.e., 0101), the thermometer encoder  590  generates an output having a value of 111111111100000 or 000001111111111. That is, an output having five 0s. 
     The scrambler  595  receives the unary encoded number from the thermometer encoder  590  and randomizes (or pseud-randomizes) the position of the 1s or 0s. The scrambler  595  does not change the number of 1s or 0s from the unary encoded number. For example, if the unary encoded value generated by the thermometer encoder  590  is 111110000000000, the scrambler  595  may scramble the ones to generate the output signal 001010000100101. 
     The scrambled signal is then used to control the sense transistor Msense  310 . That is, since the ones in the sense control signal  550  are scrambled, the digital encoder  580  randomizes which transistors  510  are being activated to achieve a desired size for the sense transistor Msense  310 . 
       FIG. 5E  is a plan view illustrating a layout of transistors  510  and the main transistor Mp  220 , according to one embodiment. The main transistor Mp  220  includes multiple fingers, each having a size of 1x. In addition, each of the transistors  510 A through  510 M have a size of 1x and are interlaced within the set of fingers of the main transistor Mp  220 . For instance, in the example of  FIG. 5E , the main transistor Mp  220  includes multiple fingers grouped in arrays of ten fingers. The transistors  510 A through  510 M are placed in between two arrays of fingers of the main transistor Mp  220 . For instance, the first sense transistor Msense_0  510 A is between a first array of ten fingers and a second array of ten fingers that are part of the main transistor Mp  220 . As such, if the fingers have mismatch due to process and temperature variations, and package stress and the properties of these fingers shift differently over time, this placement of the transistors  510 A through  510 M reduces the dependency of the dynamic auto-ranging current sense circuit  300  on those process variations. 
       FIG. 6  is a circuit diagram illustrating the variable sense resistor  370  for the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to one embodiment. The variable sense resistor  370  may include, among other components, a chain of resistors  610 A through  620 P connected in series between the first terminal  630  and the second terminal  640 . The first terminal  630  may be coupled to the second terminal  570  of the sense transistor Msense  310  and the second terminal  640  may be coupled to ground or second supply voltage (Vss). Moreover, the variable sense resistor  370  includes multiple switches  620 A through  620 P. Each of the switches  620  is configured to bypass one or more resistors when closed. When one of the switches  620 A through  620 P is closed, one of the resistors  610  is connected to the second terminal  6740 . For instance, if a jth switch is closed, the jth resistor is connected to the second terminal  6740 , bypassing the (j+1)th to pth resistor. 
     Each of the switches  620  is controlled by a resistor control signal  650 . In some embodiments the resistor control signal  650  is the control signal Rcontrol received from the controller  390 . In one embodiment, the resistor control signal  650  is generated using an address decoder (not shown) based on the binary signal Rcontrol received from the controller  390 . 
       FIG. 7  is a circuit diagram illustrating the controller  390  for the dynamic auto-ranging current sense circuit  300  of  FIG. 3 , according to one embodiment. The controller  390  receives load voltage Vload from the main transistor Mp  220 , and generates control signals Dcontrol, Scontrol, and Rcontrol for controlling the driver  330 , sense transistor Msense  310 , and the sense resistor Rsense  370 . The controller  390  may include, among other components, multiple comparators  710 , an up/down counter, and an oscillator. 
     Each comparator  710  compares the drain-to-source voltage (Vds) of the main transistor Mp  220  to a threshold voltage. For example, the first comparator  710 A compares Vds to a first threshold voltage VTH_LOW, a second comparator  710 B compares Vds to the second threshold voltage VTH_HIGH, and the third comparator  710 C compares Vds to a third threshold voltage VTH_FAST. In some embodiments, each comparator  710  receives load voltage Vload and compares Vload to a threshold voltage. As used herein, the load voltage Vload is the voltage at the source terminal of the main transistor Mp, wherein Vds=Vd−Vload. For example, the first comparator  710 A compares Vload to a first threshold voltage Vd−VTH_LOW, the second comparator  710 B compares Vload to a second threshold voltage Vd−VTH_HIGH, and the third comparator  710 C compares Vload to a third threshold voltage Vd−VTH_FAST, where Vd is the drain voltage of the main transistor Mp  220 . In some embodiments, the drain voltage Vd of the main transistor Mp  220  is a supply voltage Vdd. 
     In another embodiment, each comparator  710  receives the drain voltage Vd of the main transistor Mp and the load voltage Vload and compares the difference between Vd and Vload to a threshold voltage. 
     When the drain-to-source voltage (Vds=Vd−Vload) of the main transistor Mp  220  is higher than VTH_LOW, the first comparator  710 A outputs a signal having a first value (e.g., 0 or LO). Conversely, when Vds of the main transistor Mp  220  reaches or decreases below VTH_LOW, the first comparator  710 A output a signal having a second value (e.g., 1 or HI). The output of the first comparator  710 A is connected to the UP input of the up/down counter  720 . When the up/down counter  720  receives a signal having the second value (e.g., 1 or HI) from the first comparator  710 A, the up/down counter  720  increases the value of a stored count. 
     When Vds of the main transistor Mp  220  is lower than VTH_HIGH, the second comparator  710 B outputs a signal having the first value (e.g., 0 or LO). Conversely, when Vds of the main transistor Mp  220  reaches or increases above VTH_HIGH, the second comparator  710 B outputs a signal having the second value (e.g., 1 or HI). The output of the second comparator  710 B is connected to the DOWN input of the up/down counter  720 . When the up/down counter  720  receives a signal having the second value (e.g., 1 or HI) from the second comparator  710 B, the up/down counter  720  decreases the value of a stored count. 
     In some embodiments, the polarity of the comparators  710  is reversed depending on the configuration of the up/down counter  720 . For instance, if the up/down counter is configured to count up or down in response to a signal having the second value (e.g., 1 or HI), the polarity of the first comparator  710 A or the second comparator  710 B may be reversed. 
     Moreover, the outputs of the first comparator  710 A and the second comparator  710 B are used to generate a clock enabled signal CLK_EN to enable the up/down counter  720  and the oscillator  730 . In some embodiments, the clock enabled signal CLK_EN is asserted when Vds of the main transistor Mp  220  is below VTH_LOW or above VTH_HIGH. That is, CLK_EN is asserted when Vds is outside of the voltage range &lt;VTH_LOW, VTH_HIGH&gt;. 
     When Vds of the main transistor Mp  220  is lower than VTH_FAST, the third comparator  710 C outputs a signal having the first value (e.g., 0 or LO). Conversely, when Vds of the main transistor Mp  220  reaches or increases above VTH_FAST, the third comparator  710 C output a signal having the second value (e.g., 1 or HI). When Vds if the main transistor Mp  220  exceeds VTH_FAST, the third comparator  710 C sends a signal to the up/down counter  720  that causes the up/down counter to reset to an initial value. For instance, the up/down counter  720  may reset to a value of 0. This causes the control signals Dcontrol, Scontrol, and Rcontrol to rapidly change to the lowest configuration. That is, when Vds of the main transistor Mp  220  exceeds VTH_FAST, the gate voltage of the main transistor Mp  220  is reset to the maximum value, the current sense ratio of the sense transistor Msense  310  is reset to the maximum value, and the resistance of the sense resistor Rsense  370  is reset to the minimum value. In some embodiments, instead of resetting the up/down counter  720 , the output of the third comparator  710 C causes the count of the up/down counter  720  to decrease by a step larger than the count down step triggered by the second comparator  710 B. That is, the output of the third comparator  710 C causes the count of the up/down counter  720  to decrease by a step larger than one. 
     Example Process for Sensing Load Current 
       FIG. 8A  is a flowchart illustrating a method for dynamically adjusting the sensitivity of the dynamic auto-ranging current sense circuit  300 , according to one embodiment. The method may include additional or fewer steps, and steps may be performed in different orders. 
     The controller  390 , as described with reference to  FIG. 3  and  FIG. 7 , monitors  810  the drain-to-source voltage (Vds) of the main transistor Mp  220 . In some embodiments, the controller  390  monitors the drain-to-source voltage (Vds) of the main transistor Mp  220  by monitoring the load voltage (Vload) at an output of the main transistor Mp  220 . The controller  390  then compares Vds to a set of threshold values. For instance, the first comparator  710 A of the controller  390  compares  820  Vds to a first threshold voltage (VTH_LOW), the second comparator  710 B of the controller  390  compares  830  Vds to a second threshold voltage (VTH_HIGH), and the third comparator  710 C of the controller  390  compares  840  Vds to a third threshold voltage (VTH_FAST). 
     Based on the comparison, the controller circuit updates a value stored in the up/down counter  720 . If Vds decreases below VTH_LOW, the controller  390  increases  825  the count stored in up/down counter  720 . If Vds increases above VTH_HIGH, the controller  390  decreases  835  the count stored in the up/down counter  720 . If Vds exceeds VTH_FAST, the controller  390  decreases  845  the count stored in the up/down counter  720  by an amount larger than 1. In some embodiments, if Vds exceeds VTH_FAST, the controller  390  resets the up/down counter  720 . 
     In some embodiments, if Vds is either below VTH_LOW or above VTH_HIGH, the controller  390  turns on oscillator  730  to generate a clock signal CLK to control the rate at which the up/down counter  720  counts up or down. That is, as long as Vds stays below VTH_LOW, the controller  390  decreases the count in response to each clock pulse generated by the oscillator  730  until Vds increases above VTH_LOW. Conversely, as long as Vds stays above VTH_HIGH, the controller  390  increases the count in response to each clock pulse generated by the oscillator  730  until Vds decreases below VTH_HIGH. 
     Based on the value of the up/down counter  720 , the sensitivity of the dynamic auto-ranging current sense circuit  300  is adjusted  850 . That is, based on the value of the up/down counter  720 , the driver  330 , the sense transistor Msense  310 , and the resistor  370  are controlled. 
       FIG. 8B  is a flowchart illustrating a process for adjusting the sensitivity of the sense circuit when the count of the up/down counter decreases, according to one embodiment. That is,  FIG. 8  illustrates a process for adjusting the sensitivity of the sense circuit as the amplitude of the load current increases. In the embodiment of  FIG. 8B , as the load current increases first the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is increased. That is, the sense transistor Msense  310  is controlled to decrease the size of the sense transistor Msense  310  (e.g., by reducing the number of transistors that are active in the sense transistor Msense  310 ). Then, when the sense ratio reaches the maximum value, the resistance value of the sense resistor Rsense  370  is decreased. Finally, when the resistance value of the sense resistor Rsense  370  reaches the minimum value, the bias voltage Vbias provided by the driver  330  is increased. That is, the driver  330  is controlled to increase the number of diode connected transistors that are active. 
     For instance, the controller  390  determines  862  whether the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is at a maximum value. If the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is not at a maximum value, the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is increased  872 . Otherwise, if the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is at a maximum value, the controller  390  determines  864  whether the resistance of the sense resistor Rsense  370  is at a minimum value. If the resistance of the sense resistor Rsense  370  is not at a minimum value, the resistance of the sense resistor Rsense  370  is decreased  874 . Otherwise, if the resistance of the sense resistor Rsense  370  is at a minimum value, the controller  390  determines whether the bias voltage Vbias provided by the driver  330  is at a maximum value. If the bias voltage Vbias is not at a maximum value, the bias voltage Vbias is increased  876 . 
       FIG. 8C  is a flowchart illustrating a process for adjusting the sensitivity of the sense circuit when the count of the up/down counter increases, according to one embodiment. That is,  FIG. 8  illustrates a process for adjusting the sensitivity of the sense circuit as the amplitude of the load current decreases. In the embodiment of  FIG. 8C , as the load current decreases first the bias voltage Vbias is decreased. Then, when the bias voltage Vbias reaches the minimum value, the resistance of the sense resistor Rsense  370  is increased. Finally, when the resistance of the sense resistor Rsense  370  reaches the maximum value, the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is decreased. 
     For instance, the controller  390  determines  882  whether the bias voltage Vbias provided by the driver  330  is at a minimum value. If the bias voltage Vbias is not at a minimum value, the bias voltage Vbias is decreased  892 . Otherwise, if the bias voltage Vbias is at a minimum value, the controller  390  determines  884  whether the resistance of the sense resistor Rsense is at a maximum value. If the resistance of the sense resistor Rsense is not at a maximum value, the resistance of the sense resistor Rsense is increased  894 . Otherwise, if the resistance of the sense resistor Rsense is at a maximum value, the controller determines  886  whether the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is at a minimum value. If the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is not at a minimum value, the sense ratio between the main transistor Mp  220  and the sense transistor Msense  310  is decreased  896 . 
     In other embodiments, the order in which the sense ratio, the bias voltage Vbias and the resistance of the sense resistor Rsense are adjusted may be different from what is shown in  FIGS. 8A and 8B . 
     Since the up/down discrete steps are changed in response to a load current range based on the voltage at the output of the driving transistor Mp  220 , the sense current ratio and the sense resistor scale factor can be controlled and are known. Therefore, a low-resolution ADC can be used while maintaining the dynamic range of the dynamic auto-ranging current sense circuit  300 . 
     While particular embodiments and applications have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and components disclosed herein and that various modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope of the present disclosure.

Metadata:
Filing Date: 20201106
Publication Date: 20220201
Grant Date: 20220201
Priority Date: 20200103
Inventors: OZALEVLI, ERHAN
Miranda, Jr., Evaldo M.
MOHTASHEMI, BEHZAD
Assignee: APPLE INC
CPC Classifications: [{"code": "H03F2200/27", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/78", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/522", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/477", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03G3/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R19/0092", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/471", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/45475", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F3/213", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/522", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/45995", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F3/45376", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/462", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/462", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/555", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R15/09", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01R15/146", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F2200/78", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K17/0822", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03K17/0822", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/27", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F1/0233", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/555", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K2217/0027", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/481", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/555", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03K17/0822", "inventive": true, "first": false, "tree": "[]"}, {"code": "H03F2200/78", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/522", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/519", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F2200/462", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01R15/146", "inventive": true, "first": true, "tree": "[]"}, {"code": "H03F2200/27", "inventive": false, "first": false, "tree": "[]"}, {"code": "H03F3/45376", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 73653570