Abstract:
A multiphase voltage regulator automatically senses the temperature of components from each phase and lowers the current through hot phases while raising the current through cool phases. Dynamic adjustments of current outputs from the various phases of the multiphase regulator allows adaptability to any change in cooling characteristics of the voltage regulator. Dynamically varying outputs from phases provides a load with a constant current while preventing heat damage to system components.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates in general to a system for regulating temperature by controlling currents in a multiphase voltage regulator.  
       BACKGROUND INFORMATION  
       [0002]     A trend in personal computers (PCs) is to provide increased performance from a smaller computer chassis. Increased performance is often achieved by increasing the clock frequency of the central processing unit (CPU). Increased clock frequencies add to performance but require more power and produce more heat. The heat generated is harder to dissipate from a smaller computer chassis because components are packed tighter, cooling components are necessarily limited in size, and the amount of cooling air in the smaller chassis is decreased. Therefore, a smaller chassis makes it more difficult to dissipate the heat generated by various computer components such as the voltage regulator. As a result, PC design requires advanced thinking in cooling as clock speed increases and chassis size decreases.  
         [0003]     Today a common method of cooling the CPU and voltage regulator is by using a heatsink with a fan. This method was acceptable when customers were not as concerned with system noise and when the power demand was not as great. As the power demanded by the processor increases, the RPMs of the fan must increase to properly cool the system. This increase in RPMs causes a corresponding increase in system noise, which could become intolerable. System designers are often required to meet acoustic level specifications before shipping computer systems. The use of active cooling with only a fan makes it a challenge to meet the acoustic level specifications.  
         [0004]     For customers requiring small systems with fast processors, the challenge for a system designer is to incorporate a high-speed processor in a small chassis without sacrificing performance by throttling the processor. Because of the high power demanded by such processors, the temperatures of some components within the voltage regulator circuit reach a critical limit that causes the printed circuit board (PCB) to become discolored and other components to get damaged. Such problems lead to failure of the system, which in turn leads to warranty claims by customers and a decrease in customer satisfaction.  
         [0005]     In an ideal world in which acoustic levels, cost, and space were not issues, devices such as fans, heat-pipes, refrigerants, and heatsinks could be used to cool processors and other components. Another solution is the use of “static current imbalance.” Static current imbalance is a way of imbalancing the currents flowing through different phases of a multiphase voltage regulator. If one phase is prone to build up heat, a system designer can decrease the current in that phase and increase the current in another phase of the multiphase voltage regulator. A drawback to such a method is that a system designer is required to determine in advance where the hot-spots might be in order to set up a current imbalance. If the location of the hot-spots changes due to, for example, a cable blocking air flow to a phase of the voltage regulator, that phase could build up heat and cause damage to system components. Therefore, what is needed is a system for automatically and dynamically changing the current balance in phases of a multiphase voltage regulator to provide a more robust system for managing the heat from such multiphase voltage regulators.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention addresses the foregoing need by providing a dynamic method for preventing the buildup of heat within a phase of a multiphase voltage regulator by steering current from hot phases to cooler phases. In an embodiment of the present invention, the temperatures of components from multiple phases are sensed. The temperatures are compared to set points. The system determines which phase is the hottest and which phase is the coolest. If any phase reaches a set point, current is steered from that phase to a cooler phase.  
         [0007]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     For a more complete understanding of the present invention and the advantages thereof, refer to the following descriptions and the accompanying drawings, in which:  
         [0009]      FIG. 1  illustrates a representative hardware environment for practicing the present invention;  
         [0010]      FIG. 2  illustrates a multiphase voltage regulator for providing current and voltage to a load such as a CPU;  
         [0011]      FIG. 3  illustrates representative steps taken by an embodiment of the present invention; and  
         [0012]      FIG. 4  illustrates a schematic of an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0013]     In the following description, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. Other details have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art.  
         [0014]     The present invention provides an alternative approach to preventing voltage regulator components from reaching a critical temperature that could lead to permanent discoloration of the PCB and component failure. In the layout, of many systems, some components may become obstructed from airflow and thus will operate at higher temperatures than other components. Such effects become more pronounced as systems become smaller. As a result of the way fans in today&#39;s computer systems are controlled, there are times when various phases in the voltage regulator circuit operate at higher temperatures than others. What is more, the operating temperatures within the phases of a voltage regulator may change from time to time. This is especially true if an object such as a cable slips into the path of the airflow of a phase or a foreign object stops the fan from spinning. A system for automatically preventing a buildup of heat in components is needed to account for changing needs of a computer system.  
         [0015]     The present invention provides a system of monitoring the temperatures within the phases of the converter and dynamically steering more current to the cooler phase(s). This steering could be done automatically and on-the-fly without affecting system performance. The computer user would likely be unaware of changes made as part of the present invention. In an embodiment of the present invention, the temperature of each phase of the voltage regulator is measured and currents from the hottest phases are dynamically steered toward cooler phases. Steering current from hot phases reduces the rate at which heat builds up in that phase and allows thermal energy to dissipate into the surrounding environment.  
         [0016]     When the temperature of a phase gets within a threshold of the set point, some of the current from that phase can be dynamically steered to a cooler phase. This shift in current does not affect the maximum current provided by the voltage regulator but allows the phase that was running hot to be cooled by diverting its current to other phase(s).  
         [0017]     The modem multiphase voltage regulators provide a method of sensing the output current in each phase. The regulators provide closed-loop control generally designed to equalize the average current flowing through each phase. Resistors are provided in a feedback path to sense the current flowing through each phase. Equal resistor values in each phase provide equal current flow through each phase. With static current imbalance methods, the resistor values can be adjusted during the design phase to provide unequal current in each phase. The drawback to this approach is that the resistor values are static. The resister values are determined during initial board design and are not changed if the temperature profile of the system changes over time.  
         [0018]     The present invention does not have the same limitations for adjusting the resistor values only during the design phase. An embodiment of the present invention allows for continuous, real-time, automatic monitoring of a phase component&#39;s temperature and dynamic adjustment of the current through that phase. Because the current through a component directly relates to the temperature of the component, adjusting the current also adjusts the component&#39;s temperature.  
         [0019]     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.  
         [0020]      FIG. 1  illustrates a representative hardware environment for practicing the present invention. Item  100  represents a motherboard architecture including a multiphase voltage regulator  102  and a CPU  106 . Voltage regulator  102  includes phases  114 ,  116 , and  118  for carrying current to CPU  106  over line  104 . To provide context to an embodiment of the present invention,  FIG. 1  illustrates northbridge  108 , memory  112 , southbridge  110 , and PCI  114  as part of motherboard architecture  100 .  
         [0021]      FIG. 2  is a schematic showing a voltage regulator  200  for providing a voltage and current to load  212 . Voltage regulator  202  could be a regulator  102  for providing power to CPU  106  as shown in  FIG. 1 . Voltage regulator controller  202  includes two signals from  224  and  222  for controlling the output current of FETs  210  and  208 . FETs  210  and  208  could be a bank of field effect transistors and associated components for providing output currents  214  and  216  based on control signals  224  and  222 . Through pins  220  and  226 , voltage regulator controller  202  receives feedback signals for controlling outputs from pins  224  and  222 . Resistors  206  and  204  may be referred to as “sense resistors.” The values of sense resistors  204  and  206  affect the signals received at pins  220  and  226 . In turn, controller  202  determines the levels of currents  214  and  216  by adjusting signals from pins  224  and  222 . Currents  214  and  216  combine to provide load  212  with current  218 . If the value of resistors  206  and  204  are equal, voltage regulator controller  202  is designed to use signals from  224  and  222  to produce equal currents  214  and  216  from FETs  210  and FETs  208 . However, the values for resistors  206  and  204  can be adjusted during the design phase to provide unequal values for currents  214  and  216 . The drawback to this approach is that the values for resistors  206  and  204  are static. The values of resistors  204  and  206  are chosen during the initial design of motherboard  100  and cannot be changed as the temperature profile of the system changes over time. What is needed is an improved system for changing the currents provided by each phase in the voltage regulator circuit by changing feedback to pins  220  and  226 .  
         [0022]      FIG. 3  illustrates representative steps taken by an embodiment of the present invention. In step  316 , the system is started and in step  302  the temperature of each phase is measured. The temperature of a phase may be measured by a thermistor located in close proximity to the bank of FETs for that phase.  FIG. 2  illustrates banks of FETs as items  210  and  208 . Items  210  and  208  each represent banks of FETs and associated components for powering each phase of the voltage regulator circuit. Because of switching and conduction losses within the FETs of items  210  and  208 , these areas tend to be the hottest in the voltage regulator circuit. Therefore, for purposes of measuring the temperature of the voltage regulator in step  302  of  FIG. 3 , the FETs  210  and  208  provide an optimal point for placement of temperature transducers. In step  304 , the temperature of each phase is compared to a critical temperature or set point. A critical temperature can be a temperature known to cause damage to some circuit components and reduced reliability of other components. A set point could be a temperature below the critical temperature. In step  306 , a determination is made whether a temperature of a phase is within the limits for safe operation. In step  306 , if the temperature is not equal or greater than the set point, the system implements a delay in step  312  and the system cycles to step  302  for more temperature readings. If step  306  determines that the temperature of a phase is equal or greater than a set point, then in step  308  the system determines the highest difference between phase temperatures. In step  310 , the system can steer current from the hottest to the coolest phase. Steering current from the hottest phase reduces the rate at which the hottest phase produces heat. After steering current from the hottest to the coolest phase, the system delays in step  314  for a period and then restarts the reading of temperatures in step  302 . If a temperature is not equal to a set point in step  306 , then step  312  delays fory seconds and then step  302  is repeated.  
         [0023]      FIG. 4  illustrates a schematic of a voltage regulator  400  which is an embodiment of the invention. Voltage regulator  400  could be configured such as voltage regulator  102  for powering CPU  106  as shown in  FIG. 1 . The system in  FIG. 4  includes a voltage regulator controller  402  for producing currents  416  and  414  to combine into current  418  for load  412 . The circuit in  FIG. 4  includes additional elements in parallel with sense resistors  404  and  406  for adjusting the effective resistance of the sense resistors which provide feedback to voltage regulator controller  402 . Adjusting the effective value of the sense resistor providing feedback to voltage regulator controller  402  provides a way of increasing or decreasing current  414  or current  416  while still achieving the desired current  418  for load  412 . Temperature transducers  440  and  442  provide current balance controller  444  with signals representing the temperatures of FETs  410  and  408 . Items  440  and  442  could be thermistors which provide variable resistances based on the temperatures of FETs  410  and  408 . Current balance controller  444  compares the temperatures from transducers  440  and  442  and determines whether FETs  410  or  408  are close to a temperature known to cause damage to circuit components. If current balance controller  444  determines that FETs  410  or  408  are at or near a critical temperature, current balance controller  444  can adjust the levels from pins  450  and  452  to turn on or off transistors  454  or  430 , which has the effect of adjusting the effective resistor values providing feedback through pins  446  and  448  to voltage regulator controller  402 . If transistor  430  is turned off, then the effective sense resistance of the second phase of the circuit is the value of resistor  404 . However, if transistor  430  is turned on, then the effective sense resistance is determined by resistors  404  and  438  in parallel. If  404  and  438  have the same resistance value, then turning on transistor  430  would have the effect of cutting the effective sense resistance in half. Likewise, the effective sense resistance to pin  446  can be changed by toggling transistor  454 . Current balance controller  444  can adjust the output level from pin  452  to turn on or off transistor  454 . If transistor  454  is turned off, the effective sense resistance is just the value of resistor  406 . However, if transistor  426  is turned on, the effective sense resistance to pin  446  is determined by taking the value of resistor  420  and the value of resistor  406  in parallel.  
         [0024]     In the embodiment depicted in  FIG. 4 , transistor  428  is configured for controlling transistor  454 . Resistor  422  is a pull-up resistor. Resistor  424  is a current limiting resistor for transistor  428 . If current balance controller  444  outputs a low voltage from pin  452 , the base of transistor  428  sees the low voltage and transistor  428  operates in cutoff mode. When transistor  428  operates in cutoff mode, transistor  454  essentially sees 12 volts at its gate. Transistor  454  is depicted in  FIG. 4  as an N-channel enhancement mode field effect transistor from Fairchild Semiconductor, although other devices could be used in embodiments of the present invention. When the gate-source voltage of transistor  454  is forward biased, transistor  454  conducts current and the sense resistance in the feedback circuit to pin  446  is calculated essentially by adding resistor  406  and resistor  420  in parallel. The gate-source voltage of transistor  454  is forward biased when transistor  428  is turned off. When transistor  428  is turned on by applying a voltage signal from pin  452  of current balance controller  444 , current conducts from the collector to the emitter of transistor  428  according to the operational characteristics including the β value of transistor  428 . Depending on the value of resistor  424 , the value of resistor  422 , and the operational characteristics of transistors  428  and  454 , the level of the voltage output from pin  452  can be adjusted to turn off transistor  454  and essentially remove resistor  420  from the sense resistor circuit by preventing current flow through transistor  454 .  
         [0025]     In the embodiment shown in  FIG. 4 , commonly known circuit elements are shown for varying the sense resistance in the feedback circuit to pins  446  and  448  of voltage regulator controller  402 . For example, transistor  428  is shown as a NPN bipolar junction transistor. One of ordinary skill in the art will recognize that other elements can be used for varying the feedback signal to the voltage regulator controller. Further, a voltage regulator controller in another embodiment of the present invention may require feedback, for instance, by a digital signal or other means. The choices of circuit elements in  FIG. 4  are not meant to limit claim scope to certain elements, and one of ordinary skill in the art will recognize other circuit elements for controlling currents  414  and  416 . Although the foregoing analysis focuses on the phase of the multiphase voltage regulator for producing current  414 , the same analysis can be applied to the phase that produces current  416 . Also, one of ordinary skill in the art can easily calculate values for resistors  406 ,  420 ,  422 ,  424  and likewise for resistors  404 ,  438 ,  436 ,  434  without undue experimentation for a particular application of the present invention. However, in an embodiment, resistors  406  and  404  could be 750 ohms, resistors  420  and  438  could be 7150 ohms, resistors  422  and  436  could be 47 Kohms, and resistors  424  and  434  could be 1 Kohms.  
         [0026]     Therefore, current balance controller  444  can be used to sense the temperatures of FETs  410  and  408 . Using these temperature values, the current balance controller  444  can turn on or off transistors  454  and  430  to affect the sense resistance values in the feedback circuits delivered to voltage regulator controller  402  through pins  446  and  448 . If the temperature in FET  410  is determined to be at a critical level or set point, current balance controller  444  may cause current  416  to increase and current  414  to decrease in order to achieve the same current  418  while lessening the burden on the first phase of voltage regulator  400 .  
         [0027]     The example shown in  FIG. 4  illustrates a voltage regulator with only two phases. The present invention is not limited to a voltage regulator with only two phases and can include voltage regulators with three or more phases. For purposes of simplification, FETs  410  and  408  have been shown in block form. One of ordinary skill in the art will understand that items  410  and  408  include one or more FET transistors and associated components for providing currents  414  and  416 . Also, the subject matter of the claims is not limited to embodiments which use field effect transistors, as other types of transistors may be used. Current balance controller  444  is shown in block diagram form, but one of ordinary skill in the art will recognize that any microcontroller or similar device can be used for implementing the steps as shown in  FIG. 3  for comparing phase temperatures, determining whether the phase temperatures are within a critical range, and adjusting the outputs from pins  450  and  452  to adjust the effective sense resistance seen by pins  446  and  448  of voltage regulator controller  402 . For example, current balance controller  444  could be implemented by a programmable system on a chip device (PSoC) which is available from Cypress Semiconductor.  
         [0028]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.