Patent Publication Number: US-2004046534-A1

Title: Reduction of external component count in variable voltage integrated dc/dc converter

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to electrical circuits and more particularly to direct current (DC) to direct current (DC) power conversion and regulation.  
       BACKGROUND OF INVENTION  
       [0002] There is an ever increasing demand for power conversion and regulation circuitry to operate with increased efficiency and reduced power to accommodate the continuous reduction in size of electronic portable devices. Many times these devices are battery powered, and it is desirable to utilize as little power as possible to operate these devices, so that the battery life is extended. Therefore, the prior 5-volt industry standard has decreased to a 3.3 volt industry standard, which may soon be replaced by an even lower standard. Voltage regulators have been implemented as an efficient mechanism for providing a regulated output in power supplies. One such type of regulator is known as a switching regulator or switching power supply, which controls the flow of power to a load by controlling the on and off duty-cycle of one or more power switches coupled to the load. Many different classes of switching regulators exist today.  
       [0003] Due to the various industry power supply standards, a variable voltage DC/DC converter allows designers to program a desired supply voltage based on the standard being implemented. The variable voltage DC/DC converter gives the designer control of the output voltage by selecting values for certain external components, but also requires that the designer provide several compensation components to compensate for phase shifts in the output voltage that effect a desired negative feedback. For example, certain variable voltage DC/DC power supply devices require that the designer provide 6-12 external compensation components. The external compensation components are required so that the poles and zeroes associated with an amplifier device on the variable voltage DC/DC converter remain stable and do not move during normal operation. The conventional variable voltage DC/DC converter employs a single error amplifier that employs customer provided external compensation components configured to provide the required output voltage, poles and zeroes. The external compensation components require a large amount of real-estate to implement the desired DC/DC conversion.  
       [0004]FIG. 1 illustrates a conventional variable DC/DC converter system  10  comprised of an integrated control circuit  12  and customer supplied components that provide both the feedback voltage and the compensation for the variable DC/DC converter system  10 . The integrated control circuit  12  includes an input feedback pin (P 1 ), an output feedback pin (P 2 ), and an output voltage pin (P 3 ). The input feedback pin (P 1 ) is coupled to a negative terminal of an amplifier device  14 . The amplifier device  14  compares a voltage at input feedback pin (P 1 ) with a reference voltage V REF . The output of the amplifier device  14  is provided at the output feedback pin (P 2 ), and as input to a pulse width modulator  16 . The pulse width modulator  16  provides a switching signal to a driver  18  coupled to the output voltage pin (P 3 ). The output of the amplifier device  14  controls the duty cycle of the switching signal provided by the pulse width modulator  16 . A customer supplied coil L is coupled to the output voltage pin (P 3 ) and a charge capacitor C.  
       [0005] Energy builds up in the inductor L when voltage is applied to the inductor L, which is transferred to charge the capacitor C to an output voltage V OUT . A supply voltage V SUPPLY  is provided at the inductor L through the driver  18  controlled by the pulse width modulator  16 . The output voltage V OUT  on the capacitor C is a function of the duty cycle of the pulse width modulator  16 . The output voltage V OUT  is fed back to the input feedback pin (P 1 ) of the control circuit  12  through a first impedance component  22 . The control circuit  12  utilizes the feedback signal to continuously adjust the duty cycle of the switching signal driving the inductor L, and as a result, providing the regulated output voltage V OUT . The output voltage V OUT  is a function of a voltage divider formed by the first impedance component Z 1  and a resistor R, and the reference voltage V REF .  
       [0006] The gain of the amplifier  14  is a function of a second impedance component  20  and the first impedance component  22 . The first impedance component  22  and the second impedance component  20  are each comprised from about 3 to about 6 different components. The components of the first impedance component  22  and the second impedance component  20  control the gain, control the constants and control the output voltage of the conventional variable DC/DC converter system  10 . The components of the first impedance component  22  and the second impedance component  22  include compensation components. The compensation components are provided to maintain a phase shift under 180°, caused by the inductor L and capacitor C combination (L-C filter), so that the feedback remains negative.  
       SUMMARY OF INVENTION  
       [0007] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.  
       [0008] The present invention relates to a variable voltage DC/DC converter system that separates the feedback voltage function and the compensation function of the DC/DC converter system into two different devices. A compensation device and compensation components can then be integrated into a single integrated circuit. A feedback voltage device is integrated into the single integrated circuit. The output voltage of the DC/DC converter is fed back to a voltage divider circuit. The voltage divider circuit includes a first resistor and a second resistor. The values of the first resistor and the second resistor determine the output voltage of the DC/DC converter system. The first and second resistors can be external to the integrated circuit and selectable by a customer. Alternatively, the first resistor is integrated into the integrated circuit, while the second resistor is external to the integrated circuit and selectable by the customer. The feedback voltage device receives the feedback signal through the voltage divider and provides the feedback signal to the compensation device. The compensation device then provides a duty cycle control signal that controls the duty cycle of a pulse width modulator. The pulse width modulator switches a supply voltage “ON” and “OFF” to an output pin. A customer supplied inductor and capacitor combination provide the desired output voltage based on the duty cycle of the pulse width modulator based on the selected resistor values.  
       [0009] In one aspect of the invention, the compensation function of the DC/DC converter system is comprised of an amplifier device, a first impedance component coupled to the input of the amplifier device, and a second impedance component coupled between the input and output of the amplifier device. The first and second impedance components include a plurality of compensation components that compensate for an output voltage phase shift to maintain a phase shift under 180°, so that the feedback signal remains negative. The feedback device is comprises of a wide band amplifier device that includes a third resistor coupled between an input and an output of the wide band amplifier device. The first and second resistors determine the output voltage of the system, while the first and third resistors determine the gain of the system to mitigate amplifier offset. The present invention also includes methods for fabricating a variable DC/DC converter system and a method for operating a DC/DC converter system in accordance with different aspects of the present invention.  
       [0010] The following description and the annexed drawings set forth certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 illustrates a schematic block diagram of a prior art DC/DC converter.  
     [0012]FIG. 2 illustrates a schematic block diagram of a DC/DC converter system in accordance with an aspect of the present invention.  
     [0013]FIG. 3 illustrates a schematic block diagram of a DC/DC converter system employing two external resistors for selecting an output voltage in accordance with an aspect of the present invention.  
     [0014]FIG. 4 illustrates a schematic block diagram of a DC/DC converter system employing a single external resistor for selecting an output voltage in accordance with an aspect of the present invention.  
     [0015]FIG. 5 illustrates a flow diagram of a methodology for providing a DC/DC converter system in accordance with an aspect of the present invention.  
     [0016]FIG. 6 illustrates a flow diagram of a methodology for selecting an output voltage of a DC/DC converter system in accordance with an aspect of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0017] The present invention relates to a variable DC/DC converter system that includes a feedback voltage device and a compensation device. Separation of the feedback voltage function and the compensation function results in a reduction of the external component count. The compensation device and compensation components are integrated into a single integrated circuit. The feedback voltage device is integrated into the single integrated circuit. Therefore, the values of a first resistor and a second resistor determine the output voltage of the DC/DC converter system. In one aspect of the invention, the first and second resistors are external to the integrated circuit and selectable by a customer. In another aspect of the invention, the first resistor is integrated into the integrated circuit, while the second resistor is external to the integrated circuit and selectable by the customer.  
     [0018]FIG. 2 illustrates a variable DC/DC converter system  40  in accordance with an aspect of the present invention. The DC/DC converter system  40  can be, for example, a switching power supply. The variable DC/DC converter system  40  includes an integrated control circuit  42  with customer supplied components provided to select a desired output voltage. The integrated control circuit  42  includes a feedback device  44  and a compensation device  46 . The feedback device  44  sets up the feedback voltage for the system  40 , while the compensation device  46  provides the compensation for the system  40 . The compensation device  46  facilitates maintaining a phase shift under 180°, caused by an output inductor (LA) and an output capacitor (CA) combination (L-C filter), so that the feedback remains negative. Since the compensation components are provided on the integrated control circuit  42 , the customer only needs to provide two resistors RA and RB to provide the necessary feedback and to select the desired output voltage.  
     [0019] The integrated control circuit  42  includes an input feedback pin (PA) and an output voltage pin (PB). The input feedback pin (PA) is coupled to the feedback device  44 . The feedback device  44  provides the selected output voltage based on a first customer supplied resistor RA and a second customer supplied resistor RB. The output of the feedback device  44  is coupled to the compensation device  46 . The compensation device  46  provides components for compensating the system  40 . Therefore, by implementing the feedback device  44  and the compensation device  46  into an integrated control circuit  42 , the customer supplied components required to set the output voltage and compensate the system  40  are reduced. The output of the compensation device  46  is provided as input to a pulse width modulator  48 . The pulse width modulator  48  provides a switching signal to a driver  50  coupled to the output voltage pin (PB). The output of the compensation device  46  controls the duty cycle of the switching signal provided by the pulse width modulator  48 . A first end of the customer supplied inductor LA is coupled to the output voltage pin (PB) and a second side of the customer supplied inductor LA is coupled to a customer supplied output charge capacitor CA.  
     [0020] Energy builds up in the inductor LA when voltage is applied to the inductor LA, which is transferred to charge the capacitor CA to an output voltage V OUTA . A supply voltage V SUPPA  is provided at the inductor LA through the driver  50  controlled by the pulse width modulator  48 . The pulse width modulator  48  switches the supply voltage V SUPPA  “ON” and “OFF” between power and ground to provide a square wave to the output voltage pin (PB). The output voltage V OUTA  on the capacitor CA is a function of the duty cycle of the square wave provided by the pulse width modulator  48 . A feedback signal from the output voltage V OUTA  of the capacitor CA is fed back to the input feedback pin (PA) of the control circuit  42  through the customer supplied resistor RB. The control circuit  42  utilizes the feedback signal to continuously adjust the duty cycle of the square wave control pulse driving the inductor LA, and as a result, providing a regulated output voltage V OUTA . The feedback voltage and the output voltage V OUTA  is a function of a voltage divider formed by the customer supplied resistor RB and the customer supplied resistor RA provided at the input pin (PA).  
     [0021]FIG. 3 illustrates a variable DC/DC converter system  70  in accordance with another aspect of the present invention. The DC/DC converter system  70  can be, for example, a switching power supply. The variable DC/DC converter system  70  includes an integrated control circuit  72  with customer supplied components provided to select a desired output voltage. The integrated control circuit  72  includes a first amplifier  74  and a second amplifier  82 . The first amplifier  74  sets up the feedback voltage for the system  70 , while the second amplifier  82  provides the compensation for the system  82 . Since the compensation components are provided on the integrated circuit, the customer only needs to provide a first resistor R 1  and a second resistor R 2  to provide the necessary feedback and to select the desired output voltage. The integrated control circuit  72  includes an input feedback pin (P INI ) and an output voltage pin (P OUT1 ). A first end of a customer supplied inductor L 11  s coupled to the output voltage pin (POUTI) and a second side of the customer supplied inductor L 1  is coupled to a customer supplied output charge capacitor Cl. The customer supplied output charge capacitor Cl charges to an output voltage V OUTI  during normal operation of the DC/DC converter system  70 .  
     [0022] During normal operation, energy will build up in the inductor LI when voltage is applied to the inductor L 1 , which is transferred to charge the capacitor C 1  to an output voltage V OUTI  when the voltage is removed. A supply voltage V SUPP1  is provided at the inductor L 1  through the driver  88  controlled by the pulse width modulator  86 . The pulse width modulator  86  switches the supply voltage V SUPP1  “ON” and “OFF” between power and ground to provide a square wave to the output voltage pin (P OUT1 ). The output voltage V OUTI  of the capacitor C 1  is fed back to the integrated control circuit  72  though the second resistor R 2 . The control circuit  72  utilizes the feedback signal to adjust the duty cycle of the square wave control pulse driving the inductor LI, and as a result, providing the regulated output voltage V OUT1 ) set by a voltage divider formed by the first resistor R 1  and the second resistor R 2 . The first resistor R 1  changes the operating point of the system  70 , but not the gain of the system  70 . Therefore, the voltage divider selects the output but does not affect the gain of the first amplifier  74 . The input feedback pin (P INI ) is coupled to a negative terminal of the first amplifier  74 . A third resistor R 3  is provided from the output of the first amplifier  74  to the input of the first amplifier  74 . The second resistor R 2  and the third resistor R 3  set up the gain of the first amplifier  74 . The gain can be selected to compensate for offset of the first amplifier  74 . For example, the gain can be in the range of about 1 times to about 10 times the input voltage. A reference voltage V REF1  is provided at the positive terminal of the first amplifier  74 .  
     [0023] The output of the first amplifier  74  is coupled to a negative terminal of the second amplifier  82  though a first impedance component (Z 1 )  78 . A reference voltage V REF2  is provided at the positive terminal of the second amplifier  82 . The second amplifier  82  is driven with the low impedance output of the first amplifier  74 , thus, facilitating stabilization of the second amplifier  82 . In one aspect of the invention, the first amplifier  74  is a wide band amplifier, which will add high frequency poles. However, the high frequency poles do not effect the operation of the second amplifier  82 . The gain from the first amplifier  74  is general constant.  
     [0024] A second impedance component (Z 2 )  80  is coupled from the output of the second amplifier  82  to the negative terminal of the second amplifier  82 . The first impedance component  78  and the second impedance component  80  include compensation components to compensate the system  70 . The compensation components are provided to maintain a phase shift under 180°, caused by the customer supplied output inductor L 1  and the customer supplied capacitor C 1  combination (L-C filter), so that the feedback remains negative. The output of the second amplifier  82  is provided as input to a pulse width modulator  86 . The pulse width modulator  86  provides a switching signal to a driver  88  coupled to the output voltage pin (P OUT1 ). The output of the second amplifier  82  controls the duty cycle of the switching signal provided by the pulse width modulator  86 .  
     [0025]FIG. 4 illustrates a variable DC/DC converter system  110  having an alternate configuration in accordance with yet another aspect of the present invention. The variable DC/DC converter system  110  includes an integrated control circuit  112  with a single customer supplied resistor (R 4 ) provided to select a desired output voltage. The integrated control circuit  112  includes a first amplifier  114  and a second amplifier  120 . The first amplifier  114  sets up the feedback voltage for the system  110 , while the second amplifier  120  provides the compensation for the system  110 . Since the compensation components are provided on the integrated circuit, the customer only needs to provide a single resistor R 4  to provide the necessary feedback and to select the desired output voltage. A second resistor R 5  is provided on the integrated control circuit  112 . The integrated control circuit  112  includes a first input feedback pin (P IN2 ), a second input feedback pin (P IN3 ) and an output voltage pin (P OUT2 ). A first end of a customer supplied inductor L 2  is coupled to the output voltage pin (P OUT2 ) and a second side of the customer supplied inductor L 2  is coupled to a customer supplied output charge capacitor C 2 . The customer supplied output charge capacitor C 2  charges to an output voltage V OUT2  during normal operation of the DC/DC converter system  110 .  
     [0026] A supply voltage V SUPP2  is provided at the inductor L 2  through the driver  126  controlled by the pulse width modulator  124 . The pulse width modulator  124  switches the supply voltage V SUPPA  “ON” and “OFF” between power and ground to provide a square wave to the output voltage pin (P OUT2 ), which builds up energy in the inductor L 2 , which is transferred to charge the capacitor C 2  to the output voltage V OUT2 . The output voltage V OUT2  of the capacitor C 2  is fed back to the integrated control circuit  112  to the second input feedback pin (P IN3 ). The second resistor R 5  is disposed internally to the integrated control circuit  112  between the first input feedback pin (P IN2 ) and the second input feedback pin (P IN3 ). The integrated control circuit  112  utilizes the feedback signal to adjust the duty cycle of the control pulse driving the inductor L 2 , and as a result, providing a regulated output voltage V OUT2  set by the customer supply resistor R 4  and the second resistor R 5  residing on the integrated control circuit  112 . The first input feedback pin (PIN 2 ) is coupled to a negative terminal of the first amplifier  114 . A third resistor R 6  is provided from the output of the first amplifier  114  to the input of the first amplifier  114 . The second resistor R 5  and the third resistor R 6  set up the gain of the first amplifier  114  to compensate for offset of the first amplifier  114 . A reference voltage V REF3  is provided at the positive terminal of the first amplifier  114 .  
     [0027] The output of the first amplifier  114  is coupled to a negative terminal of the second amplifier  120  though a first impedance component (Z 3 )  118 . A reference voltage V REF4  is provided at the positive terminal of the second amplifier  120 . The second amplifier  120  is driven with the low impedance output of the first amplifier  114 , thus, facilitating stabilization of the second amplifier  120 . The first amplifier  114  and the second amplifiers  120  can be wide band amplifiers. A second impedance component (Z 4 )  122  is coupled from the output of the second amplifier  120  to the negative terminal of the second amplifier  120 . The first impedance component  118  and the second impedance component  122  include compensation components to compensate the system  110 . The compensation components are provided to maintain a phase shift under 180°, caused by the customer supplied output inductor L 2  and the customer supplied capacitor C 2  combination (L-C filter), so that the feedback remains negative. The output of the second amplifier  120  is provided as input to a pulse width modulator  124 . The pulse width modulator  124  provides a switching signal to a driver  126  coupled to the output voltage pin (P OUTA ). The output of the second amplifier  120  controls the duty cycle of the switching signal provided by the pulse width modulator  124 .  
     [0028] In view of the foregoing structural and functional features described above, methodologies in accordance with various aspects of the present invention will be better appreciated with reference to FIGS.  5 - 6 . While, for purposes of simplicity of explanation, the methodologies of FIGS.  5 - 6  are shown and described as executing serially, it is to be understood and appreciated that the present invention is not limited by the illustrated order, as some aspects could, in accordance with the present invention, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect the present invention.  
     [0029]FIG. 5 illustrates one particular methodology for fabricating a variable DC/DC converter. The methodology begins at  200  where a compensation amplifier is selected. The methodology then proceeds to  210 . At  210 , compensation components are determined to provide appropriate compensation for the system. The methodology then advances to  220 . At  220 , a feedback amplifier is selected. In one aspect of the invention, the feedback amplifier and the compensation amplifier are wide band amplifiers. The methodology then proceeds to  230  where internal feedback components are determined. The internal feedback components can include a first feedback resistor, or alternatively, a first feedback resistor and a second feedback resistor. If the internal feedback components includes a first feedback resistor, the voltage output can be selected by employing two external resistors to set the feedback and the output voltage. If the internal feedback components includes a first feedback resistor and a second feedback resistor, the voltage output can be selected by employing a single external resistor to set the feedback and the output voltage. A pulse width modulator and a driver are then selected at  240 . The variable DC/DC converter device is then fabricated on a die with external pins for feedback and voltage output.  
     [0030]FIG. 6 illustrates one particular methodology for selecting and operating a variable DC/DC converter in accordance with an aspect of the invention. The methodology begins at  300  where a desired output voltage is determined based on a particular implementation. The methodology then proceeds to  310 . At  310 , at least one external feedback resistor is selected to provide a desired output voltage. The methodology then advances to  320 . At  320 , an output inductor is selected. The methodology then proceeds to  330 . At  330 , an output capacitor is selected. At  340 , the at least one selected external feedback resistor is coupled to one or more input feedback pins. The output inductor is coupled to an output feedback pin on one end and the charge capacitor on the other end. The capacitor is grounded on one end and provides an output voltage on the end connected to the inductor. The output voltage is then fed back to one of the one or more selected resistors, or a second input feedback pin if one of the feedback resistors resides on the die. The methodology then proceeds to  350  where power is applied to the DC/DC converter.  
     [0031] What has been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.