Abstract:
An integrated circuit includes an output terminal. A plurality of feedback terminals receives a feedback signal. A voltage regulator has a feedback input in communication with the plurality of feedback terminals to receive the feedback signal. The voltage regulator has a power output in communication with the output terminal. The voltage regulator is responsive to the feedback signal to generate the power output.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 10/846,717 filed May 13, 2004. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    An aspect of this invention relates to power systems for electronic circuits. 
       BACKGROUND 
       [0003]    Most modern electronic systems are powered by one or more voltage regulators that provide regulated output power to the system. A typical voltage regulator includes a feedback signal extending from the power input to the system back to the DC/DC converter. The feedback signal is used in the voltage regulator to regulate the output power at the input to the system, thereby reducing error in the regulated output that might be caused by conduction losses between the voltage regulator and the system. 
         [0004]      FIG. 1  shows a typical conventional feedback system used with a voltage regulator  12  and electronic system  14 . An integrated circuit  16  may include the voltage regulator  12  and connect via a pin  17  to external filter components such as an output inductor  18  and output capacitor  20 . A feedback signal  22  from the regulated output, Vout, may connect to the voltage regulator via a pin  19 . The feedback signal  22  is typically received from a junction of the output inductor  18  and the output capacitor  20  so that gain and phase associated with the filter components is included within the control loop of the voltage regulator  12 . The feedback signal may additionally be obtained from a point nearer to the input to the electronic system  14  to minimize the error caused by parasitic effects such as conduction losses and leakage inductance. 
         [0005]    Although, sensing the junction of the filter components to generate the feedback signal may improve the stability and accuracy of the regulated output of the voltage regulator  12 , if the line carrying the feedback signal becomes electrically degraded, the regulated output may drift outside of the regulation limits causing the voltage regulator  12  to shutdown. 
       SUMMARY 
       [0006]    An integrated circuit comprising a feedback terminal to receive a feedback signal. A voltage regulator has a feedback input to receive the feedback signal from the feedback terminal. The voltage regulator has a power output in communication with an output terminal. The voltage regulator being responsive to the feedback signal, to generate the power output. A voltage generator to generate a pull-up voltage having an amplitude greater than a DC voltage amplitude of the power output. The pull-up voltage being derived separately from the power output. A pull-up resistor in communication with the pull-up generator and the feedback input of the voltage regulator. 
         [0007]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a block diagram of an aspect of a conventional power supply feedback system. 
           [0009]      FIG. 2  is a block diagram of a power distribution system that includes an aspect of a feedback protection system. 
           [0010]      FIG. 3  is a block diagram of a power distribution system that includes another aspect of a feedback protection system. 
           [0011]      FIG. 4  is a block diagram of a power distribution system that includes another aspect of a feedback protection system. 
       
    
    
       [0012]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION  
       [0013]      FIG. 2  shows a block diagram of an aspect of a power distribution system  30  for supplying a regulated output voltage, Vout, to a system  35  such as an electronic system. The power distribution system  30  includes a feedback protection system  50  to protect the power distribution system  30  from the potential effects of a feedback line  32  that is electrically degraded from normal operation, wherein electrically degraded is defined as having an increased impedance that causes a feedback signal on the feedback line  32  to be of insufficient quality for the control loop of the power distribution system  30  to control the regulated output voltage. The increased impedance of the feedback line  32  may be due to any cause such as a cold solder joint, the feedback line  32  being partially disconnected from the regulated output voltage, and the feedback line  32  being completely disconnected from the regulated output voltage. 
         [0014]    A voltage regulator  34  may generate the regulated output voltage, Vout, from an input voltage, Vin, and supply that regulated output voltage to the system  35 . The voltage regulator  34  may be any type of voltage regulator such as switching regulators and linear regulators. An integrated circuit  36  may include the voltage regulator  34  and connect via one or more output terminals  38  to external filter components such as an output inductor  40  and output capacitor  42 . Any type of terminals may be used for the output terminals  38  such as pins, ball grid arrays, and connectors. The voltage regulator  34  may generate a power output, Vc, that is filtered by the external filter components to generate Vout. The power output, Vc, may be any type of power output to be used for powering the system  35  such as a chopped output of a switching regulator that is filtered by the external filter components, and a DC output from either a switching regulator or a linear regulator. 
         [0015]    The feedback line  32  may connect from the regulated output, Vout, to the voltage regulator via one or more feedback terminals  44 . Any type of terminals may be used for the feedback terminals  44  such as pins, ball grid arrays, and connectors. A feedback signal carried on the feedback line  32  may be sensed at a junction of the output inductor  40  and the output capacitor  42  such as near an input  37  to the system  35 . 
         [0016]    The integrated circuit  36  may include a feedback protection system to protect the system  35  if the feedback line  32  is electrically degraded. In another aspect, the feedback protection system  50  may monitor the feedback line  32  and detect if feedback line  32  is electrically degraded. The feedback protection system  50  may include a pull-up resistor  46  connected between the feedback line  32  and a pull-up voltage. The pull-up resistor  46  may apply the pull-up voltage through the relatively high impedance of the pull-up resistor  46  to the feedback line  32 . The pull-up resistor  46  advantageously causes the output voltage to decrease if the feedback line  32  is electrically degraded. 
         [0017]    In one aspect, when the feedback line  32  is electrically degraded, a voltage that is greater than Vout is applied through the pull-up resistor  46  to the voltage regulator  34  causing the control loop of the voltage regulator  32  to reduce the conduction time of the converter  32  leading to a decrease in the output voltage. Conventional DC/DC converters that have a disconnected feedback line is electrically degraded, typically generate a greater output voltage that may cause an overvoltage circuit to trigger, leading to shutdown of the converter. The feedback protection circuit  50  may advantageously operate if the feedback line  32  is electrically degraded to cause the control loop of the voltage regulator  32  to decrease the output voltage instead of relying on a overvoltage protection circuit. In addition, the feedback protection circuit  50  may cause the output voltage to decrease without first increasing. 
         [0018]    In another aspect, if the feedback line  32  is electrically degraded from the integrated circuit  36  the pull-up voltage that is applied through the pull-up resistor  46  is high enough to cause the overvoltage circuit in the voltage regulator  34  to trigger an overvoltage shutdown of the voltage regulator  34  causing the output voltage to decrease to approximately zero volts. Although the overvoltage circuit operates to shutdown the voltage regulator  34  if the feedback line  32  is electrically degraded, the output voltage does not initially increase, but instead initially decreases. Although the shutdown circuit eventually causes the voltage regulator  34  to shutdown, the initial decrease in the output voltage may be due to operation of either the control loop or the overprotection circuit depending on their relative speed of operation. 
         [0019]    The pull-up resistor  46  may be any suitable resistance to pull-up the feedback line  32  to approximately the pull-up voltage if the feedback line  32  is electrically degraded. Exemplary values of the resistance may range from approximately 100 ohms to 1 Meg ohms, although the resistance may be greater than or less than this range depending on several design factors such as the differential between the pull-up voltage and the output voltage, and the impedance of interface circuits that connect to the pull-up resistor  46 . Although only a single pull-up resistor  46  is shown, another pull-up resistor may be coupled to a feedback return line if differential feedback sensing is employed. 
         [0020]    A voltage generator  54  may generate the pull-up voltage that is applied to the pull-up resistor  46 . The pull-up voltage may be any voltage that is greater than Vout such as a voltage that is approximately 20% greater than Vout. Any energy source may be used for generating the pull-up voltage such as the input voltage, Vin, and voltages from the voltage regulator  34 . 
         [0021]    A feedback monitor  56  may monitor the feedback line  32  within the integrated circuit  50  to detect if the portion of the feedback line  32  extending from the regulated output voltage through the feedback terminal  44  is electrically degraded. The feedback monitor  56  may communicate a feedback degraded signal to the voltage regulator  34  to indicate that the feedback line  32  has an increased impedance. In one aspect, the feedback monitor  56  may compare the voltage on a portion of the feedback line  32  internal to the integrated circuit  36  to a reference voltage to determine if the feedback line  32  is electrically degraded. 
         [0022]      FIG. 3  shows an aspect of a power distribution system  100  for supplying a regulated output voltage, Vout, to a system  102  such as an electronic system. The power distribution system  100  includes a feedback protection system  104  to protect the power distribution system  100  from the potential effects of a feedback line  106  that is electrically degraded from normal operation, wherein electrically degraded is defined as having an increased impedance that causes a feedback signal on the feedback line  106  to be of insufficient quality for the control loop of the power distribution system  100  to control the regulated output voltage. The increased impedance of the feedback line  106  may be due to any cause such as a cold solder joint, the feedback line  106  being partially disconnected from the regulated output voltage, and the feedback line  106  being completely disconnected from the regulated output voltage. 
         [0023]    A voltage regulator  108  may generate the regulated output voltage, Vout, from an input voltage, Vin, and supply that regulated output voltage to the system  102 . The voltage regulator  108  may be any type of voltage regulator such as switching regulators and linear regulators. An integrated circuit  110  may include the voltage regulator  108  and connect via one or more output terminals  112  to external filter components such as an output inductor  114  and output capacitor  116 . The voltage regulator  108  may generate a power output, Vc, that is filtered by the external filter components to generate Vout. The power output, Vc, may be any type of power output to be used for powering the system  35  such as a chopped output of a switching regulator that is filtered by the external filter components, and a DC output from either a switching regulator or a linear regulator. 
         [0024]    Multiple feedback lines  106  may connect from the regulated output, Vout, to the voltage regulator via two or more feedback terminals  118 . A feedback signal carried on the feedback lines  106  may be sensed at a junction of the output inductor  114  and the output capacitor  116  such as near an input  120  to the system  102 . The feedback protection system  104  may comprise the feedback terminals  118  and interconnection of the feedback terminals  118  within the integrated circuit  110 . The feedback protection system  104  advantageously provides redundant feedback lines  106  and feedback terminals  118  to prevent the electrical degradation of any one of the feedback lines from affecting the operation of the voltage regulator  108 . For example, if there is a cold solder joint at one of the feedback terminals  118  causing the impedance of the associated feedback line  106  to increase, the other feedback line(s)  106  and feedback pin(s)  106  provide a redundant low impedance path for the feedback signal. 
         [0025]      FIG. 4  shows an aspect of another power distribution system  230  for supplying a regulated output voltage, Vout, to a system  235  such as an electronic system. The power distribution system  230  is similar to power distribution system  30  in function with corresponding elements numbered in the range  230 - 260 , except that the power distribution system  230  includes a signal generator  254  instead of the voltage generator  54  and the pull-up resistor  46 . 
         [0026]    The signal generator  254  may be any type of high impedance signal generator such as a current generator, and a voltage generator with a series resistor. The output impedance of the signal generator may be selected to be sufficiently high to not load down the source of the feedback signal. For example, if the feedback signal is derived from an inductor-capacitor filter such as inductor  240  and capacitor  242  the source impedance of the inductor-capacitor filter is very low, being approximately 0 ohms, therefore the output impedance may be any impedance greater than approximately 10 ohms. 
         [0027]    The signal generator  254  may be any type of source including an alternating current (AC) source and a direct current (DC) source. In one aspect, when the signal generator  254  is an AC source, a tone detector may monitor the feedback input of the voltage regulator  234  to detect an AC signal from the AC source, which indicates a degraded electrical condition of the feedback line  232  and feedback terminal  244 . In one aspect, the feedback monitor  256  may comprise the tone detector. 
         [0028]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.