# Patent

## Title
Voltage regulator feedback protection method and apparatus

## 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.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
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
An aspect of this invention relates to power systems for electronic circuits.
BACKGROUND
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.
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.
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
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.
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
FIG. 1 is a block diagram of an aspect of a conventional power supply feedback system.
FIG. 2 is a block diagram of a power distribution system that includes an aspect of a feedback protection system.
FIG. 3 is a block diagram of a power distribution system that includes another aspect of a feedback protection system.
FIG. 4 is a block diagram of a power distribution system that includes another aspect of a feedback protection system.



Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

## Claims

1. An integrated circuit comprising;
an output terminal;
a plurality of feedback terminals, wherein each of the plurality of feedback terminals is configured to receive a feedback signal;
a voltage regulator having a feedback input and a power output, wherein the feedback input is directly connected to the plurality of feedback terminals and is configured to receive the feedback signal, wherein the power output is in communication with the output terminal and is directly connected to the plurality of feedback terminals, and wherein the voltage regulator is configured to generate a regulated output voltage at the power output in response to the feedback signal; and
redundant feedback lines connected between the output terminal and the plurality of feedback terminals.

2. A power distribution system comprising:
the integrated circuit of claim 1; and
external filter components connected to the output terminal, wherein the external filter components comprise
an output inductor, and
an output capacitor configured to (i) filter the regulated output voltage and (ii) generate a filtered output voltage.

3. The integrated circuit of claim 1, wherein:
the voltage regulator comprises a switching regulator or a linear regulator;
the output terminal comprises a pin, a ball grid array, or a connector; and
the plurality of feedback terminals comprises one or more of pins, ball grid arrays, and connectors.

4. The integrated circuit of claim 1, further comprising an interconnection circuit configured to interconnect each of the plurality of feedback terminals to the feedback input of the voltage regulator.

5. The integrated circuit of claim 1, further comprising a filter configured to generate a filtered output voltage based on the regulated output voltage,
wherein the feedback signal is derived from the filtered output voltage.

6. A power distribution system comprising:
the integrated circuit of claim 1; and
a filter configured to generate a filtered output voltage in response to the regulated output voltage, wherein the redundant feedback lines are configured to conduct the feedback signal from the output terminal to the plurality of feedback terminals.

7. An integrated circuit comprising,
an output terminal;
a plurality of feedback terminals, wherein each of the plurality of feedback terminals is configured to receive a feedback signal;
a voltage regulator having a feedback input and a power output, wherein the feedback input is directly connected to the plurality of feedback terminals and is configured to receive the feedback signal, wherein the power output is in communication with the output terminal, and wherein the voltage regulator is configured to generate a regulated output voltage at the power output in response to the feedback signal;
a voltage generator configured to generate a pull-up voltage having an amplitude greater than a DC voltage amplitude of the power output, wherein the pull-up voltage is derived separately from the power output;
a pull-up resistor connected between the voltage generator and the feedback input of the voltage regulator and configured to pull-up a voltage of the feedback input; and
redundant feedback lines connected between the output terminal and the plurality of feedback terminals.

8. The integrated circuit of claim 7, wherein:
the pull-up voltage is approximately 120% of the DC voltage amplitude of the power output;
the pull-up resistor has an impedance in a range of approximately 100 ohms to 1,000,000 ohms; and
the voltage generator comprises an AC source or a DC source.

9. An integrated circuit comprising;
an output terminal;
a feedback terminal configured to receive a feedback signal;
a voltage regulator having a feedback input and a power output, wherein the feedback input is configured to receive the feedback signal from the feedback terminal, wherein the power output is in communication with the output terminal, and wherein the voltage regulator is configured to generate a regulated output voltage at the power output and is responsive to the feedback signal; and
a signal generator having an output impedance at least ten times greater than an output impedance of the feedback terminal, wherein the signal generator is configured to generate a pull-up signal in communication with the feedback input.

10. The integrated circuit of claim 9, further comprising:
a filter configured to generate a filtered output voltage based on the regulated output voltage,
wherein the feedback signal is derived from the filtered output voltage.

11. A power distribution system comprising:
the integrated circuit of claim 10; and
a feedback line configured to conduct the feedback signal from the output terminal to the feedback terminal.

12. A power distribution system comprising:
integrated circuit of claim 9; and
external filter components connected to the output terminal, wherein the external filter components comprise an inductor and a capacitor, wherein the inductor and the capacitor are configured to (i) filter the power output and (ii) generate a filtered output voltage, and
wherein the feedback signal is derived from the filtered output voltage.

13. The integrated circuit of claim 9, wherein:
the voltage regulator comprises a switching regulator or a linear regulator;
the output terminal comprises a pin, a ball grid array, or a connector; and
the feedback terminal comprises a pin, a ball grid array, or a connector.

14. The integrated circuit of claim 11, further comprising a feedback monitor configured to detect a connection that is electrically degraded, wherein the connection is electrically degraded when an impedance of the connection is increased to a level which prevents the voltage regulator from controlling an amplitude of the regulated output voltage, and wherein the connection is between the feedback terminal and the power output.

15. The integrated circuit of claim 14, wherein the connection includes (i) a cold solder joint, (ii) the feedback line being partially disconnected from the regulated output voltage, or (iii) the feedback line being completely disconnected from the regulated output voltage.

16. The integrated circuit of claim 14, wherein the feedback monitor is configured to compare a voltage of the feedback terminal to a reference voltage to detect the electrically degraded connection.

17. The integrated circuit of claim 9, further comprising a plurality of feedback terminals, wherein each of the plurality of feedback terminals is configured to receive the feedback signal.

18. A power distribution system comprising:
integrated circuit of claim 17;
a filter configured to generate a filtered output voltage based on the regulated output voltage; and
redundant feedback lines connected between the output terminal and the plurality of feedback terminals, wherein the redundant feedback lines are configured to conduct the feedback signal from the output terminal to the plurality of feedback terminals.

19. The integrated circuit of claim 17, further comprising an interconnection circuit configured to interconnect the plurality of feedback terminals.

20. The integrated circuit of claim 7, wherein the voltage regulator is configured to decrease the DC voltage amplitude based on the pull-up voltage.

21. The integrated circuit of claim 7, wherein the pull-up resistor directly connects the voltage generator to the feedback terminal.

22. The integrated circuit of claim 9, further comprising a pull-up circuit that is connected between the signal generator and the feedback input and provides the pull-up signal to the feedback input.

23. The integrated circuit of claim 22, wherein the pull-up circuit includes a pull-up resistor.

24. The integrated circuit of claim 23, wherein the pull-up resistor directly connects the signal generator to the feedback input.

25. The integrated circuit of claim 9, wherein the pull-up signal has an amplitude greater than an amplitude of the regulated output voltage and is provided to the feedback input when a feedback line of the feedback terminal is degraded.

26. The integrated circuit of claim 7, wherein the pull-up resistor is configured to pull-up the voltage of the feedback input to the pull-up voltage.