Abstract:
A voltage sequencing circuit powers-up electrical systems by sequentially enabling a series of power supply lines to the electrical system. After each power supply line is enabled, the voltage sequencing circuit waits a pre-programmed delay time before enabling the next power supply line. The delay time allows the newly enabled power supply line to settle. Additionally, the voltage sequencing circuit constantly monitors previously enabled power supply lines while continuing to enable the remaining power supply lines. If any of the previously enabled lines fail, the voltage sequencing circuit disables the power supply line before reinitiating a complete power-up sequence.

Description:
This application is a continuation of Application No. 09/729,239, filed Dec. 5, 2000, which issued as U.S. Pat. No. 6,333,650 on Dec. 25, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates generally to power systems and, more particularly, to the initial application of power to electrical systems. 
     B. Description of Related Art 
     In certain electrical systems, such as computer and communication systems, different parts of the system may be designed to be powered from different power sources. For example, a computer system may include a first component designed to operate with a 1.5 volt source, a second component designed to operate with a 3.3 volt source, and a third component designed to operate with a 10 volt source. Typically, such electrical systems provide the power to each component through a series of regulators that convert power from a main power supply to a power level appropriate for each component. Because each regulator draws from the same main power supply, the different voltages (or currents) supplied to the components are not fully independent of one another. That is, power fluctuations caused by one of the components can affect the power supplied to the other components. This effect can be exacerbated by the fact that the components may be further tied to one another through electrical connections at the signal level. 
     Due to this lack of isolation between the components of the electrical system, when initially powering-up each component, it is desirable to sequentially power up each component and wait until the power to the component stabilizes before supplying power to the next component. In this manner, large, potentially damaging power spikes can be avoided. This can be particularly important when dealing with sensitive electronic equipment. 
     Conventional sequential power-up circuits were either manually operated by a user or automated through a simple on/off architecture that delayed power to each component using a resistor/capacitor structure. Such circuits can be inadequate for highly sensitive components in modern electrical systems. 
     Thus, there is a need in the art to improve power-up sequencing when supplying varying power levels to multiple components in an electrical system. 
     SUMMARY OF THE INVENTION 
     Systems and methods consistent with the present invention address this need by providing a reliable power-up sequencing circuit that monitors and sequentially enables power to components in an electrical system. 
     In accordance with an aspect of the present invention as embodied and broadly described herein, a voltage sequencing circuit is described that includes multiple elements. These elements include electrical power sources configured to supply power to electrical components having differing power requirements. Additionally, a power monitor connects to the outputs of the electrical power sources to detect failures in the electrical power sources. A decision logic component connects to the electrical power sources and to an output of the power monitor. The decision logic performs a power-up sequence by sequentially enabling the electrical power sources and verifying, based on outputs from the power monitor, that an enabled one of the electrical power sources is stable before enabling a next one of the electrical power sources. 
     A method consistent with another aspect of the present invention provides power-up services to an electrical system from multiple different power sources. The method includes: (a) enabling a first of the power sources to source power to the electrical system; (b) waiting a predetermined period for the power from the first of the power sources to settle; and (c) beginning to monitor an output of the first of the power sources for a failure in the sourced power. Additionally, (a), (b) and (c) are repeated for each additional power source, and all of the power sources are disabled when any of the monitored power sources fail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, explain the invention. In the drawings, 
     FIG. 1 is a block diagram of a system, including a voltage sequencing circuit consistent with an aspect of the present invention; 
     FIG. 2 is a flow chart illustrating methods consistent with the present invention for powering-up an electrical system; and 
     FIG. 3 is a timing diagram illustrating the interaction of various signal lines shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims and equivalents. 
     As described herein, a voltage sequencer reliably powers-up electrical systems requiring multiple voltage levels. Control sequencing logic within the voltage sequencer monitors power sources at the output of a number of power regulators and determines when to enable each of the power regulators. The delay time between enabling power regulators can be individually set by the system designer. 
     FIG. 1 is a block diagram of an electrical system  101  connected to a voltage sequencer  103  that provides power to electrical system  101 . Electrical system  101  includes exemplary electrical components, labeled as circuit  110 , circuit  111 , and circuit  112 . As illustrated by communication paths  113 , circuits  110 - 112  may communicate with or otherwise be electrically coupled to one another. 
     Electrical system  101  may be any type of electronic device that requires a sequential power-up from multiple power levels. A high performance network switch or router is one possible example of an implementation of electrical system  101 . Voltage sequencer  103  provides power to circuits  110 - 112  in electrical system  101 , and generally includes power regulators  120 - 122  and control sequence component  123 . Power regulator  120  provides power to circuit  110 , power regulator  121  provides power to circuit  111 , and power regulator  122  provides power to circuit  112 . Each of power regulators  120 - 122  may receive their input power from a main power supply source  130 . As illustrated, power regulator  120  converts power from power source  130  into a 3 volt DC output, power regulator  121  converts power from power source  130  into a 5 volt DC output, and power regulator  122  converts power from power source  130  into a 10 volt DC output. 
     Control sequencing component  123  monitors and controls regulators  120 - 122 . In particular, control sequencing logic  123  includes monitor circuits  127 , which are each connected to the output of one of regulators  120 - 122  through monitor signal lines  128 . Each of monitor circuits  127  continuously monitors its input signal line  128  and signals decision logic  129  when the power on its line fails. A power failure may be triggered by, for example, a complete loss of the power, a power spike that exceeds a preset threshold, or an abnormal power drop off. 
     Decision logic  129  of control sequencing component  123  decides, based on signals from monitor circuits  127 , whether to activate enable signal lines  126 . When one of enable signal lines  126  is activated, the corresponding power regulator is “enabled,” and will source power to electrical system  101 . When the enable signal line  126  is not activated, the corresponding power regulator is disabled, and stops transmitting power to electrical system  101 . 
     Voltage sequencer  103  may also include components that provide visual feedback to a user, such as light emitting diode (LED)  140 . As shown, LED  140  is controlled by control sequencing component  123 . Control sequencing component  123  may additionally provide electrical feedback to other system components, such as control component  135 , as to the result of a power-up sequence. Control component  135  may also initiate a power-up sequence. Although shown external to electrical system  101 , control component  135  may be a part of electrical system  101 . 
     Although monitor circuits  127  are shown as multiple separate circuits in FIG. 1, one of ordinary skill in the art will recognize that monitor circuits  127  may be implemented as a single circuit. 
     FIG. 2 is a flow chart illustrating methods performed by voltage sequencer  103  in powering-up electrical system  101 . 
     To begin a power-up sequence, decision logic  129  holds each of the enable signals  126  in their disabled state. Accordingly, at this point, no power is transmitted to electrical system  101  from voltage sequencer  103 . After V in  is applied for the main power source  130 , decision logic  129  waits a preset time period (e.g., one second) for V in  to settle. (Act  201 ). 
     When V in  has settled, decision logic  129  activates the enable signal line  126  corresponding to the first power regulator  120 . (Act  202 ). In response, the power regulator begins to apply power to the circuits in electrical system  101  that are connected to the power regulator (i.e., circuit  110 ). Decision logic  129  waits a preset time period for the newly supplied power to settle and for the supplied circuit  110  to stabilize. (Act  203 ). This time period may be individually set for each power regulator by storing the time period for each power regulator in a memory in control sequencing component  123 . In this manner, the designer can easily adjust settle times based on requirements of the particular power regulator and the circuits in the electrical system  101 . 
     After the preset wait time, if the monitor circuit  127  corresponding to the enabled power regulator  120  indicates that the newly supplied power has settled, decision logic  129  enables the next power regulator in the sequence (e.g., power regulator  121 ). (Acts  204 ,  206 , and  207 ). Additionally, the monitor circuit begins to constantly monitor the power regulator that was turned on. (Acts  205  and  211 ). If any of the monitor circuits  127  for the turned on power regulators detect an error, or if the power from a regulator has not settled after the designated time, control sequence component  123  initiates a failure operation by disabling the power regulators  120 - 122  via de-assertion of the enable signal lines  126 . (Acts  204 ,  205 ,  208 , and  211 ). Control sequence component  123  may then reinitiate a power-up sequence, beginning at Act  202 . (Act  209 ). 
     When all the circuits in the electrical system  101  have been successfully powered-up, voltage sequencer  103  may display a visual indication of the successful power up, such as by activating a light emitting diode. (Act  210 ) 
     To increase the linearity of the power-up sequence and to decrease power fluctuations, V 1 , through V n  in voltage sequencer  103  may be arranged so that either the powered-up voltages sequentially increase (as illustrated) or sequentially decrease. 
     FIG. 3 is a timing diagram illustrating the interaction of various signals shown in FIG.  1 . 
     As illustrated, V in  is activated at time t 1 . After a preset time period, decision logic  129  activates the enable signal line corresponding to voltage V 1  (labeled as V 1 _en at time t 2 ), which causes the power regulator  120  to begin to source voltage V 1 . As shown in FIG. 3, voltage V 1 , when turned on, may be increased gradually in a ramp fashion to decrease the chance that circuit  110  will be adversely affected by the power surge. At time t 3 , decision logic  129  checks the result of the monitor circuit  127  (labeled as V 1 _fail). As shown, V 1 _fail is at a low logic level, indicating that V 1  is stable. 
     Voltage sequencer  103  repeats a similar sequence for voltage V 2 . More specifically, at time t 3 , V 2 _en is asserted, which turns on voltage V 2 . At time t 4 , decision logic  129  checks the result of the monitor circuit  127  (labeled as V 2 _fail). Because V 2 _fail indicates that V 2  is also stable, the process continues. When voltage sequencer  103  successfully gets to the last power regulator (labeled as voltage V 9 ), it may activate the LED  140  by activating the “Led_ok” signal line, which produces a visual indication that electrical system  101  has successfully powered-up. 
     If the power-up sequence repeatedly fails, voltage sequencer  103  may, after a number of attempts, completely abort the power-up sequence. In this situation, voltage sequencer  103  may identify the failing power regulators to a user for problem-solving purposes. 
     The foregoing description of preferred embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. 
     Although described as being primarily implemented in hardware, the present invention may be embodied in hardware and/or in software (including firmware, resident software, micro-code, etc.). Furthermore, the present invention may take the form of a computer program product on a computer-usable or computer-readable storage medium having computer-usable or computer-readable program code embodied in the medium for use by or in connection with an instruction execution system. 
     The scope of the invention is defined by the claims and their equivalents.