System and method for power good monitor for multiple information handling system power supplies

A switched power rail monitor compares voltages provided by a switched power rail and a power source to detect a predetermined differential indicative of a fault at the switched power rail. A switched power rail fault is communicated to a power manager to take corrective action, such as cutting off power to information handling system components. In one embodiment, a pair of bipolar junction transistors monitor the voltage differential to send an enable signal if the differential is within limits and a disable signal if the differential exceeds limits.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the field of information handling system power supplies, and more particularly to a system and method for power good monitor for multiple information handling system power supplies.

2. Description of the Related Art

One way that information handling systems provide flexibility to accomplish a variety of tasks is that they are built from a variety of processing components. Selection of appropriate processing components, such as CPUs, hard disk drives, embedded controllers, etc . . . , allows an end user to achieve a desired performance level for a given cost. The result is that an information handling system can have a wide variety of components, each with its own power supply requirements. To meet the power needs of processing components, an information handling system often includes power supplies with multiple voltage levels and varied power capabilities. In some instances, information handling systems, such as portable system, use power rail switches to further partition power supply wells. Using power rail switches provides a “subset” power source that aids portable information handling system power management and provides increased flexibility in available power supply sources within a system with reduced cost and footprint.

One difficulty with the use of power rail switches to partition power supply is that each switched power rail should be monitored to ensure that it remains within operating limits. Typically, an information handling system monitors power rails to generate a combined “Power Good” feedback signal that indicates the power rails are working properly. If a failure of any power rail is detected, the Power Good feedback signal is terminated so that a power manager of the information handling system, typically found in an embedded controller, knows that one or more power rails needed for operation of the information handling system are not operational and can take appropriate corrective steps. Failure to detect defective power rails may violate power sequencing specifications, leading to an extreme overheating of integrated circuits that receive power from a failed power rail. Without a failure indication, control logic in the embedded controller, such as a PMC, would continue to enable power delivery to partially-powered target integrated circuits causing severe backdrive and overheating of the integrated circuit. Extreme heat from partial power applied to an integrated circuit may result in catastrophic failure to the information handling system. Although the application of partial power from a switched power rail failure can result in catastrophic damage, switched power rails often remain unmonitored due to the expense of “power good”solutions. Generally, monitoring of non-switched rails by DC-DC regulators or comparator integrated circuits is relied upon to detect and correct power system failures.

SUMMARY OF THE INVENTION

Therefore, a need has arisen for a system and method that detects failures at switched power rails to provide Power Good feedback to an information handling system power manager.

In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for detecting information handling system power system failures. Switched power rails of an information handling system are monitored to detect faults so that power can be shut off to information handling system components in the event of a partial power failure due to a switched power rail failure.

More specifically, an information handling system's components are powered by plural switched power rails that interface with a power source by selectively engaging or disengaging a switch. A switched power rail monitor associated with each switched power rail compares the voltage of the switched power rail with the source voltage to detect a fault at a predetermined differential. For example, first and second bipolar junction transistors monitor the switched power rail and source voltages to send an enable signal if the voltages are within limits and a disable signal if the voltages exceed the predetermined differential. In one embodiment, plural switched power rail monitors communicate the enable or disable signal to a cascade monitor that performs an OR function to issue a disable signal to a power manager if any one switched power rail monitor outputs a disable signal.

The present invention provides a number of important technical advantages. One example of an important technical advantage is that switched power rails are monitored to detect failures and to report the failures by disabling a Power Good feedback signal. Monitoring of switched power rails prevents application of partial power to integrated circuits by cutting off power when the Power Good feedback signal indicates any failure. The use of bipolar junction transistors provides a low cost comparator-based power good circuit solution that is practical for commercial use in an information handling system having multiple switch power rail circuits. Monitoring for a Power Good feedback signal that includes switched power rails helps to prevent partial power failures that might otherwise lead to overheating of integrated circuits in an information handling system.

DETAILED DESCRIPTION

Referring now toFIG. 1, a block diagram depicts an information handling system10having a power supply12with plural switched power rails14. Information handling system10has plural processing components that cooperate to process information, such as a CPU16, a hard disk drive (HDD)18, RAM20, a modem22, a network interface card (NIC)24, chipset26and an embedded controller28. Power supply12provides power to the processing components with switched power rails14and other types of power rails that are connected with the processing components through a motherboard30. A power manager32running on embedded controller28manages the power output by power supply12. A power good monitor34associated with power supply12monitors switched power rails14for failures and reports the failures to power manager32for appropriate corrective action, such as shutting down information handling system10.

Referring now toFIG. 2, a circuit diagram depicts the interaction of a switched power rail14with a power supply12and embedded controller28. An unregulated power source enters a DC-DC regulator36at pin1and outputs a non-switched power source Vcc from pin3. Application of power to DC-DC regulator36results in a Power Good signal from pin4to a Vcc Power Good pin3of embedded controller28. As long as a Power Good signal enters embedded controller28at pin4, such as from a switched power monitoring38, embedded controller28returns an enable signal from pin to DC-DC regulator36pin5to continue to apply power to the information handling system. However, if switched power monitor circuit38fails to provide Power Good signal, embedded controller28ceases the Power Good enable signal from pin1to pin5of DC-DC regulator36so that power is turned off to the information handling system. Power output as Vcc proceeds to a power switch40that controls the application of power to a switched power rail14. When power switch40is closed to provide power to switched power rail14, power also enters switched power rail monitor38for a comparison with VCC. If the difference between the voltage Vcc at the non-switched power rail differs by more than a predetermined amount from the voltage of switched power rail14, switched power rail monitor38ceases a Power Good signal to pin4of embedded controller28so that power is turned off from DC-DC regulator36.

Referring now toFIG. 3, a circuit diagram depicts an example embodiment of a switched power rail monitor38. Switch power rail monitor38provides a low cost comparator-based power good monitor using a low base emitter voltage (Vbe) saturation voltage of PNP bipolar junction transistors (BJT), which are normally used as an electronic switch. The BJTs monitor the voltage difference between the reference voltage Vcc and the switched power rail voltage to generate a power good signal for predetermined voltage parameters. If the switched power rail voltage falls below Vcc by more than a predetermined circuit threshold voltage, the power good signal is deasserted. The circuit threshold voltage is determined by the difference of a forward BJT Vbe saturation voltage, such as 0.6Volts, and a diode forward voltage, such as 0.3Volts. Thus, the combined threshold voltage using these examples is about 0.3Volts.

As depicted inFIG. 3, switched power rail monitor385V_RUN is a switched power rail14that derives power from 5V_ALW through a power switch40, as depicted inFIG. 2. A base emitter junction of a BJT Q27is connected across the switch for the monitored switched power rail from 5V_ALW to 5V_RUN. Switched power rail monitor circuit38operates based upon the voltage differential of deltaV=V—5RUN−V—5ALW. When the deltaV is greater than Vbe_bjt_Q27minus Vdiode_forward_d14, such as a value of 0.3V, current flows from the base node of the transistor to ground through resistors R261and R240. This allows current to flow from the source BJT collector node of Q27to the base node of the NPN BJT Q24, thus turning on transistor Q24to pull the collector node to ground. Thus, in the example depicted inFIG. 3, the power good signal output from transistor Q24is low to indicate a fault when V—5RUN<4.7V where V—5ALW is 5V. When the source power rail and switched power rail are within the predetermined limits, such as 0.3V, the voltage at the base node of PNP BJT Q27will be V—5VALW minus Vdiode_d14and have a value of less 0.6V for Vbe. This prevents the flow of base-emitter current so that PNP BJT Q27is off, resulting in NPN BJT Q24turning off to float the collector node. The collector node of Q24is pulled up with a pull-up resistor so that a logic high-level output from Q24indicates a positive power good signal. A series resistor R261disposed between the reference voltage 5V_ALW and the switched rail 5V_RUN to limit the base-emitter current of BJT Q27. A diode D14prevents backdrive between the reference and switched rails when the switched rail is off.

Referring now toFIG. 4, a circuit diagram depicts cascaded switched power rail monitors38input to a cascade monitor42to provide a single Power Good signal from plural monitors38. A switched power rail monitor is associated with each of plural switched power rails. The output of each switched power rail monitor forms a wired OR function to output a single Power Good signal from cascade monitor42. In addition to cascading of the switched power rails, other open-drain or open-collector power good signals are cascaded from other source power supplies. Thus, a combined Power Good signal is obtained to indicate that both switched rails and non-switched rails are within the predetermined Vf-Vbe limit of the circuit. Control logic within the embedded controller can utilize the power good signal for power sequencing and diagnostics.

Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations could be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.