Abstract:
Embodiments of the present invention provide methods and circuitry for protecting a circuit during hot-swap events. Hot swap protection circuitry includes as overcurrent detection circuit which decouples power from a load. Circuitry is provided to detect ground-fault conditions. Noise detection circuitry is provided to reduce noise in the power that is delivered to the load.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   The present application is a continuation application of U.S. application Ser. No. 10/029,593, filed Dec. 21, 2001, now U.S. Pat. No. 6,771,478 which is related to and claims priority from U.S. Provisional Application No. 60/258,004, filed Dec. 22, 2000, both of which are herein incorporated by reference for all purposes. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to integrated circuits. More particularly, the invention relates to a method and circuitry for hot-swap protection circuits. 
   A hot swap operation is an insertion action or a removal action of a device while the system using it is receiving power, coupling the power from the system to the device. Such an operation can cause external capacitors to draw currents high enough to disturb system operations or even cause permanent damage to either or both the device and the system. 
   Hot-swap protection circuits enable electronic circuits to be connected to each other and disconnected from each other while powered. Hot-swap protection circuits are required in many applications where it is not practical to shut down an electronic system while replacing or adding circuit boards to it. Such protection circuits, or systems, are used in telephone switching hubs, corporate network server hubs, and in laptop or desktop computers with PCMCIA connectors. All of the examples require connection or disconnection under power and so on. 
   Conventional hot-swap protection circuits employ connectors with at least one set of sensor pins, which are a set of extra long and extra short pins, connected to voltage detectors. These sensor pins allow immediate detection of connection and/or disconnection by sensing the presence and/or absence of the applied voltage. It is well known that a single set of sensor pins—whether at the top, middle, or bottom—might not be enough to detect a hot-swap event. 
   For the best reliability, it is often necessary to use two sets of sensor pins, one set at the top and one set at the bottom of a hot-swappable card. Adding additional sets of sensor pins increase reliability, but increases costs to the overall system. Additionally, conventional hot-swap protection systems using sensor pins do not always detect the application or removal of power to a system. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides a method and circuitry for hot swap operations. Application of power from a source of power is detected by first circuitry. A switch couples the power to the device in a gradual manner in responsive to the first circuitry. Circuitry is provided which detects an overcurrent condition in which the current draw by the device exceeds a predetermined level. The switch decouples the device from the power responsive to the circuitry. Circuitry is provided detects events in which power is removed momentarily, as occurs in a ground-fault condition, or permanently as in a disconnect event, and in response thereto a signal is produced indicative of the occurrence. Circuitry, which is responsive to noise in the power, is operatively coupled with the switch which varies its conductance in response to the detected noise. 
   Embodiments of the present invention achieve their purposes and benefits in the context of known circuit and process technology and known techniques in the electronic and process arts. Further understanding, however, of the nature, features, and advantages of the present invention is realized by reference to the latter portions of the specification, accompanying drawings, and appended claims. Other features and advantages of the present invention will become apparent upon consideration of the following detailed description, accompanying drawings, and appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a simplified high-level block diagram of an electronic hot-swap protection circuit, according to one embodiment of the present invention; 
       FIG. 2  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 1 , according to one embodiment of the present invention; 
       FIG. 3  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 1 , according to another embodiment of the present invention; 
       FIG. 4  is a simplified high-level block diagram of an electronic hot-swap protection circuit, according to another embodiment of the present invention; 
       FIG. 5  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 4 , according to one embodiment of the present invention; 
       FIG. 6  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 5 , according to another embodiment of the present invention; 
       FIG. 7  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 4 , according to another embodiment of the present invention; and 
       FIG. 8  is a simplified high-level schematic diagram of the hot-swap protection circuit of  FIG. 7 , according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a simplified high-level block diagram of an electronic hot-swap protection circuit  100 , according to one embodiment of the present invention.  FIG. 1  shows a detector  102  coupled in series, via a connector  105 , to an electrical power source  107 . Detector  102  also couples in series to a fast-disconnect, slow-reconnect switch  110 . Switch  110  couples in series along a power supply conductor between a load  112  (circuit to be protected, target circuit, device, etc.) and power source  107 . Detector  102  includes an overcurrent detector module  115  and a control circuit  117 . Detector module  115  is series-coupled between switch  110  and a first terminal of connector  105 . Control circuit  117  is coupled to a second terminal of connector  105 . Detector module  115  includes an output that feeds into control circuit  117 . 
   In this specific embodiment, detector module  115  and switch  110  couple to the positive terminal of power supply  107 , and control circuit  117  couples to the negative terminal of power supply  107 . Alternatively, detector module  115  and switch  110  can be located on the negative terminal of power source  107 , with appropriate modifications to the circuitry. 
   In operation, detector  102  detects whether load  112  is hot-swapped in, i.e., reconnected to power source  107 . When detector  102  detects a reconnect event, it outputs a hot-swap occurrence indication, or “indication,” or “control signal.” More specifically, detector  102  sends a hot-swap occurrence indication, i.e., a reconnect control signal, to switch  110  instructing it to close, i.e., turn on, in accordance with the invention. 
   Hot-swap Occurrence Indication 
   In this and in other embodiments of the present invention, the hot-swap occurrence indication can serve other functions and will depend on the specific application. For example, the indication can be coupled to drive an LED to notify a user of the hot-swap occurrence. The indication can also be coupled to a controller or microprocessor in the form of an interrupt signal, for example, so that appropriate processing can be performed. 
   In this specific embodiment, the reconnect control signal is produced by control circuit  117 . Also, in this specific embodiment, switch  110  opens quickly but closes slowly. Upon reconnection, the conductivity of switch  110  gradually increases to a fully conductive state, i.e., non-binary change of state that is gradual as opposed to discrete. 
   Upon detection of a reconnect event, detector module  115  produces a signal indicative of a reconnect event. The signal feeds to control circuit  117  which then produces an indication signal and a control signal. The control signal feeds to switch  110 . As will be explained below, the control signal is of a nature as to cause switch  110  to gradually increase its conductance (i.e., gradually decrease its resistance). 
   A reconnect event is typified by a detection of a presence of voltage following the absence of current. The term “reconnect” implies the load  112  was previously connected. However, it is possible that a load might never have been connected to the powered system, in which case the term “connect” is more appropriate. For purposes of this disclosure, however, the terms “reconnect” and “connect” are used interchangeably, since both situations are the same from the point of view of a hot swap operation. 
     FIG. 2  is a simplified high-level schematic diagram of a hot-swap protection circuit  100  in accordance with an illustrative embodiment of the present invention. Hot-swap protection circuit  100  is implemented with commonly available integrated circuits including discrete-active and -passive components (see  FIGS. 6 and 8 , for example). Hot-swap protection circuit  100  includes detector  102  and switch  110 , both of which are located on the negative terminal of power source  107 . Alternatively, in other embodiments, detector  102  and switch  110  can be located on the positive terminal of power source  107  (as in FIG.  1 ), with appropriate modifications to the circuitry. 
   In this specific embodiment, load  112  couples in parallel to a capacitor  120 .  FIG. 2  shows a schematic of the switch. Typically, the switch  110  is a MOSFET device such as the one shown in  FIG. 2  having a part number BUK456. Of course, other commercially available switches can be substituted; e.g.,  FIG. 6  shows a FET having a part number IRF2807. 
   Detector module  115  includes an operational amplifier  127 , or op-amp  127 , configured to output a hot-swap occurrence indication, e.g., a reconnect control signal. The non-inverting input of op-amp  127  couples to switch  110  and inverting input of op-amp  127  couples to the negative terminal of power source  107  via a voltage source  130 . A resistor  132  couples between the inverting and non-inverting inputs of op-amp  127 . In this specific embodiment, for example, op-amp  127  is implemented with an integrated circuit operational amplifier identified by the part number MC33174. Other commercially available op-amps or similar devices can be used. 
   Control circuit  117  includes a diode  135 , resistor  137 , and a Zenor diode  140  coupled in series between the positive and negative terminals of power source  107 . A resistor  142  and a capacitor  144  couple in parallel between the positive and negative terminals of power source  107 . A resistor  147  and a capacitor  150  couple in series with capacitor  144 . A transistor  152  couples between a gate switch  110  (node V GATE ) and the negative terminal of power source  107 . Transistor  152  has a gate coupled to the output of op-amp  217 . Node V GATE  couples control circuit  117  to switch  110 . 
   In operation, generally, hot-swap protection circuit  100  of  FIG. 2  functions to enable the soft (gradual) application of the voltage at node V IN  to the load  112 . This soft application reduces the stress to the components within load  112  as well as to capacitor  120 . Such stress can cause physical damage to these components. For example, if an instantaneous voltage is applied across load  112  or capacitor  120 , it is theoretically possible to cause infinite current flow through load  112  or capacitor  120 . This can either degrade them or immediately cause them to explode, causing physical damage and possible destruction. 
   Suppose that after load  112  is reconnected for a sufficient amount of time such that the voltage at node V OUT  settles to a voltage close that at node V IN , and a steady state current flow through load  112  is established. The difference between voltages at nodes V OUT  and V IN  is simply the load current through load  112  times the sum of the resistances of resistor  132  and a resistance Rdson of switch  110  in the conducting state. 
   Operation of Detector  102  Upon Reconnection 
   Upon reconnection, hot-swap protection circuit  100  enables a soft turn-on of switch  110  through resistor  147 . The soft start sequence is as follows. First, assume that all of the capacitors in control circuit  117 , as well as capacitor  120  across the load  112 , are discharged so that the potential at node V IN  at connector  105  is at zero potential. Second, power source  107  couples to detector module  102  via connector  105 . The application of the voltage at node V IN  at the output of the connector  105  causes the presence of a voltage E IN , i.e., voltage of power source  107  at node N. Capacitor  144  then charges through resistor  137  to 12V, the voltage of which is determined and limited by Zenor diode  140 . In other embodiments, Zenor diode  140  can have other values. During this time, the voltage at node V GATE  ramps up from zero potential through resistor  147 , implementing a “soft” or slow turn-on of switch  110 . The voltage at node V OUT  then quickly ramps up from a zero potential to the voltage at node V IN . The ramp-up rate is determined by the turn-on rate of switch  110  and the size of capacitor  120  across the load  112 . 
     FIG. 3  is a simplified high-level schematic diagram of a hot-swap protection circuit  100  in accordance with another illustrative embodiment of the invention. Hot-swap protection circuit  100  of  FIG. 3  is similar to that of FIG.  2 . In the embodiment shown in  FIG. 3 , detector  102  includes circuit  160 . 
   Circuit  160   
   Circuit  160  includes an operational amplifier  162 , or op-amp  162 . An output of op-amp  162  couples to the gate of switch  110 , or node V GATE , via a resistor  165 . Node V GATE  couples between resistor  147  and capacitor  150  via a diode  167 . A bias voltage source  170  couples in parallel to capacitor  150 . In this particular embodiment, bias voltage source  170  is a voltage divider. Bias voltage source  170  includes a resistor  172  and a resistor  175 . An inverting input of op-amp  162  couples between resistors  172  and  175  via a resistor  177  and to node V GROUND  via a capacitor  180 . 
   In the specific illustrative embodiments of  FIGS. 2 ,  3 ,  5 ,  6 ,  7 , and  8 , V GROUND  located at the positive terminal of power source  107  because the protection circuit of these specific embodiments operates in the negative voltage range. The specific voltage range in which the protection circuit operates will depend on the specific application. For example, the operating voltage range can also be in both the negative and positive voltage ranges. In some embodiments, the operating voltage range can only positive voltage ranges, for example, where V GROUND =0V. 
   Operation of Circuit  160   
   Circuit  160  protects load  112  from noise that might be present in power source  107 . Circuit  160  operates in conjunction with switch  110  to effectively function as a low pass filter of the power from power source  107 , thus reducing the effects of noise present in the power. The op-amp  162  is configured as a voltage follower. Noise from power source  107  will propagate through network  170  to the inverted input  13  of op-amp  162  through the network of resistor  177  and capacitor  180 . The noise components will cause a differential input to appear at the input of op-amp  162 . The resulting output of op-amp  162  will drive switch  110  to alter its conductivity as a function of the noise. This in turn alters the current flow to load  112 . Consequently, the power delivered to load  112  will be effectively low-pass filtered by the switch. Thus, by altering the conductivity of the switch  110  in response to noise present in the power, the noise components in the power delivered to the load  112  can be reduced. 
   Operation of Overcurrent Detector Module  115  (Load Connected) 
   The following description assumes that load  112  has been connected to power source  107  through switch  110 , which is on, and through overcurrent detector module  115 . As long as the voltage drop across resistor  132  is less than voltage source  130 , e.g., Vcl=100 mV, the output of op-amp  127  will be low, or at the voltage at node V IN . This keeps transistor  152  of control circuit  117  off and node V GATE  high which keeps switch  110  on. 
   An overcurrent condition is one where load  112  demands a much higher than normally expected current. For example, suppose that the current is so high that the voltage drop across resistor  132  is greater than 100 mV. This causes the non-inverting input of op-amp  127  to become more positive than its inverting input. Note that the voltage differential across the non-inverting and the inverting inputs occurs when a detected overcurrent condition is detected. In this specific example, an overcurrent is detected when the voltage drop across resistor  132  is greater than 100 mV, or if greater than 10 amps of current flow through resistor  132 . The threshold current which defines an overcurrent condition can be predetermined by setting voltage level of voltage source  130  accordingly. 
   Upon detection of an overcurrent condition, overcurrent detector module  115  causes the output of op-amp  127  to go high, or +12V. This turns on transistor  152  to discharge capacitor  150  to the voltage at node V IN . This discharged of capacitor  150 , Vcl=˜0V, causes switch  110  in switch  110  to turn off which results the disconnection of load  112 . After switch  110  turns off, the output of op-amp  127  drops back down to 0V, or the voltage at node V IN , because the current through resistor  132  is cut off. Also, capacitor  150  begins to recharge. 
   The same logical high signal with respect to node V IN  (which is available from op-amp  127 ) becomes an indication output. This indication output indicates an overcurrent fault shut down. 
     FIG. 4  is a simplified high-level block diagram of an electronic hot-swap protection circuit  100 , according to another embodiment of the present invention. Hot-swap protection circuit  100   FIG. 4  is configured similarly to that of  FIG. 1  except that circuit  100  of  FIG. 4  includes a detector  181  that detects whether load  112  is hot-swapped out, i.e., disconnected from power source  107 . In this specific embodiment, detector  102  couples in parallel to a switch  110 . Switch  110  couples in series to a terminal of power source  107  via connector  105  and to load  112 . 
   When detector  102  detects a disconnect event, it outputs a hot-swap occurrence indication, or “indication,” or “control signal.” More specifically, detector  102  sends a hot-swap occurrence indication, i.e., a disconnect control signal, to switch  110  causing it to open, i.e., turn off. Switch  110  opens quickly. 
   Hot-swap Occurrence Indication 
   As stated above, the hot-swap occurrence indication can serve other functions which depend on the specific application. For example, the indication can be coupled to drive an LED to notify a user of the hot-swap occurrence. The indication can also send a signal to a controller or microprocessor as an interrupt signal to perform appropriate processing in the occurrence of a disconnect. During a disconnect event in a storage device, for example, certain cleanup operations can be performed before the drive loses all of its power. 
     FIG. 5  is a simplified high-level schematic diagram of a hot-swap protection circuit  100 , which in some embodiments of the present invention, can be used to implement the hot-swap protection circuit of FIG.  4 . Like hot-swap protection circuit  100  of  FIG. 4 , that of  FIG. 5  is implemented with commonly available integrated circuits including discrete-active and -passive components. 
   Hot-swap protection circuit  100  of  FIG. 5  includes detector  181  and switch  110 , both of which are located on the negative terminal of power source  107 . Alternatively, in other embodiments, detector  181  and switch  110  can be located on the positive polarity conductor of the power source  107  (as in FIG.  4 ), with appropriate modifications to the circuitry. 
   In this specific embodiment, detector  181  of  FIG. 5  includes the same elements and configuration as that of  FIG. 2  with a few exceptions. Detector  181  of  FIG. 5  includes a ground-fault protection circuit  185  in place of overcurrent protection circuit  115  of FIG.  2 . 
   Upon detection of a disconnect event, detector module  185  sends an output indication, or “signal,” to control circuit  117 . Accordingly, if the signal is triggered by a disconnect event, control circuit  117  sends a disconnect control signal to switch  110  instructing it to open. 
   Switch  110  couples between the non-inverting input and the inverting input of an op-amp  187  via a voltage source  192 . 
   Operation of Detector  181  Upon Disconnection 
   In operation, hot-swap protection circuit  100  of  FIG. 5 , functions as a load-disconnect protection circuit. Prior to disconnection, assuming that load  112  is powered normally and operational. The voltage at node V OUT  is approximately equal to that at node V IN , less the voltage drop across switch  110 . The voltage drop across switch  110  is such that the voltage at node V OUT  is more positive than that at node V IN , because current is being supplied to load  112  through switch  110  from node V IN . Op-amp  187  of detector  181  connects across switch  110 . The non-inverting input of op-amp  187  couples to a voltage source Vos  192 . The value of voltage source  192  is approximately −10 mV and can vary depending on the specific application. The −10 mV ensures that the output of op-amp  187  is low relative to the voltage at node V IN , regardless of the current flow of load  112 , or regardless of any finite built-in offset voltages of op-amp  187  (assuming that the input offset voltage of op-amp  187 &lt;10 mV). This keeps transistor  152  off so that node V GATE  is charged to 12V, keeping switch  112  on. 
   Operation of Ground-fault Protection Circuit  185  (Load Gets Disconnected) 
   The following description assumes that at some time T 1  connector  105  disconnects due to a ground fault-condition. Because there are no capacitors connected between nodes V GROUND  and V IN , the voltage at node V IN  has the tendency to move towards the voltage at node V GROUND . However, this does not happen because the charge on capacitor  120 , which was initially charged to the voltage at node V OUT . Capacitor  120  sustains a current flow from node V OUT  to node V IN . As long as there is available charge in capacitor  120  to sustain the current needed by detector  181 , it will function properly. 
   In operation, detector  181  recognizes immediately that the voltage across switch  110  is now reversed, i.e., the voltage at node V OUT  is more positive than that at node V IN . The output of op-amp  187  goes high to turn on transistor  152 , which in turn discharges capacitor  150 . This causes switch  110  in switch  110  to turn off which results the disconnection of load  112 . This also stops the discharge of capacitor  120  by the detector  181 . 
   In some embodiments of the invention, because the logical high signal that op-amp  187  outputs also functions as a hot-swap occurrence indication, the indication can be sent to other circuits, e.g., LED, controller, microprocessor, etc., for other purposes. 
   This circuit technique detects the presence (indication low) or absence (indication high) from detector  181 , and represents an automatic ground fault detection without the need for separate ground sense pins as needed in the prior art. 
   It is to be understood that this specific implementation as depicted and described herein is for illustrative purposes only and should not limit the scope of the claims herein, and that alternative circuit implementations exist for the same functionality. For example, any IC chip, proprietary or otherwise, can be used to implements the circuits described herein. 
   The foregoing circuits can be readily implemented using any of a number of commercially available integrated circuit devices. For example,  FIG. 6  illustrates how the hot-swap protection circuit according to the present invention as shown in  FIG. 5  can be provided using conventional hot-swap IC devices. Attached as Appendix A is a data sheet for the IC device. Following is a description of the pin outs of the chip:
         Pin  1  (INV) provides an invert input function. The invert input controls GSNSin&#39;s polarity. When invert input is high compared to AGND, then GSNSin low indicates an insertion/removal event. When invert input is low, then GSNSin high indicates an insertion/removal event.   Pin  15  (GSNSin) provides a ground sense input. The INV pin controls the polarity sense of this input. A 3uA internal pull-up current source causes logic high when there is no connection at this pin. With INV low or connected to AGND, a GSNSin low (or connected to AGND) will keep RSTout and GATE low, and the external power switch, Q 1 , off. A disconnected GSNSin pin or when Vcc is applied to it will allow normal operation.   Pin  2  (VCCin) is the supply voltage positive power-supply voltage input.   Pin  3  (SHNToff) is the shunt off pin. This pin serves to control the enabling of the shunt circuit. When the pin is high compared to AGND, then the shunt regulator is in off position. A low level at this pin activates the shunt regulator.   Pin  4  (CAPin) is an active lowpass filter capacitor input. The output of the power active filter tracks this pin. Adding an external RC network matching the input noise with respect to the 3 db point of the filter could reduce the noise to a minimum.   Pin  5  (VDROP) is an active filter offset voltage pin. This pin sets the drop out MOSFET voltage across the active filter.   Pin  6  (SLOPE) is a slope input pin. This input controls the current slope during power up and controls inrush currents. Adding external capacitors to this pin allow regulation and adjustment of the rate of the current slope.   Pin  7  (OFFTM) is the off-time pin. The OFFTM pin sets the delay time between powerdown and restart of IXHQ100. Delay time can be increased by adding external capacitors to this pin.   Pin  8  (AGND) is the ground pin. This pin provides a system zero reference pin.   Pin  9  (VDDout) is the regulator output voltage pin. The regulator output voltage provides current to drive the external circuits with respect to AGND.   Pin  10  (VCL) is the vercurrent threshold bias voltage pin. This pin sets the overcurrent threshold bias voltage.   Pin  11  (SOURCE) is the current input sensor pin. This serves as the input pin for sensing current through the power device with respect to AGND.   Pin  12  (GATE) in the output pin. This is control voltage pin for driving an external MOSFET.   Pin  13  (OUTsns) is the out sensor signal pin. This signal pin senses the output voltage of the circuit.   Pin  14  (RSTout) is the output reset pin. A low at this pin indicates detection of an insert/removal event or overcurrent detection.   Pin  16  (NC) N/A Not Connected       

     FIG. 7  is a simplified high-level schematic diagram of a hot-swap protection circuit  100 , which in some embodiments of the present invention, can be used to implement the hot-swap protection circuit of FIG.  4 . Hot-swap protection circuit  100  of  FIG. 7  is similar to that of  FIG. 5  except that it includes a filter  160 . In this particular embodiment, filter  160  is an active filter. Also, filter  160  of this specific embodiment is implemented with commonly available integrated circuits and discrete active and passive components. 
   Filter  160  of  FIG. 7  includes the same elements and is configured similarly to that of  FIG. 3  except that the non-inverting input of op-amp  162  couples to the drain of switch  110  as well as to the inverting input of op-amp  187 . 
     FIG. 8  further illustrates how the hot-swap protection circuit according to the present invention as shown in  FIG. 5  can be provided using conventional hot-swap IC devices. The circuit shown in  FIG. 8  uses the IC device described in the data sheet of Appendix A that can be used to implement the hot-swap protection circuit of FIG.  7 . In addition,  FIG. 1  in the data sheet of Appendix A shows a configuration which implements a hot swap protection circuit according to the present invention as shown in FIG.  3 . 
   Other similar commercially available IC devices can be used to implement the hot swap protection circuits disclosed herein. For example, Linear Technology sells a line of hot swap controllers such as part nos. LT1640AH and LT1640AL. Texas Instruments Incorporated sells a line of hot swap IC devices such as TPS2320 and TPS2321. Maxim Integrated Products sells IC devices such as the MAX5904 which can be used. The disclosed hot swap protection circuitry according to the present invention can be made using such IC devices in conjunction with appropriate external components. 
   Specific embodiments of the present invention are presented above for purposes of illustration and description. The full description will enable others skilled in the art to best utilize and practice the invention in various embodiments and with various modifications suited to particular uses. After reading and understanding the present disclosure, many modifications, variations, alternatives, and equivalents will be apparent to a person skilled in the art. The foregoing, therefore, is not intended to be exhaustive or to limit the invention to the specific embodiments described. The claimed invention is intended to be accorded the widest scope consistent with the principles and novel features disclosed herein, and as recited in the following claims.