Abstract:
An apparatus for suppressing power bus bouncing in a hot-swappable system has been developed. The apparatus includes a connection module with three interior pins for: the power return; the power supply; and the system ground. The system ground pin is shorter than the other two so that it makes contact with the power bus after the bouncing from the return and supply pins has subsided.

Description:
BACKGROUND 
     Contact bounce is a common occurrence during the activation or deactivation of electrical contacts. These electrical contacts may include: push-button switches; toggle switches; electromechanical relays; or power connection devices. FIG. 1A shows a graph of a typical contact bounce in an electrical circuit. The graph represents a digital signal  10  that is switched from off (low)  12  to on (high)  18 . When the electrical contact is activated  14 , the signal goes through a contact bounce period  16  until it eventually stabilizes. FIG. 1B shows an alternative graph of a contact bounce where the electrical contact is switched from on (high)  22  to off (low)  28 . As can be seen, a contact bounce period  26  occurs when the contact is de-activated  24  in a similar manner as shown in FIG.  1 A. 
     For devices such as a lamp or electric motor, contact bounce is not usually a problem. The contact bounce periods  16  and  26  lasts a minute fraction of a second and will not affect the performance of the device. However, if the device being used is micro-processor, contact bounce can have a significant impact on performance since these devices perform operations in microseconds. 
     FIG. 2 shows a schematic of a prior art embodiment of a “hot-swap” controller circuit  30 . “Hot-swapping” or “hot-plugging” refers to the insertion and removal of circuit boards into an active device, such as a computer motherboard, while the device is powered on. This circuit  30  is design to control inrush current so that an integrated circuit board can be safely inserted to and removed from a live backplane. In this embodiment, the controller circuit  30  represents the LT® 1640 Hotswap™ Controller produced by Linear Technology. Various pin connections for the chip are indicated by name in FIG.  2 . The circuit  30  combines the controller chip  32  with additional components to provide control signals  33  to the system voltage converters (not shown). The power for the circuit  30  is provided by a power supply bus that includes: a 48 V line  34 ; a 48 V Return line  36 ; and a Board Engage (or Ground) line  38 . 
     When the power supply bus is connected, the circuit may be susceptible to the problems of contact bounce. The contact bounce that results can cause an excess transient current and could potentially affect operation of the circuit  30 . However, the controller circuit  30  includes a circuit breaker (not shown) that is internal to the controller chip  32 . If the circuit  30  were to experience an excessive transient current, it would be transmitted from the GATE pin on the controller chip  32  through the output line  41  to the MOSFET  40 . The MOSFET  40  would direct the majority of the excess current to the 48 V Return line  36 . Additionally, a trace current would be transmitted back to the SENSE gate of the controller chip  32  via the trace current line  42 . Upon receipt of a trace current, the circuit breaker within the controller chip  32  will go to a “Latch Off” state which disable the circuit  30 . 
     SUMMARY OF INVENTION 
     In an alternative embodiment, the invention relates to a connection module for a hot-swappable system power supply bus comprising: a module body; a power return pin extending from the module body, the power return pin having a first length; a power supply pin extending from the module body, the power supply pin having a second length; and a system ground pin extending from the module body, the system ground pin having a third length, wherein the third length is less than the first length and the second length such that the system ground pin makes a connection with the hot-swappable system subsequent to insertion of the power return pin and the power supply pin. 
     In an alternative embodiment, the invention relates to a connection module for a hot-swappable system power supply bus comprising: means for connecting a power return source to the hot-swappable system; means for connecting a power supply source to the hot-swappable system; and means for connecting a ground source to the hot-swappable system such that the ground source is connected after a contact bounce period of the power supply source and a contact bounce period of the power return source. 
     In an alternative embodiment, the invention relates to a method for connecting a power connection module to a hot-swappable system comprising: creating an over-voltage condition in the hot-swappable system by connecting a power supply pin and a power return pin to a power supply bus; allowing a contact bounce period to elapse during the over-voltage condition; and connecting a system ground pin to the power supply bus after the contact bounce period has elapsed. 
     The advantages of the invention include, at least, a power connection module that prevents excessive transient current, due to contact bounce, from being detected, by creating an over-voltage condition that allows the contact bounce to terminate before the system ground is connected. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1A shows a graph of a typical contact bounce in an electrical circuit. 
     FIG. 1B shows a graph of an alternative contact bounce in an electrical circuit. 
     FIG. 2 shows a schematic of a prior art embodiment of a hot-swap controller circuit. 
     FIG. 3 shows a schematic of one embodiment of a hot swap controller circuit in accordance with the present invention. 
     FIG. 4A shows a side cut-away view of one embodiment of a power module connector in accordance with the present invention. 
     FIG. 4B shows a bottom view of one embodiment of a power module connector in accordance with the present invention. 
     FIG. 5 shows an alternative embodiment of a connector with dual system ground pins. 
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the invention will be described with reference to the accompanying drawings. Like items in the drawings are shown with the same reference numbers. 
     FIG. 3 shows a schematic of one embodiment of the present invention of a hot swap controller circuit  46 . The schematic of the circuit  46  shows a similar configuration to the controller circuit  30  shown in FIG. 2 with the exception of an additional voltage divider circuit. As in the previous figure, the controller chip  32  in this embodiment is the LT® 1640 Hotswap™ Controller produced by Linear Technology. In FIG. 3, the voltage divider circuit includes three separate resistors  44   a ,  44   b , and  44   c . In one embodiment, the resistors  44   a ,  44   b , and  44   c  have the values of 301 kΩ, 4.7 kΩ, and 43.2 kΩ respectively. However, other values could be used in alternative embodiments in accordance with system parameters. 
     FIG. 4A shows a side cut-away view of one embodiment of a power module connector  50  in accordance with the present invention. FIG. 4B shows a bottom view of the same connector  50 . The connector includes a body  58  which houses three separate blades (or pins)  52 ,  54 , and  56  which provide the actual connections for the power lines. In one embodiment, the longest blade  52  is the connection for the 48 V Power Return line  36  as shown in FIG.  3 . The second longest blade  54  is the connection for the 48 V Power Supply line  34  also shown in FIG.  3 . The shortest blade  56  is the connection for the Board Engage (or Ground) line  38  which is shown in FIG. 3 as well. In one embodiment, the actual lengths of the blades  52 ,  54 , and  56  are 12 mm, 10.5 mm, and 4.75 mm from longest to shortest. The lengths may vary in alternative embodiments according to the specifications and characteristics of the system. As shown in FIG. 4B, each of the blades  52 ,  54 , and  56  is enclosed within the body  58  of the connector  50 . Contact with the blades  52 ,  54 , and  56  is provided through a series of three slots  60  with one slot  60  for each blade  52 ,  54 , and  56 . 
     By utilizing a Board Engage blade  56  that is shorter in length than either the 48 V Return blade  52  or the 48 V Supply blade  54 , an over-voltage condition is created until the shorter blade  56  makes stable (non-bouncing) contact with ground. The duration of over-voltage condition allows the multiple bounces to become settled by the differences in physical lengths of the blades. Specifically, the system power bus becomes stabilized from the effects of contact bounce by the time the shortest pin is engaged to the ground connector. 
     The over-voltage condition created by the initial connection with the longest two power blades can be potentially harmful to the circuit. However, it will not damage the circuit if the condition is recoverable (i.e., it diminishes over time). In the present embodiment, this is precisely what happens because once the shortest blade contacts system ground, the over-voltage condition will dissipate. Additionally, the voltage divider network with its three resistors  44   a ,  44   b , and  44   c , protects the load  48  to within its voltage design specifications. Finally, an over-voltage condition will result in shutting off the MOSFET  40  of the circuit  46 , and as a result, no trace current will be detected by the controller chip  32  such that the internal circuit breaker will not “latch off”. 
     While the disclosed embodiment shows a design for use with the LT® 1640 Hotswap™ Controller Circuit as shown in FIG. 3, it is fully contemplated that arrangement of the connection module as shown in FIG. 4A and 4B could be adapted for use with other circuits. This would most likely involve altering the dimensions of the connection blades and/or the arrangement of the voltage divider circuit, if one is necessary, to comply with the specifications of the circuit. 
     One example of an alternative embodiment uses a connector  50  similar to the arrangement shown in FIG. 4A and 4B except that the connector only holds two blades internally. These blades would be the 48 V Power Return  52  and the Power Supply  54 . The System Ground Pin  56  would be mounted externally from the body  58 . Another example of an embodiment of a connector  62  is shown in FIG.  5 . In this embodiment, the connector has dual System Ground Pins  56  which are located externally from the connector body  58 . 
     The advantages of the disclosed invention includes at least the following: a power connection module that prevents excessive transient current due to contact bounce by creating an over-voltage condition that allows the contact bounce to be settled before the system ground is connected. 
     While the invention has been disclosed with reference to specific examples of embodiments, numerous variations and modifications are possible. Therefore, it is intended that the invention not be limited by the description in the specification, but rather the claims that follow.