Abstract:
A multi-channel power shut-down circuit that includes a plurality of channel disabler circuits formed on a common substrate where each of the channel disabler circuits includes a first combinational logic and a second combinational logic having an input coupled to an output of the first combinational logic and having a channel disable output, and a channel overcurrent detector coupled to an input of the first combinational logic. A thermal warning detector is also formed on the common substrate and coupled to the inputs of the first combinational logic of the plurality of channel disabler circuits. A thermal shutdown detector formed on the common substrate and coupled to the inputs of the second combinational logic of the plurality of channel disabler circuits.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to thermal shutdown control on computer boards and more particularly to thermal shutdown control for motherboards having a number of channels receptive to daughterboards.  
         BACKGROUND OF THE INVENTION  
         [0002]    Motherboards in modem electronic systems can carry one or more daughterboards, each of which can plug into the motherboard. These daughterboards receive power from and exchange signals with the motherboard. During operation, various conditions can occur that can damage the daughterboards, including overly high operating temperatures and over-current conditions. To replace the damaged daughterboards, the entire power supply for the motherboard often needs to be turned off to prevent damage to the motherboard.  
           [0003]    In the past, circuits were developed to monitor temperature and over-current conditions in an attempt to prevent damage from occurring to the daughterboards. For example, when an over-temperature and/or over-current condition occurred, the power to that daughterboard could be turned off. While these circuits may successfully protect the daughterboards from damage, it required increasing the motherboard size and component count. This resulted in increased costs because each daughterboard required its own chip to monitor for temperature and current and to provide power shutdown abilities. Additionally, when a fault condition occurred (due to a defective daughterboard), the power to the entire motherboard had to be shut off to allow the replacement of the defective daughterboard. Unfortunately, this also shutoff power to all of the daughterboards carried by the motherboard. Replacing a daughterboard with power still applied could potentially cause a short circuit and overload the main power supply.  
           [0004]    Accordingly, what is needed is a way to monitor for over-temperature and overcurrent conditions to daughterboards while minimizing additional board space and component count. Also, the ability to replace individual daughterboards while the main power supply is on is also needed (also referred to as ‘hot-swapping’).  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides an improved circuit and method for shutting down power to individual channels on an electronics board, without greatly increasing board size and component count.  
           [0006]    A multi-channel power shut-down circuit in accordance with the present invention includes a plurality of channel disabler circuits formed on a common substrate. Each of the channel disabler circuits includes a first combinational logic and a second combinational logic having an input coupled to an output of the first combinational logic. A channel disable output and a channel overcurrent detector are coupled to an input of the first combinational logic. A thermal warning detector is formed on the common substrate and is coupled to the inputs of the first combinational logic of the plurality of channel disabler circuits. A thermal shutdown detector formed on the common substrate and is coupled to the inputs of the second combinational logic of the plurality of channel disabler circuits.  
           [0007]    A method in accordance with the present invention for powering down multiple channels including individually monitoring each of a plurality of channels for an overcurrent condition. A thermal warning signal is developed at a first temperature and a thermal shutdown signal is developed at a second temperature greater than the first temperature. A channel is shutdown upon an occurrence of an overcurrent condition for that channel and upon an occurrence of a thermal warning signal. All channels are shutdown upon an occurrence of the thermal shutdown signal.  
           [0008]    The present invention therefore provides an improved circuit and method for shutting down power to individual channels on an electronics board. The present invention provides less expensive, more compact and more reliable electronics to be built and maintained. Furthermore, the present invention allows for all of the channels to be shutdown simultaneously if a sufficiently adverse operating condition is detected.  
           [0009]    These and other advantages of the invention will become apparent upon a reading of the following descriptions and a study of the various figures of the drawings.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic of a multi-channel thermal shutdown logic circuit of the present invention;  
         [0011]    [0011]FIG. 2 is a diagram illustrating power being supplied to various channels under different temperature conditions;  
         [0012]    [0012]FIG. 3 is an example of a thermal threshold detector that can be used in the present invention; and  
         [0013]    [0013]FIG. 4 is an example of an over-current detector that can be used in the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    [0014]FIG. 1 is a schematic diagram a multi-channel thermal shutdown logic circuit of the present invention. It comprises several components including channel A shutdown logic  10 , channel B shutdown logic  20 , channel N shutdown logic  30 , thermal warning detection  40  and thermal shutdown protection  50 . Channel A, B through N represents the shutdown logic corresponding to individual daughterboards (each channel has its own set). As used herein, “channel” and “daughterboard” are used somewhat synonymously although it is understood that a daughterboard plugs into a channel socket attached to the motherboard. Thus the invention can be implemented for any number of daughterboards plugged into a motherboard.  
         [0015]    Contained within channel A shutdown logic  10 , there is the channel A overcurrent detector  60 , first combinational logic  70  and second combinational logic  80 . Each channel has the same component setup as channel A-channel B is the same, channel N is the same, and so on.  
         [0016]    The first combinational logic  70  preferably includes an AND gate  90 , a NOR gate  100  and a flip flop  110 . The output of the AND gate  90  is connected to the Set input of the flipflop  110  and has one input connected to the channel A overcurrent detector  60  and another input connected to the thermal warning detector  40 . The output of the NOR gate  100  is connected to the Reset input of the flipflop  110  and has one input connected to the channel A overcurrent detector  60  and another input connected to the thermal warning detection  40 . The Quit output of flipflop  110  is connected to an input of the second combinational logic  80 .  
         [0017]    The second combinational logic  80  comprises an OR gate  120  which has one input connected to the output of the first combinational logic  70  (the output of the first combinational logic  70  is the same as the Quit output of the fiipflop  110 ). The other input of the OR gate  120  is connected to the output of the thermal shutdown detection  50 .  
         [0018]    The thermal warning detection  40  is connected to one input of each AND gate  90  and NOR gate  100  contained in each first combinational logic  70  for each channel. The thermal shutdown detection  50  is connected to one input of every OR gate  120  contained in each second combinational logic  120  for each channel. The threshold for turning on the thermal warning detection  40  and the thermal shutdown detection  50  are set at two different temperatures. The thermal shutdown detector  50  is set at a higher temperature.  
         [0019]    In operation, when the current to a particular channel starts to increase, there is a corresponding increase in temperature. If an overcurrent condition is detected by the channel A overcurrent detector  60 , a high signal is sent out. At the same time, it is likely that the temperature is rising and the thermal warning detection  40  will send out a high signal once the preset temperature is reached. Since two high signals are received at the AND gate  90 , a high output is sent to the set input of the flipflop  110 . Since both the inputs at the NOR gate  100  are high as well, it will continue to send out a low signal. The flipflop  110  sends out a high signal since the set input received a high signal. Concurrently, the higher temperature threshold of the thermal shutdown detection  50  has not been reached and thus it continues to send out a low signal to the OR gate  120 . The OR gate  120  is now receiving a high signal from the fiipflop  110  and a low signal from the thermal shutdown detection  50 . This results in a high signal output and the power to channel A is disabled.  
         [0020]    If the temperature continues to increase, channel A will continue to be disabled and eventually the threshold for the thermal shutdown detection  50  will be reached. At this point, the thermal shutdown detection  50  sends out a high signal which is received at all of the OR gates  120 . As a result, all the channels are shut down.  
         [0021]    Once the temperature and current start to decrease, all of the channels will turn back on once the overcurrent detectors  60 , thermal warning detector  40  and the thermal shutdown detection  50  goes low. Applied specifically to channel A, the AND gate  90  will have low signal inputs and will thus have a low signal output. The NOR gate  100  will also have two low signal inputs and will therefore send a high signal output to the reset input of the flipflop  110 . This causes the quit output of the flipflop  110  to go low. At the OR gate  120 , both inputs are low-low inputs from the thermal shutdown detection  50  and flipflop  110 . Thus the output of channel A  10 , as well as all the other channels turn back on.  
         [0022]    The invention can further be appreciated with reference to FIG. 2 which depicts a temperature diagram and the flow of power to each channel. The vertical axis  128  represents power flow to each of the individual channels (channel A  152 , channel B  154 , channel C  156  and channel N  158 ). It should be noted that the vertical axis  128  is organized into sections defined by each channel. In other words, the channels located above channel A  152  on vertical axis  128  do not operate at a higher power level than channel A  152 . Rather, each channel operates at the same power level when turned on or off. The horizontal axis  130  represents temperature and more specifically, T1  140  represents the threshold for the thermal warning detection  40  and T2  150  represents the higher threshold for the thermal shutdown detection  50 .  
         [0023]    Below temperature T1  140 , all the channels are on. As the T1  140  temperature threshold is reached, an over-current is detected at channel A  152 . This results in the power to channel A  152  being shut off. On channel B  154  and channel C  156 , no over-current is detected so it continues to operate as normal.  
         [0024]    As the temperature continues to rise, but well before temperature T2  150  is reached, an over-current is detected at channel C  156  and thus its power is shutdown. Meanwhile at channel B  154 , no over-current is detected so it continues to function as before. Finally the temperature T2  150  is reached and the power is shutdown to all channels. The shaded box  159  on channel N represents that other channels can still have power turned on to them even though power to other channels have been shutoff.  
         [0025]    While the function of this invention was described in terms of high and low signal inputs and outputs, it will be readily appreciated by one skilled in the art that a variety of signal types could be used and still achieve the same function. For example, the output signal to shutdown the channels could be defined as a logic level low instead of a logic level high as described above, or with multi-level logic.  
         [0026]    [0026]FIG. 3 is an exemplary implementation of a thermal threshold detector useful in the present invention. This implementation may be used for the thermal warning detection  40  and the thermal shutdown detection  50 . Voltage level V 1    160  is constant with temperature. Voltage levels V 2    170  and V 3    180  are directly proportional to temperature. Current I 1    190  is determined by the following formula:  
         
       I 
       1 
       =V 
       BG 
       /R 
       1  
     
         [0027]    V BG  is the voltage due to the bandgap of silicon and R 1    200  is a resistance. Currents I  2    210  and I 3    220  are similarly determined using resistors R 2    230  and R 3    240 , but instead of the bandgap voltage reference they use a temperature dependent voltage:  
         
       I 
       2 
       =V 
       T 
       /R 
       2 
     
         
       I 
       3 
       =V 
       T 
       /R 
       3  
     
         [0028]    [0028]FIG. 4 is an exemplary implementation of an over-current detector, such as over-current detector  60 . The circuit depicted operates in two different modes. In switch mode, the current I L    250  is less than the current I REF    260 :  
         
       I 
       L 
       ·R 
       SENSE 
       &lt;I 
       REF 
       ·R 
       REF 
       →I 
       L 
       &lt;I 
       REF 
       ·R 
       REF 
       /R 
       SENSE  
     
         [0029]    R REF    270  and R SENSE    280  are resistances. Since the current I L    250  is less than the current I REF    260 , the MOSFET switch  290  is completely closed and the OTA  300  forces an output voltage equal to the supply voltage (V SUPPLY    310 ) and thus, the gate to source voltage on the MOSFET switch  290  is also equal to V SUPPLY    310 . In regulation mode, the current I L    250  is limited once it reaches a pre-set limit:  
         
       I 
       L 
       =I 
       REF 
       ·R 
       REF 
       /R 
       SENSE  
     
         [0030]    It will be appreciated by one skilled in the art that thermal threshold detection and overcurrent detection are well known and can be achieved by various methods.  
         [0031]    While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above described exemplary embodiments, but in accordance with the true spirit and scope of the present invention.