Abstract:
A temperature control system and method for integrated circuits, particularly those having a plurality of channels or power devices. The temperature control system for an integrated circuit includes at least a heat generating device; a sensor element providing a signal correlated to the working conditions of said the heat generating device such as a signal proportional to the dissipated power of the heat generating device; an elaboration circuit of the signal correlated to the working conditions of the heat generating device; and a turning off circuit of said at least a heat generating device responsively to a signal of said elaboration circuit.

Description:
TECHNICAL FIELD 
     The present invention refers to a temperature control system and method for integrated circuits, particularly for those having a plurality of channels or power devices. 
     BACKGROUND OF THE INVENTION 
     Most of the integrated circuits have inside a circuit (commonly referred to as Thermal Warning) that senses the silicon temperature, and when it senses a prefixed value, the circuit generates an alarm signal. This signal is usually used to turn off the devices or circuit blocks that are responsible for the excessive heat dissipation. 
     When such an emergency occurs all the circuits that could have generated the temperature increase are usually deactivated. However, there are applications in which totally interrupting the device functions could jeopardize the personal safety of the users or create problems to other parts of the apparatus. Therefore it has been attempted to interrupt only the channels or the devices that at that time are dissipating the most heat. 
     The most immediate way to realize a temperature sensor is that of using the base-emitter junction of a bipolar transistor. The voltage at the junction terminals varies with a constant gradient as the temperature varies (around −2 mV/° C.). Knowing the base-emitter voltage at a prefixed temperature it is possible to effect a fairly accurate measurement of this parameter. 
     At environment temperature the bipolar transistor, used like a temperature sensor, is off, and therefore the collector voltage is at a high level, as the temperature increases, the threshold voltage of the base-emitter junction decreases. At the prefixed temperature as activation value of the circuit, the transistor switches on and its collector signal goes to low level, signaling an anomaly. 
     In a multi-channel device, a method used to establish when a device anomaly occurs, in order to switch off only such a device, is that of increasing the number of temperature sensors, one for each device, and putting them near the critical points. The bias circuit of the various transistors used as temperature sensors, can be, for instance, only one, and in proximity of the critical points only the sensor used for the measurement could be placed. 
     With this solution a further sensor is usually combined that senses the silicon temperature in the part of the device where there is never a high power dissipation. This sensor has a more elevated temperature activation threshold than the previous sensor and has the purpose to switch off the device totally in case it reaches such a threshold. 
     An intrinsic problem for this type of solution is related to the temperature profiles that occur during brief transients (in the order of milliseconds) in which an elevated power is dissipated. The elevated power dissipation of a channel during a transient, seen in the proximity between the various channels placed in an integrated circuit, could make the temperature rise also in the area near the channel. In such a case, the turning off of a channel could also occur even if there is not a real malfunctioning. 
     Such a danger increases when the devices must work in boundary conditions, near to the thermal protection intervention temperature, such as happens for instance in automotive circuits placed in proximity to the car elements that carry the environmental temperature above 100 degrees centigrade. 
     SUMMARY OF THE INVENTION 
     In view of the described state of the art, the disclosed embodiment of the present invention provides a temperature control system for an integrated circuit that is able to identify correctly the device that is making the temperature of the integrated circuit rise. 
     According to one embodiment of the present invention, a temperature control system for an integrated circuit is provided, including: 
     at least one device that generates heat because of elevated dissipated power values; 
     a sensor element providing a signal correlated to the working conditions of the at least one heat generating device; 
     an elaboration circuit for said signal correlated to the working conditions of said at least a heat generating device; 
     a turning off circuit of said at least one heat generating device responsive to a signal of said elaboration circuit; 
     wherein said sensor element provides a signal proportional to the dissipated power of the at least one heat generating device. 
     A temperature control method for an integrated circuit is provided that has at least a heat generating device, and includes the following phases: 
     sensing the working conditions of the at least one heat generating device; 
     elaborating the information relative to the working conditions of the at least one heat generating device; 
     generating a turning off signal of the at least one heat generating device responsively to the elaborated information; 
     wherein the sensed working conditions are relative to the dissipated power of the at least one heat generating device. 
     With the device and method of the present invention, it is possible to realize a temperature control system for integrated circuits that correctly identifies the device that is overcoming the dissipation limits by obtaining the information relative to the dissipated power and not relative to the device temperature that could be altered by the nearby circuits. 
     Furthermore, the use of only a sensor, placed at a certain distance from the power transistors or channels, enables filtering of temperature transients that could distort the measurement and cause the turning off of a channel as well when this works correctly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and the advantages of the present invention will be more evident from the following detailed description of a particular embodiment, illustrated as a non-limiting example in the annexed drawings, wherein: 
     FIG. 1 represents a block schematic of a temperature control system for an integrated circuit in accordance with the present invention; 
     FIG. 2 shows through the silicon temperature diagram at the varying of the time how the control circuit according to the present invention activates itself; 
     FIG. 3 represents a block schematic of the temperature determination means in accordance with the present invention; 
     FIG. 4 represents a block schematic of the control system of FIG. 1; 
     FIGS. 5 a - 5   c  represent schematics of circuits able to provide a voltage proportional to the dissipated power; 
     FIG. 6 represents a block schematic of the elaboration system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 it is possible to see a block scheme of a temperature control system for a multichannel integrated circuit in accordance with one embodiment of the present invention. In FIG. 1 only 4 channels  15   a ,  15   b ,  15   c  and  15   d  are represented for descriptive simplicity but they could be a greater or a lesser number. The channels represent a power device or a block of circuit that when activated could dissipate such a power to make the temperature of the integrated circuit silicon rise, such a device or block could be deactivated on command. To the aims of the present invention, each channel also comprises a circuit able to provide a signal proportional to its own dissipated power as explained in more detail below. Each of the 4 channels  15   a ,  15   b ,  15   c  and  15   d  has a channel turning off (or reset) input, respectively R 1 , R 2 , R 3  and R 4 , for a turning-off circuit, and an output signal proportional to its own dissipated power, respectively Pd 1 , Pd 2 , Pd 3  and Pd 4 . The signals Pd 1 , Pd 2 , Pd 3  and Pd 4  are connected in input to an identification system  11  of the information on the dissipated power, at the output of which are available the outputs B 0 , B 1  connected in input to a control system  12  of the information on the dissipated power, that provides in turn in output the turning off signals of the above channels, respectively R 1 , R 2 , R 3  and R 4 . 
     The outputs B 0 , B 1  identify which channel, at a stated moment, is dissipating the greatest power quantity. In general, if n is the number of the channels ( 15   a ,  15   b ,  15   c  and  15   d ) and m the output number (B 0 , B 1 ) of identification of the channel, it will be 2 m ≧n. 
     On the device are present temperature determination means  10  placed at a distance from the points in which power is dissipated, that is from the channels. This means that the temperature increase due to the dissipation of the impulsive type is integrated by the silicon thermal capability. They provide to the control system  12  an overcoming signal VTL of a first prefixed threshold TL and an overcoming signal VTH of a second prefixed threshold TH. Particularly, the signal VTL is at high level until the achievement of the temperature TL after which it goes to low levels, and the signal VTH is at a high level until the achievement of the temperature TH, after which it goes to a low level. 
     With reference now to FIG. 2, shown therein is an example of the diagram of the silicon temperature T measured by the means  10  at the varying of the time t. All the channels are working until the device average temperature, measured by the means  10 , is lower than the temperature TL. When this temperature overcomes the first prefixed threshold TL, at point A of FIG. 2, the control system  12  deactivates the channel that dissipates the highest power, by means of the respective turning off signal, and it prevents it from switching on again as long as the temperature is above TL. The channel that dissipates the highest power is determined on the basis of a calculation of the real power dissipated by each channel and provided to the identification system  11  by the signals Pd 1 , Pd 2 , Pd 3  and Pd 4 . 
     After a channel turns off, the device temperature should decrease. If this does not happen, like in FIG. 2, and on the contrary the temperature increases, then when the second prefixed threshold TH is overcome at point B, all the channels are turned off, to avoid damage to the device. At this point the temperature can only decrease. When it reaches the temperature TL, at point C, all the channels can be turned on. 
     The temperature variation is generally a much slower signal than the electric signals present in an electronic circuit. Slow fluctuations of the temperature around TL (also of the fraction of degree) could cause multiple channel turning off. To avoid this problem it is convenient to add a small temperature hysteresis at the threshold TL. The problem does not exist at the higher threshold as the channels could not be reactivated once the temperature TH has been overcome. 
     Possible values of the thresholds could be for instance 160° C. for TL and 180° C. for TH. 
     The temperature determination means  10  that provide to the control system  12  an overcoming signal of a first prefixed threshold TL and an overcoming signal of a second prefixed threshold TH, can for instance be constituted by two sensors that sense the temperatures TH and TL by means of suitable reference circuits. At the sensor output are preferably present two low-pass filters that effect a necessary filtration to eliminate possible fast interferences that could cause unwanted turning off of the channels. 
     The use of a circuit as described above could not be an optimal solution, since the measurement tolerances between the two sensors could dangerously approach the two thresholds. 
     A more sure and preferable solution is that of using only one sensor. In FIG. 3 is illustrated a possible embodiment. 
     The temperature determination means  10  comprise a sensor  30 , connected to a current generator  31 . The output circuit of the sensor  30  can be for instance constituted by a current generator connected to a transistor collector the emitter of which is connected to ground and the base opportunely biased, the output terminal is connected to the transistor collector. The current generator  31  is activated by a signal coming from the inverted-Q output of the D type flip-flop  34 . The current generator  31  is connected to the input D of the flip-flop  34  and also to an input of a NAND gate  33 , the other input of the NAND gate  33  is connected to the Q output of the flip-flop  34 . The output of the NAND  33  enables the working of an oscillator  32 , the output of which is connected to the clock of the flip-flop  34 , to the clock of another D type flip-flop  36  and also to the input of a pulse counter  35 , the reset input of which is connected to the inverted-Q output of the flip-flop  34 . The Q output of the flip-flop  34  is also connected to the D input of the flip-flop  36  and to the input of a NAND gate  37 ; to the other input of the NAND gate  37  the Q output of the flip-flop  36  is connected. The output of the NAND gate  37  corresponds to the signal VTL, the output of the pulse counter  35  corresponds to the signal VTH. 
     If the temperature is lower than TL the current generator  31  is turned off and the oscillator  32  is deactivated by the NAND gate  33 . When the temperature overcomes the threshold TL and stays under TH, the signal TWN, that is at the output of the generator  31 , goes to a low level, the oscillator  32  is activated, and at the first leading edge the flip-flop  34  switches over, the output Q goes to a logical low level and the inverted-Q output goes to a logical high level, the generator  31  is activated, taking again the signal TWN to a high level. At the following leading edge of the oscillator  32 , the flip-flop  34  switches over again, the current generator  31  is deactivated and starts another cycle. The signal TWN, when the temperature is comprised between TL and TH has a waveform that alternates between the low level and the high level. 
     The signal VTL is generated by means of a further D type flip-flop  36  in combination with the NAND gate  37 . The filter function is provided by the oscillator period. 
     If the temperature overcomes TH, the signal TWN stays always low. The voltage VTH is generated by the output of the pulse counter  35  that counts K prefixed periods of the oscillator  32  fulfilling a filtering function. The number of the K periods are opportunely chosen on the basis of the filtering requirement. 
     FIG. 4 represents a block schematic of the control system  12  that comprises a register  41  which receives in input the signals B 0 , B 1  of channel identification that dissipates the greater power quantity and is enabled by the signal VTL provided by the temperature determination means  10 . 
     The datum stored by the register  41  is a binary number indicating the channel that dissipates more power. To send a turning off signal to the selected channel, the demultiplexer  42  is used, the outputs of which are placed at the inputs of a series of AND gates  43  that provide the turning off signal of the interested channel to a series of AND gates  44 . To the other inputs of the AND gates  43  is applied the signal VTL, inverted through the inverter  45 . 
     The turning off signal is generated, with a delay Dt with respect to the signal VTL, by means of the delay circuit  46  placed between the signal VTL and the inverter  45 . This delay is necessary to assure that the turning off signal is generated only after the correct information storage in the register  41 . 
     The memory circuit of the register  41  is used to prevent turning off other channels in addition to the channel with the greatest dissipation, as the turning off of a channel carries to the output a modification of the identification circuit that, with the lack of such a register  41 , will result in all of the channels being turned off in sequence. 
     The register  41  can be placed either before or after the demultiplexer  42  without altering the circuit operations. 
     The output of the AND gates  43  is set in input to a series of AND gates  44 , the signal VTH is set at the other input of the AND gates  44 . 
     The output of the AND gates  44  provides the turning off signal R 1 -R 4  to each of the channels. In the case of overcoming of the threshold VTL, the AND gates  43  provide to the AND gates  44 , that in this case are transparent, the signal of turning off of only a channel at a time. In case of overcoming of the threshold VTH, the AND gates  44  are forced to send a turning off signal to all the present channels. 
     The signals proportional to the dissipated power of each channel in input at the identification system  11  are voltages proportional to the dissipated power. These voltages could be obtained with known circuits, some of these are illustrated as examples in FIG.  5 . The circuit of FIG. 5 a  could be used with switch circuits toward ground (low-side), where a current proportional to the output voltage is obtained. It is a current mirror, well known to the skilled in the art, which comprises an external terminal (Pad) connected to a resistance and therefore to a first transistor connected like a diode, the first transistor is connected to a second transistor in which the current determined by the voltage applied to the Pad, by the resistance and by the diode characteristics is mirrored. Generally the low-side type circuits have a low voltage drop at their terminals, the output voltage starts to increase only when the protective circuit for the current limitation starts to work. When that happens the dissipated power increases considerably. Generally this current is constant and known, in this case the only variable in the power calculus is the output voltage. Opportunely choosing the resistance R value, we will get a current proportional to the power dissipated in play. A similar discussion is valid for the switch circuits toward battery (High-side), in this case the circuit of FIG. 5 b  will be used. It is a current mirror similar to that of FIG. 5 a  with the only difference that it provides a current coming out from its terminal. The circuit of FIG. 5 c  is instead used for a more generic application, that is when the channel can have notable voltage drops with varying currents, for instance in the case of the voltage regulators, power output stages etc. In this case in addition to the circuit seen before that provides a current Ii proportional to the current that flows in the channel, another circuit is necessary that mirrors a current Iv proportional to the voltage at the channel terminals. To get a current proportional to the dissipated power it is used a circuit like for instance that of FIG. 5 c , that is a known current multiplier  51 , that receives in input the Iv and Ii signals. If there is an interest in a voltage proportional to the dissipated power, and not in a current as that flowing out from the multiplier a resistance R is applied between the output and the ground, as shown in FIG. 5 c . 
     The identification system  11  receives the information on the dissipated power as an analog or digital signal, in our example it is a voltage proportional to the dissipated power, and it determines which channel is dissipating the highest power. A possible way to realize the elaboration of this information is represented in FIG.  6 . The circuit elaborates the analog signals V 0 , V 1 , V 2  and V 3  (proportional to the power dissipated by the channels  15   a ,  15   b ,  15   c  and  15   d ) applied to the inputs of two voltage comparators  61  and  62 . They have also been applied respectively to a terminal of the controlled switches  63 ,  64 ,  66  and  67 . 
     The outputs of the comparators  61  and  62  are applied to the inputs of a multiplexer  70 . The comparator  61  output is applied directly to the control of the switch  63 , and applied through an inverter  65  to the control of the switch  64 . The comparator  62  output is applied directly to the control of the switch  66 , and applied through an inverter  68  to the control of the switch  67 . 
     The other terminals of the switches  63  and  64  are connected together and applied to the input of a further voltage comparator  69 . The other terminals of the switches  66  and  67  are connected together and applied to the input of a further voltage comparator  69 . 
     The comparator  69  output provides the most significant bit B 1  of the binary number that enables identification of the channel with the most dissipation. This output signal has also been applied to the multiplexer  70  selection input which provides as output the least significant bit B 0 . If at the selection input B 1 =0 is applied the multiplexer  70  will select the signal at the comparator output  61 , if B 1 =1 is applied the multiplexer  70  will select the signal at the comparator output  62 . 
     With this circuit, by the opening and closing of the switches  63 ,  64 ,  66  and  67 , the most heat dissipating channels are selected and the information of these are examined again at the following stage. 
     In this way at the last stage (comparator  69 ) the two most dissipating channels will always be present, for the last comparison. The circuit in FIG. 6 represents the case in which there are four channels, but adding other stages, this circuit could be easily widened to manage a greater number of channels.