The present invention relates to a thermal protection circuit and a method for protecting a power delivery circuit, and especially to a thermal protection circuit arranged in an integrated circuit for protecting the power delivery circuit.
Thermal protection is an important requirement for a power delivery circuit to prevent permanent damage due to prolonged operation at excessive temperatures. The maximum operation temperature of the power delivery circuit is limited by a thermal shutdown circuit which provides a necessary protection by sensing a temperature of the power delivery circuit and automatically shutting down the power delivery circuit when the temperature of the circuit exceeds a predictable threshold value.
Normally, a base-emitter voltage VBE of a transistor which is a function of temperature is used as a temperature-sensing element. The base-emitter voltage VBE of the transistor used for this purpose typically operates at forward conduction. However, the base-emitter voltage VBE with a negative temperature coefficient of voltage (TC=xe2x88x922 mV/xc2x0 C.) decreases as the temperature of the power delivery circuit increases. When the temperature of the circuit rises, the base-emitter voltage VBE will decrease until the temperature of the circuit reaches a threshold value, thereby causing the thermal shutdown circuit to shut down the power delivery circuit. The power delivery circuit may oscillate by turning itself on and off through the thermal shutdown circuit. Therefore, a hysteresis protection circuit is applied to the power delivery circuit in order to reduce thermal oscillations at a shutdown temperature.
FIG. 1 shows a current waveform of a power delivery circuit with a hysteresis protection circuit arranged in an integrated circuit according to the prior art. Please refer to FIG. 1. It shows the current waveform of a general power delivery circuit with the hysteresis protection circuit. When the power delivery circuit sustains an excessive loading current, the current waveform (where an unusual condition occurs), which is out of specification, is like a curve 101. Thereby, the power delivery circuit is turned off by the hysteresis protection circuit, and the current waveform is like a curve 102. Because the power delivery circuit is turned off, the temperature of the power delivery circuit is decreasing into a threshold value, thereby the power delivery circuit being turned on again. Moreover, the current which passes through the integrated circuit with a constant value (where the current waveform is like a curve 103) might increase the temperature of the integrated circuit. And then, the temperature of the integrated circuit will reach the threshold value to turn off the power delivery circuit again. Although the hysteresis protection circuit is designed in the power delivery circuit, the thermal oscillation can not be avoided (where the current waveform is like a curve 104). When the power delivery circuit is turned off with the constant current, the integrated circuit will be oscillated in the designed hysteresis temperature region, which is called thermal oscillation. The ICs design needs to avoid this because the different coefficient of thermal expansion might cause crack between package and die.
It is therefore attempted by the applicant to deal with the above situation encountered by the prior art.
It is therefore an object of the present invention to propose a thermal protection circuit for protecting a power delivery circuit to limit a maximum current passing through the power delivery circuit by using a thermal feedback servo loop to adjust the conductive resistance of the power delivery circuit.
It is therefore another object of the present invention to propose a thermal protection circuit for protecting a power delivery circuit to limit a maximum current passing through the power delivery circuit by using a pulse width modulation technique which is a function of the temperature of the power delivery circuit.
It is therefore another object of the present invention to propose a method for protecting a power delivery circuit to limit a maximum current passing through the power delivery circuit by using a thermal feedback servo loop to adjust the conductive resistance of the power delivery circuit.
It is therefore an additional object of the present invention to propose a method for protecting a power delivery circuit to limit a maximum current passing through the power delivery circuit by using a pulse width modulation technique which is a function of the temperature of the power delivery circuit.
The thermal protection circuit for protecting a power delivery circuit includes a first thermal sensing circuit exhibiting a negative temperature coefficient characteristic for sensing a temperature at the power delivery circuit and providing a first voltage, a second thermal sensing circuit exhibiting a positive temperature coefficient characteristic for transforming the temperature of the power delivery circuit to a second voltage, an amplifier electrically connected to the first voltage and the second voltage for providing a control signal, wherein the amplifier is a function of a voltage difference between the first voltage and the second voltage, and a switch electrically connected to an output of the amplifier for limiting a maximum current passing there through in response to the control signal.
According to an aspect of the present invention, the first thermal sensing circuit includes a current source, and a transistor having an emitter terminal grounded, a collector terminal electrically connected to the current source, and a base terminal electrically connected to the collector for providing a base-emitter voltage of the transistor as the first voltage.
Preferably, the transistor is a bipolar transistor (BJT).
Preferably, the amplifier is an operational amplifier (OP amplifier).
Preferably, the thermal protection circuit further includes a load electrically connected to the switch.
Preferably, the load is a passive load.
Preferably, the load is an active load.
Preferably, the second thermal sensing circuit includes a third voltage proportional to an absolute temperature of the ambient temperature, a thermal circuit having a thermal resistance for transforming the temperature at the power delivery circuit to a fourth voltage, and an adder electrically connected to the third voltage and the fourth voltage for providing the second voltage that is a sum of the third voltage and the fourth voltage.
It is therefore another object of the present invention to propose a thermal protection circuit for protecting a power delivery circuit, including an amplifier electrically connected to a reference voltage and a first voltage that is a function of a temperature on the power delivery circuit for providing a second voltage by a difference of the reference voltage and the first voltage, a comparator electrically connected to the second voltage and a sawtooth waveform voltage for comparing the second voltage and the sawtooth waveform voltage to generate a pulse width modulation signal, and a switch electrically connected to an output of the comparator for limiting a maximum current passing there through in response to the pulse width modulation signal.
Preferably, the amplifier is an operational amplifier (OP amplifier).
Preferably, the thermal protection circuit further includes a load electrically connected to the switch.
Preferably, the load is a passive load.
Preferably, the load is an active load.
It is therefore another object of the present invention to propose a method for protecting a power delivery circuit which includes a first thermal sensing circuit, and a second thermal sensing circuit, including the steps of: (a) sensing a temperature at the power delivery circuit and providing a first voltage that decreases when the temperature rises by the first thermal sensing circuit, (b) transforming the temperature of the power delivery circuit to a second voltage that increases when the temperature rises by the second thermal sensing circuit, and (c) providing a control signal by comparing the first voltage and the second voltage, thereby the control signal capable of limiting a maximum current passing through the power delivery circuit.
Preferably, the step of transforming the temperature of the power delivery circuit to a second voltage that increases when the temperature rises, includes the steps of: (a) sensing an ambient temperature and providing a third voltage proportional to an absolute temperature of the ambient temperature, (b) transforming the temperature of the power delivery circuit to a fourth voltage by a thermal resistance, and (c) providing the second voltage which is a sum of the third voltage and the fourth voltage.
It is therefore an additional object of the present invention to propose a method for protecting a power delivery circuit, including the steps of: (a) providing a second voltage by a difference of a reference voltage and a first voltage that is a function of a temperature at the power delivery circuit, (b) generating a pulse width modulation signal by comparing the second voltage and a sawtooth waveform voltage, and (c) limiting a maximum current passing through the integrated circuit in response to the pulse width modulation signal.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: