This invention relates to electronic circuits, and more specifically to a system and method for regulating an output of a switching supply circuit.
Switching regulators have been implemented as an efficient mechanism for providing a regulated output in power supplies. One such type of regulator is known as a switching supply circuit, which controls the flow of power to a load by controlling the “ON” and “OFF” duty-cycle of one or more high-side switches coupled to the load. Many different classes of switching supplies exist today. One type of switching supply circuit is known as a synchronous switching supply circuit. In a synchronous switching supply circuit, an inductor is used to maintain current flow that is switched from two separate sources. The two sources can include a high-side switch, such as a high-side field-effect transistor (FET), and a low-side switch, such as a low-side FET. After the high-side FET is deactivated, the low side FET becomes activated. The low side FET thus conducts current from ground to the inductor because magnetic power stored in the inductor dissipates to force current through the inductor by changing the voltage of the inductor source node to negative relative to ground. In this way, current continuously flows through the inductor, even at times when the high-side switch is deactivated.
It is desirable in the design of switching supplies to ensure that the output of the switching supply circuit is properly regulated. For example, if a load at the output of the switching supply circuit changes, it may be necessary to change the switching operation, such as by adjusting the switching duty cycle, to regulate the output voltage to a relatively constant level. Regulation is typically accomplished through feedback control, by either a voltage feedback technique, in which the output voltage of the switching supply is monitored, or a current feedback technique, in which both the output voltage and the inductor current are monitored. The current feedback technique can monitor the inductor current by connecting a current sense resistor in series with the output inductor. However, a resistor connected in series with the output inductor can result in a degradation of the performance efficiency of the switching supply circuit. Another way to accomplish the current feedback technique is by measuring a current flow through the high-side FET. However, this measurement control may result in inaccurate regulation because the feedback is based only on the high-side current information.
In one embodiment of the present invention, a switching supply circuit comprises a high-side field-effect transistor (FET), a low-side FET, and a driver control circuit operative to switch the high-side FET and the low-side FET between opposing “ON” and “OFF” states. The system further comprises a simulated output generator that is operative to combine both a first output waveform associated with the high-side FET and a second output waveform associated with the low-side FET to generate a simulated output signal that is a substantial representation of an output signal of the switching supply circuit, the simulated output signal being provided as a feedback to the driver control circuit.
In another embodiment of the present invention, a method for regulating an output current in a switching supply circuit comprises measuring a first output waveform associated with a high-side FET, measuring a second output waveform associated with a low-side FET, and combining the first output waveform and the second output waveform to generate a combined output waveform. The method further comprises generating a simulated output signal based on the combined output waveform, the simulated output signal being a substantial representation of the output current of the switching supply circuit, and providing the simulated output signal as a feedback to a driver control circuit.
In yet another embodiment of the present invention, a switching supply circuit comprises means for a measuring a first output signal associated with a high-side FET, means for a measuring a second output signal associated with a low-side FET, and means for combining the first output signal and the second output signal to generate a simulated output signal. The simulated output signal is a substantial representation of the output of the switching supply circuit. The switching supply circuit further comprises means for regulating the output of the switching supply circuit based on the simulated output signal.
The present invention relates to electronic circuits, and more specifically to a system and method for regulating an output of a switching supply circuit. In a switching supply circuit, an output waveform (e.g., voltage waveform, current waveform) is measured through each of a high-side field effect transistor (FET) and a low-side FET. The output waveforms are combined to generate a combined output waveform. The combined output waveform is input to a track-and-hold circuit that removes switching gaps from the combined output waveform. The resulting combined output waveform can be input to a simulated output generator to generate a simulated output signal. The simulated output signal is a substantial representation of the output current of the switching supply circuit. The simulated output signal is a feedback signal that is input to a driver control circuit for the switching supply circuit. The driver control circuit can thus use the feedback from the simulated output signal to regulate the output of the switching supply circuit.
The switching supply circuit 10 also includes an output inductor 20. The output inductor 20 is interconnected between the switching node 18 and the output VOUT of the switching supply circuit 10, the output VOUT being coupled to ground by a series connected resistor 22 and capacitor 24. The output inductor 20 maintains a relatively constant current IL flowing to the output of the switching supply circuit 10, as described above. Because the load at the output of the switching supply circuit 10 may change in response to the operation of other circuit components to which the switching supply circuit 10 is supplying power, the output of the switching supply circuit 10 may need to be regulated to maintain relatively constant values of the output current IL, as well as the corresponding output voltage VOUT. Accordingly, the switching supply circuit 10 includes a simulated output generator 26 that supplies feedback to the driver control circuit 12, the feedback being a simulated output signal that is a substantial representation of the output current IL.
The simulated output generator 26 receives inputs from a high-side sense circuit 28 and a low-side sense circuit 30. The high-side sense circuit 28, upon activation of the high-side FET 14, measures a first output waveform of the high-side FET 14, which could be a voltage potential across a sense resistor connected in parallel with the high-side FET 14. The first output waveform is output from the high-side sense circuit 28 to the simulated output generator 26. The low-side sense circuit 30, upon activation of the low-side FET 16, measures a second output waveform of the low-side FET 16, which could be a voltage potential across a sense resistor connected in parallel with the low-side FET 16. The second output waveform is output from the low-side sense circuit 30 to the simulated output generator 26.
The simulated output generator 26 combines the first output waveform and the second output waveform, such as through an analog multiplexer, to generate a combined output waveform. The combined output waveform may have signal conditioning performed on it, such as by removing switching gaps inherent through the alternating activation of the high-side FET 14 and the low-side FET 16. The resultant signal is the simulated output signal that is a substantial representation of the output current IL. The simulated output signal could be a current signal, such that it is a simulated output current signal that is a substantial reproduction of the inductor output current IL. Alternatively, the simulated output signal could be a voltage waveform that corresponds approximately to the output current IL. The driver control circuit 12 receives the simulated output signal as feedback for the purpose of regulating the output current IL through the inductor 20, for example, by controlling the amount of time (e.g., duty cycle) that the high-side FET 14 is “ON” relative to the low-side FET 16. It is to be understood that the driver control circuit 12 could receive feedback in the form of both a simulated output signal and a separate output voltage signal, such as in the above described current feedback technique, for the purpose of regulating the output current IL through the inductor 20.
The switching supply circuit 50 also includes an output inductor 60. The output inductor 60 is interconnected between the switching node 58 and the output VOUT of the switching supply circuit 50, the output VOUT being coupled to ground by a series connected resistor 62 and capacitor 64. The output inductor 60 maintains a relatively constant current IL flowing to the output of the switching supply circuit 50. To regulate the output based on various applied loads, the switching supply circuit 50 includes a simulated output generator 66 that supplies feedback to the driver control circuit 52, the feedback being a simulated output signal that is a substantial representation of the output current IL.
The simulated output generator 66 includes an analog multiplexer 68 that receives an input from each of a high-side sense circuit 70 and a low-side sense circuit 72. The high-side sense circuit 70 includes a sense resistor 74, a sense FET 76, and a voltage converter circuit 78. The sense resistor 74 and the sense FET 76 are connected in series with each other, with the series connection of the sense resistor 74 and the sense FET 76 being connected in parallel with the high-side FET 54. The voltage converter circuit 78 is connected in parallel with the sense resistor 74. The sense FET 76 has a gate terminal that is connected to a gate terminal of the high-side FET 54, such that the driver control circuit 52 activates both the high-side FET 54 and the sense FET 76 concurrently. As the sense FET 76 is not used to supply power to the switching node 58, the sense FET 76 may be substantially smaller in size than the high-side FET 54. The sense FET 76 could also be matched to the high-side FET 54, such that the sense FET 76 and the high-side FET 54 have substantially the same electrical characteristics, and such that the sense FET 76 is a scaled down version of the high-side FET 54.
Upon activation of the high-side FET 54, the sense FET 76 also becomes activated and current flows through the sense resistor 74. The current flow through the sense resistor 74 is a significantly scaled down equivalent to the current flow through the high-side FET 54. The current flow through the sense resistor 74 is thus measured and converted to a high-side voltage waveform by the voltage converter 78 (e.g., a differential amplifier), the voltage waveform being associated with the current flow through the high-side FET 54 over time.
Referring back to
Upon activation of the low-side FET 56, the sense FET 82 also becomes activated and current flows through the sense resistor 80. The current flow through the sense resistor 80 is a significantly scaled down equivalent to the current flow through the low-side FET 56. The current flow through the sense resistor 80 is thus measured and converted to a low-side voltage waveform by the voltage converter 84 (e.g., a differential amplifier), the voltage waveform being associated with the current flow through the low-side FET 56 over time.
Referring back to
Referring back to
Referring back to
The switching supply circuit 50 may also include other feedback signals to regulate the output current IL. Accordingly, the switching supply circuit 50 may also include a comparator 90. The comparator 90 receives the output voltage VOUT of the switching supply circuit 50 as an input to a positive terminal, and a preset voltage VREF as an input to a negative terminal. The comparator 90 has an output terminal that is input as a feedback signal to the driver control circuit 52, such that the driver control circuit 52 has a redundant feedback to regulate the output current IL of the switching supply circuit 50. In the example of
In view of the foregoing structural and functional features described above, certain methods will be better appreciated with reference to
What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.