Patent Application
20170141680
This application claims priority to and the benefit of Chinese Patent Application No. 201510770698.X, filed Nov. 12, 2015, which is incorporated herein by reference in its entirety.
The present invention relates to electronic circuits, more specifically, the present invention relates to DC-DC converter with COT (constant on time) control and the method thereof.
Most electric devices such as notebook, desktop computer and PDA need a regulated voltage to power function blocks. DC-DC converters with COT control characterized with fast transient response and simple structure are widely used in the above fields. Typically, DC-DC converters with COT control need slope compensation to stabilize the output voltage.
A slope compensation signal has a fixed slope in prior art. It is reset to zero when a main power switch in the converter turns on. Then it increases with a fixed slope until the slope compensation signal is reset again when the output voltage of the converter drops to a sum of the slope compensation signal and a reference voltage. This process repeats during the operation of the converter.
However, if load step occurs (e.g. the load steps to heavy load from light load, or the load steps to light load from heavy load), the output voltage decreases rapidly and falls below the reference voltage in a short time period.
It is an object of the present invention to provide an improved DC-DC converter with transient control, which solves the above problems.
In accomplishing the above and other objects, there has been provided, in accordance with an embodiment of the present invention, a DC-DC converter with transient control, comprising: a power switching circuit, configured to receive an input voltage and to provide an output voltage; a transient unit, configured to generate a transient current signal indicative of the transient information of a current flowing through the power switching circuit; a comparing circuit, configured to generate a set signal based on a reference voltage, a feedback voltage indicative of the output voltage, a slope compensation signal and the transient current signal; and a logical control circuit, configured to generate a switching control signal to control the operation of the power switching circuit based on the set signal.
In addition, there has been provided, in accordance with an embodiment of the present invention, a DC-DC converter with transient control, comprising: a power switching circuit, configured to receive an input voltage and to provide an output voltage; a resistor, having a first end and a second end, wherein the first end is configured to receive a current sense signal indicative of the current flowing through the power switching circuit; a capacitor, coupled between the second end of the resistor and a reference ground; a comparing circuit, configured to generate a set signal based on a reference voltage, a feedback voltage indicative of the output voltage, a slope compensation signal, the current sense signal and a voltage across the capacitor; and a logical control circuit, configured to generate a switching control signal to control the operation of the power switching circuit based on the set signal.
Furthermore, there has been provided, in accordance with an embodiment of the present invention, a method used in a DC-DC converter, the DC-DC converter including a power switching circuit configured to receive an input voltage and generate an output voltage, the method comprising: detecting whether the DC-DC converter is in steady state condition or in transient state condition; comparing a sum of a slope compensation signal and a reference voltage with the feedback voltage to generate a set signal when the DC-DC converter is in steady state condition; and generating a transient current signal indicative of the transient information of a current flowing through the power switching circuit, and comparing a sum of the slope compensation signal and the reference voltage with a sum of the feedback voltage and the transient current signal to generate the set signal when the DC-DC converter is in transient state condition.
The use of the similar reference label in different drawings indicates the same of like components.
Embodiments of circuits for DC-DC converter are described in detail herein. In the following description, some specific details, such as example circuits for these circuit components, are included to provide a thorough understanding of embodiments of the invention. One skilled in relevant art will recognize, however, that the invention can be practiced without one or more specific details, or with other methods, components, materials, etc.
The following embodiments and aspects are illustrated in conjunction with circuits and methods that are meant to be exemplary and illustrative. In various embodiments, the above problem has been reduced or eliminated, while other embodiments are directed to other improvements.
V
FB
+V
tra
<V
REF
+V
SL (1)
In one embodiment, the current sense signal ICS may be a current signal or a voltage signal.
In one embodiment, the slope compensation signal VSL is reset to zero and increases with a fixed slope when a main power switch in the power switching circuit 103 turns on.
In one embodiment, the transient current signal Vtra generated by the transient unit 104 is indicative of the transient information (i.e. the AC component) of the current sense signal ICS.
During the operation of the DC-DC converter, when the load step occurs (e.g. the load jumps to heavy load from light load very fast and within a short period of time), the output voltage VO decreases. The frequency of the switching control signal PWM increases, and the current flowing through the power switching circuit 103 increases, i.e. the current sense signal ICS increases. The transient current signal Vtra also increases. Thus the variation of the output voltage VO slows down according to expression (1). As a result, the set signal postpones triggering the switching control signal PWM, which reduces the pulses of the switching control signal PWM. So the energy stored in the inductor is reduced during the load step, and the overshoot is eliminated, which ensures the system stability.
When the system is in operation, if the load step occurs (e.g. the load jumps to heavy load from light load), the current sense signal ICS increases. Then the voltage across the resistor 41 also increases, i.e. the transient current signal Vtra increases. According to expression (1), the variation of the output voltage VO slows down, and the set signal postpones triggering the switching control signal PWM, which reduces the pulses of the switching control signal PWM. So the energy stored in the inductor is reduced during the load step, and the overshoot is eliminated as discussed above. In steady state, due to the existence of the capacitor 42, the average voltage across the resistor 41 is zero. So the transient current signal Vtra provided by the transient unit 104 reflects the transient information of the current sense signal ICS. That is, the transient current signal Vtra reflects the transient information (the alternating information) of the current flowing through the power switching circuit 103.
In one embodiment, if the current sense signal ICS is in current form, the DC-DC converter 200 further comprises a current-voltage converter as shown in
When the system is in operation, the current sense signal ICS is delivered to the first input terminal of the comparator 53 via the first adder 51, and is delivered to the second input terminal of the comparator 53 via the resistor 41, the capacitor 42 and the second adder 52. So the current sense signal ICS is counteracted in steady state condition. But in transient state condition, e.g. when the load suddenly jumps to heavy load from light load, the current sense signal ICS increases rapidly. Because of the existence of the capacitor, the voltage across the capacitor 42 (i.e. the transient current signal Vste) cannot change so fast, so the transient information of the current sense signal ICS is delivered to the first input terminal of the comparator 53. As a result, the variation of the output voltage VO slows down, and the set signal postpones triggering the switching control signal PWM, which reduces the pulses of the switching control signal PWM. Thus the energy stored in the inductor is reduced during the load step, and the overshoot is eliminated.
Step 301, deriving a feedback signal indicative of the output voltage, and a current sense signal indicative of a current flowing through the power switching circuit.
Step 302, detecting whether the DC-DC converter is in steady state condition or not, if the DC-DC converter is in steady state condition, go to step 303; and if the DC-DC converter is in transient state condition, go to step 304.
Step 303, comparing a sum of a slope compensation signal VSL and a reference voltage VREF with the feedback voltage VFB to generate a set signal.
Step 304, generating a transient current signal Vtra indicative of the transient information of the current sense signal.
Step 305, comparing a sum of the slope compensation signal VSL and the reference voltage VREF with a sum of the feedback voltage VFB and the transient current signal to generate the set signal.
Step 306, generating a switching control signal in response to the set signal, to control the operation of the power switching circuit.
It is to be understood in these letters patent that the meaning of “A” is coupled to “B” is that either A and B are connected to each other as described below, or that, although A and B may not be connected to each other as described above, there is nevertheless a device or circuit that is connected to both A and B. This device or circuit may include active or passive circuit elements, where the passive circuit elements may be distributed or lumped-parameter in nature. For example, A may be connected to a circuit element that in turn is connected to B.
This written description uses examples to disclose the invention, including the best mode, and also to enable a person skilled in the art to make and use the invention. The patentable scope of the invention may include other examples that occur to those skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201510770698.X | Nov 2015 | CN | national |
