METHOD FOR IMPROVING TRANSIENT RESPONSE FOR POWER CONVERTERS IN PULSE FREQUENCY MODE (PFM)

A first input of a modulator circuit is coupled to a current feedback terminal. An output of the modulator circuit is coupled to an input of a power stage circuit. A first input, a second input, and an output of a voltage compensation circuit are coupled to a voltage feedback terminal, a voltage reference terminal, and a compensation terminal, respectively. A first input of a summing circuit is coupled to the output of the voltage compensation circuit. An output of the summing circuit is coupled to a second input of the modulator circuit. An output of an offset generation circuit is coupled to a second input of the summing circuit. An input of a filter circuit is coupled to the output of the voltage compensation circuit. An output of the filter circuit is coupled to an input of the offset generation circuit.

BACKGROUND

Direct current (DC)-to-DC converters and alternating current (AC)-to-DC converters, which may be referred to collectively as power converters, are widely employed in devices of today to perform power conversion. Generally, power converters receive a nominal voltage from a power source, such as a battery, and provide a regulated output voltage at one or more voltage levels. A variety of power converters and topologies can be employed to perform this power conversion. For example, buck converters, boost converters, and buck-boost converters are three basic types of power converter technologies.

SUMMARY

A circuit includes a power stage circuit, a modulator circuit, a voltage compensation circuit, a summing circuit, an offset generation circuit, and a filter circuit. The power stage circuit has an input and an output. The modulator circuit has a first input, a second input, and an output. The first input of the modulator circuit is coupled to a current feedback terminal. The output of the modulator circuit is coupled to the input of the power stage circuit. The voltage compensation circuit has a first input, a second input, and an output. The first input of the voltage compensation circuit is coupled to a voltage feedback terminal. The second input of the voltage compensation circuit is coupled to a voltage reference terminal. The output of the voltage compensation circuit is coupled to a compensation terminal. The summing circuit has a first input, a second input, and an output. The first input of the summing circuit is coupled to the output of the voltage compensation circuit. The output of the summing circuit is coupled to the second input of the modulator circuit. The offset generation circuit has an input and an output. The output of the offset generation circuit is coupled to the second input of the summing circuit. The filter circuit has an input and an output. The input of the filter circuit is coupled to the output of the voltage compensation circuit. The output of the filter circuit is coupled to the input of the offset generation circuit.

A circuit includes a voltage-to-current converter, a summing circuit, a current mirror circuit, a current valve circuit, a current source circuit, and a filter circuit. The voltage-to-current converter circuit has an input, a first output, and a second output. The summing circuit has a first input, a second input, and an output. The first input of the summing circuit is coupled to the first output of the voltage-to-current converter circuit. The current mirror circuit has an input and an output. The output of the current mirror circuit is coupled to the second input of the summing circuit. The current valve circuit has an input, an output, and a control terminal. The output of the current valve circuit is coupled to the input of the current mirror circuit. The current source circuit has an output coupled to the input of the current valve circuit. The filter circuit has an input and an output. The input of the filter circuit is coupled to the second output of the voltage-to-current converter circuit. The output of the filter circuit is coupled to the control terminal of the current valve circuit.

A circuit includes a power stage circuit, a modulator circuit, a voltage compensation circuit, a summing circuit, an offset generation circuit, and a filter circuit. The power stage circuit is configured to output a switching signal based on a modulated signal. The modulator circuit is configured to output the modulated signal based on a comparison between a first feedback signal indicating a feedback current and a target signal indicating a target current peak. The voltage compensation circuit is configured to output a voltage compensation signal based on a comparison between a second feedback signal indicating a feedback voltage and a reference signal indicating a reference voltage. The summing circuit is configured to output the target signal based on the voltage compensation signal and an offset signal. The offset generation circuit is configured to output the offset signal based on a filtered voltage compensation signal. The filter is configured to output the filtered voltage compensation signal based on the voltage compensation signal.

The same reference numbers or other reference designators are used in the drawings to designate the same or similar (functionally and/or structurally) features.

DETAILED DESCRIPTION

The following description provides many different examples for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present description. The drawings are not drawn to scale.

FIG. 1 is a circuit diagram of some examples of a system including a voltage converter circuit 100. The voltage converter circuit 100 includes a power stage circuit 108, a modulator circuit 110 and a voltage compensation circuit 114. The system includes the voltage converter circuit 100, a voltage source 130, an inductor 132, a load circuit 134, a capacitor 136, and a current sensing circuit 138. In the example illustrated in FIG. 1, the system forms a DC-DC buck converter which generates a voltage across the load circuit 134 that is less than a voltage across the voltage source 130.

A first terminal 108a of the power stage circuit 108 is coupled to a first terminal 102 of the voltage converter circuit 100. A second terminal 108b of the power stage circuit 108 is coupled to a second terminal 104 of the voltage converter circuit 100. A third terminal 108c of the power stage circuit 108 is coupled to a third terminal 106 of the voltage converter circuit 100.

An output 110c of the modulator circuit 110 is coupled to a control terminal 108d of the power stage circuit 108. A first input 110a of the modulator circuit 110 is coupled to a current feedback terminal 112 of the voltage converter circuit 100.

A first input 114a of the voltage compensation circuit 114 is coupled to a voltage feedback terminal 116 of the voltage converter circuit 100. A second input 114b of the voltage compensation circuit 114 is coupled to a voltage reference terminal 118. An output 114c of the voltage compensation circuit 114 is coupled to a compensation terminal 120 of the voltage converter circuit 100.

A first terminal 130a of the voltage source 130 is coupled to terminal 102 of the voltage converter circuit 100. A second terminal 130b of the voltage source 130 is coupled to ground 140. A first terminal 132a of the inductor 132 is coupled to terminal 104 of the voltage converter circuit 100. A second terminal 132b of the inductor 132 is coupled to a first terminal 134a of the load circuit 134. A second terminal 134b of the load circuit 134 is coupled to ground 140. The voltage feedback terminal 116 of the voltage converter circuit 100 is coupled to the first terminal 134a of the load circuit 134. A first terminal 136a of the capacitor 136 is coupled to the second terminal 132b of the inductor 132 and the first terminal 134a of the load circuit 134. A second terminal 136b of the capacitor 136 is coupled to ground 140. The current sensing circuit 138 is coupled between the second terminal 132b of the inductor 132 and the first terminal 134a of the load circuit 134. An output 138a of the current sensing circuit 138 is coupled to the current feedback terminal 112 of the voltage converter circuit 100.

The voltage compensation circuit 114 receives a second feedback signal FB2 at input 114a from the voltage feedback terminal 116. The second feedback signal FB2 indicates a feedback voltage (the voltage across the load circuit 134). The voltage compensation circuit 114 receives a reference signal REF at input 114b from the voltage reference terminal 118. The reference signal REF indicates a reference voltage. The voltage compensation circuit 114 outputs a voltage compensation signal COMP at output 114c based on a comparison between the second feedback signal FB2 and the reference signal REF.

The modulator circuit 110 receives a first feedback signal FB1 at input 110a from the current feedback terminal 112. The first feedback signal FB1 indicates a feedback current (e.g., the current in the inductor 132 as measured by the current sensing circuit 138). The modulator circuit 110 receives a target signal TAR at input 110b. The target signal TAR indicates a target current peak. The modulator circuit 110 outputs a modulated signal MOD at output 110c based on a comparison between the first feedback signal FB1 and the target signal TAR.

The power stage circuit 108 receives the modulated signal MOD at control terminal 108d. The power stage circuit 108 selectively couples terminal 102 to terminal 104 and selectively couples terminal 104 to terminal 106 based on the modulated signal MOD.

In some examples, the voltage converter circuit 100 operates in a peak current control mode where the modulator circuit 110 sets the modulated signal MOD to a first value (e.g., a logic “low” value) in response to the first feedback signal FB1 reaching the target signal TAR. Further, the modulator circuit 110 periodically (e.g., according to a clock signal) sets the modulated signal MOD to a second value (e.g., a logic “high” value).

In response to the modulated signal MOD having the second value (logic “high”), the power stage circuit 108 couples terminal 102 to terminal 104 and decouples terminal 104 from terminal 106, thus coupling the voltage source 130 to the load circuit 134 through the inductor 132. In response, current flows through inductor 132 from terminal 132a to terminal 132b and to the load circuit 134.

In response to the modulated signal MOD having the first value (logic “low”), the power stage circuit 108 decouples terminal 102 from terminal 104 and couples terminal 104 to terminal 106, thus decoupling the voltage source 130 from the inductor 132 and coupling the inductor 132 to ground 140. In response, inductor 132 generates a current which flows from terminal 132a to terminal 132b and to the load circuit 134.

The power stage circuit 108 performs this switching (coupling and decoupling between terminals 102, 104, 106) at relatively high frequencies. Consequently, switching losses in the power stage circuit 108 are increased. These increased switching losses cause the voltage converter circuit 100 to suffer from reduced efficiency when operating at lighter loads (e.g., when the current demand from the load circuit 134 is decreased).

To improve the efficiency of the voltage converter circuit 100 at lighter loads, the voltage converter circuit 100 includes a target control circuit 122 coupled between the output 114c of the voltage compensation circuit 114 and input 110b of the modulator circuit 110. An input 122a of the target control circuit 122 is coupled to the output 114c of the voltage compensation circuit 114. An output 122b of the target control circuit 122 is coupled to input 110b of the modulator circuit 110.

The target control circuit 122 receives the voltage compensation signal COMP at input 122a and outputs the target signal TAR at output 122b based on the voltage compensation signal COMP. In response to the load falling below a load threshold, the target control circuit 122 causes the voltage converter circuit 100 to switch from peak current control mode to frequency control mode. For example, in response to the load falling below a load threshold, the target control circuit 122 sets the target signal TAR to a controllable reference target value. This causes the power stage circuit 108 to perform the switching (coupling and decoupling between terminals 102, 104, 106) at a controllable reference target frequency, independent of voltage compensation signal COMP. Conversely, in response to the load rising above the load threshold, the target control circuit 122 causes the voltage converter circuit 100 to switch from frequency control mode to peak current control mode. For example, in response to the load rising above the load threshold, the target control circuit 122 sets the target signal TAR based on the voltage compensation signal COMP. By reducing the reference target frequency when operating in frequency control mode (during lighter loads), the switching losses in the power stage circuit 108 can be reduced. Thus, efficiency can be improved during lighter loads.

The target control circuit 122 includes a summing circuit 124 and an offset generation circuit 126. A first input 124a of the summing circuit 124 is coupled to output 114c of the voltage compensation circuit 114. A second input 124b of the summing circuit 124 is coupled to an output 126b of the offset generation circuit 126. An output 124c of the summing circuit 124 is coupled to input 110b of the modulator circuit 110.

The summing circuit 124 receives the voltage compensation signal COMP at input 124a and an offset signal OFF at input 124b. The summing circuit 124 outputs the target signal TAR at output 124c based on a sum of the compensation signal COMP and the offset signal OFF.

In some examples, the offset generation circuit 126 receives the voltage compensation signal COMP at input 126a and outputs the offset signal OFF based on the voltage compensation signal COMP. However, in such examples, the voltage converter circuit 100 may exhibit reduced performance during transitions between peak current control mode and frequency control mode.

For example, as shown in FIG. 2, in response to the load decreasing, the first feedback signal FB1 (indicating feedback current) decreases and the second feedback signal FB2 (indicating feedback voltage) increases. In response to the second feedback signal FB2 increasing, the voltage compensation signal COMP decreases. In examples where the offset generation circuit 126 outputs the offset signal OFF based on the voltage compensation signal COMP, the offset signal OFF increases in response to the voltage compensation signal COMP reaching (e.g., falling to or below) a compensation threshold THCOMP, as shown by dashed line 202, so the target signal TAR (the sum of the offset signal OFF and the compensation signal COMP) does not fall below the reference target value Tref, as shown by dashed line 204. Because the target signal TAR is prevented from falling below the reference target value Tref (despite the voltage compensation signal COMP continuing to fall after the target signal TAR reaches the reference target value Tref), the voltage converter circuit 100 takes longer to correct the second feedback signal FB2 at this transition from peak current control mode to frequency control mode. As a result, the second feedback signal FB2 has increased overshoot at the transition, as shown by dashed line 206.

Further, as shown in FIG. 2, in response to the load increasing, the first feedback signal FB1 increases and the second feedback signal FB2 decreases. In response to the second feedback signal FB2 decreasing, the voltage compensation signal COMP increases. In examples where the offset generation circuit 126 outputs the offset signal OFF based on the voltage compensation signal COMP, the offset signal OFF decreases in response to the voltage compensation signal COMP increasing, as shown by dashed line 208. Because the offset signal OFF decreases as the voltage compensation signal COMP increases, the target signal TAR (the sum of the offset signal OFF and the voltage compensation signal COMP) remains approximately unchanged until the voltage compensation signal COMP reaches the compensation threshold THCOMP (and offset signal OFF reaches zero), as shown by dashed line 210. Only after the voltage compensation signal COMP reaches the compensation threshold THCOMP (and offset signal OFF reaches zero) does the target signal TAR begin substantially increasing, as shown by dashed line 212. Because of this delay in the target signal TAR response to the change in the voltage compensation signal COMP, the voltage converter circuit 100 takes longer to correct the second feedback signal FB2 at this transition from frequency control mode to peak current control mode. As a result, the second feedback signal FB2 has increased undershoot at the transition, as shown by dashed line 214.

To improve performance during the transitions between peak current control mode and frequency control mode, the target control circuit 122 of the voltage converter circuit 100 of FIG. 1 includes a filter circuit 128 coupled between the voltage compensation circuit 114 and the offset generation circuit 126. The filter circuit 128 is or includes a low pass filter. An input 128a of the filter circuit 128 is coupled to the output 114c of the voltage compensation circuit 114. An output 128b of the filter circuit 128 is coupled to the input 126a of the offset generation circuit 126.

The filter circuit 128 receives the voltage compensation signal COMP at input 128a and outputs the filtered voltage compensation signal FIL at output 128b based on the voltage compensation signal COMP. The offset generation circuit 126 receives the filtered voltage compensation signal FIL at input 126a and outputs the offset signal OFF at output 126b based on the filtered voltage compensation signal FIL. The filter circuit 128 adds a delay at the input 126a of the offset generation circuit 126 to improve the performance of the voltage converter circuit 100 during the transitions between the control modes.

For example, as shown in FIG. 2, in response to the load decreasing, the first feedback signal FB1 (indicating feedback current) decreases and the second feedback signal FB2 (indicating feedback voltage) increases. In response to the second feedback signal FB2 increasing, the voltage compensation signal COMP decreases. In response to the voltage compensation signal COMP decreasing, the filtered voltage compensation signal FIL decreases (at a reduced rate compared to voltage compensation signal COMP). In response to the filtered voltage compensation signal FIL reaching (e.g., falling to or below) the compensation threshold THCOMP, the offset signal OFF increases. Because the filtered voltage compensation signal FIL decreases at a reduced rate (compared to the voltage compensation signal COMP), the filtered voltage compensation signal FIL reaches the compensation threshold THCOMP after the voltage compensation signal COMP is substantially below the compensation threshold THCOMP (e.g., when the voltage compensation signal COMP is approximately zero). Because of this delay in the filtered voltage compensation signal FIL reaching the compensation threshold THCOMP, the target signal TAR (the sum of the offset signal OFF and the voltage compensation signal COMP) falls substantially below the reference target value Tref. Because the target signal TAR decreases according to the decrease in the voltage compensation signal COMP during this transition from peak current control mode to frequency control mode, the voltage converter circuit 100 corrects the second feedback signal FB2 more quickly at the transition. As a result, the second feedback signal FB2 has reduced overshoot at the transition. For example, the overshoot may be reduced by about 5 percent or more. By reducing the overshoot in the second feedback signal FB2 (which indicates the voltage across the load circuit 134), voltage stress on the system can be reduced, reliability of the system can be improved, and functional safety of the system can be improved.

Further, as shown in FIG. 2, in response to the load increasing, the first feedback signal FB1 increases and the second feedback signal FB2 decreases. In response to the second feedback signal FB2 decreasing, the voltage compensation signal COMP increases. In response to the voltage compensation signal COMP increasing, the filtered voltage compensation signal FIL increases (at a reduced rate relative to the voltage compensation signal COMP). In response to the filtered voltage compensation signal FIL increasing at a reduced rate, the offset signal OFF decreases at a reduced rate. Because the decrease in the offset signal OFF is slower than the increase in the voltage compensation signal COMP, the target signal TAR (the sum of the offset signal OFF and the voltage compensation signal COMP) increases as the voltage compensation signal COMP increases. Thus, the delay illustrated by dashed line 210 can be reduced or eliminated. By reducing this delay, the voltage converter circuit 100 can correct the second feedback signal FB2 more quickly at this transition from frequency control mode to peak current control mode. Thus, the second feedback signal FB2 has reduced undershoot at the transition. For example, the undershoot may be reduced by about 6 percent or more. By reducing undershoot in the second feedback signal FB2 (which indicates the voltage across the load circuit 134), the reliability of the system can be improved. Further, the size of output capacitor 136 can be reduced and thus the cost of the system may be reduced.

Although FIG. 1 illustrates a buck converter, it will be appreciated that in some examples, the system may alternatively be configured as a boost converter, a buck-boost converter, or the like. In some examples, the system may be configured as a multi-phase DC-DC converter including a plurality of voltage converter circuits coupled to a corresponding plurality of inductors.

In some examples, the system is an automotive system where the voltage source 130 is a car battery (e.g., a 12 volt battery) and the load circuit 134 is a vehicle infotainment device, a vehicle instrument cluster, a vehicle stereo, an Advanced driver-assistance systems (ADAS), a sensor fusion system, a vehicle radar system, a motor drive system, or the like. In some examples, the voltage converter circuit 100 is formed on a single monolithic integrated chip.

FIG. 3 is a circuit diagram of some examples of a voltage converter circuit 300 similar to the voltage converter circuit 100 of FIG. 1.

The target control circuit 122 includes a voltage-to-current converter circuit 310. An input 310a of the voltage-to-current converter circuit 310 is coupled to the output 114c of the voltage compensation circuit 114. A first output 310b of the voltage-to-current converter circuit 310 is coupled to input 124a of the summing circuit 124. A second output 310c of the voltage-to-current converter circuit 310 is coupled to the input 128a of the filter circuit 128.

The offset generation circuit 126 includes a current source circuit 302, a current valve circuit 304, and a current mirror circuit 306. The current source circuit 302 is coupled to a voltage source 312. An output 302a of the current source circuit 302 is coupled to an input 304a of the current valve circuit 304. A control terminal 304c of the current valve circuit 304 is coupled to the output 128b of the filter circuit 128. An output 304b of the current valve circuit 304 is coupled to an input 306a of the current mirror circuit 306. An output 306b of the current mirror circuit 306 is coupled to input 124b of the summing circuit 124.

The target control circuit 122 includes a slope compensation circuit 308. An output 308a of the slope compensation circuit 308 is coupled to a third input 124d of the summing circuit 124.

The voltage-to-current converter circuit 310 receives the voltage compensation signal at input 310a from the output 114c of voltage compensation circuit 114. The voltage-to-current converter circuit 310 outputs a converted voltage compensation signal at output 310b (e.g., converted from a voltage signal to a current signal) based on the voltage compensation signal. In addition, the voltage-to-current converter circuit 310 outputs an amplified voltage compensation signal at output 310c based on the voltage compensation signal.

The filter circuit 128 receives the amplified voltage compensation signal at input 128a and outputs the filtered voltage compensation signal at output 128b based on the amplified voltage compensation signal and a cutoff frequency of the filter circuit 128.

The current source circuit 302 outputs a reference target current signal at output 302a. The current valve circuit 304 receives the reference target current signal at input 304a and receives the filtered voltage compensation signal at control terminal 304c. The current valve circuit 304 outputs an offset current signal at output 304b. The offset current signal has a magnitude equal to a portion of the magnitude of the reference target current signal. The portion is based on the filtered voltage compensation signal. For example, the portion increases in response to the filtered voltage compensation signal increasing, and the portion decreases in response to the filtered voltage compensation signal decreasing. The current mirror circuit 306 receives the offset current signal at input 306a and outputs a copy of the offset current signal at output 306b.

The slope compensation circuit 308 outputs a slope compensation ramp signal at output 308a. The summing circuit 124 receives the copy of the offset current signal at input 124b, the converted voltage compensation signal at input 124a, and the slope compensation ramp signal at input 124d. The summing circuit 124 outputs the target signal based on a sum of the copy of the offset current signal, the converted voltage compensation signal, and the slope compensation ramp signal.

FIG. 4 is a circuit diagram of some examples of a voltage converter circuit 400 similar to the voltage converter circuit 300 of FIG. 3.

The target control circuit 122 includes a current-to-voltage converter circuit 402. An input 402a of the current-to-voltage converter circuit 402 is coupled to the output 124c of the summing circuit 124. An output 402b of the current-to-voltage converter circuit 402 is coupled to input 110b of the modulator circuit 110.

The circuit 400 includes a current sense amplifier circuit 404. A first input 404a of the current sense amplifier circuit 404 is coupled to current feedback terminal 112. A second input 404b of the current sense amplifier circuit 404 is coupled to a second current feedback terminal 406. An output 404c of the current sense amplifier circuit 404 is coupled to input 110a of the modulator circuit 110. In some examples, the current sense amplifier circuit 404 is coupled to a current sense resistor (not shown) which is coupled between an inductor (e.g., 132 of FIG. 1) and a load circuit (e.g., 134 of FIG. 1). For example, input 404a is coupled to a first terminal of the current sense resistor (through terminal 112) and input 404b is coupled to a second terminal of the current sense resistor (through terminal 406).

The current-to-voltage converter circuit 402 converts the target signal from a current signal to a voltage signal. The current sense amplifier circuit 404 converts the first feedback signal from a current signal to a voltage signal.

The modulator circuit 110 includes a comparator circuit 408 and a logic circuit 410. A first input 408a of the comparator circuit 408 is coupled to the output 404c of the current sense amplifier circuit 404. A second input 408b of the comparator circuit 408 is coupled to the output 402b of the current-to-voltage converter circuit 402. A first input 410a of the logic circuit 410 is coupled to an output 408c of the comparator circuit 408. A second input 410b of the logic circuit 410 is coupled to a clock terminal 418 of the voltage converter circuit 400.

The comparator circuit 408 receives the target signal at input 408b and the first feedback signal at input 408a. The comparator circuit 408 outputs a comparator output signal at output 408c based on a comparison between the target signal and the first feedback signal. The logic circuit 410 receives the comparator output signal at input 410a and a clock signal at input 410b. The logic circuit 410 outputs the modulated signal at output 410c based on the comparator output signal, the clock signal, and the logic of the logic circuit 410 (e.g., a logic table or the like).

The power stage circuit 108 includes a transistor driver circuit 412. An input 412a of the transistor driver circuit 412 is coupled to an output 410c of the logic circuit 410. In some examples, the power stage circuit 108 includes transistors 414, 416. A first terminal 414a of transistor 414 is coupled to terminal 102. A second terminal 414b of transistor 414 and a first terminal 416a of transistor 416 are coupled to terminal 104. A second terminal 416b of transistor 416 is coupled to terminal 106. A control terminal 414c of transistor 414 is coupled to a first output 412b of the transistor driver circuit 412. A control terminal 416c of transistor 416 is coupled to a second output 412c of the transistor driver circuit 412.

The transistor driver circuit 412 receives the modulated signal at input 412a. The transistor driver circuit 412 outputs a first driver signal at output 412b and a second driver signal at output 412c. The driver signals control transistors 414, 416 which selectively couple terminals 102, 104, 106 based on the driver signals.

In some examples, transistors 414, 416 are external to voltage converter circuit 400. In such examples, output 412b is coupled to terminal 102, output 412c is coupled to terminal 104, and terminal 106 is omitted from the voltage converter circuit 400. In such examples, transistors 414, 416 may be off-chip (on a separate chip) and control terminals 414c, 416c may be coupled to terminals 102, 104, respectively, by wiring that is external to the chips.

FIG. 5 is a circuit diagram of some examples of a voltage converter circuit 500 similar to the voltage converter circuit 400 of FIG. 4.

The voltage compensation circuit 114 includes an error amplifier 502. A first input 502a of the error amplifier 502 is coupled to the feedback voltage terminal 116. A second input 502b of the error amplifier 502 is coupled to an output 508a of a reference voltage generation circuit 508. The output 502c of the error amplifier 502 is coupled to the input 310a of the voltage-to-current converter circuit 310 and the compensation terminal 120.

The voltage compensation circuit 114 includes an input impedance circuit 504 coupled between the feedback voltage terminal 116 and input 502a of the error amplifier 502. For example, a first terminal 504a if the input impedance circuit 504 is coupled to the voltage feedback terminal 116 and a second terminal 504b of the input impedance circuit 504 is coupled to the first input 502a of the error amplifier.

The voltage compensation circuit 114 includes a feedback impedance circuit 506 coupled between input 502a of the error amplifier 502 and the output 502c of the error amplifier 502. For example, a first terminal 506a of the feedback impedance circuit 506 is coupled to the first input 502a of the error amplifier 502 and a second terminal 506b of the feedback impedance circuit 506 is coupled to the output 502c of the error amplifier 502.

A transfer function of the voltage compensation circuit 114 has at least one pole and at least one zero. The low pass filter of the filter circuit 128 has a time constant corresponding to a time delay. The time constant of the filter circuit 128 and the zero of the transfer function of the voltage compensation circuit 114 are approximately equal to optimize the delay generated by the filter circuit 128. In some cases, if the time constant is less than the zero and thus the delay is too short, the rate of change of the filtered voltage compensation signal may not be slow enough and thus the second feedback signal may have poor overshoot/undershoot at the transitions. If the time constant is too high and thus the delay is too long, the rate of change of the filtered voltage compensation signal may be too slow, the delay may be longer than necessary and thus performance may be reduced. By setting the time constant of the filter circuit 128 and the zero of the transfer function of the voltage compensation circuit 114 to be approximately equal, the length of the delay at the filter circuit 128 may be optimized according to the performance of the voltage compensation circuit 114 (e.g., the delay can be long enough but not too long).

FIG. 6A and FIG. 6B are a circuit diagram of some examples of a voltage converter circuit 600 similar to the voltage converter circuit 500 of FIG. 5.

The voltage-to-current converter circuit 310 includes an amplifier 602, a transistor 604, and a resistor 606. A first terminal 602a of the amplifier 602 is coupled to the output 502c of the error amplifier 502. A second terminal 602b of the amplifier 602 is coupled to a second terminal 604b of transistor 604 and a first terminal 606a of resistor 606. An output 602c of the amplifier 602 is coupled to a control terminal 604c of transistor 604 and the input 128a of the filter circuit 128. A first terminal 604a of transistor 604 is coupled to input 124a of the summing circuit 124. A second terminal 606b of resistor 606 is coupled to ground 630. Transistor 604 passes a current from terminal 406a to terminal 604b. The magnitude of the current is based on the voltage at terminal 602a.

The filter circuit 128 includes a resistor 608 and a capacitor 610. A first terminal 608a of resistor 608 is coupled to the output 602c of amplifier 602. A second terminal 608b of resistor 608 is coupled to a first terminal 610a of capacitor 610 and the control terminal 304c of the current valve circuit 304. A second terminal 610b of capacitor 610 is coupled to ground 630.

The current valve circuit 304 includes a transistor 612 and a resistor 614. A first terminal 612a of transistor 612 is coupled to the output 302a of the current source circuit 302 and the input 306a of the current mirror circuit 306. A second terminal 612b of transistor 612 is coupled to a first terminal 614a of resistor 614. A control terminal 612c of transistor 612 is coupled to terminal 608b of resistor 608 and terminal 610a of capacitor 610. A second terminal 614b of resistor 614 is coupled to ground 630. A first portion of the current from output by the current source circuit 302 is output to the current mirror circuit 306. Transistor 612 passes a second portion of the current from the current source circuit 302 to ground 630 based on the magnitude of the voltage at terminal 608b of resistor 608 and terminal 610a of capacitor 610.

The current mirror circuit 306 includes a first transistor 616 and a second transistor 618. A first terminal 616a of transistor 616 is coupled to the output 302a of the current source circuit 302 and the first terminal 612a of transistor 612. A second terminal 616b of transistor 616 is coupled to ground 630. A control terminal 616c of transistor 616 is coupled to a control terminal 618c of transistor 618 and to terminal 616a of transistor 616. A first terminal 618a of transistor 618a is coupled to input 124b of summing circuit 124. A second terminal 618b of transistor 618 is coupled to ground 630.

The summing circuit shorts input 124a, input 124b, and input 124d to output 124c. For example, terminal 618a of transistor 618, terminal 604a of transistor 604, and output 308a of the slope compensation circuit 308 are coupled together and to input 408b of the comparator circuit 408.

The current-to-voltage converter circuit 402 includes a resistor 620 and a voltage terminal 632 (e.g., a voltage supply terminal or a ground terminal). A first terminal 620a of resistor 620 is coupled to terminal 618a of transistor 618, terminal 604a of transistor 604, output 308a of the slope compensation circuit 308, and input 408b of comparator circuit 408. A second terminal 620b of resistor 620 is coupled to the voltage terminal 632.

The input impedance circuit 504 includes a resistor 622 having a first terminal 622a coupled to terminal 116 and a second terminal 622b coupled to input 502a of the error amplifier 502.

The feedback impedance circuit 506 includes a resistor 624, a capacitor 626, and a capacitor 628. A first terminal 624a of resistor 624 and a first terminal 628a of capacitor 628 are coupled to input 502a of error amplifier 502. A second terminal 624b of resistor 624 is coupled to a first terminal 626a of capacitor 626. A second terminal 626b of capacitor 626 and a second terminal 628b of capacitor 628 are coupled to the output 502c of error amplifier 502.

As described with regard to FIG. 5, the time constant of the filter circuit 128 is approximately equal to the zero of the transfer function of the voltage compensation circuit 114 to optimize the delay caused by the filter circuit 128. In other words, the cutoff frequency of the filter circuit 128 is approximately equal to the zero frequency of the transfer function of the voltage compensation circuit 114. This can be achieved in the circuit 600 of FIG. 6A and FIG. 6B by making the product of the resistance of resistor 608 and the capacitance of capacitor 610 approximately equal to the product of the resistance of resistor 624 and the capacitance of capacitor 626.

Although the voltage compensation circuit 114 of FIG. 6A and FIG. 6B includes internal compensation where the input impedance circuit 504 and the feedback impedance circuit 506 are internal to the voltage converter circuit 600 (e.g., the input impedance circuit 504 and the feedback impedance circuit 506 are on the same chip as the other components of circuit 600), it will be appreciated that in some other examples, the voltage compensation circuit 114 may include external compensation where the input impedance circuit 504 and the feedback impedance circuit 506 are external to the voltage converter circuit 600 (e.g., the input impedance circuit 504 and the feedback impedance circuit 506 are a different chip than the other components of circuit 600). In such examples, the feedback impedance circuit 506 is coupled to the compensation terminal 120 and the input impedance circuit 504 is coupled to the voltage feedback terminal 116 by external wiring. In such examples, resistor 608 and capacitor 610 are variable so that their resistance and capacitance, respectively, can be adjusted (e.g., via an additional terminal of the circuit 600) based on resistance and capacitance of the external feedback impedance circuit in order to optimize the delay of the filter circuit 128 according to the external feedback impedance.

Although the voltage compensation (of the zeros and poles) circuit 114 of FIG. 6A and FIG. 6B includes a type II compensator, it will be appreciated that voltage compensation circuit 114 could alternatively include a type III compensator or some other type of compensator.

The methods are illustrated and described above as a series of acts or events, but the illustrated ordering of such acts or events is not limiting. For example, some acts or events may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Also, some illustrated acts or events are optional to implement one or more aspects or embodiments of this description. Further, one or more of the acts or events depicted herein may be performed in one or more separate acts and/or phases. In some embodiments, the methods described above may be implemented in a computer readable medium using instructions stored in a memory.

While the use of particular transistors are described herein, other transistors (or equivalent devices) may be used instead with little or no change to the remaining circuitry. For example, a metal-oxide-silicon FET (“MOSFET”) (such as an n-channel MOSFET, nMOSFET, or a p-channel MOSFET, pMOSFET), a bipolar junction transistor (BJT—e.g. NPN or PNP), insulated gate bipolar transistors (IGBTs), and/or junction field effect transistor (JFET) may be used in place of or in conjunction with the devices disclosed herein. The transistors may be depletion mode devices, drain-extended devices, enhancement mode devices, natural transistors or other type of device structure transistors. Furthermore, the devices may be implemented in/over a silicon substrate (Si), a silicon carbide substrate (SiC), a gallium nitride substrate (GaN) or a gallium arsenide substrate (GaAs).