WO2016127175A1

WO2016127175A1 - Power regulator and slope compensation

Info

Publication number: WO2016127175A1
Application number: PCT/US2016/017003
Authority: WO
Inventors: Joseph G. RENAUER; Joel N. BRASSFIELD
Original assignee: Texas Instruments Japan Ltd; Texas Instruments Inc
Current assignee: Texas Instruments Japan Ltd; Texas Instruments Inc
Priority date: 2015-02-06
Filing date: 2016-02-08
Publication date: 2016-08-11
Anticipated expiration: 2017-08-06
Also published as: US20160233772A1

Abstract

In described examples, a power regulator (400) for converting an input voltage V_INto an output voltage V_OUT includes an inductor L2. The output voltage V_OUT of the regulator (400) is in response to charging of the inductor L2 at a clock frequency. An error amplifier (420) has an inverting input coupled to the regulator output, and a non-inverting input coupled to a reference voltage V_REF. A slope compensation circuit is for generating a signal for charging the inductor L2. The compensation circuit includes an output coupled the circuitry for charging the inductor L2. A signal on the output is generated in response to the input voltage V_IN, the output voltage V_OUT, and the clock frequency.

Description

POWER REGULATOR AND SLOPE COMPENSATION

BACKGROUND

[0001] Modular power regulators convert an input voltage to a regulated output voltage. Many of these power regulators are intended to be general purpose devices that operate over a wide range of input and output voltages. Some power regulators regulate their output voltages by charging and discharging a fixed value inductor that is coupled to the output of the power regulators. For these power regulators, the control architecture includes a feedback loop to regulate the output voltage. The feedback loop includes an error amplifier.

[0002] Many of the error amplifier topologies exhibit the undesirable characteristic that their system transient responses change dramatically with the output voltage setting. For example, higher output voltage settings may result in higher transient responses. Optimizing the transient responses requires modifying the frequency compensation of the power regulator. For example, each output voltage value has a particular optimum compensation value, which requires changing components in the power regulator (or associated with the power regulator) to match the particular optimum compensation value. Accordingly, when a user changes the output voltage value, the components associated with the frequency compensation have to be changed, which is burdensome on the users.

SUMMARY

[0003] In described examples, a power regulator for converting an input voltage to an output voltage includes an inductor. The output voltage of the regulator is in response to charging of the inductor at a clock frequency. An error amplifier has an inverting input coupled to the regulator output, and a non-inverting input coupled to a reference voltage. A slope compensation circuit is for generating a signal for charging the inductor. The compensation circuit includes an output coupled the circuitry for charging the inductor. A signal on the output is generated in response to the input voltage, the output voltage, and the clock frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 is a block diagram of a conventional modular step-down switching power regulator. [0005] FIG. 2 is a graph of example transient response variations in the output voltage VOU_T of the power regulator of FIG. 1 as the load current supplied by VOU_T is changed.

[0006] FIG. 3 is a graph of example loop gains at different output voltages as a function of frequency for the power regulator of FIG. 1.

[0007] FIG. 4 is a block diagram of an example power regulator that overcomes issues related to the power regulator of FIG. 1.

[0008] FIG. 5 is a block diagram of an example power stage of the power regulator of FIG. 4.

[0009] FIG. 6 is a circuit that generates an adaptive slope compensation signal for a valley current mode power regulator, such as the power regulator of FIG. 4.

[0010] FIG. 7 is a block diagram of a power regulator that includes slope compensation and an error amplifier.

DETAILED DESCRIPTION OF EXAMPLE EMB ODEVIENT S

[0011] FIG. 1 is a block diagram of a conventional modular step-down switching power regulator 100. Power regulators, such as the power regulator 100, are often implemented as power modules. The power regulator 100 includes an input 102 that receives an input voltage V_IN and an output 103. The power regulator 100 generates an output voltage VOU_T at the output 103.

[0012] The input 102 is coupled to a power stage 110 that generates a drive signal into an inductor LI . In the example of FIG. 1, the drive signal is a pulse width modulated (PMW) signal. The widths of the pulses are proportional to a control signal received at an input 112 of the power stage 110. In the example of FIG. 1, the control signal is a voltage that is proportional to the difference between the output voltage VOU_T and a target output voltage. The inductor LI is fed with a signal, such as PWM pulses of the input voltage Vi_N. These PWM pulses are rectangular pulses of voltage and are integrated by the inductor LI into triangular current pulses that charge a capacitor CI . The charging current into the capacitor CI determines the output voltage VOUT-

[0013] The output 103 is coupled to a voltage divider 116 that consists of two resistors Ra and Rb. The resistor Rb is variable. As described below, the value of the resistor Rb sets the value of the output voltage VOU_T- The output of the voltage divider 116 is a node Nl that is coupled to the inverting input of an error amplifier 120. The non-inverting input of the error amplifier 120 is coupled to a reference voltage V_REF, which in some examples is a very stable and precise reference voltage. The output voltage VOU_T is set by the voltage divider 1 16. More specifically, the output voltage VOU_T is divided down, so that the voltage at the inverting input of the error amplifier 120 is equal to the value of the reference voltage V_REF-

[0014] In the example of FIG. 1 , the error amplifier 120 is a transconductance amplifier, so it generates an output current that is proportional to the difference in the voltages at the inverting and non-inverting inputs. The output of the error amplifier 120 drives frequency compensation components consisting of a resistor Rc and a capacitor Cc. The output of the error amplifier 120 also drives the control input 1 12 of the power stage 1 10. As described above, the control input is used for generating the drive signal generated by the power stage 1 10. The example of the drive signal in the power regulator 100 is a PWM signal. The control signal determines the widths of the PWM signal to maintain the output voltage VOU_T at its target value.

[0015] Power regulators, such as the power regulator 100, have the undesirable characteristic that the system loop bandwidth varies directly with the amount of attenuation produced by the voltage divider 1 16. As the target output voltage increases, the attenuation required by the voltage divider 1 16 increases.

[0016] In a conventional power regulator, such as the power regulator 100, a fixed reference voltage V_REF is applied to the non-inverting input of the error amplifier 120. The output voltage VOU_T is set by the resistive voltage divider 1 16. As the target output voltage VOU_T increases, the required attenuation by the voltage divider 1 16 increases. The principal disadvantage of this configuration is that the loop gain of the power regulator 100 is attenuated by the same amount as the voltage applied to the inverting input to the error amplifier 120. The voltage change at the input to the error amplifier 120 causes the loop gain of the power regulator 100 to change with the output voltage VOU_T- The change in loop gain degrades the transient response of the power regulator 100 as described below. When the power regulator 100 is implemented in an integrated circuit package, another disadvantage is that an additional node is required to monitor the output voltage VOU_T of the power regulator 100. More specifically, the power regulator 100 does not monitor the actual value of the output voltage VOU_T; instead, the output voltage VOU_T is always attenuated to the same value as the reference voltage V_REF-

[0017] FIG. 2 is a graph 200 of example transient response variations in the output voltage VOU_T of the power regulator 100 as the load current supplied at the output 103 is changed or due to changes in the load current. As described above, the output voltage VQU_T is set by changing the value of the resistor Rb. The graph 200 shows the normalized voltage deviation in the output voltage VOU_T in response to a 10A load transient with an input voltage of 12V and output voltages of 5V, 3.3V and 1.2V. In the graph of FIG. 2, only the output voltage VOU_T was changed by varying the resistance of the resistor Rb. The frequency compensation components and output capacitance values are the same in all cases. As shown by the graph 200, the voltage deviation for the 5V output is almost three times the voltage deviation for the 1.2V output. If this variation is not acceptable to a user, then the frequency compensation of the power regulator 100 has to be modified to reduce the amplitude of the transient swing. Each output voltage value will have its own optimum compensation value. This configuration is difficult to implement, especially in circuit packages where users do not have access to the compensation components.

[0018] FIG. 3 is a graph 300 of example loop gains at different output voltages as a function of frequency for the power regulator 100 of FIG. 1. The graph 300 shows the loop bandwidth of the power regulator 100 at the three different output voltages shown in the graph 200 of FIG. 2. The crossover frequency, where the gain is zero, varies from 100kHz down to approximately 25kHz. As shown by the graph 300, the crossover frequency is 100kHz when the output voltage VOU_T is set to 1.2V, but it decreases to about 25kHz when the output voltage VOU_T is 5 V.

[0019] Transient response behavior is a direct function of loop bandwidth. As the loop bandwidth increases, the power regulator 100 will respond faster to load changes, and output voltage deviation is reduced. Lower loop bandwidth degrades transient response as shown by the graphs 200 and 300. The low loop bandwidth may require a user of the power regulator 100 to add more output capacitance to reduce the swing of the output voltage VOU_T- In other situations, the low loop bandwidth may require changing the value of the compensation components to restore the loop bandwidth to its optimum value. In many power regulators, the compensation components are internal and fixed, so the user has no access to them.

[0020] FIG. 4 is a block diagram of an example power regulator 400 that overcomes issues related to the power regulator 100 of FIG. 1. The power regulator 400 greatly reduces the variation in loop gain over a wide range of input and output voltages. The loop gain is maintained, so that a user does not have to recalculate the value of any compensation components when selecting a different output voltage. The power regulator 400 includes a voltage input 402 and a voltage output 403. The power regulator 400 receives an input voltage V_IN at the input 402 and generates an output voltage VQU_T at the output 403. [0021] The voltage input 402 is coupled to a power stage 410. The power stage 410 generates a drive signal into an inductor L2. In the example of FIG. 4, the drive signal is a pulse width modulated signal. The widths of the pulses are proportional to a control signal received at an input 412 of the power stage 410. In the example of FIG. 4, the control signal is a voltage that is proportional to the difference between the output voltage V_OUT and a target output voltage. The inductor L2 is fed with pulse width modulated pulses of the input voltage. These rectangular pulses of voltage are integrated by the inductor L2 into triangular current pulses that charge a capacitor C2. The charging current into the capacitor C2 determines the output voltage V_OUT- [0022] The voltage output 403 is coupled to a voltage divider 416 consisting of two resistors R5 and R6. In the example power regulator 400, the voltage divider 416 is set to a fixed value. More specifically, neither the resistor R5 nor the resistor R6 is a variable resistor. The output of the voltage divider 416 is a node N2, which is coupled to the inverting input of an error amplifier 420. In the example of FIG. 4, the voltage divider 416 divides the output voltage V_OUT by two, so the voltage at the node N2 is half the output voltage V_OUT-

[0023] In the example power regulator 400, the error amplifier 420 is substantially similar or identical to the error amplifier 120 of FIG. 1. The example error amplifier 420 is a transconductance amplifier, so it generates an output current that is proportional to the difference in the voltages at the inverting and non-inverting inputs. The output of the error amplifier 420 drives frequency compensation components consisting of a resistor R_C2 and a capacitor Cc₂. The output of the error amplifier 420 also drives the control input 412 of the power stage 410. As described above, the control input 412 receives a control signal generated by the error amplifier 420. The example of the drive signal generated by the power stage 410 is a PWM signal. The control signal determines the widths of the pulses of the PWM signal to maintain the output voltage VOUT at its target value.

[0024] The non-inverting input of the error amplifier 420 is coupled to a resistor R7 and a resistor R8. The resistor R8 is a variable resistor. The resistor R8 is coupled to ground, and the resistor R7 is coupled to a reference voltage V_REF- Unlike the conventional error amplifiers, the voltage V_SET presented to the non-inverting input of the error amplifier 420 is not fixed. The voltage V_SET is set by the user to set the output voltage V_OUT- In the example power regulator 400, the voltage V_SET is derived from a voltage divider that includes the reference voltage V_REF- In the embodiment of FIG. 4, the voltage reference V_REF is a precision fixed reference voltage of 3.00V. In the example power regulator 400, the voltage divider from VOU_T to the inverting input of the error amplifier 420 is set to a fixed value of one half. Accordingly, the required value for VS_ET is VOU_T/2. In one example, the power regulator 400 has a target output voltage VOU_T of 1.20V, so the voltage VS_ET is set to 0.60V. The power regulator 400 enables the output voltage VOU_T of the voltage regulator 400 to be very low. For example, output voltages less than 0.6 volts can be achieved, because the set voltage VS_ET is not constrained to a fixed lower limit. Accordingly, the output voltage can be taken as low as needed to achieve the target output voltage VOU_T, because the set voltage VS_ET is less than the reference voltage V_REF- The use of the resistors R7 and R8 is an example of the generation of the set voltage VS_ET- Other circuitry may be implemented to generate the set voltage VS_ET-

[0025] FIG. 5 is a block diagram of an example power stage 410 from the power regulator 400 of FIG. 4. The power stage 410 includes two switches, which in the embodiment of FIG. 4 are field-effect transistors (FETs) Ql and Q2. Transistor Ql is referred to as the high side FET, and Q2 is referred to as the low side FET. A node N3 is located between the two FETs Ql and Q2 and couples to the inductor L2. The FETs Ql and Q2 are turned on and off for different periods, which charge and discharge the inductor L2. The charge and discharge time of the inductor L2 sets the output voltage VOU_T- Some power stages or power supplies have components that measure the current I_L flowing through the inductor L2. Some power stages deduce the current flowing in the inductor L2 by measuring the current flowing through transistor Ql during the on-time of the PWM pulse, or measuring the current flowing through transistor Q2 during the off-time of the PWM pulse.

[0026] When using peak-current mode control, the minimum PWM pulse width that can be generated by the power stage 410 is determined by how fast a valid sample of the current through the inductor L2 can be obtained during the time that the high side FET Ql is on. When the high side FET Ql turns on, it creates a large amount of noise in the power stage 410 and the power regulator 400 (FIG. 4). During the turn on, the voltage at the node N3 slews from a ground potential (or other predetermined potential) to the value of the input voltage Vi_N in a few nanoseconds. In many instances, the fast slew produces ringing at the node N3, which interferes with the accurate measurement of the current through the inductor L2. In some examples, a blanking interval is required that allows the ringing to decay before the current through the inductor L2 can be measured. Usually, the blanking interval is approximately 100ns, which dictates the minimum pulse width that can be generated by the power stage 410.

[0027] The minimum pulse width sets the maximum Vi_N to VOU_T step-down ratio that can be achieved at a given switching frequency. This yields the minimum output voltage Vou_T(min) as a function of the minimum pulse width PW(min) and switching frequency Fsw, given by equation (1) as:

ou_T(min) = Vi_N*PW(min)*Fsw Equation (1)

In one example, the minimum pulse width is 100ns, the input voltage V_IN is 12V, and the switching frequency Fsw is lMHz. In this example, the minimum output voltage is 1.2V. To provide a higher input voltage V_IN or a lower output voltage VOU_T, the switching frequency Fsw must be lowered. If the power regulator 400 is operated beyond the minimum pulse width, pulses will typically be skipped, which lowers the switching frequency, which increases ripple and causes other anomalies.

[0028] In some examples of the power regulator 400, when current mode control is used as part of the regulation method, slope compensation is provided to prevent sub-harmonic oscillations of the output voltage under certain V_M and V_0UT conditions. A slope compensation ramp voltage V_RA_MP (described below) is summed with the inductor current sense signal and is applied to one input of a comparator. The other input to the comparator is the output of the error amplifier 420. If valley-current mode is implemented as part of the regulation method, when the falling summed V_RA_MP and the current sense signal crosses the signal output by the error amplifier 420 signal, the comparator fires and sets a latch. The firing of the latch starts the PWM pulse. The latch is reset on the next system clock, such as the rising edge of a clock, providing the switching frequency Fsw. The clock signal terminates the PWM pulse. This produces leading-edge modulation. The PWM pulse may be generated in the controller 500 and drives the gate of the high side FET Ql, and an inverted PWM pulse drives the gate of the low side FET Q2.

[0029] If peak-current mode is implemented as part of the regulation method, the PWM signal begins when the system clock sets a PWM latch. When the rising edge of the summed voltage V_RA_MP and the current sense signal cross the signal output of the error amplifier, the comparator fires and resets the latch, terminating the PWM pulse. This produces trailing-edge modulation.

[0030] Many slope compensation ramp functions are static and cannot accommodate changes in the power regulator operating conditions. These ramp functions do not provide the optimum slope compensation waveforms. The circuits and methods described herein overcome the above-described problems by generating an adaptive slope compensation ramp that has an amplitude that varies as the input voltage ViN, the output voltage VOU_T, or the switching frequency Fsw varies. For peak current mode systems, the ideal slope compensation ramp obeys equation (2) as:

Se = VOU_T * Ri/L Equation (2)

where Ri is the current sense gain in volts/amp, and L is the inductance value of the inductor L2. For valley current mode, the ideal slope follows equation (3) as:

Se = (V_IN - V_0UT)*Ri L Equation (3)

In both cases, the value of the output voltage VOU_T is required to generate the optimum compensation ramp slope. The power regulator 400 provides the output voltage VOU_T with the feedback signal V_FB at the node N2.

[0031] FIG. 6 is a circuit 600 that generates an adaptive slope compensation signal V_RA_MP for a valley current mode power regulator, such as the power regulator 400. The signal V_RA_MP produced by the circuit 600 automatically adjusts for variation in the input voltage V_IN, the output voltage VOU_T, and the switching frequency Fsw. In generating the signal V_RA_MP, the circuit 600 implements equation (3). The circuit 600 includes a first input 602 that is coupled to the input voltage Vi_N. A second input 604 is coupled to the node N2 of the power regulator 400. The voltage at the node N2 is referred to as the feedback voltage V_FB and is proportional to the output voltage VOU_T- A third input 606 is coupled to the system clock CLK and operates a switch SW61 at the switching frequency Fsw.

[0032] The first input 602 is coupled to a resistor R61 that is coupled to a resistor R62 at a node N61. The resistors R61 and R62 may divide the input voltage Vi_N down, so that the voltage at the node N61 is one fifth the input voltage V_IN. The second input 604 is coupled to a resistor R63 that is coupled to a resistor R64 at a node N62. The feedback voltage V_FB in these examples is half the output voltage VOU_T- The resistors R63 and R62 divide the feedback voltage down to where the voltage at the node N62 is one fifth the output voltage VOU_T- Accordingly, the voltage at the node N61 is the same proportion of the input voltage V_IN as the voltage at the node N62 is to the output voltage VOU_T-

[0033] The circuit 600 includes a voltage controlled current source U61 that has a non-inverting input and an inverting input. The non-inverting input is coupled to the node N61, and the inverting input is coupled to the node N62. The net effect of these connections is to produce a signal that is proportional to (VlN - VOUT). The current source U61 provides current to charge a ramp capacitor C_RA_MP- The gain of the current source U61 may be adjusted to account for the values of Ri and L. The ideal gain of the current source U61 is (5*C_RA_MP*RI)/L, based on the inputs to the power stage being one fifth of the input voltage V_IN and the output voltage VOU_T- In one example, C_RA_MP is 10pF, Ri is 40m V/ A, L is 0.4uH, and the gain of the current source Ul is set to 5uS. The switch SW61 discharges the capacitor C_RA_MP at the beginning of each switching period with a narrow pulse by the coupling of the switch SW61 to the clock CLK operating at the switching frequency Fsw.

[0034] The voltage across the ramp capacitor C_RA_MP is referred to as the slope compensation ramp voltage VS_LP- The peak value of the slope compensation ramp voltage V_PR is captured and held by a switch SW62 and a capacitor C61. The switch SW62 is controlled by a pulse SMP that is generated just before the clock pulse CLK discharges the ramp capacitor C_RA_MP- A differential buffer U62 subtracts the slope compensation ramp voltage VS_LP from the peak value of the slope compensation ramp voltage V_PR and outputs the above-described ramp voltage V_RA_MP- The ramp voltage V_RA_MP is the downward sloping compensation ramp that valley mode control uses to switch the FETs Ql and Q2 of FIG. 5. For a peak current mode control system, a similar circuit that implements equation (2) is used.

[0035] When the adaptive slope compensation of the circuit 600 is implemented, the transient response is uniform as the input voltage V_IN is changed over a wide range, such as a 3 : 1 range. The gain and phase of the power regulator 400 do not vary with changes in the input voltage V_IN- When the benefits of this adaptive slope compensation circuit are combined with the benefits of the revised error amplifier topology described above, the loop bandwidth of the power regulator 400 does not change with variations in input voltage VlN or output voltage VOU_T- This stabilization of the loop bandwidth eliminates the need for custom compensation for each different output voltage VOU_T- With this solution, one value of inductor LI is useful over a wide input voltage Vi_N and output voltage VOU_T range. Another advantage of transient response of the circuit 400 is a reduction in the amount of output capacitance required to meet a particular transient requirements, which reduces overall size and cost of the power regulator 400, especially when it is fabricated as a power module. Furthermore, the circuit 600 enables very narrow PWM pulse widths, such as down to approximately 20ns. This capability is useful for creating high V_IN/VOU_T step-down ratios, and/or operation at higher switching frequencies Fsw. Higher frequency operation enables higher loop bandwidth, which improves transient performance and reduces the size of the power regulator 400.

[0036] FIG. 7 is a block diagram of a power regulator 700 that includes slope compensation 600 and an error amplifier 702. The error amplifier 702 may include the error amplifier 420 of FIG. 4 and the associated components. As shown in FIG. 7, the slope compensation 600 works with the power stage to generate the PWM pulses that drive the current through the inductor L2. The combination of the slope compensation as described with reference to FIG. 6 and the error amplifier 702 yields the improved frequency bandwidth and other improvements over conventional power regulators.

[0037] Modifications are possible in the described embodiments, and other embodiments are possible, within the scope of the claims.

Claims

CLAIMS What is claimed is:

1. A power regulator for converting an input voltage to an output voltage, the power regulator comprising:

a regulator input for coupling the power regulator to the input voltage;

a regulator output for outputting the output voltage;

a power stage having a power stage input coupled to the regulator input, a control input, and a power stage output;

an inductor coupled between the power stage output and the regulator output, the power stage for charging the inductor in response to a clock signal;

an error amplifier having an output coupled to the control input, an inverting input coupled to the regulator output, and a non-inverting input coupled to a reference voltage; and a slope compensation circuit for generating a signal for charging the inductor by the power stage, the compensation circuit including an output coupled the power stage, wherein a signal on the output is generated in response to the input voltage, the output voltage, and the frequency of the clock signal.

2. The power regulator of claim 1, wherein the error amplifier includes a transconductance amplifier.

3. The power regulator of claim 1, further comprising a voltage divider coupled between the regulator output and a ground, the voltage divider having an output coupled to the inverting input of the error amplifier.

4. The power regulator of claim 1, further comprising a voltage divider for reducing the output voltage presented to the inverting input of the error amplifier.

5. The power regulator of claim 1, further comprising a voltage divider for presenting one half the output voltage to the inverting input of the error amplifier.

6. The power regulator of claim 1, wherein the voltage at the non-inverting input of the error amplifier is variable.

7. The power regulator of claim 1, further comprising:

a first resistor coupled between the non-inverting input of the error amplifier and the reference voltage; and

a second resistor coupled between the non-inverting input of the error amplifier and a ground, wherein the second resistor is variable.

8. The power regulator of claim 1, wherein the slope compensation circuit includes: a first input coupled to the regulator input; a second input coupled to the regulator output; and a third input coupled to the clock for generating pulses to charge the inductor.

9. The power regulator of claim 1, wherein the slope compensation circuit includes:

a voltage controlled current source having a first input coupled to the first input of the slope compensation circuit, a second input coupled to the second input of the slope compensation input, and an output;

a first switch coupled between the output of the voltage controlled current source and a ground, the first switch having a control coupled to the third input; and

a first capacitor coupled in parallel with first switch, wherein the first switch is for discharging the first capacitor.

10. The power regulator of claim 9, wherein the slope compensation circuit further includes: a differential buffer having a buffer first input, a buffer second input, and a buffer output, wherein the buffer output is coupled to the output of the compensation circuit, and wherein the buffer first input is coupled to the output of the voltage controlled current source;

a second switch coupled between the output of the voltage controlled current source and the buffer second input, the second switch for opening during peak voltages across the first capacitor; and

a second capacitor coupled between the buffer second input and ground, the second capacitor for storing the peak voltages.

11. The power regulator of claim 1, wherein the power stage includes:

a high side field-effect transistor (FET) coupled between the power stage input and the power stage output;

a low side FET coupled between the power stage output and ground;

a controller coupled to the gate of the high side FET and the gate of the low side FET, the controller for turning the high side FET and the low side FET on and off in response to the signal output by the slope compensation.

12. A power regulator comprising:

a regulator for receiving an input voltage and generating an output voltage by driving current into an inductor, the regulator including a clock operating at a clock frequency for setting time that the current is driven into the inductor;

a slope compensation circuit for generating a signal for driving current into the inductor, the slope compensation circuit including: a first input coupled to the input voltage; a second input coupled to the output voltage output; a third input coupled to the clock; and a slope compensation output coupled the regulator, wherein a signal on the slope compensation output is generated in response to the input voltage, the output voltage, and the frequency of the clock.

13. The power regulator of claim 12, wherein the slope compensation circuit further includes: a voltage controlled current source having a first input coupled to the first input of the compensation circuit, a second input coupled to the second input of the compensation input, and a current output;

a first switch coupled between the current output and a ground, the first switch having a control coupled to the third input; and

a first capacitor coupled in parallel with the first switch, wherein the first switch is for discharging the first capacitor in response to the frequency of the clock.

14. The slope compensation circuit of claim 13, further comprising:

a differential buffer having a buffer first input, a buffer second input, and a buffer output, wherein the buffer output is the coupled to the output of the compensation circuit, and wherein the buffer first input is coupled to the current output;

a second switch coupled between the current output and the buffer second input, the second switch for opening during peak voltage levels across the first capacitor; and

15. The power regulator of claim 12, wherein the regulator includes:

a regulator input for coupling to an input voltage;

a regulator output for outputting an output voltage;

a power stage having a power stage input coupled to the regulator input, a control input, and a power stage output, the power stage for driving current into the inductor;

an error amplifier having an output coupled to the control input, an inverting input coupled to the regulator output, and a non-inverting input coupled to a reference voltage, the error amplifier for generating signals to control signals from driving current into the inductor.

16. The power regulator of claim 15, further comprising a voltage divider coupled between the regulator output and a ground, the voltage divider having an output coupled to the inverting input of the error amplifier.

17. The power regulator of claim 15, further comprising a voltage divider for reducing the output voltage presented to the inverting input of the error amplifier.

18. The power regulator of claim 15, further comprising a voltage divider for presenting one half the output voltage to the inverting input of the error amplifier.

19. The power regulator of claim 15, wherein the voltage at the non-inverting input of the error amplifier is variable.

20. A power regulator for converting an input voltage to an output voltage, the power regulator comprising:

a regulator input for coupling the power regulator to the input voltage;

a regulator output for outputting the output voltage;

an error amplifier having an output coupled to the control input, an inverting input coupled to the regulator output, and a non-inverting input coupled to a reference voltage; and a slope compensation circuit for generating a signal for charging the current, the slope compensation circuit including: a first input coupled to the input voltage; a second input coupled to the output voltage output; a third input coupled to the clock signal; and a slope compensation output coupled the regulator, wherein a signal on the slope compensation output is generated in response to the input voltage, the output voltage, and the frequency of the clock.