Soft start techniques for control loops that regulate DC/DC converters
First Claim
1. A soft start circuit in a control loop, the control loop coupled to a DC/DC converter circuit, the soft start circuit comprising;
- a counter circuit that generates a digital signal in response to a clock signal, wherein the clock signal is used to generate a ramp signal that determines a switching frequency of the DC/DC converter;
a voltage-to-current converter circuit that converts at least one voltage indicative of the ramp signal into a current signal; and
a digital-to-analog converter circuit that converts the current signal into an output voltage signal that varies at a rate determined by the digital signal, wherein the output voltage signal is applied to an error amplifier during a soft start period.
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Abstract
Improved soft start techniques for control loops that regulate DC/DC converter circuits are provided. An improved soft start circuit provides a varying voltage at the output of an error amplifier in the control loop during the start-up phase of the DC/DC converter. The varying voltage generated by an improved soft start circuit is related to the amplitude of the saw-tooth ramp signal that controls the switching duty cycle. The varying voltage generated by an improved soft start circuit is also related to the switching frequency of the DC/DC converter. These features allow the duty cycle of the DC/DC converter to gradually increase from zero during power-on. An effective soft start function is provided for DC/DC converters that have a variable switching frequency or a variable saw-tooth ramp signal.
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Citations
28 Claims
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1. A soft start circuit in a control loop, the control loop coupled to a DC/DC converter circuit, the soft start circuit comprising;
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a counter circuit that generates a digital signal in response to a clock signal, wherein the clock signal is used to generate a ramp signal that determines a switching frequency of the DC/DC converter;
a voltage-to-current converter circuit that converts at least one voltage indicative of the ramp signal into a current signal; and
a digital-to-analog converter circuit that converts the current signal into an output voltage signal that varies at a rate determined by the digital signal, wherein the output voltage signal is applied to an error amplifier during a soft start period. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method for controlling current through an inductor in a DC/DC converter during a soft start period using a control loop, the method comprising:
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providing a digital signal that indicates a frequency of a clock signal, wherein the clock signal is used to generate a ramp signal that determines a switching frequency of the DC/DC converter;
converting a voltage indicative of an amplitude of the ramp signal into a current signal; and
generating an output voltage in response to the current signal, the output voltage varying at a rate determined by the digital signal, wherein the output voltage is applied to an error amplifier in the control loop during the soft start period. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A DC/DC converter circuit comprising:
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an error amplifier, a ramp generator generating a ramp signal that determines a switching frequency of the DC/DC converter; and
a soft start circuit hiving an output coupled to the error amplifier and a first input coupled to the ramp generator, wherein the soft start circuit generates a soft start signal at the output coupled to the error amplifier, the soft start signal being generated in response to a signal received at the first input that is indicative of a characteristic of the ramp signal. - View Dependent Claims (22, 23, 24, 25)
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26. A method for controlling current through an inductor in a DC/DC converter during a power-on phase, the method comprising:
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generating a ramp signal that determines a switching frequency of the DC/DC converter;
generating an error signal using an error amplifier in response to a feedback signal received from an output of the DC/DC converter; and
generating a soft start signal using a soft start circuit at an input of the error amplifier in response to a signal that is indicative of a characteristic of the ramp signal, the soft start signal providing a soft start function during the power-on phase of the DC/DC converter. - View Dependent Claims (27, 28)
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Specification