Zero-cross detection circuit and detection method used for synchronous buck converter

Abstract

The invention discloses a zero-cross detection circuit and detection method used for a synchronous buck converter. The zero-cross detection circuit comprises a state judging circuit, a logic circuit, an adding and subtracting counting circuit, a digital-to-anology converting circuit and a zero-crossing comparator; the direction of a current passing through an inductor can be judged according to the state of a body diode of a lock-in tube, if the body diode is powered on, it is illustrated that a threshold value of zero-cross detection is positive, the threshold value can be decreased in the next period, it is illustrated that the threshold value of zero-cross detection is negative until the diode is cut off, and the threshold value can be increased in the next period. Output of the digital-to-anology converting circuit is regulated through the adding and subtracting counting circuit to decrease and increase the threshold value, signals are optimized through a balance module to form correction analog signals, and therefore positive and negative correction within a certain range is achieved, dynamic balance of zero-cross detection at a zero point is achieved, automatic correction of an offset voltage of the zero-crossing comparator is achieved, and circuit power consumption is reduced.

Description

technical field [0001] The invention relates to the field of step-down converters, in particular to a zero-crossing detection circuit and a detection method for synchronous step-down converters. Background technique [0002] In the synchronous buck converter, the main switch is turned on at the beginning of each cycle, the inductor current rises, the electric energy input at the input terminal is converted into magnetic energy and stored in the magnetic field of the inductor, and the main switch is turned off when a certain duty cycle is reached. , the inductor current gradually decreases through the continuous flow of the synchronous tube, and the magnetic energy is converted into electrical energy and released to the output terminal to complete a cycle conversion. When the load is large, the inductor current will not return to zero during the entire cycle, so that the circuit is usually in the connection conduction mode (CCM); when the load is light, the inductor current g...

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Problems solved by technology

[0005] But due to the zero-crossing comparator offset voltage V OS The existence of ', in high-power applications, the resistance of the synchronous tube is very small (such as: 2mΩ), the offset voltage (such as: ±10mv) will cause a large error, and the fluctuation range of the zero-crossing point of the inductor current is large. When there is no load, the zero-crossing comparator cannot be triggered, and the zero-crossing point cannot be detected, making the circuit work in forced continuous conduction mode (Force CCM), which increases the power consumption of the circuit

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