New soft start circuit and soft start method based on dac technology

Abstract

The invention disclosed a DAC (Digital-to-Analog Converter) technology based novel soft start circuit and a soft start method thereof. The novel soft start circuit comprises a clock generation module, a digital signal generator, a binary switch, an R-2R trapezoidal resistance network and a soft start end control module. According to the novel soft start circuit disclosed by the invention, a soft start voltage with a rising trend from gentle to steep and then from steep to gentle is generated by adopting the clock generation module on the basis of the DAC technology; a quiescent current of a numerical part circuit is zero, and integral power consumption is controlled within 2n W, and therefore, energy is greatly saved and the requirements of development are met; the electrifying overshoot of an inductive current is inhibited within 1.3 A in the process of soft start, and therefore the requirements of a system are met; the rising process of an output voltage is stable, and therefore, oscillation is prevented from appearing and needed voltage values are fast and stably reached; the response time of a power management IC (Integrated Circuit) in a start stage is furthest shortened and controlled at about 200 microseconds; and the response speed of the integral system is greatly increased, and therefore a circuit is more suitable for a high-speed work environment.

Description

Technical field: [0001] The invention belongs to the field of switching power supplies, and relates to a circuit using DAC (digital-to-analog conversion) technology to provide a soft start function for a DC-DC switching power supply. Background technique: [0002] The soft start circuit module is an important module of the DC-DC switching power supply chip. If there is no soft-start module, during the power-on process of the switching power supply circuit, a large inrush current in the inductor will be directly poured into the output capacitor, causing an overshoot of the output voltage of the switching power supply. The main function of the soft start circuit is to prevent the output voltage from overshooting and causing damage to the chip components when the DC-DC switching power supply chip is powered on. The early method is to use a current source to charge a large capacitor to obtain a ramp-up soft-start voltage, and use the soft-start voltage to replace the reference ...

AI Technical Summary

Problems solved by technology

However, this soft-start circuit based on DAC technology only provides a linearly rising soft-start reference voltage, and the rising time is relatively long, about 1.5ms to 2ms, which causes the DC-DC switching power supply chip to start too slowly, and from It can be seen from the actual simulation that the output voltage waveform does not completely follow the rising trend of the soft-start voltage during the soft-start process, but rises to a certain value and then remains flat or even declines. This process will last for a long time , and then the output voltage continues to rise until the required voltage value. In the process of the output voltage being flat or falling, the average value of the inductor current will be relatively small, so that the inductor current will cross zero. At this time, the entire DC-DC switching power supply Working in the discontinuous conduction mode (DCM) will cause the drain voltage of the power tube to oscillate, thereby reducing the efficiency of the entire circuit in the soft-start phase and causing energy loss

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