DC-DC switch power soft-start circuit of digital-to-analogue conversion control

Abstract

The invention discloses a DC-DC switch power soft-start circuit of digital-to-analogue conversion (DAC) control, comprising an oscillator, a counter, a digital-to-analog converter, an error comparator, a PWM comparator and an on-off controller. In the invention, a Q output end of the on-off controller is connected with a grid of an outer switch rectifier tube, a QN output end is connected with a grid of an outer follow current tube, the output end of the PWM comparator and the output end of the oscillator are connected with the input end of the on-off controller, the input end of the PWM comparator is respectively connected with the output end of the oscillator and the output end of the error comparator, one end of the input end of the error comparator outputs sample voltage, the other end of the input end of the error comparator inputs the voltage generated by the digital-to-analog converter, the output end of the error comparator outputs a difference value amplifying signal of the sample voltage and the voltage generated by the digital-to-analog converter, one end of the counter is connected with the output end of the oscillator, and the other end of the counter is a zero clearing signal and outputs an 8-digit parallel signal. When the power is electrified, the reference voltage of the input end of the error comparator is controlled to enable the reference voltage to rise step by step from small to large, and the voltage of the output end of the error comparator goes up slowly with the reference voltage, thereby avoiding overshoot voltage in the starting procedure and realizing the function of soft-start.

Description

technical field [0001] The invention belongs to integrated circuit chip technology, and in particular relates to a soft start circuit of a DC-DC switching power supply controlled by digital-to-analog conversion. Background technique [0002] When the DC-DC switching power supply is powered on, the power supply voltage rises from the minimum value to the maximum value. At this time, the output voltage also rises from the minimum value. The switching tube inside the chip charges the external inductor through the switching action, and the inductor accumulates energy. As the voltage at the terminal rises, the output voltage rises accordingly. If the output voltage terminal is not connected to the load or the load is relatively small, the electric energy in the inductor will discharge slowly, which will easily cause a relatively large overshoot of the output voltage during the power-on process. The specific performance is that the output voltage is much greater than the chip sett...

AI Technical Summary

Problems solved by technology

There are mainly the following types of soft start in the currently applied switching circuits: one is to use a constant current to charge the capacitor, and use the voltage of the capacitor to rise slowly to control the output voltage to rise slowly, but this method requires a relatively large capacitor value. It is difficult to integrate into the chip. The chip needs to add an extra pin to connect the capacitor, which increases the application cost. The other type is to use digital control method to control the output voltage. This method can be integrated into the chip, but It is very complicated to control, the chip occupies a large area, and the cost is high

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