A BUCK Chip Which Controls Fan Speed Based On Temperature

As a heat dissipation method produced in the early days,air cooling still has strong vitality.Although it has disadvantages such as larger noise and larger volume,but its low price,better heat dissipation and other advantages still make it the best choice for many users.As the main body of heat dissipation-the fan which needs buck chip to be used for power supply and speed control.The traditional solution is to separate speed control and power supply.The chip designed in this paper combines speed control and power supply and is well compatible with mainstream fans on the market(rated voltage 12 V,rated power10W).The buck chip designed in this paper uses a ripple-based control mode,which is characterized by fast transient response and does not require compensation network and PWM module.The duty cycle is completely determined by the inductance of the L in the main topology.The fan driver chip also has several different working modes such as normal working mode,sleep mode and multiple fault working modes.The fault working mode includes negative temperature coefficient resistance leakage mode and over-current and over-temperature protection modes.The core of the control loop in the normal working mode is the main loop comparator module,and the comparison voltages at both ends are the external feedback voltage and the reference voltage obtained by calculation inside the chip.Its main function is to control the turn-on time of the power tube.It uses a two-stage comparator structure.The delay time of the comparator is less than 30 n S at the full process corner,and the offset voltage of the comparator is less than 500μV at the full process corner.The most important module in the negative temperature coefficient resistance leakage mode is the hysteresis comparator,which uses the temperature and current-voltage characteristics of the triode to achieve hysteresis,and the temperature hysteresis window is5°C.The most important thing in overcurrent protection is the current detection module,which uses the same external conditions to control the sampling tube and the power tube(mainly the aspect ratio is proportional,and the VGS and VDS are the same)to achieve current sampling,and the current limit is taken the inductor current reaches 800 m A as its upper limit.These several sub-modules are given in the relevant analysis and design process in this article.This paper first uses SIMPLIS to carry on the systematic modeling to this buck chip,afterwards carries on the design and simulation analysis to the main module in the chip based on Magnachip 0.13μm BCD technology.After completing the design and simulation of the main sub-modules,several main operating modes of the chip are simulated as a whole.The simulation results show that the ripple of the chip is about 150 m V,the output voltage of the internal linear regulator is 5V,the current sampling upper limit is 800 m A,the overcurrent protection limit is 2A,and the internal power tube on-resistance is about 370mΩ,which meets the needs of use.