| DC switching power provides a great convenience to the human daily life, however, there are a lot of supply voltages and their operating frequencies are variable in the human safety voltage range. In order to use the same chip, a condition of changing the parameters of external components is set to meet different supply voltage and operating frequency. This paper aims to design a step-up DC-to-DC controller with a wide range of input voltage, adjustable operating frequency, high precision current sense and high efficiency. Therefore, this chip uses current mode synchronous rectification. To reduce chip area and the use of high-voltage devices, the chip integrates a high-voltage LDO to provide operating voltage for other internal modules. In order to make the operating frequency adjustable, an external resistance is set, so the operating frequency and resistor satisfy a proportional relationship. To expand the applicable range, this paper uses an external sense resistor and sets the appropriate sampling gain by changing the sampling resistor. To improve the conversion efficiency, two external NMOS power transistors are used.This paper first describes the background and overview of power management chip and then analyzes several common DC-DC converter topologies and their working principles. Then it introduces the different modulation modes of power transistors, and emphatically analyzes working principle of PWM and PFM modes and their advantages and disadvantages. The paper describes the voltage mode and peak current mode feedback loop and the impact on system performance as well. On the basis of linear model of the power transistor, the paper gives peak current-mode boost converter equivalent linear loop and derives the transfer function of the inductor current and output voltage which is relevant with duty ratio. Finally, the paper provides an equivalent small-signal flow chart of the system and derives the loop gain of the whole system. Relying on the loop gain and reasonable compensation parameters, the loop stability can be analyzed conviniently. Based on the theoretical analysis, the key sub modules of the system are designed and simulated, including bandgap reference circuit, soft start circuit, adjustable frequency oscillator, current sampling circuit and negative current detection circuit. Finally, the simulation results of XD1496 are given including electrical performance parameters and overall functionality.Relying on the EDA tools of Cadence, the chip is implemented using a 0.6μm CMOS process and its overall system functionality and electrical performance is verified. Simulation results show that the overall system functionality and electrical performance parameters meet the entire specification. The system can work under the 3 ~ 30 V input range. In the 19 V, 12 V and 5V, three typical applications can achieve 2A, 3A and 4A maximum load. The system can depend on the load automatically switch between PWM and PFM mode, and ensure that the system meets the design requirements of the conversion efficiency. In sleep mode, the quiescent current reaches to 55μA, and through simulation, system conversion efficiency is as high as 96%. Within 50 k Hz ~ 1MHz range, the operating frequency can be linearly adjusted, and the system can work properly. Relying on external sense resistor, inductors’ current sampling accuracy is over 93%. Besides, system has a protection circuits such as over-temperature, over-voltage, over-current and other non-normal operating mode. This chip can be widely used in notebook computers, mobile power, automotive electronics and portable medical devices and other systems. It can not only improve power conversion efficiency, but also reduce static power consumption in sleep mode, which greatly improves the battery endurance. |
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