| Highly Integrated DC-DC converters used for lifting and polarity reversal, are an extremely important power management. These converters are designed to regulate the output voltage against the changes of the input voltage and load current. Due to the high conversion efficiency, transient response and high load capacity, they are widely used in portable electronic devices such as mobile phones, digital cameras and PDA, etc.Based on the DC-DC converter, this paper mainly studies the basic principle, the control mode and the way to work of a step-down DC-DC converter. From the starting of the converter characteristics, the paper mainly studies the input voltage range, output voltage ripple, load transient response and conversion efficiency. A dual-channel peak current mode synchronous buck pulse width modulation DC-DC chip XD1577 is designed. Peak current mode pulse width modulation can response to input voltage and output load current changes instantaneously, adjusts the system loop dynamically, stabilizes the output voltage. Meanwhile, pulse width modulation detects the inductor current by-cycle, which has the function of instantaneous peak current limiting, can protect the power tubes effectively. For the current mode control, the inductor current is involved in the regulation of the loop in each cycle, so timely and accurate detection of the inductor current become the critical of its technology. This paper studies the main factors influencing the current detection circuit, from the current sampling detection precision, power loss degree, structure design and circuit integration, the paper proposes a new current sensing methods, namely the inductance dc equivalent resistance sensing technology, compared with the External RSENSE, Triode Mode Current Mirroring, Power FET RDSON Sensing, the inductance dc equivalent resistance sensing technology without power loss, can provide higher work efficiency and precision, under low-voltage and high-current output applications. Under the current control mode, when the duty ratio is greater than 50%, the system appearance the sub-harmonic oscillation, the introduction of the slope compensation circuit is designed. At the same time, for the decline of load capacity caused by slope compensation, This paper presents an adaptive slope compensation circuit, and increase the clamping voltage to increase the maximum peak inductor current, which effectively eliminate the influence of slope compensation on the load ability. The Chip has zero crossing detection circuit, the circuit comparing the both ends of the voltage sampling circuit detect whether the inductance current becomes zero, in order to avoid the delay of synchronous transistor turning off caused by logic circuit delay, an offset voltage between the detection circuit inputs is designed, which effectively reduces the inductance current intrusion phenomenon. The Chip can work in continuous conduction mode or discontinuous conduction mode. Under the light load, it can work in skip cycle mode, which reduces the switching loss and effectively improve the system efficiency. The Chip with programmable soft start function, which can reduce the current surge and voltage overshoot in the start-up process, ensuring that the output voltage rises smoothly to the steady-state value.Based on 0.35μm 40V BCD process, circuit design and simulation of Chip XD1577 are accomplished by using the EDA tools of Cadence.4.5V to 26.5V input,0.6V to 5.5V output, lOmV voltage ripple, the maximum 8A load, and the chip has been taped out. |
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