| A step-down DC-DC converter is analyzed and designed. It has features that supply voltage can change from DC 5V to DC 25V, yields out-put DC current up to 2A and the out-put voltage is programmable that depends on the out-put resistors. Its oscillator frequency is 400 KHz. The DC-DC converter has been designed with integrated power switch transistors and synchronous power transistors inside. Therefore, it is very convenient for customers because only a few outside devices are needed when the converter is used. The converter has a high ynamic-responding speed, a very small over-range voltage and over-range current when the chip is powered up.Firstly, the different control modes of monolithic switch power converter were introduced and the current-control-mode and voltage-control-mode were compared in this paper. A current-control-mode has been selected to build the converter due to the design specification. Then the chip based on the process module, especially the current feed-back loop, loop compensation, error amplifier and band gap circuits was analyzed and designed. Some units of the original circuits were modified to fit the fabrication process. The layout design was discussed after the circuits design.Finally, the whole circuit and layout were simulated based on the .8u BiCMOS module with different supply voltage, different environment temperature. The resistance change coming from the process has also been considered in the design. The simulation circumstance was Cadence Spectre. |
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