The Design Of Adaptive 1X/2X Regulating Charge Pump

With the rapid development of portable electric equipments, there are high performance requirements to the power management chips, for example: small board space, low quiescent and low cost. The traditional way to Pressure Raising and Reducing is practiced by inductance, by the BUCK or BOOST converter. So there are inevitable EMI. With the evolution of charge pump's structure, it is used extensively in light load application and higher output currents condition. At the same time, it replaces inductance by capacitance, which made EMI to be much smaller.The chip is a linear mode charge pump which is fabricated by 0.6μm BiCMOS technology. By the structure, we can get a one time or two times voltage and low output ripple. When VDD is big enough, the system is in one time mode, and the circuit works just like LDO. And if VDD is very low, the system will be in two times mode to get a constant VOUT. In one time mode, power MOS and two switch MOS are on, but the fourth one is off. In the system, there are a zero and three poles. The zero is produced by Miller effect in error amplifier. The three poles are: the first pole of EA, the pole produced by the power MOS and the output pole. To get a stability system, the pole because of power MOS should be in high frequency. In two times mode, the SOFTSTART is divided into two stages. The one is one time stage, and after 512us, the system will be in the second stage: the two times stage. And then the output voltage will be stability. Because of the linear control mode, the output voltage ripple is low. According to the load, the mode can be changed timely, when VDD is lower, the one time mode will be replaced by the two times mode. The block is a Non-symmetric comparator, VDD and VOUT will be compared in the blocks, and the offset voltage is decided by the load. According to the load, the efficiency is high. It also pays attention to the underlay voltage of the power MOS, the voltage is keep to be the bigger one by a comparator.There is an enable blocks in the system, according to the enable signals EN1 and EN2, there will be three differently invariable currents. When RCS is 0.27Ω, the maximal one is 1.2A. And by the external resistor RCS, we can set the full-scale LED current. The efficiency of the chip is high, when the gate-length of the power MOS is the minimum one, the efficiency is 95%. By the linear control mode, the maximum ripple is less then 95mV. The switching frequency is 1MHz.There are always some protective blocks. Such as: thermal-shutdown protection, over-voltage protection and under-voltage-lockout protection. The highest temperature of the chip is 160°C , and the chip will be off at a higher temperature. When the temperature is lower then 140°C , the chip will be on again. The hysterisis one is 20°C . The under-voltage block will shutdown the chip when VDD is lower then 2.3V. When VOUT is bigger then 5.3V, the over-voltage block will be active. With these blocks, the system can work safely and be well-balanced.During the process of design and analysis, SPICE is used to simulate and validate the electrical characteristics, and there are the details of the results. The results are very well, and it validate the academic analysis.