In today’s consumer market, high efficiency low-voltage DC-DC power converters are in great demand for battery-operated portable electronic devices. Current-mode switching converter is widely used due to its automatic over-current protection and fast dynamic response when compared with the voltage-mode counterpart. Inductor current sensing is critical in the converter design as it introduces an extra current loop in the controller. However, the conventional current sensing circuitry would lower the overall efficiency and a more complicated control is needed....[ Read more ]

In today’s consumer market, high efficiency low-voltage DC-DC power converters are in great demand for battery-operated portable electronic devices. Current-mode switching converter is widely used due to its automatic over-current protection and fast dynamic response when compared with the voltage-mode counterpart. Inductor current sensing is critical in the converter design as it introduces an extra current loop in the controller. However, the conventional current sensing circuitry would lower the overall efficiency and a more complicated control is needed.

In this thesis, a new internal current sensing scheme is proposed. The sense of the inductor current is realized by a matched PMOS transistor with the aspect ratio much smaller than the power PMOS transistor in the power stage. With this proposed sensing scheme, the complexity and efficiency can be significantly improved. Moreover, the converter can be implemented monolithically.

Two IC chips are implemented by AMS 0.6 μm CMOS process and tested. Measurement results show that the proposed current sensing scheme can successfully operate from switching frequency of 300 kHz to 1 MHz with the duty-ratio from 0.2 to 1 and at the supply voltage from 3 V to 4 V. The difference between the sensing signal and inductor current can be less than +/- 5 mV. In addition, the converter can regulate properly for different switching frequencies, 500 kHz and 1 MHz, and provide good line regulation and load regulation.