In this paper, an integrated low-voltage control circuit is introduced for a charge pump DC-DC boost converter. By exploiting the advantage of the integration of the feedback control circuit within CMOS technology, the charge pump boost converter offers a low-current operation with small ripple voltage. The error amplifier, comparator, and oscillator in the control circuit are designed with the supply voltage of 3.3 V and the operating frequency of 1.6~5.5 MHz. The charge pump converter with the 4 or 8 pump stages is measured in simulation. The test in the 0.35 μm CMOS process shows that the load current and ripple ratio are controlled under 1 mA and 2% respectively. The output-voltage is obtained from 4.8 ~ 8.5 V with the supply voltage of 3.3 V.

A low power CMOS control circuit is applied in an integrated DC-DC buck converter. The integrated converter is composed of a feedback control circuit and power block with 0.35 μm CMOS process. A current-sensing circuit is integrated with the sense-FET method in the control circuit. In the current-sensing circuit, a current-mirror is used for a voltage follower in order to reduce power consumption with a smaller chip-size. The N-channel MOS acts as a switching device in the current-sensing circuit where the sensing FET is in parallel with the power MOSFET. The amplifier and comparator are designed to obtain a high gain and a fast transient time. The converter offers wellcontrolled output and accurately sensed inductor current. Simulation work shows that the current-sensing circuit is operated with an accuracy of higher than 90% and the transient time of the error amplifier is controlled within 75 μsec. The sensing current is in the range of a few hundred μA at a frequency of 0.6~2 MHz and an input voltage of 3~5 V. The output voltage is obtained as expected with the ripple ratio within 1%.

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Purpose This paper aims to propose a low-power complementary MOS (CMOS) current sensor for control circuit in an integrated DC-DC buck converter. Design/methodology/approach The integrated DC-DC converter, which is composed of feedback control circuit and power block, is designed with 0.35-µm CMOS process. Current sensor in the control circuit is integrated with sense-FET and voltage-follower circuits to reduce power consumption and improve its sensing accuracy. In the current-sensing circuit, the size ratio of the power metal oxide semiconductor field effect transistor (MOSFET) to the sensing transistor (K) is 1,000, and a current-mirror is used for a voltage follower. N-channel MOS acts as a switching device in the current-sensing circuit, where the sensing FET is in parallel with the power MOSFET. The amplifier and comparator are designed to obtain a high gain and a fast transient time. Findings Experiment shows that the current sensor is operated with accuracy of more than 85 per cent, and the transient time of the error amplifier is controlled within 100 µs. The sensing current is in the range of a few hundred µA at a frequency of 0.6-2 MHz and an input voltage of 3-5 V. The output voltage is obtained as expected with the ripple ratio within 5 per cent. Originality/value The proposed current sensor in DC-DC converter provides an accurately sensed inductor current with a significant reduction in power consumption in the range of 0.2 mW. High-accuracy regulation is obtained using the proposed current sensor. As the sensor utilizes simple switch-type voltage follower and sense-FET, it can be widely applied to other low-power applications such as high-frequency oscillator and over-current protection circuit.