Voltage Regulator Module, called VRM is a dedicated module for supplying power to microprocessor units. Recently, significant improvement of microprocessor units arises new challenges for supplying stable power. For stable and efficient control, multiphase interleaved topology is often used in today's VRM. To achieve high performance VRM, a current sensing circuit with both high efficiency and high accuracy is demanded. To achieve high accuracy, thermal dependency is a problem to be solved. In this paper, a novel alternating voltage controlled current sensing method is proposed for suppressing thermal dependency. In the proposed method, a high frequency AC voltage is superposed on the gate-ON-voltage. Then, the AC channel current is generated, and its amplitude becomes proportional to inductor current. The AC channel current is detected through a LC filter. The proposed current sensing method is very effective for realizing a current mode control DC-DC converter. In first, we simulated the relationship between our proposed current sensing method and a electrical characteristic of a power MOSFET. We used a power MOSFET device model published by a manufacture in this simulation. From the results, we find the gate parasitic capacitance of power MOSFET effects on the sensitivity of the current sensing circuit. Besides, the power dissipation in a power MOSFET increases by the frequency of applied gate ac voltage. Moreover, the proposed current sensing circuit based on the proposed method was designed and simulated the operations by Hspice. From the results, the designed current sensing circuit based on the proposed method has enough wide sensing window from 3A to 30A for VRM applications. Moreover, comparing to the conventional current sensing circuits with the MOSFET ON-resistance, the error of the proposed current sensing circuit can be decreased over 25% near 100°C.

In this paper, a high accuracy, high efficiency, and wide current-sensing range current-mode PWM buck converter with on-chip current-sensing technique is presented. The proposed current-sensing circuit uses simple switch technique to achieve high accuracy, high power efficiency, and high line regulation. The test chip is fabricated using TSMC 0.18 µm 1P6M 3.3 V CMOS process. The measurement results show that the buck converter with on-chip current-sensing circuit can operate from 700 kHz to 3 MHz with a supply voltage of 1.5-5 V and the output voltage of 0.5-4.5 V for lithium ion battery applications. The accuracy of the proposed current-sensing circuit is exceeds 89.8% for load current from 50 mA to 500 mA and for temperature from 0C to 100C. The peak power efficiency of the buck converter is up to 95.5%.

In this paper, we propose the use of second-order slope compensation for a current-mode PWM buck converter. First, the current feedback loop in a current-mode PWM buck converter using a conventional slope compensation is analyzed by the small-signal transfer function. It becomes clear that the stability and frequency bandwidth of the current feedback loop is affected by the external input voltage and the output voltage of the converter. Next, the loop with second-order slope compensation is analyzed, and the result shows that the loop becomes unconditionally stable with the adoption of second-order slope compensation with appropriate parameter values and a current sensing circuit whose current is sensed across an impedance that is inversely proportional to the input voltage. In order to verify our theory, we designed whole circuits of a current-mode PWM buck converter including the new inductor current sensing circuit and the second-order voltage generator circuit using device parameters from the 0.6 µm CMOS process. The circuit simulation results under the conditions of 4 MHz switching frequency, 3.6 V input voltage and 2.4 V output voltage are presented.