An On-Chip High-Speed Current Sensor Applied in the Current-Mode DC–DC Converter

A current-mode dc–dc converter with an on-chip current sensor is presented in this letter. The current sensor has significant improvement on the current-sensing speed. The sensing ratio of the current sensor has low sensitivity to the variation of the process, voltage, temperature and loading. The current sensor combines the sensed inductor current signal with the compensation ramp signal and the output of the error amplifier smoothly. The settling time of the current sensor is less than 10 ns. In the current-mode dc–dc converter application, the differential output of the current sensor can be directly sent to the pulse-width modulation comparator. With the proposed current sensor, the dc–dc converter could realize a low duty cycle with a high switching frequency. The dc–dc converter has been fabricated by CSMC 0.5-μm 5-V CMOS process with a die size of 2.25 mm
$^{2}$
. Experimental results show that the current-mode converter can achieve a duty cycle down to 0.11 with a switching frequency up to 4 MHz. The measured transient response time is less than 6 μs as the load current changes between 50 and 600 mA, rapidly.