Design of Fast-Response On-Chip Current Sensor for Current-Mode Controlled Buck Converters with MHz Switching Frequency

In this work, techniques to design fast-response on-chip current sensor for buck converter (BC) with MHz-range switching frequency is successfully developed. Unwanted voltage spike at the sensor output, which not only degrades the response time of sensor but also interrupts the operation of BC, is minimized by carefully controlling the activation and deactivation time of current sensor. Response time of sensor is also improved by specially designed error amplifier, which provides large slew-rate in both positive and negative direction during transient response and consumes only small quiescent current at steady-state operation. Sensing accuracy at small inductor current is also improved in the proposed design. It is shown that the proposed current sensor is able to respond to a BC with 10 MHz switching frequency at only 8-muA quiescent current consumption.