An Ultra-Low-Noise Buck Converter for Noise-Sensitive Applications

An ultra-low-noise buck converter for noise-sensitive applications is presented, which utilizes a novel pseudo average current-mode control (ACMC) with an adaptive ramp generator to decrease the baseband noise. Also, in order to suppress electromagnetic interference (EMI) and high-frequency spurs, spread spectrum and secondary filter are used, respectively. The proposed ACMC buck converter suppresses the switching frequency perturbation effect on the output voltage, and as a result in the spread spectrum condition, only a small amount of noise is added to the output voltage in the baseband frequency. For the spread spectrum with an external clock, a phase-locked loop is used, which synchronizes the internal oscillator and adapts the ramp generator slope to suppress spread spectrum baseband noise. The proposed ACMC converter achieves only 58 mu Vrms noise in 100 Hz-100 kHz frequency range. Also, a +/- 10% random spread spectrum architecture suppresses the EMI level by 11 dB while achieving only 88 mu Vrms and 156 mu Vrms noise for internal and external clock synchronization, respectively. The peak efficiency of the converter is 95% and the output voltage disturbance is 100 mV at a 2-A load step with 16 mu s settling time. The proposed design is implemented on a 180-nm BCD technology occupying a 1.65x3.70 mm2 die size.