Comparator-Controlled Rectification at Monolithic Buck Converters for Higher Input Voltages

An integrated CMOS buck converter for input voltages up to 20 V is presented. It uses an improved comparator to control the low-side switch for asynchronous rectification. To protect the comparator under high voltage condition without relevant power dissipation (losses), a high-ohmic voltage limiter is used. To overcome the speed limitation resulting for the zero-voltage detection, the comparator exploits small-area input transistors and auto-zero circuitry to combine fast decision and low offset voltage. Simulations show a power consumption of 110 μW of the comparator. The measurements of the whole buck converter show up to 92% efficiency with 330-ns pulses at 314-mA output current for 20-V input voltage and 3.6-V output voltage.