An ultra-low-power digitally-controlled buck converter IC for cellular phone applications

This paper describes a dual-mode digitally-controlled buck converter IC for cellular phone applications. An architecture employing internal power management is introduced to ensure voltage compatibility between a single-cell lithium-ion battery voltage and a low voltage integrated circuit technology. Special purpose analog and digital interface elements are developed. These include a ring-oscillator based ADC (ring-ADC), which is nearly entirely synthesizable, robust against switching noise, and has flexible resolution control, and a very low power ring oscillator-multiplexer based digital PWM generation module (ring-MUX DPWM). The chip, which includes an output power stage rated for 400 mA, occupies 2 mm² active area in 0.25 μm CMOS. Very high efficiencies are achieved over a load range of 0.1 to 400 mA. Measured quiescent current in PFM mode is 4 μA.