Slew-rate controlled output stages for switching DC-DC converters

Large supply bouncing due to the fast switching current and parasitic inductance of the supply rail may cause reliability and electromagnetic interference (EMI) problems, especially for ICs with the pulse-width modulation (PWM) technique, such as switching DC-DC converters. In this paper, a new slew-rate controlled (SRC) output stage is proposed to appropriately increase the rise and fall times of the PWM output by combining a feedback capacitor technique and a distributed-and-weighted design. Therefore, the supply bouncing during PWM switching can be reduced. The SRC output stage is successfully integrated into a DC-DC converter implemented with a 0.35mm 1P4M 3.3V mixed-signal CMOS process for verification. With an input voltage of 3.3V, an output voltage of 1.8V, a switching frequency of 500 kHz, and a load current range of 700mA, the active area of the converter is 2.3mm2. With a merely 0.035mm2 control circuit for the SRC output stage, the measured supply bouncing of the designed converter can be reduced by 40% and thus the reliability and the EMI can be improved.