Slew-Rate Booster and Frequency Compensation Circuit for Automotive LDOs

This paper presents a slew-rate booster and frequency compensation circuit for automotive LDOs. The proposed circuit addresses three major LDO design challenges: frequency compensation for a wide range of output currents and load capacitors, fast response to load transients and reduced sensitivity to the supply variations. It was used to implement an LDO that provides a 5V output voltage and up to 50mA output current over a wide range of supply voltages - from 5.25V to 40V - and temperatures, -40 degrees C to +150 degrees C, while burning as little as 30 mu A. The slew-rate booster ensures that the output voltage overshoot and undershoot caused by load jumps of 50mA/mu s remain below 4% of the nominal Vout value. Moreover, the LDO meets the E-06 test requirements within the LV124 automotive standard: the output voltage varies within 10% of its nominal value when sinusoidal voltages with amplitudes up to 20V peak-to-peak and frequency varying between 15Hz and 100kHz are injected into the LDO supply line. This feature is achieved while using a capacitor of only 1 mu F at the output, up to 10 times smaller than the decoupling capacitors used by similar LDOs reported previously.