Linear Voltage Regulators With Gate-Driving Buffer for Automotive Applications

This work presents a novel linear voltage regulator that fulfills two key requirements for automotive applications: it operates over a wide input voltage range and passes a very challenging test, compulsory for vehicles of up to 3.5t. The main contribution is the voltage buffer that drives the gate of the NMOS pass transistor: it consists of two complementary buffers in cascade, a topology that ensures large capability for both sinking and sourcing current and enables the closure of local feedback loops, that do not include the (usually slower) error amplifier. The novel gate-driving buffer helps address two general design challenges for voltage regulators: fast response to load transients and reduced sensitivity to supply variations. Two design examples validate this proposal: first, the response to large and steep input voltage variations of the proposed buffer was compared against two conventional counterparts; next, the buffer was used to implement a linear voltage regulator that delivers a 3.3 V output voltage and up to 100 mA output current over an input supply voltage ranging from 7 V to 20 V, while burning only $12.5~\mu $ A. When load jumps of 100 mA/50 ns occur at the regulator output, the complementary voltage buffer is able to provide a reduction of the resulting output voltage undershoot and overshoot by up 72% and 30%, respectively, compared to a reference regulator, built by using the very same error amplifier and pass transistor but a conventional common-drain gate-driving buffer. Moreover, the regulator meets the E-06 test requirement within the LV124 automotive standard: the output mean deviation is only 0.1% of its nominal value when a sinusoidal voltage of 6.5 V amplitude and variable frequency from 2 kHz to 100 kHz was superimposed on the 13.5 V DC input supply line. The same test applied to the reference regulator yields an output mean deviation 20 times larger.