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The U552 is a single chip, switched mode power supply (SMPS) for automotive engine controllers. It is a complete power supply for microprocessor based systems and includes several support functions to provide improved efficiency, higher reliability, size reduction, decreased parts count and significant cost savings over other implementations. The current mode SMPS runs at 100KHz via an on chip oscillator with an accuracy of +/-10%. Noise suppression and supply rejection are achieved by powering all linear and digital blocks from an internally pre-regulated 5V supply. A precision reference provides 2% output voltage accuracy from -40 to +150 degrees C. Connected directly to the battery, a low quiescent current, stand-by regulator powers SRAM containing on-board diagnostics (OBD). Two 100mA, linear tracking regulators are on chip to drive sensors such as manifold absolute pressure (MAP) and throttle position.

Several methods of indirectly measuring total harmonic distortion (THD) in a power amplifier by measuring characteristics of the input and output waveforms are presented. The relative accuracies of each method is discussed. While the emphasis is on practical methods that can be implemented in a automobile car radio, sensing THD levels within 1% of the target level can be realized.