A Simple Digital Auto-Tuning For Analog Controller in SMPS

This paper discusses the self-tuning capabilities of an analog current-mode controller for switch-mode DC-DC converters. The proposed tuning techniques are based on the insertion of non-linear blocks in the analog control loop and the generation of a controlled oscillation on the output voltage in order to measure the closed-loop properties like gain margin, phase margin and crossover frequency and to tune the analog controller according to the desired specifications. The non-linear blocks are based either on the non-linear gain or non-linear phase. The most relevant properties are: (1) the oscillation amplitude is controlled by the non-linear action during the tuning procedure; (2) A/D converters are not required; (3) the parameter variations can be obtained with ancillary analog blocks (variable gain operational transconductance amplifier (OTA), switched capacitors, etc.); (4) the tuning digital control algorithm is simple. Experimental results on a 10 A, 1.5 V point-of-load converter, where the controller tuning has been implemented using components off-the-shelf (COTS) and a field programmable gate array (FPGA) for the digital tuning algorithm, are provided to show the properties of the proposed system.