Elektrotermiczny makromodel monolitycznego impulsowego regulatora napięcia L296 dla programu SPICE

摘要

This paper deals with the problem of modelling a class of monolithic integrated circuits with the use of SPICE. The STMicroelectronics regulator L296 intended for switching-mode power supplies based on the BUCK converter has been chosen for investigations. A new electrothermal macromodel of L296 (including selfheating) for SPICE, is presented. In this macromodel formulated in the network form with the use of some controlled sources accessible in SPICE, the fundamental physical phenomena responsible for the feedback loop operation, as well as the description of blocks protecting from the over-current effect and the dangerous increase of the junction temperature are taken into account. In the macromodel, the regulation of the output voltage is realised by the control loop consisting of the error amplifier (EA), the reference voltage source (V_(REF)) of the efficiency equal to 5.1 V, the PWM comparator (K1), the oscillator of the saw-tooth waveform (OSC) and the power output stage (OS) based on the bipolar transistor (BJT) operating as the power switch. The soft-start circuit (SSC) limits the slew rate of the output of the error amplifier what protects the power transistor against the current surge appearing after the switching-on of the supply. The CP and TP blocks are in order to switch-off the output circuit when the admissible values of the bipolar transistor current or the inner temperature of the regulator exceed their limits. The thermal model of L296 consists of the current source of the efficiency equal to the electrical real power dissipated in the device, the voltage source of the efficiency equal to the ambient temperature and the RC two- terminal network modelling the thermal time constant of L296. The macromodel parameter values are obtained after measuring results and catalogue data. The correctness of the proposed macromodel has been verified experimentally in BUCK converter circuit both for opened and closed feedback loop in the wide range of changing the input voltage, load resistance and the regulation voltage. In the considered cases a good agreement between the measurements and calculations results was obtained. The analysis of the influence of BJT model parameters values on the characteristics of BUCK converter including considered regulator is performed as well.%W pracy zaproponowano elektrotermiczny makromodel impulsowego regulatora napięcia L296 dla programu SPICE. Makromodel ten umożliwia analizę impulsowych układów zasilających w stanie ustalonym i składa się z dwóch podstawowych części: modelu elektrycznego i modelu termicznego. W modelu elektrycznym występują takie bloki jak: oscylator, komparator, wzmacniacz błędu i stopień wyjściowy, układ miękkiego startu oraz zabezpieczenie termiczne i przetężeniowe, natomiast model termiczny ma postać sieci kanonicznej Cauera. Wartości parametrów modelu wyznaczono na podstawie pomiarów oraz danych katalogowych. Poprawność opracowanego modelu zweryfikowano eksperymentalnie.