PWM控制器的SPICE建模 (外文翻譯).pdf

SPICE Modelling of PWM Controllers Janusz Zarebski Krzysztof G6recki Department of Marine Radioelectronics Gdynia Maritime University GUadalaJXa MEXICO Morska 83 8 1 225 Gdynia POLAND October 20 24 Abstract In the paper the problem of electrothermal modelling of PWM controllers for SPICE is considered SPICE library macromodel and a new form of the authors electrothermal macromodel of SG3S2SA controller are presented To illustrate the correctness and usefulness of these macromodels some results of measurements and calculations of SG352SA controller operating in catalogue test circuit and in the real BOOST converter are given as well OSC PWM Comparator PWM Error Amplifier EA Output Circuit OC and Shutdown Circuit SC are described in the catalogue data 7 81 in details The working frequency range from 100 Hz to 400 kHz is determined by the external passive elements CT and RT connected to the 5th and 6th terminals I INTRODUCTION Today switching power electronic converters SPEC are a very important class of power electronic circuits While considering typical operating conditions of semiconductor devices especially the power switching devices and the other components subcircuits used in SPEC selfheating should be taken into account It influences the important parameter values and the reliability of SPEC considerably As a result of selfheating the device junction inner temperature TJ differs sometimes considerably from the ambient temperature T In the computer aided design and analysis of SPEC the proper and accurate models of the whole circuits or their components including among others selfheating are needed I Such models called electrothermal ones e g 2 are formulated first of all for power devices However there are no trends to formulate the electrothermal models of low power or signal devices and circuits operating in SPEC The authors proved that the temperature affects strongly the performance of a class of the integrated PWM controllers especially its parameter values and characteristics called nonisothermal ones e g 3 In the paper the electrothermal macromodel of PWM SG3525A controller dedicated for SPICE appropriated to the electrothermal transient analysis is proposed This macromodel is the improved version of the other ones published in 4 5 61 The results of measurements and calculations illustrating the correctness and usefulness of the proposed macromodel are presented as well 11 THE STRUCTURE AND THE LIBRARY MACROMODEL The controllers considered here are appropriated for controlling PWM pulse dc dc converters The block diagram of SG3525A controller is shown in Fig 1 The specified blocks in Fig 1 as the voltage reference source VRS the undervoltage lock out UVLO Flip Flop FF Oscillator 0 7803 7640 4 02 17 00 0 2002 IEEE 61 V Oscilator output Synchron RT a Discharge Compens Inv input Non mv input Soft start Shutdown 3VREF 3VC 9 3 9 GND Output A 3utput B Fig The block diagram of SG3525A controller The proposed by MicroSim macromodel of SG3525A is available in SPICE library SWIT REG LIB 9 This macromodel is of the very large scale of complexity and it consists of 18 logic circuits 4 controlled sources 9 independent sources 5 D A and A D interfaces 4 diodes 5 BJTs 4 switches and 20 passive elements The macromodel includes the fundamental features of the controller as the influence of the reference voltage V on the output pulses duration time t limitation of the linear dependence oft on V f soft start and two outputs signals of the form of the rectangular waves shifted to each other by 180 Unfortunately three essential phenomena like selfheating the influence of supply voltage Vcc and the temperature on time t as well as the dependence of the supply current and voltage shapes on the temperature and supply voltage are not included in the library macromodel TIT THE ELECTROTHERMAL MACROMODEL FORM Worked out by authors the electrothermal macromodel ETM of SG3525A includes the phenomena omitted in the library macromodel As it results from 4 51 these phenomena are substantial in the range of the higher values of the supply voltage and oscillator output frequency Futhermore as a consequence of adopting the nonlinear controlled sources available in the latest version of SPICE to form ETM its construction compared to the library macromodel consists of considerably fewer nodes and elements These elements are of the analogue form only that means there are no D A and A D interfaces in the macromodel Such philosophy of building ETM should lead to the reduction of the analysis time consuming compared to the library isothermal macromodel Since to ETM is appropriated for the circuit analysis in the steady state the soft start effect and the possibility of the external shutdown which are only important immediately after the supply is switched on are not included in the proposed macromodel According to the principles of electrothermal model formulation IO the worked out macromodel showed in Fig 2 consists of three essential blocks A B and C representing the electrical model along with the parameters dependent on temperature block A the thermal model block B and the model of the real power dissipated in the considered device block C The structure of the block A has been created on the basis of the analysis of PWM controller working principle of the operation described in 7 81 The output circuit is realised in the form of Totem Pole controlled by the rectangular waves formed in the output of VINA and V NB sources Transistors T3 and T7 cause the faster switching on of T1 and T5 transistors whereas the role of D1 and D2 diodes is to make the faster switching off of the same transistors Transistors distinguished in Fig 2 are described by the electrical BJT model proposed in 2 in which some phenomena as avalanche breakdown Early effect in view of the restriction of the voltages switching over range the temperature dependence of the junction capacitances the poor dependence 101 and the dependence of the current gain factor on the temperature and the collector current to get the simpler form of the model could be omitted The signal circuit consists of the current and voltage sources generating the proper signals controlling VmA and VINB sources The current supply of the signal circuit of the efficiency equal to 16 mA is represented by the current source Isup The voltage source V R represents the reference voltage section The error amplifier is represented by the source of the output voltage AV the resistor RV the current source I K o p and the transistor T9 The output value of AV source is proportional to the difference of the reference voltage Vref and the error one V Moreover because for AV AVmax t t const the output value of this source can be described by AV LIMIT A verr vr e X vmin Avm 1 where A denotes the amplification of the error amplifier whereas LIMIT is the built in function of SPICE I i 4 VSUP Fig 2 The electrothermal macromodel of SG3525A controller The emitter follower composed of the bipolar transistor T9 and the current source IKoMP limits the output current of the error amplifier up to about 100 PA This limitation is important in the real operating conditions of the controller e g it assures a low value of the output voltage ripples in the stabilisers As it results from PWM principle of operation l 1 121 the oscillator represented here by Vosc source should generate the triangle pulses of the period time equal to T 2 and the slope y equal to that of the isothermal characteristics AV t in the linear range However as it results from 5 for AV AV t const the two parameters AV and AV limiting the linear range of AV t characteristics have to be included in the model Finally the following description of VOSC output value on time denoted here as t can be given in the form Since the slope of the triangle pulses can be changed in the 62 analysis run the standard PULSE function cannot be used for the definition of the output value V0sc This problem has been solved with the use of the additional artificial voltage source described by vo trunc 2 t T 24 where trunc x denotes the integer part of x Now one can introduce Vo variable instead of the variable t in Eq 2 The comparator is represented by the source VCMp described by the equation As the output signal of VI and VmB sources are shifted by 180 VcMp voltage has to control the bases of T4 and T8 transistors every other period The output signals of VTNA and V I N sources are of the form 5 where the output signals of VI and V2 in the form of the rectangular waves shifted to each other by 180 are described by the period time equal to T the time duration equal to T 2 and the voltage levels equal to 0 and 1 V respectively These two voltage signals are synchronous to voltage Vo As it results from the measurements of the considered controller the time pulse duration tw depends strongly on the voltage V E R R supply voltage VSm junction temperature T and the output signal frequency f To formulate the proper functional dependence the following types of the isothermal characteristics were measured the dependence of the output pulse time duration t on the reference voltage and the supply voltage the dependence of the pulse time duration tw on the ambient temperature T at the supply voltage Vsup const and the reference voltage Vref const On the basis of the measured results the searched dependence has been proposed as foilows where T denotes the junction temperature To is the reference temperature Vsupo denotes the minimum catalogue value of the supply voltage and y b e d Two are the macromodel parameters Next the thermal model block 3 describes the dependence of the rise of the junction temperature AT on the dissipated power P calculationc macromodel 1 measurements 0 0 20 40 60 T x 8b 100 120 140 Fig 4 The dependence of tw on the ambient temperature T at V UP const and V t const 2500 I f 200 kHz library model I i 2000 1500 1000 500 0 I 1 5 2 2 s 3 3 5 4 Fig 5 The isothermal and nonisothermal dependencies oft on VEt Note that in spite of the ambient temperature supply voltage signal frequency and dissipated power are less then their allowable values the junction temperature exceeds the allowable temperature given in catalogue T 7OoC As seen the value of t for Vref 1 9 V is approximately equal to that from Fig 3 corresponding to the ambient temperature T 70 C So due to the strong temperature the dependence t can be selected as the thermal sensitive parameter which can serve for the estimation of the thermal state of IC 14j To see how selfheating influences the features of the considered controller in the real working conditions the boost converter Fig 6 has been investigated In this figure protected circuit PC assures the proper shape of the gate voltage It was assumed that selfheating exists only in SG3525A whereas the other part of the investigated circuit is considered to be the isothermal one The isothermal conditions for BOOST converter have been achieved with the use of the quasi ideal cooling of IRF530 and BY229 heat sink of a very large area Two cases were considered the first with the feedback loop opened switch S at point 1 and the other with the loop closed S at point 2 Boost converter i LI 630 i v p 3 o J l 8 1 f 200 kHz 7 i T 2 5 0 C 1 library model 0 0 5 1 1 5 2 2 5 3 3 5 4 Fig 7 Measurement and calculation results of BOOST converter 64 The results of BOOST calculations and measurements are shown in Fig 7 In this figure the solid lines denote the results of electrothermal analysis using the electrothermal macromodel the dotted lines the results of calculations using the library model and squares measurements results As seen the calculation results nonisothermal characteristics obtained with the use of ETM fit very well to the measurements both when the feedback loop is opened and closed However the library macromodel allows to get the moderately fitting results only for Vsup 8 V when selfheating does not influence the controller characteristics whereas the simulation results for Vsup 30 5 V the 7 controller inside temperature is equal to about 140 C are of I31 a I51 t61 the very high error 81 roi V CONCLUSIONS W 3 Stepowicz D C Nonisothermal Output Characteristics of a Bipolar Transistor Including Breakdown Bulletin o f the Polish Academy of Sciences Technical Sciences Vol XXX No 5 6 1982 p 85 J ZarZ bski and K Gorecki PWM controller electrothermal macromodel dedicated for SPICE Electronics and Telecommunications Quarterly Vol 47 No 4 2001 s 539 J Zare bski and K Gdrecki Macromodels of the PWM controllers for SPICE Elektronika Not Sigma Warszawa No 11 2001 s 24 in Polish J ZarZ bski and K Gorecki PWM controller dynamic electrothermal macromodel for SPICE 371h Internatinal Conference on Microelectronics Devices and Materials MlDEM 2001 Bohinj Sowenia 2001 p 99 Regulating Pulse Width Modulators SG3525A Catalogue data STMicroelectronics 1998 Regulating Pulse Width Modulators UCISZSA UC2525A UC3525A Catalogue d