Mixed electrical-thermal and electrical-mechanical simulation of electromechatronic systems using PSpice (1994)

The design methodology and technique is presented to expand the power of commercial SPICE to simulate mixed electricalthermal-mechanical microsystems, consisting of motors being driven by smart power ICs. New electro-thermal and electro-mechanical models of mixed system elements are developed and included into SPICE model library as subcircuits. Practical examples are discussed illustrating the possibilities of developed techniques and software tools. CMOSs, sensors, specific multifunctional elements; § operating with high current, voltage, temperature conditions for power elements and high linearity and stability for sensor and analog elements; § strong electrical and thermal intercommunion between the elements on the chip. The thermal effects is the main limiting factor in stationary and transient smart power IC operation. Accurate thermal IC driver modeling is necessary to: 1)obtain the realistic evaluation of the reliability of circuit from electro-thermal standpoint; 2) stabilization of electrical characteristics by reducing temperature gradients; 3) reduction of thermal/mechanical chip deformation and stress. Introduction As a result the smart power IC driver must be considered as a mixed electronic-thermal microsystem. The CAD of such system can't be made by the traditional way with commercial software tools PSPICE, PCAD at el., which give good choice to simulate the system consisting especially of electronic components. Electromechatronic systems are the basic elements of robotics, automotive, avia, naval and space navigation, computer peripherals, telecommunication products. In this paper we consider the electromechatronic system as motor-drive system which consist of electronic and electromechanical parts (see fig. 1). From this point of view the system design is divided in two parts: for the smart power IC driver and for the motor being controlled. The high power dissipation and the strong electro-thermal intercommunions induce high local temperatures of the elements and change there electrical regimes. This situation is not forced in standard commercial PSPICE where the temperature is used as an external parameter identical for all elements on the chip. Mixed electrical-thermal IC driver simulation. The smart power IC is the complex microelectronic one chip system which consists of the high power output bipolar or DMOS transistors or circuit driving the motor windings and middle/low power circuits or elements which carry out the functions of sensoring, control, protection, testing, A/D or D/A convertion, memorizing (see fig.1). For this IC which is realized by monolith or hybrid technologies occur the following specificities: To overcome this problem we developed the compact electro-thermal models of middle/low power BJT, high power BJT, MOSFET, CMOS, high power DMOSFET and passive elements: resistors and capacitors. These models were included into PSPICE model library as subcircuits. The electro-thermal BJT and MOSFET (DMOSFET) models consist of electrical and thermal parts are shown in fig. 2. They were developed for a real IC construction fig. 3 and taken into account a thermal interaction between the neighboring elements § arrangement of high power, middle/low power, sensor elements on the chip; § use of the circuit elements with different physical operating mode: BJTs, FETs, MOSFETs, DMOSs, Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.  1994 ACM 0-89791-687-5/94/0009 3.50 on the chip. We have added one more local temperature node TQi to the traditional electrical voltage nodes (e, b, c) of BJT and (g, d, s, sub) of MOSFET. 4. The high power multi-section output transistors Q46 and Q53 are symmetrical and occupy more than 30% of chip area. Because the squares of transistors Q46 and Q53 are very large they are layout on the chip as three subsquares (see fig. 4). Accordingly in SPICE transistor Q46 (Q53) is modeled by three transistors electrically connected in parallel, by thermally they are connected through thermal resistances. Thus each of this transistors Q46 and Q53 is described by three local temperatures. The multi-section representation of large square power elements improves the accuracy of the modeling. Some results of electro-thermal simulation of OA fig. 4 are given in Table 1. It is clear that the maximal temperature of transistors Q46 and Q53 is high (about 70°C) and the neighboring middle power elements are being under a strong thermal influence which varies their electrical regimes. In the electrical subcircuit fig.2 the internal transistor is described by standard BJT or MOSFET PSPICE model and the current source GTQi is governed by local temperature TQi. In the thermal subcircuit the voltage source VT0 represents the ambient temperature T0; the current source GPQi is governed by the total dissipated electrical power of the transistor PQi; RTQi and CTQi thermal resistance and capacitance of the transistor Qi from the ambient to the bottom of the chip; RTQiQj mutual thermal resistance between transistors Qi and Qj on the chip. The thermal subcircuit is equal to the discrete representation of classic heat flow equation which describe the 3D-temperature distribution T(x,y,z) inside the real IC structure We have analyzed the convergence of SPICE simulation process of electro-thermal modeling for different types of power ICs and didn't discover insurmountable problems. ∇ ∇ = ⋅ λ ρ ∂ ∂ (T) T(x,y,z,t) C T(x,y,z,t) t (1) To increase the possibilities of power IC electro-thermal design we have connected the modified PSPICE with the 3D temperature simulators of monolith and hybrid ICs [3] which are based on numerical solution of heat flow equations (1)-(3) with conventional boundary conditions taking into account the real IC packaging construction. These simulators provide two very important functions: 1) design of mutual thermal resistance matrix RTQiQj, thermal resistance and capacitance columns RTQi, CTQi which are input data for electro-thermal circuit simulation with PSPICE; 2) optimization of IC layout and package construction reducing the rise in temperature caused by heat generation. For example, the final 2D-temperature distribution on OA chip layout is shown in fig. 4. with the boundary condition on the top of the chip