application note new levels of integration in automotive electronics by riccardo ferrari , marco morelli introduction since the early seventies, more and more func- tions have been added to our cars not only with the purpose of guaranteeing a better comfort to drivers and passengers, but also to reduce oper- ating costs and finally to ensure compliance with new regulations concerning noise and pollution are concerned. because of all these needs, cars have to house more and more modules designed to perform more or less complex operations (fig. 1). this growth makes more and more evident the need to reduce the room taken by each module, with the double target of minimizing the cost of the particular function and increasing the number of functions in a specific car; in parallel, by in- creasing the number of modules, it becomes mandatory to increase the reliability of each of them, otherwise the reliability of the total car would be badly affected. all these issues recently pushed the manufactur- ers of automotive systems to refer very often to producers of integrated circuits asking for the de- velopment of monolithic devices capable of re- placing effectively a number of discrete compo- nents, passive parts included; anyway the trend to a total integration is not over by just designing onto a simple piece of silicon a complete function, but it carries on implementing in the same device a number of auxiliary services, that would add a substantial cost if achieved by discrete compo- nents, that can easily find place on a few extra square millimeters of silicon. to that purpose the example given by the alterna- tor regulator, subject of a specific description in the following pages, is particularly enlightening. figure 2 shows briefly the evolution of the alter- nator regulator paralleled with the evolution of the silicon technology; it is evident that the key issue to pursue the monolithic design of very complex functions in the automotive environment is the availability of process capable to host on the same chip high density signal circuitry, together with power stages managing currents of several amperes; a process with these characteristics is usually called asmart powero process. AN449/1192 one of the fastest growth areas today in electronics is in the automotive field. in this note the authors describe the particular needs of this field and some typical dedicated ics developed by sgs-thomson. safety & convenience body control power train driver information rear window defogger cruise control ignition digital gauges climate control intermittent wipar spark timing digital clock keyless entry antitheft devices voltage regulator multitons alarms automatic door lock electr. suspension alternator engine diagn. results light drimmer electr. steering idle speed control service reminders traction control multiplex wiring turbo control miles to empty antiskid braking module to module emission system shift indicator window control communications transmiss. control head-up display memory seat load sensit. braking diagnostics crt display heasted windshield hard/soft ride control audio annunciator voice controlled trunk airbag restraints figure 1: electronics in present and future automobiles. 1/10
technology overview over the years sgs-thomson has developed various technologies that allow the realization of smart power circuits. the simplest way to classify these technologies is to refer to the process type, which can be purely bipolar or mixed, that is, in- cluding on a single piece of silicon both mos structures (of control and power) and bipolar structures. another method (figure 3) is to examine the way in which the current flows through the power sec- tion; horizontal, with the current entering and leaving through the upper surface, or vertical, where the current enters through the upper sur- face and leaves through the lower surface; for this lower connection, instead of wire, the tie bar of the package is used. figure 2: alternator regulator evolution. figure 3: integrated dmos structures. 1 or more hv ldmos devices with common source many power vdmos devices any configuration 1 or more hc vdmos devices with common drain application note 2/10
the choice of one technology rather than another depends on various elements. by simplifying as far as possible the criteria, we can say that verti- cal technologies can guarantee, for a given area, lower resistances but they have the limitation of being able to include just one power device per circuit (or more than one, but always with the col- lectors or drains short-circuited). horizontal tech- nologies instead make it possible to have power structures that are completely independent. it is therefore evident that a vertical technology will give excellent results in the design of a light switch, while a horizontal technology will be equally well suited to the design of a multiple ac- tuator. finally we have to underline that the continuous evolution of the silicon technologies has already made available, for the design activity, second generation processes, offering to the user both higher component density in the signal section and higher current density in the power area, so that in some cases the limit to achieve very low values of resistance does not come from the sili- con, but from the bonding wires. an example of comparison between a first generation smart power technology - today in full industrial produc- tion - and a second generation one - today avail- able for new designs - is given in table 1: the way is open to processes that will allow the de- sign - on the same chip-actuators - of several am- peres together with microcontroller of not negli- gible power. it is important at this point to underline that a smart power circuit does not consist of just silicon technology, but relies heavily on package tech- nology. in fact it is well known that a signal device is bonded using gold wires with a diameter of 25 microns; however, gold wires can be used effec- tively up to diameters of 50 microns, which allows reliable operations with currents up to 2a, pro- vided that the wire is surrounded by resin (the current capacity drops by 50% for wires in free air - that is, in the case of hermetic packages). bcd20/60 bcd60ii junction isolation down up and down field oxide tapered oxide locos + field implant vdmos r on* area ( w *mm 2 ) 0.9 0.5 ldmos r on* area ( w *mm 2 ) 0.6 0.25 cmos tr. density (mm -2 ) 650 1500 cmos thres. voltage (v) 1.3 1 min. npn area (mil 2 )11 4 min. pnp area (mil 2 )15 5 number of masks 12/14 13/15 multipower bcd/60 vs. bcd60ii figure 4: mixed bonding technology. application note 3/10
when, however, one has to deal with very high currents (more than 5a in single-point injection actuators, and more than 10a for window lift mo- tors) gold wires are no longer suitable for obvious cost reasons so it is necessary to turn to alumi- num wires with a diameter from 180 microns to 375 microns; clearly in this case it will be neces- sary to have adequately dimensioned bonding pads on the die, with a significant waste of silicon area. optimization is obtained with a mixed bonding technology where signal pads are bonded with thin gold wires and power pads with thick alumi- num wires (figure 4). a further optimization is ob- tained by orienting the pads in the pad-to-bond- post direction. finally, another key area for a real industrial im- plementation of a smart power device is packag- ing; sgs-thomson has a reputation of unparal- leled excellence in the development and in the production of packaging techniques to meet power dissipation even in the presence of high pin count, and several innovative sgs-thomson packages have been adopted as worldwide in- dustry standards; in figure 5 several types are displayed, including hermetic metal can, particu- larly suitable for components, such as the alterna- tor regulators, that have to operate at a rather high temperature, with junction temperature that may exceed 150 c, in an extremely severe envi- ronment, since the regulator is usually exposed to any kind of dangerous element, such as grease, sand, dust, salt water and so on. a quite original power package for surface mounting, combining a low r th j-case (less than 3 c) with a small ge- ometry, is under development in our laboratory. three examples the alternator regulator. we have already briefly mentioned the evolution of the alternator regulator, but it is worth covering with some more details the history of this func- tion. since the simple realization of so-called mono- function regulators by means of discrete compo- nents - diodes, transistors and resistors - the pro- gress of the technology allowed the design of a monolithic component, still monofunction: in par- allel, to provide the driver with more information about the status of the charging function, multi- function regulators were designed, but the power remained external, on a separate component. a further improvement came with the assembly technology on a ceramic substrate, housed in a single package, but still several chips of silicon were needed. now sgs-thomson has reached the maximum level of integration by designing a monolithic mul- tifunction regulator and offering to the customer a device that minimizes the assembly operations and maximizes the reliability because of the sin- gle piece of silicon and the minimum number of connections between the silicon itself and the rest of the system: nevertheless the accuracy of the regulation and the number of possible malfunc- tions monitored by the circuit are well above what offered so far by the market. figure 5: power packages. application note 4/10
the main characteristics of the device are sum- marized in table 2 and the block diagram of the circuit is displayed in figure 6. the choice of the technology required a particular care and was driven by the following factors: 1)a circuit for the regulation of the alternator voltage, even if equipped with a complex di- agnostic, is however a circuit where the power section, including the field drive in low side configuration and the free wheeling di- ode plus a big active zener diode, takes a sig- nificant share - about one third of the total, (see figure7); therefore a bipolar process has been selected. 2)on the other side, about 600 small signal de- vices had to be integrated, and because of that a technology with a good intensity was mandatory, otherwise the total economy of the program would have been affected. 3)finally an alternator regulator must be able to withstand very severe voltage transients, as fixed by iso 7637/1, with voltages up to 270v and energy up to 50 joule, that arise on the car electrical network, for instance, if a sud- den misconnection of the alternator occurs. figure 6: block diagram of alternator regulator. table 2: monolithic alternator regulator low side configuration no external component accuracy on regulated voltage better than 1% precise temperature coefficient self-oscillating analog regulation loop minimized field current at alternator stopped (500 ma max) maximum field current trimmed at 5a, with 1.5v saturation voltage full diagnostic: alternator stopped broken belt extravoltage broken wire alternator-battery protected against short circuit (current limita- tion and thermal shutdown ) protected against short circuit of fault lamp driver protected against extravoltages according to iso 7637/1 application note 5/10
considering all of the above, sgs-thomson has selected a high voltage process, internally named bsoii, fully bipolar, horizontal, with lithography of 3 m m, and more than 100v of breakdown voltage in the vcbo condition. the device is encapsulated in an hermetic pack- age, to-3 multileads, with bonding wires of 5 mils, able to carry continuous current up to 7 am- peres (see again figure 7). the peak & hold injector driver let us now consider the u140, another compo- nent designed by sgs-thomson to make avail- able to the user a complex function on a simple chip; it is an actuator to drive in low side configu- ration the fuel injector in asingle pointo injection system. as it is well known, quite essential for a good effi- ciency of the injection system is the capability to fix in the best way the time while the injector is opened, since that time is directly proportional to figure 7: die of the alternator regulator. figure 8: injector driver. application note 6/10
the quantity of fuel transferred to the intake mani- fold. particularly important to fix the fuel volume are the opening and the closing time of the nozzle, since both must be extremely fast; now, a single point injector needs a consistent current in the opening phase - up to 5a at the apeako - but once opened, less current is enough to maintain the status - aholdo -. at the end of the cycle, fi- nally the driving current must be switched off in a time as short as possible. the u140 meets all the above mentioned requirements: in addition, in the aholdo phase a further reduction of the current is achieved by switching on and off the driver stage (figure 8), so reducing the power consumption and, as a consequence,the junction temperature. a special mention shall be paid to the transition from aholdo to the aoffo condition; as already said, it is quite important to reduce as much as possible this time; in the u140 that is achieved by discharging the inductor through an active zener set at a quite high voltage (about 70v), and that guarantees the closing of the injector in less than 50 sec. the same diode is set at 3v in the hold time. no external component is required by this circuit, that interfaces directly the microcontroller of the engine management system; by the way, the microntroller has just to fix the start and the end of the injection time, since the u140 is totally autonomous in fixing the current levels in the dif- ferent phases, as well as the sampling of the holding current. (figure 9). the device incorporates a very sophisticated di- agnostic (see again figure 8), and transfers to the microcontroller all the relevant information on the status of the load. the advantages of this monolithic devices are quite evident, if compared with existing solutions which need not less than 15 components includ- ing at least one ic and two discrete transistors, but are not limited to cost and room reduction, and to a consistent increase of the reliability: as a matter of fact the monolithic design allows to get, practically at zero cost, a very accurate value of the voltage of the recirculation diode, improving the accuracy on the on time of the injector, and, last but not least, a diagnostic covering all the possible failure modes of the load. the circuit is realized with sgs-thomson's bcd technology, a mixed process including bipolar, cmos, and dmos structures on the same chip; the input section is therefore able to interface di- rectly a microcontroller, and the low side driver is designed with a dmos having an r dson of less than 0.5 ohm. as already explained the recircula- tion diode is set at 70 volt in the transition from figure 9: the injector drive is totally autonomous in fixing the current levels in the different phases, as well as the sampling of the holding current. application note 7/10
hold to off; because of that we selected the bcd100, an option with a minimum breakdown drain-source voltage of 100v. all the main features of this innovative device are listed in table 3. rearview mirror driving while we are on the subject of higher levels of in- tegration it is useful to mention the development of circuits for the multiplex wiring system, which replaces conventional cabling with a common bus and aintelligento switches. the intelligent switch circuits are key components for the multiplex system, and one of these is a multiple driver ic,the l9946, developed by sgs- thomson for rearview mirror driving applications. this ic integrates all of the control functions and power circuits needed in the electronic external rear-view mirror unit now being adopted for high end cars and is the first chip to integrate these functions. (see figure 10). an important feature is that the ic is controlled di- rectly by a microprocessor e all of the possible drive conditions are controlled by loading 4-bit commands and the l9946 generates the appro- priate motor control signals. no external power circuits are needed because the l9946 drives directly the two motors used for mirror orientation ( m p/down and left/right), the mo- tor that afoldso the mirror for maneuvering and the demister heating element. in a typical application the chip is used in multiplex door wiring system where the door is connected to the body by three wires and all door functions controlled remotely using smart chips. inside the chip are four dmos half bridge power stages which drive the three bidirectional dc mo- tors, plus a dmos high side driver that drives the demister element. control logic integrated on the table 3: monolithic peak and hold injector driver low side configuration peak current function of battery voltage to provide a constant charging time fast recirculation voltage independent from battery voltage slow recirculation at max 3v off time and peak current in hold condition internally fixed full diagnostic: - open load - short circuit to ground and battery - thermal warning figure 10: block diagram of the l9946. application note 8/10
chip decides how these transistors are to be switched to achieve the desired motion e includ- ing rapid braking. two of the half bridges are rated at 1a output current; the other two half bridges and the high side driver are capable of delivering up to 4.75a. in common with many other dedicated automotive ics the l9946 incorporates diagnostic functions. conditions such as overload and open load are signalled to the control micro so that appropriate action can be taken. in addition there is a standby pin that allows the micro to put the l9946 into a dormant state when it is not needed. conclusions we think we have demonstrated that the indus- trial availability of processes capable to match, on the same silicon, high power and complex control functions is the key element to the integration of completed functions on a single chip of silicon. the examples described demonstrate that sgs- thomson has developed a technology portfolio that can offer different answers for different appli- cations, always optimizing the trade-off among the various needs. on the other side, all the above considerations would have a merely academic interest if they were not associated with a convenient cost. it is clear that the monolithic integration of complex functions implies the use of not negligible areas of silicon, and that even in presence of high den- sity processes. it is therefore important to devote adequate re- sources to the diffusion technique, to increase the yield of each process. today's chips, up to 30mm 2 (and all the thee ex- amples are below that limit) can be produced at prices competitive with an equivalent discrete so- lution, and in the second half of the 90's the tar- get will be expanded up to areas of 40mm 2 , giv- ing a green light to the monolithic design of complete modules. table 4: multiple half-bridge driver 4.75a total output current very low consumption in off state overload diagnostic open load diagnostic grounded case application note 9/10
information furnished is believed to be accurate and reliable. however, sgs-thomson microelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of sgs-thomson microelectronics. specifications men- tioned in this publication are subject to change without notice. this publication supersedes and replaces all information previously supplied. sgs-thomson microelectronics products are not authorized for use as critical components in life support devices or systems without ex- press written approval of sgs-thomson microelectronics. ? 1995 sgs-thomson microelectronics - all rights reserved sgs-thomson microelectronics group of companies australia - brazil - france - germany - hong kong - italy - japan - korea - malaysia - malta - morocco - the netherlands - singapore - spain - sweden - switzerland - taiwan - thaliand - united kingdom - u.s.a. application note 10/10
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