Part # Application Note Power Supply And datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics


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AN447 APPLICATION NOTE SMART POWER TECHNOLOGY EVOLVES TO HIGHER LEVELS OF COMPLEXITY by Bruno Murari Smart power devices are the shooting stars in power semiconductors, because it s possible tointegrate digital and analog functions together with multiple power stages on the same siliconchip. The trend towards higher density will continue. Since it was first introduced in 1986, mixed bipolar/CMOS/DMOS smart power technology has evolvedrapidly, extending voltage capability and integrating highly complex subsystems on single switchmode op-eration is very low it is possible to produce ICs capable of delivering substantial power to the load withoutthe usual heatsinks, cooling fans and so on. Moreover, because it perchips containing thousands of tran-sistors. Figure 1. An example of the complexity now possible in smart power ICs. This custom LSI device developed by STMicroelectronics for a computer peripheral application that integrates a servo positioning system, DC motor controller/driver and various other "glue" func-tions" not integrated in the other ICs on the board. Integrated circuit fabrication technologies that combine bipolar, CMOS and power DMOS structures onthe same chip have had a significant impact on "smart power" integrated circuit design. Since the dissipa-tion of power DMOS stages in mits the integration of high-density CMOS and multiple DMOS power stag-es the traditional constraints on complexity are removed and circuits containing complete subsystemshave been produced. An example of this is shown in figure 1 -- a custom IC that integrates a motor controlsystem, servo positioning system, a step up converter, microprocessor interface and other circuits. December 2003 1/5 AN447 APPLICATION NOTE BCD TECHNOLOGYA power IC technology combining bipolar, CMOS and power DMOS was first introduced by STMicroelec-tronics in 1986. Called Multipower-BCD, this was a 60V process created by merging a conventional junc-tion-isolated bipolar IC process with vertical DMOS technology. The result is a process requiring 12 masksin the standard version --no more complex than modern bipolar technologies.Where this process departed significantly from previous smart power processes is that it employs isolatedDMOS power devices. The significance of this is that designers are not limited to a single power DMOStransistor per chip, but can have any number (hence "Multipower") and connect them in any way. Thus itis possible to integrate any power stage configuration (low side, high side, half bridge or bridge), or evento have several complete power stages on the same chip. Clearly the combined BCD process gives circuitdesigners the possibility of choosing the optimal technology for each circuit function: bipolar is the firstchoice for linear functions where high precision and low offsets are required; CMOS is best for complexanalog and digital signal functions because of its high density; and power DMOS is ideal for power stages.It is the possibility of integrating power DMOS stages that gives BCD technology its greatest advantage:low dissipation. Unlike bipolar power transistors, power DMOS devices need no driving current in DC con-ditions and operate very efficiently in fast switching operations.This low dissipation can be exploited to increase the amount of useful power that can be achieved with agiven package. For example, both STMicroelectronics s L296 bipolar power switching regulator and thefunctionally similar L4970 BCD type are assembled in the Multiwatt package, but the bipolar version de-livers up to 160W while its BCD counterpart delivers up to 400W. An alternative way to profit from low dis-sipation is to use less costly low power packages in place of high power packages. Very often a bipolarpower IC in a power package can be replaced by a BCD part in a DIP, or even PLCC or SO, package.This can bring substantial savings not only because power packages are more costly, but also becausethey are more costly to mount on the board and are not well suited to automatic assembly. For example,a 4A bipolar switching regulator IC in the Multiwatt package can be replaced by a BCD switching regulatorin a DIP package (figure 2) which delivers almost the same current. Figure 2. The low dissipation of power DMOS can be exploited to make power ICs in low power packages, which are less expensive and easier to mount. This DIP-packaged switching regulator delivers 3.5A, replacing a Multiwatt packaged bipolar IC. 2/5 AN447 APPLICATION NOTE Recently STMicroelectronics has introduced a "shrink" version of the original BCD process --called BCD-II -- which greatly increases the circuit and current density that can be achieved (figure 3). The originalMultipower-BCD process family used 4 micron lithography.In the BCD-II versions this is reduced to 2.5 microns.Consequently the current density and component density are approximately doubled. In the case of the60V version, the shrink increases signal component density from 650 transistors/mm2 to 1500 tr/mm2; atthe same time the RON.Area is reduced from 0.9 ohms/mm2 to 0.5 ohms/mm2. Figure 3. A shrink version of the Multipower-BCD technology has now been introduced. Called BCD-II, this version doubles the component density, making high complexity devices much less expensive. STANDARD BCD PRODUCTSThe first BCD chips to be marketed were the L6202 and L6203 DMOS bridge driver ICs -- actually thesame die assembled in DIP (L6202) and Multiwatt (L6203) packages. Both of these devices have an ONresistance of 0.3 ohms, which gives a maximum continuous current of about 1.5A (DIP version) and 3A(Multiwatt version). These were followed by a variety of power ICs for computer peripheral, industrial andautomotive applications. Typical examples include switching regulator ICs, lamp drivers for automotive ap-plications and motor drivers of various types. All of the early chips and many introduced more recently arestandard devices in the sense that they are normally used in various end products, like standard linearsor standard logic. In the late eighties, however, designers began to apply BCD technology to make powerICs with a complexity that can truly be called LSI. LSI COMPLEXITY IN POWER ICs We have seen that BCD technology allows an arbitrary number of complete power stages on one chip andthe dissipation of each is low enough to ensure that the cumulative dissipation of these power stages iswithin the limit of practical packages. Moreover, high density CMOS allows signal level circuits of LSI com-plexity to be added on the same chip.An interesting consequence of these factors is that BCD technology allows the IC designer to build com-plex systems on a single chip. Moreover, the technological limit on complexity is beyond the complexity ofa wide range of end products.The first example of a circuit that exploits the possibilities of LSI smart power is the L6280, a device intro-duced in 1989 for a portable typewriter application (figure 4). This IC integrates two 1A motor drivers, a3A solenoid driver, a 5V/1A SMPS and microprocessor interfacing circuitry --all of the power subsystemsof the typewriter. The L6280 behaves like a microprocessor peripheral, latching commands from the bus.All of the functions can be controlled by software -- even the output stage configurations.Surprisingly, perhaps, the overall dissipation of this complex IC is so low -- less than 1.5W -- a power pack-age was not needed. In fact the L6280 is assembled in a PLCC 44 chip carrier, though the 11 pins on oneside are all connected together and used to conduct heat to the PCB tracks. 3/5

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