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1、1Linear Technology Chronicle April 1996Product of the MonthA Showcase of Linear Technologys Focus ProductsLinear Technology ChronicleApril 1996Vol. 5 No. 4Multiple Output Power Supply ICs for Portable Computers Have Wide Input Range and Constant Switching Frequency, LTC and LT are registered tradema
2、rks of Linear Technology Corporation.Continued on page 2satisfy the ever increasing need for maintain- ing long battery life in the face of increasing power demands of new high performance microprocessors. These highly integrated ICs operate from a wide input voltage range of 3.5V to 36V, operate at
3、 constant switch- ing frequency, have high efficiency over a wide range of load current and drive low cost N-channel power MOSFETs.The LTC1439 contains all the control circuitry needed to implement up to a 4-out- put power supply with an overall efficiency of better than 90% over a wide range of loa
4、d current while maintaining constant switching frequency of up to 400kHz. The LTC1439 was designed to provide all the necessary functions for battery power conversion with- out sacrificing flexibility or small size. The block diagram and simplified 4-output appli- cation pictured in Figure 1 illustr
5、ates the following key functional areas.Synchronous controllers 1 and 2 pro- vide an all N-channel MOSFET drive for highest efficiency with the excellent dy- namic performance inherent with true current mode control. Gate drive of these controllers is sufficient to drive MOSFETs capable of supplying
6、 output currents in ex- cess of 8A; 99% maximum switch duty cycle assures low dropout operation. A new Adaptive PowerTM mode uses a small N-channel MOSFET which operates under low load conditions while maintaining con- stant switching frequency. This conserves power that would otherwise be consumed
7、driving the larger main switches used during high load current conditions. If this third FET is not used, the device reverts to stan- dard Burst ModeTM operation which maintains high efficiency at low loads with variable frequency.An auxiliary linear regulator driver al- lows the use of an inexpensi
8、ve external bipo- lar pass transistor to obtain up to 500mA at 12V for PCMCIA or low noise audio adjust- able power supplies. For use with CPUs such as the Intel Pentium processor for portable computers, the auxiliary driver can also beAdaptive Power and Burst Mode are trademarks of Linear Technolog
9、y Corporation. Pentium is a registered trademark of Intel Corporation.SECONDARY? FEEDBACK? CONTROLOSCILLATORPHASE ? DETECTOR? (PLL)POWER-ON? RESETSYNCHRONOUS? CONTROLLER? 1SYNCHRONOUS? CONTROLLER? 2RUN/SOFT? START 1RUN/SOFT ? START 2AUXILIARY? LINEAR? REGULATOR ? DRIVERSOME COMPONENTS OMITTED FOR CL
10、ARITYINT VCC? REGULATORINT VCC? STANDBY 5VVINVIN12V5V3.3VZETEX? FZT849 2.9V 316k 221k12VPLL IN0.1F11.3kMBRS140MBRS140100k0.030.024.7k0.1FPOR1439 F01LTC14390.01F10H3.3F? 20V200F? 10V200F? 10V330F? 6.3V+2907AThe LTC1438 and LTC1439 high efficiency power conversion ICs offer the industrys most highly i
11、ntegrated and flex- ible solution for maximum battery life inportable computers. These dual controllers are the first and most complete members of a new family of ultrahigh efficiency voltage conversion products. They are designed toZero Drift, 3V Op Amp Operates Rail-to-Rail. 2 500kHz Buck/Boost Co
12、nverter Needs No Heat Sink . 3 50Mbps Quad Differential Receiver Offers Guaranteed 3ns Skew. 3 Five Improved Industry Standard DACs Now Available from Linear Technology . 41996 Power Solutions Brochure Now Available . 4Inside This Issue:Figure 1. Complete Notebook Computer Power Supply2Linear Techno
13、logy Chronicle April 1996LTC1438/LT1439 from page 1 configured as shown in the block diagram to obtain the 2.9V core logic voltage at up to 3A regulated off of the main 3.3V out- put. When this is done, 12V for PCMCIA can be derived using an overwinding from the main 5V output. Secondary winding fee
14、dback control allows the 12V to remain in regulation even when the 5V power de- mand is low by forcing continuous opera- tion of the section.A phase-locked loop is provided which allows the LTC1439 to be synchronized to an external clock for applications such as communications and GPS systems. In th
15、ese systems it is commonly desired to have switching frequencies positioned so as not toLTC1438 contains the two main output con- trollers, the low-battery detector/comparator, secondary feedback control and power-on reset on output 2. Single output controllers which offer various combinations of the fea- tures described above are planned for release in the coming weeks. Future issues of Linear Technology Chronicle will detail these prod- ucts as well as new versions of the dual output devices.Both chips ar
