LT1070 Design Manual (Linear Technology)

Application Note 19 June 1986 LT1070 Design Manual Carl Nelson
INTRODUCTION
Three terminal monolithic linear voltage regulators ap- Finally, there has been a notable lack of comprehensive peared almost 20 years ago, and were almost immediately and practical application literature support from manufac- successful for a variety of reasons. In particular, there turers. were relatively few engineers capable of designing a good These considerations are reminiscent of the state of linear linear voltage regulator. The new devices were also easy to regulator design when the first three terminal monolithic use, and inexpensive. In currently popular parlance they regulators appeared. Given this historical lesson, the were “expert systems,” containing a good deal of their LT®1070 five terminal switching regulator has been de- designer’s knowledge in silicon form. Because of these signed for ease of use and economy. It does not require the advantages, the regulators quickly eclipsed discrete and user to be well-schooled in switching regulator design, earlier monolithic building blocks and dominated the and is versatile enough to be used in all the popular market. switching regulator configurations. To obtain maximum More recently, there has been increasing interest in switch- user benefit, a significant applications effort has been ing-based regulators. Switching regulators, with their associated with this part. This note covers both ancillary high efficiency and small size, are increasingly desirable tutorial material as well as direct operating considerations as overall package sizes have shrunk. Unfortunately, switch- for the part. It is intended to be used “as required.” For ing regulators are also one of the most difficult linear those in a mission-oriented hurry, much of the discussion circuits to design. Mysterious modes, sudden failures, can be ignored, and breadboards constructed with a high peculiar regulation characteristics and just plain explo- probability of success. The more academically inclined sions are common occurrences during the design of a reader may choose to peruse the material more carefully. switching regulator. Either approach is valid and the note is intended to satisfy both. Most switching regulator ICs are building blocks. Many discrete components are required, and substantial exper- — Jim Williams tise is assumed on the part of the user. Some newer devices include the power switch on the die, but still , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. require a significant amount of engineering to apply. All other trademarks are the property of their respective owners. an19fc AN19-1