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LT1931 数据表(PDF) 5 Page - Linear Technology |
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LT1931 数据表(HTML) 5 Page - Linear Technology |
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5 / 12 page  5 LT1931/LT1931A 1931fa APPLICATIO S I FOR ATIO LT1931A AND LT1931 DIFFERENCES: Switching Frequency The key difference between the LT1931A and LT1931 is the faster switching frequency of the LT1931A. At 2.2MHz, the LT1931A switches at nearly twice the rate of the LT1931. Care must be taken in deciding which part to use. The high switching frequency of the LT1931A allows smaller cheaper inductors and capacitors to be used in a given application, but with a slight decrease in efficiency and maximum output current when compared to the LT1931. Generally, if efficiency and maximum output current are critical, the LT1931 should be used. If applica- tion size and cost are more important, the LT1931A will be the better choice. In many applications, tiny inexpensive chip inductors can be used with the LT1931A, reducing solution cost. Duty Cycle The maximum duty cycle (DC) of the LT1931A is 75% compared to 84% for the LT1931. The duty cycle for a given application using the dual inductor inverting topol- ogy is given by: DC V VV OUT IN OUT = + || || | | For a 5V to –5V application, the DC is 50% indicating that the LT1931A can be used. A 5V to –16V application has a DC of 76.2% making the LT1931 the right choice. The LT1931A can still be used in applications where the DC, as calculated above, is above 75%. However, the part must be operated in the discontinuous conduction mode so that the actual duty cycle is reduced. INDUCTOR SELECTION Several inductors that work well with the LT1931 are listed in Table 1 and those for the LT1931A are listed in Table 2. Besides these, there are many other inductors that can be used. Consult each manufacturer for detailed information and for their entire selection of related parts. Ferrite core inductors should be used to obtain the best efficiency, as core losses at frequencies above 1MHz are much lower for ferrite cores than for powdered-iron units. When using coupled inductors, choose one that can handle at least 1A of current without saturating, and ensure that the inductor has a low DCR (copper-wire resistance) to minimize I2R power losses. If using uncoupled inductors, each inductor need only handle one-half of the total switch current so that 0.5A per inductor is sufficient. A 4.7 µH to 15µH coupled inductor or a 15 µH to 22µH uncoupled inductor will usually be the best choice for most LT1931 designs. For the LT1931A, a 2.2 µH to 4.7µH coupled inductor or a 3.3 µH to 10µH uncoupled inductor will usually suffice. In certain applications such as the “Charge Pump” inverting DC/DC converter, only a single inductor is used. In this case, the inductor must carry the entire 1A switch current. Table 1. Recommended Inductors—LT1931 L Size PART ( µH) (L × W × H) mm VENDOR CLS62-100 10 6.8 × 6.6 × 2.5 Sumida CR43-150 15 4.5 × 4.0 × 3.2 (847) 956-0666 CR43-220 22 www.sumida.com CTX10-1 10 8.9 × 11.4 × 4.2 Coiltronics CTX15-1 15 (407) 241-7876 www. coiltronics.com LQH3C100K24 10 3.2 × 2.5 × 2.0 Murata LQH4C150K04 15 (404) 436-1300 www.murata.com Table 2. Recommended Inductors—LT1931A L Size PART ( µH) (L × W × H) mm VENDOR ELJPC3R3MF 3.3 2.5 × 2.0 × 1.6 Panasonic ELJPC4R7MF 4.7 (408) 945-5660 www.panasonic.com CLQ4D10-4R71 4.7 7.6 × 4.8 × 1.8 Sumida CLQ4D10-6R82 6.8 (847) 956-0666 www.sumida.com LB20164R7M 4.7 2.0 × 1.6 × 1.6 Taiyo Yuden LB20163R3M 3.3 (408) 573-4150 www.t-yuden.com LQH3C4R7K24 4.7 3.2 × 2.5 × 2.0 Murata LQH4C100K24 10 (404) 436-1300 www.murata.com 1Use drawing #5382-T039 2Use drawing #5382-T041 |
类似零件编号 - LT1931 |
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类似说明 - LT1931 |
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