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MAX630MJA Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX630MJA Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 14 page Potted Toroidal Inductors A typical 1mH, 0.82 Ω potted toroidal inductor (Dale TE- 3Q4TA) is 0.685in in diameter by 0.385in high and mounts directly onto a PC board by its leads. Such devices offer high efficiency and mounting ease, but at a somewhat higher cost than molded inductors. Ferrite Cores (Pot Cores) Pot cores are very popular as switch-mode inductors since they offer high performance and ease of design. The coils are generally wound on a plastic bobbin, which is then placed between two pot core sections. A simple clip to hold the core sections together com- pletes the inductor. Smaller pot cores mount directly onto PC boards through the bobbin terminals. Cores come in a wide variety of sizes, often with the center posts ground down to provide an air gap. The gap pre- vents saturation while accurately defining the induc- tance per turn squared. Pot cores are suitable for all DC-DC converters, but are usually used in the higher power applications. They are also useful for experimentation since it is easy to wind coils onto the plastic bobbins. Toroidal Cores In volume production, the toroidal core offers high per- formance, low size and weight, and low cost. They are, however, slightly more difficult for prototyping, in that manually winding turns onto a toroid is more tedious than on the plastic bobbins used with pot cores. Toroids are more efficient for a given size since the flux is more evenly distributed than in a pot core, where the effective core area differs between the post, side, top, and bottom. Since it is difficult to gap a toroid, manufacturers produce toroids using a mixture of ferromagnetic powder (typically iron or Mo-Permalloy powder) and a binder. The perme- ability is controlled by varying the amount of binder, which changes the effective gap between the ferromag- netic particles. Mo-Permalloy powder (MPP) cores have lower losses and are recommended for the highest effi- ciency, while iron powder cores are lower cost. Diodes In most MAX630 circuits, the inductor current returns to zero before LX turns on for the next output pulse. This allows the use of slow turn-off diodes. On the other hand, the diode current abruptly goes from zero to full peak current each time LX switches off (Figure 1, D1). To avoid excessive losses, the diode must therefore have a fast turn-on time. For low-power circuits with peak currents less than 100mA, signal diodes such as 1N4148s perform well. For higher-current circuits, or for maximum efficiency at low power, the 1N5817 series of Schottky diodes are recommended. Although 1N4001s and other general- purpose rectifiers are rated for high currents, they are unacceptable because their slow turn-on time results in excessive losses. CMOS Micropower Step-Up Switching Regulator _______________________________________________________________________________________ 7 MANUFACTURER TYPICAL PART NUMBER DESCRIPTION MOLDED INDUCTORS Dale IHA-104 500µH, 0.5 Ω Nytronics WEE-470 470µH, 10 Ω TRW LL-500 500µH, 0.75 Ω POTTED TOROIDAL INDUCTORS Dale TE-3Q4TA 1mH, 0.82 Ω TRW MH-1 600µH, 1.9 Ω Torotel Prod. PT 53-18 500µH, 5 Ω FERRITE CORES AND TOROIDS Allen Bradley T0451S100A Tor. core, 500nH/T 2 Siemens B64290-K38-X38 Tor. core, 4µH/T 2 Magnetics 555130 Tor. core, 53nH/T 2 Stackpole 57-3215 Pot core, 14mm x 18mm Magnetics G-41408-25 Pot core, 14 x 8, 250nH/T 2 Table 1. Coil and Core Manufacturers Note: This list does not constitute an endorsement by Maxim Integrated Products and is not intended to be a comprehensive list of all manufacturers of these components. |
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