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LT1941 数据表(PDF) 15 Page - Linear Technology |
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LT1941 数据表(HTML) 15 Page - Linear Technology |
15 / 24 page 15 LT1941 1941f APPLICATIO S I FOR ATIO can handle at least 1.5A of current without saturating and ensure that the inductor has a low DCR (copper-wire re- sistance) to minimize I2R power losses. If using uncoupled inductors, each inductor need only handle one-half of the total switch current so that 0.75A per inductor is sufficient. A 4.7 µH to 15µH coupled inductor or two 15µH to 20µH uncoupled inductors will usually be the best choice for most LT1941 inverter designs. A 4.7 µHto15µHinductorwillbe the best choice for most LT1941 boost designs. In this case, the single inductor must carry the entire 1.5A peak switch current. Diode Selection A Schottky diode is recommended for use with the LT1941 inverter/boost regulator. The Microsemi UPS120 is a very good choice. Where the input to output voltage differential exceeds 20V, use the UPS140 (a 40V diode). These diodes are rated to handle an average forward current of 1A. For applications where the average forward current of the diode is less than 0.5A, use an ON Semiconductor MBR0520L diode. The load current for boost, SEPIC and inverting configurations is equal to the average diode current. BIAS2 Pin Considerations The BIAS2 pin provides the drive current for the inverter/ boost switch. The voltage source on the BIAS2 line should be able to supply the rated current and be at a minimum of 2.5V. For highest efficiency, use the lowest voltage source possible (VOUT = 3.3V, for example) to minimize the VBIAS2 • IBIAS2 power loss inside the part. INPUT CAPACITOR SELECTION Bypass the input of the LT1941 circuit with a 10 µForhigher ceramic capacitor of X7R or X5R type. A lower value or a less expensive Y5V type will work if there is additional bypassing provided by bulk electrolytic capacitors, or if the input source impedance is low. The following paragraphs describe the input capacitor considerations in more detail. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input ca- pacitor is required to reduce the resulting voltage ripple at the LT1941 input and to force this switching current into a tight local loop, minimizing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively and it must have an adequate ripple current rating. With two switchers operating at the same frequency but with different phases and duty cycles, calculating the input capacitor RMS current is not simple; however, a conservative value is the RMS input current for the chan- nel that is delivering the most power (VOUT times IOUT): CI VV V V I IN RMS OUT OUT IN OUT IN OUT () • – = () < 2 Table 4. Inductors VALUE ISAT(DC) DCR HEIGHT PART NUMBER ( µH) (A) ( Ω) (mm) Coiltronics TP3-4R7 4.7 1.5 0.181 2.2 TP4-100 10 1.5 0.146 3.0 Sumida CD73-100 10 1.44 0.080 3.5 CDRH5D18-6R2 6.2 1.4 0.071 2.0 CDRH5D28-100 10 1.3 0.048 3.0 CDRH4D28-100 10 1.0 0.095 3.0 Coilcraft D03314-103 10 0.8 0.520 1.4 1008PS-103 10 0.78 0.920 2.8 Output Capacitor Selection Use low ESR (equivalent series resistance) capacitors at the output to minimize the output ripple voltage. Multi- layer ceramic capacitors are an excellent choice; they have an extremely low ESR and are available in very small packages. X7R dielectrics are preferred, followed by X5R, as these materials retain their capacitance over wide voltage and temperature ranges. A 4.7 µF to 20µF output capacitor is sufficient for most LT1941 applications. Solid tantalum or OS-CON capacitors will work but they will occupy more board area and will have a higher ESR than a ceramic capacitor. Always use a capacitor with a suffi- cient voltage rating. |
类似零件编号 - LT1941 |
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类似说明 - LT1941 |
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