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LT3519-1 Datasheet(PDF) 11 Page - Linear Technology |
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LT3519-1 Datasheet(HTML) 11 Page - Linear Technology |
11 / 20 page LT3519/LT3519-1/LT3519-2 11 3519fa APPLICATIONS INFORMATION ESL and have an adequate ripple current rating. A 2.2μF ceramic type capacitor is usually sufficient for LT3519 (400kHz version). A capacitor of proportionately less value for LT3519-1/LT3519-2 (higher frequency version) can be used. Output Capacitor Selection The selection of output capacitor depends on the load and converter configuration, i.e., step-up or step-down and the operating frequency. For LED applications, the equivalent resistance of the LED is typically low, and the output filter capacitor should be sized to attenuate the current ripple. To achieve the same LED ripple current, the required filter capacitor value is larger in the boost and buck-boost mode applications than that in the buck mode applications. Lower operating frequencies will require proportionately higher capacitor values. For LED buck mode applications, a 1μF ceramic capacitor is usually sufficient. For the LED boost and buck-boost mode applications, a 2.2μF ceramic ca- pacitor is usually sufficient. Very high performance PWM dimming applications may require a larger capacitor value to support the LED voltage during PWM transitions. Use only ceramic capacitors with X7R, X5R or better dielec- tric as they are best for temperature and DC bias stability of the capacitor value. All ceramic capacitors exhibit loss of capacitance value with increasing DC voltage bias, so it may be necessary to choose a higher value capacitor to get the required capacitance at the operation voltage. Always check that the voltage rating of the capacitor is sufficient. Table 2. Recommended Ceramic Capacitor Vendors VENDOR PHONE WEB TDK (516)535-2600 www.tdk.com Kemet (408)986-0424 www.kemet.com Murata (814)237-1431 www.murata.com Taiyo Yuden (408)573-4150 www.t-yuden.com Inductor Selection The inductor used with the LT3519/LT3519-1/LT3519-2 should have a saturation current rating of 1A or greater. For buck mode LED drivers, the inductor value should be chosen to give a ripple current 150mA or more. In the buck mode, the inductor value can be estimated using the formula: LµH ()= DBUCK •VIN –VLED () fOSC (MHz)•0.15A µH • A •MHz V ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ DBUCK = VLED VIN VLED is the voltage across the LED string, VIN is the input voltage to the converter, and fOSCistheswitchingfrequency. In the boost configuration, the inductor can be estimated using the formula: LµH ()= DBOOST •VIN fOSC (MHz)•0.15A µH • A •MHz V ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ DBOOST = VLED –VIN () VLED Table 1. Recommended Inductor Vendors VENDOR PHONE WEB Sumida (408)321-9660 www.sumida.com Toko (408)432-8281 www.toko.com Cooper (561)998-4100 www.cooperet.com Vishay (402)563-6866 www.vishay.com Input Capacitor Selection For proper operation, it is necessary to place a bypass capacitor to GND close to the VIN pin of the LT3519/ LT3519-1/LT3519-2. A 1μF or greater capacitor with low ESR should be used. A ceramic capacitor is usually the best choice. In the buck mode configuration, the capacitor at the input to the power converter has large pulsed currents. For best reliability, this capacitor should have low ESR and |
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Similar Description - LT3519-1_15 |
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