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FAN5608DMPX Arkusz danych(PDF) 8 Page - Fairchild Semiconductor |
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FAN5608DMPX Arkusz danych(HTML) 8 Page - Fairchild Semiconductor |
8 / 17 page PRODUCT SPECIFICATION FAN5608 8 REV. 1.0.3 6/28/04 Application Information Inductor Selection The inductor is one of the main components required by the boost converter to store energy. The amount of energy stored in the inductor and transferred to the load is controlled by the regulator using PWM and pulse skipping techniques. In most cases the FAN5608 operates the inductor in discontinuous conduction mode. To ensure proper operation of the current regulator over the entire range of conditions, select the inductor based on the maximum required power (POUT) and the minimum input voltage (VIN). where units of L, VIN, and POUT are in µH, Volt, and Watt, respectively and F = 0.4 is a factor depending upon the FAN5608 architecture. The above relation is applicable up to POUT = 0.6W and L = 4.3 µΗ , or greater. At lower inductor values the effi- ciency decreases due to the resistive loss in the switching Power FET. Using L = 4.3 µΗ and increasing the load to 12 LED x 20mA (POUT = 800mW) requires VIN > 3.5V to maintain a constant 20mA current through LEDs. The induc- tor L = 4.3 µH ensures proper operation for 2 x 4 white LEDs with 20mA at 3.5V for VIN > 2.8V. For any lighter load or higher VIN, the inductance can be increased to improve the system efficiency. Application examples are given in Figure 1 through Figure 4. The peak current in the inductor is: which gives the maximum rated current for the inductor. For L = 4.3 µH, TON_Max = 1.25µS and VIN_Max = 4.2V, the inductor saturation current should be at least 1A. Capacitor Selection Low ESR capacitors should be used to minimize the input and output ripple voltage. Use of CIN = 4.7µF/6.3V and COUT = 4.7µF/25V type X5R/X7R multi layer ceramic capacitor is recommended. A larger value input capacitor placed as close as possible to FAN5608 may be needed to reduce the input voltage ripple in noise sensitive applications. An additional LC filter between the battery and the FAN5608 input can help to further reduce the battery ripple to the level required by a particular application. Schottky Diode Selection The FAN5608HMPX and FAN56508MPX require the use of an external Schottky diode. This diode should be rated at 200mA to 500mA average rectified current and 20V maximum repetitive reverse voltage. The MBR0520L (Fairchild) Schottky diode is recommended. Driving Higher Current LEDs To increase the LED current range to 50mA, the CH1 and CH2 outputs may be connected, as shown below: L V IN () 2 F × P OUT -------------------------- < I T ON_Max V IN_Max × L ------------------------------------------------- = Analog Brightness Control A1 VIN IND IND GND CH1 CIN VEXTERNAL L = 4.7 µH 4.7 µF 2.7V to 5.5V CH2 A2 Digital Brightness Control A1 B1 B2 IND IND GND CH1 CIN DAC Inputs L = 4.7 µH 4.7 µF 2.7V to 5.5V CH2 A2 |
Podobny numer części - FAN5608DMPX |
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Podobny opis - FAN5608DMPX |
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