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AP5725 Datasheet(PDF) 9 Page - Diodes Incorporated |
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AP5725 Datasheet(HTML) 9 Page - Diodes Incorporated |
9 / 17 page AP5725 WHITE LED STEP-UP CONVERTER AP5725 Document number: DS31844 Rev. 3 - 2 9 of 17 www.diodes.com July 2010 © Diodes Incorporated Applications Information Inductor Selection A 10 μH~22μH inductor is recommended for most AP5725 applications. For high efficiency the inductor should have low core losses at 1.2MHz and low DCR (copper wire resistance). The inductor saturation current rating should also exceed the peak input current, especially for high load current applications (like 3S8P). Capacitor Selection The small size of ceramic capacitors are ideal for AP5725 applications. X5R and X7R types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as Y5V or Z5U. A 1 μF input capacitor and a 1μF output capacitor are sufficient for most AP5725 applications. For high output current applications like 3S8P, larger output capacitor of 2.2uF ~ 4.7uF is recommended to minimize output ripple. Diode Selection Schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AP5725 applications. The forward voltage drop of a Schottky diode represents the conduction losses in the diode, while the diode capacitance (CT or CD) represents the switching losses. For diode selection, both forward voltage drop and diode capacitance need to be considered. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance, which can cause significant switching losses at the 1.2MHz switching frequency of the AP5725. Schottky diodes with higher current ratings usually have lower forward voltage drop and larger diode capacitance. Larger Schottky diode capacitance can cause significant switching losses at the 1.2MHz switching frequency of the AP5725. A Schottky diode rated at 100mA to 200mA is sufficient for most AP5725 applications. LED Current Control The LED current is controlled by the feedback resistor (RSET in Figure 1). The feedback reference is 0.25V. The LED current is 0.25V/ RSET. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for RSET selection are shown below. RSET = 0.25V/ILED (See Table 1) Table 1. RSET Resistor Value Selection ILED (mA) RSET (Ω) 5 50 10 25 15 16.6 20 12.5 30 8.3 |
Similar Part No. - AP5725_10 |
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Similar Description - AP5725_10 |
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