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SC4505 Datasheet(PDF) 9 Page - Semtech Corporation |
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SC4505 Datasheet(HTML) 9 Page - Semtech Corporation |
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9 / 15 page  9 2006 Semtech Corp. www.semtech.com SC4505 POWER MANAGEMENT Table 5. Recommended Ceramic Capacitor Manufacturers Applications Information VENDOR PHONE WEBSITE KEMET 408-986-0424 www.kemet.com Murata 814-237-1431 www.murada.com Taiyo Yuden 408-573-4150 www.t-yuden.com Output Rectifying Diode Selection Schottky diodes are the ideal choice for SC4505 due to their low forward voltage drop and fast switching speed. Table 6 shows several different Schottky diodes that work well with the SC4505. Make sure that the diode has a voltage rating greater that the possible maximum ouput voltage. The diode conducts current only when the power switch is turned off. So a 1A diode will be sufficient for most designs. Table 6. Recommended Rectifying Diodes T R A PR O D N E V 3 1 S S 4 1 S S y a h s i V m o c . y a h s i v . w w w 5 1 0 Q B 0 1 r e if it c e R l a n o it a n r e t n I m o c .f r i. w w w Output Current Programming The SC4505 features two independent LED current regulators. The LED current setpoints are chosen using external resistors. The relationships between the programming resistors and the two channel output current setpoints are shown as in the Figure 2 and Figure 3 below. The relationships between the programming resistor value and the output current setpoint can be described as follows: O1 O1SET I / V) 140 R ( = O2 O2SET I / V) 154 R ( = Where R O1SET and RO2SET are in Ohms. IO1 and IO2 are in Amperes. Figure 2. I O1SET Resistor Selection Chart Figure 3. I O2SET Resistor Selection Chart PWM Dimming Either of the enable pins can be toggled by external circuitry to allow PWM dimming. In a typical application, a microcontroller sets a register or counter that varies the pulsewidth on a GPIO pin. The SC4505 allows dimming over two decades in frequency (50Hz-50 kHz) in order to allow compatibility with a wide range of devices, including newest dimming strategies that avoid the audio band by using high frequency PWM dimming. In this manner, a wide range of illumination can be generated while keeping the instantaneous LED current at its peak value for luminescent efficiency and color purity. Furthermore, advanced lighting effects such as backlight “dim-on” or photographic red-eye reduction can be implemented as the SC4505 can resolve PWM from 10% to 90% duty at its highest frequency. IO1SET Resistor Selection Chart 0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 IO1 Current (mA) IO2SET Resistor Selection Chart 0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 120 140 IO2 Current (mA) |
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