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RT8532GQW Datasheet(PDF) 9 Page - Richtek Technology Corporation |
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RT8532GQW Datasheet(HTML) 9 Page - Richtek Technology Corporation |
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9 / 14 page  9 RT8532 DS8532-04 January 2014 www.richtek.com © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Application Information The RT8532 is a general purpose 6-CH LED driver capable of delivering an adjustable 5mA to 50mA LED current. The IC is a current mode boost converter integrated with a 43V/2.5A power switch and can cover a wide VIN range from 2.5V to 24V. The part integrates both built-in soft- start and with PWM dimming control; moreover, it provides over voltage, over temperature and current limiting protection features. It also integrates PWM and mixed mode dimming function for accurate LED current control. The PWM dimming frequency can operate from 100Hz to 20kHz without inducing any inrush current in LED or inductor. Input Capacitor Selection Low ESR ceramic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input ripple voltage caused by the switching operation. Two 2.2 μF low ESR ceramic capacitors are sufficient for most applications. Nevertheless, this value can be decreased for applications with lower output current requirement. Another consideration is the voltage rating of the input capacitor, which must be greater than the maximum input voltage. Output Capacitor Selection Output ripple voltage is an important index for estimating chip performance. This portion consists of two parts. One is the product of the inductor current ripple with the ESR of the output capacitor, while the other part is formed by the charging and discharging process of the output capacitor. As shown in Figure 3, ΔVOUT1 can be evaluated based on the ideal energy equalization. According to the definition of Q, the Q value can be calculated as the following equation : where fSW is the switching frequency and ΔIL is the inductor ripple current. Move COUT to the left side to estimate the value of ΔVOUT1 according to the following equation : IN L OUT IN L OUT IN OUT OUT1 OUT SW 11 1 QI I I I I I 22 2 V 1 C V Vf Finally, taking ESR into account, the overall output ripple voltage can be determined by the following equation : Figure 3. The Output Ripple Voltage without the Contribution of ESR Time Time Inductor Current Output Current Output Ripple Voltage (ac) (1-D)TS ΔVOUT1 ΔIL Input Current OUT OUT1 OUT SW DI V Cf OUT OUT IN OUT SW DI VI ESR Cf Inductor Selection The inductor value depends on the maximum input current. As a general rule the inductor ripple current is 20% to 40% of maximum input current. If 40% is selected as an example, the inductor ripple current can be calculated according to the following equation : OUT OUT(MAX) IN(MAX) IN RIPPLE IN(MAX) VI I V I0.4 I |
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