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RT8560 Datasheet(PDF) 12 Page - Richtek Technology Corporation |
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RT8560 Datasheet(HTML) 12 Page - Richtek Technology Corporation |
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12 / 15 page  RT8560 12 DS8560-01 April 2011 www.richtek.com Applications Information The RT8560 is a current mode boost converter operated at 1MHz to power up to 60 white LEDs with a programmable current for uniform intensity. The part integrates current sources, soft-start, and easy analog and digital dimming control. The protection block provides the circuitry for over-temperature, over-voltage and current- limit protection features. Input UVLO The input operating voltage range of the RT8560 is 7V to 40V. An input capacitor at the VCC1 and VCC2 pin can reduce ripple voltage. It is recommended to use a ceramic 10uF or larger capacitance as the input capacitor. This IC provides an under voltage lockout (UVLO) function to enhance the stability when startup. The UVLO threshold of input rising voltage is around 6.2V. Power Sequence Please refer to the below Figure 5 and 7. The recommended power-on sequence is that the PWM ready before EN and/or VIN ready. If not, the Soft-Start function will be disabled. As to power-off sequence, the EN/VIN must be pulled low within 10ms to prevent “Hard-Start” shown as Figure 7. LED ISET 5.36k I = 20mA R × Soft Start The RT8560 employs a soft start feature to limit the inrush current. The soft-start circuit prevents the excessive inrush current and input voltage droop. The soft-start time is determined by capacitor CSS connected to SS with a 7uA constant current to charge CSS. The value of capacitor CSS is user-defined to satisfy designer' requirement. LED connection The RT8560 equips 4 channel LED divers and each channel supports up to 15 LEDs. The 4 LED strings are connected from VOUT to pin 15, 16, 17 and 18 respectively. If one of the LED channel is not used, the LED pin should be opened directly. Setting and Regulation of LED current The LED current can be calculated by the following equation : EN must be turned on late than VIN and PWM signal EN must be turned off early than VIN and PWM signal Power-on sequence EN VIN PWM Power-off sequence UVLO VOUT Soft-Start No Soft-Start Abnormal Power- on sequence If PWM turns on late Figure 5. Power-On Sequence Control by EN VIN must be turned on late than EN and PWM signal VIN must be turned off early than EN and PWM signal Power-on sequence EN VIN PWM Power-off sequence UVLO VOUT Soft-Start No Soft-Start Abnormal Power- on sequence If PWM turns on late Figure 6. Power-On Sequence Control by VIN PWM EN/VIN EN and/or VIN should be pulled low once PWM pull low for over 10ms 10ms Figure 7. To Prevent “Hard-Start” Sequence |
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