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LDS8711 Datasheet(PDF) 7 Page - IXYS Corporation |
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LDS8711 Datasheet(HTML) 7 Page - IXYS Corporation |
7 / 12 page ![]() LDS8711 © 2010 IXYS Corp. 7 Doc. No. 8711DS, Rev. N1.0 Characteristics subject to change without notice BLOCK DIAGRAM Figure 3. LDS8711 Functional Block Diagram BASIC OPERATION At power-up, EN/PWM pin should be logic LOW. The LDS8711 starts operating when EN/PWM pin is asserted logic high. The device becomes enabled and wait for the first pulse that determines mode, at which device will operate. If first pulse is equal tSETUP1, LED current sets to factory programmed value and every next incoming pulse will be rec ognized as PWM signal. If first pulse is equal tSETUP2, device enters Smart OneWire ™ interface mode and wait for command. Every next of 16 incoming pulses will be recognized as command. After LDS8711 accepts command, the current sets in respect to programmed value, and device changes mode to PWM. If device is not able to recognize command due some error, it enters shutdown mode after 10 ms. If the input voltage is sufficient to regulate all LED currents, the device remains in operating mode. The low dropout Current regulator performs well at VOUT voltage up to 250 mV above summary LED forward voltage significantly increasing driver’s efficiency. If the input voltage is insufficient or falls to a level where the regulated currents cannot be maintained, the Under-Voltage protection turns device off setting it in shutdown mode. The LDS8711 has soft start function that prevent high input current spike at device’ wake-up. The EN/PWM pin should be held low for more than 10 ms to completely turn device in low current shutdown mode. LED Current Setting The maximum current value in the LED string may be factory preset in the range from 10 to 30 mA in 0.125 mA steps, or set by Smart OneWire ™ interface in the range from 0.125 to 32 mA. The average LED string current that determines LED brightness may be controlled applying PWM signal to the EN/PWM pin. The maximum PWM frequency is 30 kHz, while frequiencies below 100 Hz are not recommended to avoid visible LED flikering. Duty cycle that determines average LED string current may vary in the range from 5% to 100% at 1 k Hz or from 20% to 100% at 30 kHz with high linearity current regulation. It gives possibility regulate brightness either in DC mode with changing color temperature, or in PWM mode with stable color temperature. To start LDS8711 in PWM Mode, the first positive pulse applied to EN/PWM pin after power-up should be equal tSETUP1 and followed by EN/PWM pin LOW |
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