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SC4505EVB Datasheet(PDF) 6 Page - Semtech Corporation |
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SC4505EVB Datasheet(HTML) 6 Page - Semtech Corporation |
6 / 15 page 6 2007 Semtech Corp. www.semtech.com SC4505 POWER MANAGEMENT The SC4505 contains a 1MHz fixed-frequency, current- mode boost converter, and two independent LED current regulators. The LED current setpoints are chosen using external resistors, and the PWM controller operates independently to keep the two currents in regulation. Since the SC4505 receives feedback from both of the LED current regulators, either or both LED strands can be on at any given time. Additionally, different numbers of LED can be used in the two strands with no resistor ballasting, or preset output voltage setpoint. A typical application would use 3-6 backlight LED, driven with 20mA, and 2-6 flash LED, driven with 20mA during torch mode (video recording), and driven with 100mA during flash mode (for photographs). Usually only the backlight LED are used, but during some cases both strands must be on at the same time. As the output voltage is different for each case, a designer is often forced to use lossy ballast resistors to balance the LED currents, or to use two separate converter ICs, greatly increasing component count and BOM cost. The SC4505 solves these issues by controlling the boost converter set point based on instantaneous requirements of the two current regulators. Therefore, only a single inductor and power switch is needed to provide power to the entire lighting subsystem, increasing efficiency and reducing part count. A digital interface allows independent control of all LED currents with no converter “babysitting”. Interface to output control is high- bandwidth, supporting digital PWM dimming on any channel at 50Hz to 50kHz dimming frequency, while aggressively shutting the entire IC down to less than 1 µA shutdown mode when all LED strands are turned off. In shutdown mode, leakage through the current regulator outputs is also < 1 µA, keeping the output capacitor charged and ready for instant activation of the LED strands. 1 MHz switching speed provides high output power using a tiny 1.0mm high inductor, maximizing efficiency for space-constrained and cost-sensitive applications. In addition, converter and output capacitor are protected from open-LED conditions by overvoltage protection, and flash LED are protected from burnout by a user-settable time-out feature. Overview The states of the two LED current regulators are chosen by a three-bit digital input. Either or both of the current regulators can be on at any given time. The converter automatically shuts down to zero-current shutdown mode if all pins are low. EN_BL – Enable Backlight regulator (I O1). EN_FL – Enable Flash/Torch regulator (I O2) FL_TRB – Select flash or torch mode for I O2. The current in torch mode is approximately 1/5 of the current in flash mode. Flash mode when FL_TRB = 1. |
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