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LM3535 Datasheet(PDF) 11 Page - Texas Instruments |
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LM3535 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 34 page LM3535 www.ti.com SNVS598A – AUGUST 2010 – REVISED MAY 2013 CIRCUIT DESCRIPTION OVERVIEW The LM3535 is a white LED driver system based upon an adaptive 3/2× - 1× CMOS charge pump capable of supplying up to 200mA of total output current. With three separately controlled Groups of constant current sinks, the LM3535 is an ideal solution for platforms requiring a single white LED driver IC for main display, sub display, and indicator lighting. The tightly matched current sinks ensure uniform brightness from the LEDs across the entire small-format display. Each LED is configured in a common anode configuration, with the peak drive current set to 25mA. An I2C compatible interface is used to enable the device and vary the brightness within the individual current sink Groups. For GroupA, 128 exponentially-spaced analog brightness control levels are available. GroupB and GroupC have 8 linearly-spaced analog brightness levels. Additionally, the LM3535 provides 1 or 2 inputs (LM3535 has 1 and LM3535-2ALS has 2) for an Ambient Light Sensor to adaptively adjust the diode current based on ambient conditions, and a PWM pin to allow the diode current to be pulse width modulated to work with a display driver utilizing dynamic or content adjusted backlight control (DBC or CABC). CIRCUIT COMPONENTS Charge Pump The input to the 3/2× - 1× charge pump is connected to the VIN pin, and the regulated output of the charge pump is connected to the VOUT pin. The recommended input voltage range of the LM3535 is 2.7V to 5.5V. The device’s regulated charge pump has both open loop and closed loop modes of operation. When the device is in open loop, the voltage at VOUT is equal to the gain times the voltage at the input. When the device is in closed loop, the voltage at VOUT is regulated to 4.3V (typ.). The charge pump gain transitions are actively selected to maintain regulation based on LED forward voltage and load requirements. Diode Current Sinks Matched currents are ensured with the use of tightly matched internal devices and internal mismatch cancellation circuitry. There are eight regulated current sinks configurable into 3 different lighting regions. Ambient Light Sensing (ALS) and Interrupt The LM3535 provides an Ambient Light Sensing input (2 inputs on LM3535-2ALS version) for use with ambient backlight control. By connecting the anode of a photo diode / sensor to the sensor input pins, and configuring the appropriate ALS resistors, the LM3535 or -2ALS version, can be configured to adjust the diode current to five unique settings, corresponding to four adjustable light region trip points. Additionally, when the LM3535 determines that an ambient condition has changed, the interrupt pin, when connected to a pull-up resistor will toggle to a '0' alerting the controller. See the I2C Compatible Interface section for more details regarding the register configurations. Dynamic Backlight Control Input (PWM Pin) A PWM (Pulse Width Modulation) pin is provided on the LM3535 to allow a display driver utilizing dynamic backlight control (DBC), to adjust the LED brightness based on the content. The PWM input can be turned on or off (Acknowledge or Ignore) and the polarity can be flipped (active high or active low) through the I2C interface. The current sinks of the LM3535 require approximately 15µs. to reach steady-state target current. This turn-on time sets the minimum usable PWM pulse width for DBC/CABC. Copyright © 2010–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LM3535 |
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