LM3535

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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.

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

regulated charge pump has both open loop and closed loop modes of operation. When the device is in open

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.

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