Software Controllable Octal LED Driver for Portable Devices

8th April 2007

ES Admin

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Semtech Corp has announced the SC620, an octal, I2C-controlled LED driver. The SC620 is designed to provide regulated currents for powering a wide range of LEDs, including white, red, blue, green or yellow, with different forward voltages. The SC620 is designed to drive the LED backlights for small to medium size LCDs in portable systems that use rechargeable lithium ion/polymer batteries, but may also be applied in systems with a fixed 5V or 3.3V bus. Its low 150mV current sink dropout voltage makes it especially suited for use with LEDs that have forward voltages that are less than the system supply voltage. All LEDs are connected in parallel, with power coming from the system battery or available power rail and each cathode connected to an independent current sink.

Up to eight parallel LEDs, or strings of LEDs, can be driven at one time, and each string can be enabled/disabled or dimmed independently using the I2C control bus. Multiple SC620 devices can be connected to the same I2C bus to provide synchronized control of large banks of LEDs. Each current sink may also be used as an addressable general-purpose output, to enable multiple devices or functions remotely using only the two lines for the I2C interface.

The current sinks are very accurate and exhibit close matching when programmed for the same current, making them ideal for LCD backlighting applications. The current setting range allows dimming ratios up to 800:1, excellent for LCD panels that are exposed to varying ambient light conditions. The flexibility to select the power source for driving the loads allows for a lower cost solution, or lets the designer select an available source that maximizes efficiency for a particular application.

An enable pin allows the system designer to set the part into an ultra-low power shutdown state where the LEDs are disconnected, preventing residual glow due to leakage. The SC620 input voltage range is 2.7V to 5.5V. The maximum total output current capability is 200mA. In a typical application (VBATT=3.6V typ.), eight white LEDs (Vf = 3.4V) can be driven at 25mA each (full brightness) with 92% efficiency.

“The versatility of this device allows full brightness control to be easily obtained using a reliable two-wire serial interface, only one external component, and an industry proven LED current control topology,” said Karl Volk, Director of Marketing for Semtech’s Portable Power Management Products Group. “Additional space savings can be accomplished for those who use any remaining SC620 outputs as general purpose controls to power additional devices within the same space-limited system.”

The ultra-small SC620 features a 3mm x 3mm MLPQ-UT-16 package with a low profile of just 0.6 mm maximum - perfect for small form factor designs. It is RoHS and WEEE compliant.

To assure safe operation across all load conditions, the SC620 contains protection features such as short circuit current limit, thermal protection and under-voltage lockout.

The SC620 is available immediately in production quantities and is priced at $0.68 each in 1,000-piece lots. Ordering code for the SC620 is SC620ULTRT.