LED, OLED Display Drivers

For Mobile Devices

SANTA CLARA, Calif., Oct. 10, 2007 -- National Semiconductor Corp. has added three new power management products for driving LEDs and powering organic LED (OLED) displays to its PowerWise energy-efficient product line. Its new products, the LM2755 LED driver, the LM2757 inductorless switched-capacitor boost regulator and the LM4510 high-voltage boost regulator, are tiny system solutions that extend battery life and enable next-generation visual effects in portable media devices, National said.

The LM2755, in a tiny, low-profile micro SMD (surface-mount device) package, enables multizone backlighting for three independent RGB (red-green-blue) or white indicator LEDs controlled by programmable pattern generators. Programmability, exponential dimming steps and an I2C compatible interface provide flexibility and customization to fit various multimedia functions such as gaming and mobile television, National said.

The charge-pump-based, constant-current driver independently drives three LEDs with a total output current up to 60 mA. The current waveform of each LED is a trapezoid whose parameters, including delay, rise time, fall time, high level and low level, can be programmed via an I2C compatible interface. The driver provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in pass-mode. The proper gain from maintaining current regulation is selected based on LED forward voltage, so that efficiency is maximized over the input voltage range. Offered in an 18-bump micro SMD package, the LM2755 achieves up to 90 percent efficiency, which prolongs battery life, the company said.

The LM2757, also in a micro SMD package, requires just four tiny ceramic capacitors for a total solution size of less than 12-mm squared. With high output current and pin-selectable output voltages, the LM2757 delivers a compelling inductor-less solution well-suited for peripheral lighting features, such as keypad lighting. The LM2757 can also be used to power USB On-The-Go (OTG) peripherals.

The LM2757 is a constant-frequency, preregulated, switched-capacitor boost regulator that operates at 1.25 MHz to produce a low-noise output voltage. Excellent efficiency is achieved without the use of an inductor by operating the charge pump in a gain of either 3/2 or 2 according to the input voltage and output voltage option selection. The device can be configured to provide up to 100 mA at 4.1 V, 110 mA at 4.5 V or 180 mA at 5 V. The LM2757 presents high impedance at the output voltage pin for applications that require the regulated output bus be driven by another supply while it is shut down. Offered in a 12-bump micro SMD package, the LM2757 achieves up to 90 percent efficiency, which prolongs battery life.

National's LM4510 is a synchronous high-voltage boost regulator that supports OLED displays which are much thinner and consume less energy than LCDs. The LM4510 features up to 85 percent efficiency for longer battery life and is offered in a small LLP package.

The LM4510 is a current-mode, step-up DC-DC converter with a 1.2A internal NMOS switch designed to deliver up to 80 mA at 18V from a Li-Ion battery. The synchronous operation at heavy loads and nonsynchronous operation at light loads allow it to achieve up to 85 percent efficiency for longer battery life in power-constrained applications. The true shutdown isolation feature eliminates leakage current paths to ground in stand-by mode.

The device reduces the total product size and cost through elimination of an external Schottky diode and from a 3.2-V input, delivering a current range from 18 to 5 V. The system designer can optimize line and load transient responses using the external compensation network in a broad range of applications, such as USB power supply or OLED display bias. The LM4510 also offers a very robust solution due to the feedback fault and short- circuit protection feature on the output and is available in a 10-pin thermally enhanced LLP package, National said.

Available now, the LM2755 and LM2757 are priced at $1.50 each, and the LM4510 is $1.80 in 1000-unit quantities.

For more information, visit: www.national.com

National Semiconductor Corp.
2900 Semiconductor Dr.
P.O. Box 58090
Santa Clara, CA 95052-8090
Phone: (408) 721-5000

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