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Smallest LED, OLED display drivers extend battery life

Santa Clara, Calif.—National Semiconductor's LM2755 LED driver, LM2757 inductorless switched-capacitor boost regulator, and LM4510 high-voltage boost regulator for OLED displays, all additions to the company's PowerWise family, extend battery life for next-generation portable media devices. National says they're the smallest in the industry.

The LM2755 charge pump, in a low-profile micro SMD package, enables multi-zone backlighting for three independent RGB (red-green-blue) or white indicator LEDs controlled by programmable pattern generators. It touts exponential dimming steps and an I2 C compatible interface for improved flexibility and customization for gaming applications and mobile television.

This constant-current LED 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, and fall time can be programmed via the I2 C bus. The charge pump operates in a 3/2 gain-mode or in pass-mode. The gain is selected based on LED forward voltage in order to maximize efficiency over its input voltage range. Offered in an 18-bump micro SMD package, the LM2755 achieves up to 90 percent efficiency.

The LM2757 charge pump, also in a micro SMD package, requires just four ceramic capacitors for a total solution size of less than 12 mm2 . With high output current and pin-selectable output voltages, the LM2757 delivers an inductorless solution suited for peripheral lighting features, such as keypad lighting. The LM2757 can also be used to power USB On-The-Go (OTG) peripherals. The constant-frequency, pre-regulated, switched-capacitor device operates at 1.25 MHz. It operates at a gain of 3/2 or 2, depending on the selected input and output voltage option. The device can be configured to provide up to 100 mA at 4.1 volts, 110 mA at 4.5 volts, or 180 mA at 5 volts. The LM2757's output impedance is high for applications where the regulated output bus is driven by another supply while the LM2757 is shut down. Offered in a 12-bump micro SMD package, the LM2757 achieves up to 90 percent efficiency.

The LM4510 is a synchronous high-voltage boost regulator that supports OLED displays (thinner and consuming less energy than LEDs). The LM4510 features up to 85 percent efficiency for longer battery life and is offered in a LLP package.

The LM4510 includes a 1.2-amp internal NMOS switch designed to deliver up to 80 mA at 18 volts from a Li-ion battery. It operates in the synchronous mode at heavy loads and in the non-synchronous mode at light loads to extend battery life in power-constrained applications. It has a true shutdown isolation feature to eliminate leakage current paths to ground in the standby mode. It doesn't need a Schottky diode. System designers can optimize line- and load-transient responses for USB supply or OLED display bias applications by using an external compensation network. The LM4510 offers feedback-fault and short-circuit protection features on the output. The chip is available in a 10-pin thermally enhanced LLP package.

Data Sheets: LM2755; LM2757; LM4510

Pricing: Available now. The LM2755 and LM2757 are $1.50 each; the LM4510 is $1.80 each, all in 1k quantities.

National Semiconductor , 1-800-272-9959, www.national.com

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