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Power managers for OLEDs offer 90% efficiency

Posted: 24 Oct 2007 ?? ?Print Version ?Bookmark and Share

Keywords:power management? LED driver? OLED display?

PowerWise family

National Semiconductor Corp. has added three new power management products for driving LEDs and OLED displays to its PowerWise energy-efficient product family. The LM2755 LED driver, the LM2757 inductor-less 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.

The LM2755 enables multi-zone backlighting for three independent RGB or white indicator LEDs controlled by programmable pattern generators. Programmability, exponential dimming steps and an I?C compatible interface provide flexibility and customization to fit various multimedia functions such as gaming and mobile TV.

The driver also provides high 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 LM2757 switched-capacitor boost regulator requires four tiny ceramic capacitors for a total solution size of less than 12mm?. With high output current and pin-selectable output voltages, the LM2757 delivers inductor-less solution suited for peripheral lighting features, such as keypad lighting. The LM2757 can also be used to power USB On-The-Go peripherals.

The constant-frequency, pre-regulated, switched-capacitor boost regulator that operates at 1.25MHz to produce a low-noise output voltage. High 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 also be configured to provide up to 100mA at 4.1V, 110mA at 4.5V or 180mA at 5V. The LM2757 presents high impedance at the output voltage pin for applications that require the regulated output bus be 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, which prolongs battery life.

Lastly, National's LM4510 is a synchronous high-voltage boost regulator that supports OLED displays, which are much thinner and consume less energy than LCDs. It is a current-mode, step-up DC/DC with a 1.2A internal NMOS switch designed to deliver up to 80mA at 18V from a Li-Ion battery. The synchronous operation at heavy loads and non-synchronous operation at light loads allow the regulator to achieve up to 85 percent efficiency for longer battery life in power-constrained applications.

Moreover, the true shutdown isolation feature eliminates leakage current paths to ground in stand-by mode. The device also reduces the total solution size and cost through elimination of an external Schottky diode and from a 3.2V input, delivering a current range from 18V to 5V. Designers 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 offers a very robust solution due to the feedback fault and short-circuit protection feature on the output. The LM4510 features up to 85 percent efficiency for longer battery life and is offered in a10-pin thermally enhanced LLP package.

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