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No-noise LED drivers suit low-cost portable devices

Posted: 05 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:LED drivers? portable devices? low-cost handset?

Leadis Technology Inc. has announced the sample availability of the LDS8845 and the LDS8846, a new family of no-noise, highly efficient 4-channel white LED drivers. These latest product offerings target a new generation of low-cost handsets and portable products that use lower-VF white LEDs and lower-cost TFT-LCD modules.

"With the LDS8845 and the LDS8846, Leadis is addressing the emerging and fast-moving trend in handset applications to using lower-VF white LEDs," said Adolfo Garcia, senior director of LED drivers for Leadis Technology. "Lower-VF white LEDs make it easier to maintain LED current absolute accuracy and channel-to-channel match by eliminating the need for an internal boost converter to increase the driver's output voltage. Eliminating the need for dual-mode (1x/2x) or tri-mode (1x/1.5x/2x) charge-pump boost converterstwo methods used in conventional white LED driver productsfurther reduces system cost by eliminating up to two ceramic capacitors required by the boost converter. Additional benefits to eliminating the boost converter include: (1) the overall circuit's form factor is reduced (by up to 13 percent); (2) the LED driver generates no noise; and (3) the current drawn from the battery by the application circuit is the same as the total LED output current, resulting in longer battery operation on a single charge."

Although the design of this family of white LED drivers has been simplified, performance has not been compromised. All products in this family will offer part-to-part LED current accuracy better than 7.5 percent and channel-to-channel matching better than 3 percentan improvement of at least 25 percent over alternative dual-mode and tri-mode charge-pump based white LED drivers. In addition, both products offer true-load disconnect in shutdown, output overcurrent protection, thermal shutdown protection and a 100kHz-rated LED current control interface for those applications where it is desirable to minimize or eliminate audio band noise injection.

To achieve 98-percent efficient operation from a single-cell Li-ion battery, the design of the LDS8845 and the LDS8846 implements the company's proprietary, ultralow-voltage dropout PowerLite Current Regulator (PCR) technology, which maintains current-sink threshold voltages below 50mV. The application of the company's PCR technology in this new family of white LED drivers permits the LDS8845 and the LDS8846 to operate at lower system cutoff voltages while maintaining excellent LED current regulation.

Leadis is one of the exhibitors at the 13th IIC-China 2008.

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