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Four-channel white LED drivers peg 98% efficiency

Posted: 10 Mar 2008 ?? ?Print Version ?Bookmark and Share

Keywords:white LED? drivers four channel? efficiency rate?

Leadis Technology Inc. is delivering samples of the LDS8845 and LDS8846, no-noise, highly efficient 4-channel white LED drivers targeting handsets and portable products that use lower-VF white LEDs and lower-cost TFT-LCD modules.

According to 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 converters reduces system cost by eliminating up to two ceramic capacitors required by the boost converter, Leadis said.

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, according to Leadis. 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 Leadis' proprietary, ultralow voltage dropout PowerLite Current Regulator (PCR) technology that maintains current-sink threshold voltages below 50mV.

Packaged in 0.8mm high, 3mm x3mm 16-lead TQFN packages, the LDS8845 operates from 2.7V to 5.5V. A 15.8k? resistor sets the LDS8845's full-scale LED output current to 30mA per channel and allows the system designer to program the full-scale LED current to lower full-scale levels, if desired. A two-wire interface is provided to program the four LEDs as a single group or individually; in addition, the control interface can accept a pulse-width modulated (PWM) signal to adjust optionally the average LED current through duty cycle control.

In addition to the 16-lead TQFN package, the LDS8845 will be made available in a 0.8mm high, 3mm x 3mm 12-lead TDFN by the close of Q2.

The LDS8846 is parametrically identical to the LDS8845, offering a third control input, in pin-compatible 0.8mm high, 3mm x 3mm and 4mm x 4mm 16-lead TQFN packages. The third control input allows the system engineer to configure the LDS8846's LED drivers in one of eight configurations.

Leadis is one of the exhibitors in the IIC-China 2008.

- Ismini Scouras

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