Leadis Tech Announces New Family Of No-Noise, 98%-Efficient, Four-Channel White LED Drivers
Leadis Technology, Inc. announced the sample availability of the LDS8845 and the LDS8846, a new family of no-noise, 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 converters – two methods used in conventional white LED driver products – further reduces system cost by eliminating up to two ceramic capacitors required by the boost converter. Additional benefits to eliminating the boost converter include: the overall circuit’s form factor is reduced (by up to 13%); the LED driver generates no noise; and 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."
The company claims that all products in this family will offer part-to-part LED current accuracy better than 7.5% and channel-to-channel matching better than 3% – said to be an improvement of at least 25% 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% efficient operation from a single-cell Li-ion battery, the design of the LDS8845 and the LDS8846 implements Leadis’ proprietary, ultra low 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 is said to permit the LDS8845 and the LDS8846 to operate at lower system cutoff voltages while maintaining excellent LED current regulation.
Packaged in 0.8mm high, 3 x 3mm 16-lead TQFN packages, the LDS8845 operates from 2.7 to 5.5V. An inexpensive, 15.8kΩ 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 4 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, 3 x 3mm 12-lead TDFN by the close of the second quarter of 2008.
The LDS8846 is parametrically identical to the LDS8845, offering a third control input, in pin-compatible 0.8mm high, 3 x 3mm and 4 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 for maximum flexibility. Like the LDS8845, the LDS8846’s control input can accept a PWM signal to adjust the average LED current. By the close of the second quarter of 2008, the company expects that a 0.8mm high, 3 x 3mm 12-lead TDFN package option for the LDS8846 will be made available.
