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LED drivers cut need for external Schottky diode

Posted: 02 Jul 2010 ?? ?Print Version ?Bookmark and Share

Keywords:LED driver? WLED? LCD? backlight? Schottky diode?

IXYS Corp. has released the LDS8710/11, LDS8720/24/26 inductor-based, high-efficiency LED driver family that eliminates the external Schottky diode normally used in the rectification loop.

The LDS8711 uses a patent pending SmartOne Wire Interface to set maximum LED current in the range from 0.5mA to 32mA in 0.25mA steps and PWM dimming control and is able to drive a string of 10 WLEDs. The LDS8710 drives a string of 10 LEDs with factory-preset maximum LED current values of 20-, 25- and 30mA with 1% accuracy, and uses pulse-width modulation (PWM) dimming to adjust LED brightness. LDS8720/24 and LDS8726 use PWM dimming to adjust the LED brightness and are able to drive 40 LEDs and, respectively, 42 WLEDs at 25mA current each. Drivers provide full output power from a single-cell Li-ion battery or supply voltage in the range of 2.7V to 5.5V.

The LDS8710/11 are tailored for (up to 7-inch) LCD display backlight applications such as smart phones, portable multimedia devices, e-books, personal navigation systems, personal medical displays and digital photo frames where battery life, display size, resolution and brightness are critical.

The LDS8720/24/26 are designed for (up to 15-inch) LCD display backlight applications such as automotive displays, GPS, netbooks, laptop PCs, tablet computers and industrial and medical displays.

Both device families are suitable to drive WLEDs for lighting applications, such as battery powered high intensity flash lights, security lights, automotive lights and home lights.

Coupled with the Zilog microcontrollers and the Zilog motion sensing technology, with these drivers, IXYS provides the whole system solution for automated, high-efficiency lighting control based on occupancy and as needed.

Each device in the family is a fixed-frequency, current-mode boost converter with cycle-by-cycle current limit and features a patent pending integrated synchronous rectifier, which eliminates the external Schottky diode and the need for complicated and costly isolation FET. This reduces the bill of material, footprint of the display subsystem, and also simplifies the design-in process and time to market of the end product.

The LDS8710/11/20 are fixed 0.7MHz frequency drivers, while the LDS8724/26 operate at 1MHz. The devices offer a wide PWM dimming frequency range (100Hz to 10kHz) and a robust protection system (overvoltage, overtemperature, undervoltage and overcurrent), while the shutdown current is below 1?A.

The LDS8710/11 do not need an external current-sense resistor that further simplifies the system while the LDS8720/24/26 require an external current-sense resistor to set LED current. Since these LED driver families operate at a high switching frequency, small, low profile passive components (10- to 33?H inductors and 1?F 50V ceramic capacitor) can be used, which further reduces the system's bill of material cost and allows a thin profile of the backlight unit. The use of integrated synchronous rectifier makes the efficiency dependent upon only one external component parameterthe inductor DCR. The system achieves efficiency higher then 86%.

All devices are available in a tiny 2mm x 3mm x 0.8mm 8-pin TDFN package.

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