Date: 23/01/2009

LED driver to drive up to fourty 120mA White LED lamps with color dimming

Linear Technology's new LED driver LT3599 is a 45V, 2.1MHz DC/DC boost mode converter designed to operate as a constant current LED driver for up to 40 white LEDs. From a 12V input, the LT3599 can drive up to four strings of LED lights, each with up to ten 120mA white LED lights in series while delivering efficiencies up to 90%. Its multichannel capability makes it ideal for medium-sized TFT-LCD backlighting applications. The LT3599’s input voltage range of 3.1V to 30V is well-suited for automotive, medical and industrial applications. The device offers 1.5% LED current matching to ensure uniform brightness of the display. Dimming ratios as high as 3,000:1 can be attained by using True Color PWM dimming. A programmable 200kHz to 2.1MHz fixed frequency operation and current mode architecture offers stable operation over a wide range of supply and output voltages while minimizing the size of the external components. Additionally, the switching frequency is synchronizable to an external clock for improved noise immunity.

The LT3599 uses a single 2A, 45V internal switch to provide a boost mode constant current source. However, even when VIN exceeds VOUT, the LT3599 will continue to regulate the LED current. The internal boost converter uses an adaptive feedback loop to regulate the output voltage slightly higher than the required LED voltage to ensure maximum efficiency. If any of the LED strings experiences an open circuit, it will continue to regulate the existing strings and signals the OPENLED alert pin. If higher current LEDs are required, multiple strings can be combined, enabling it to drive up to two strings of ten 240mA LEDs. Additional features include LED current derating based on junction temperature and/or LED temperature and programmable overvoltage protection when all LED strings are disconnected.

Other important features are,

1. Output Voltage Up to 44V
2. Disconnects LEDs in Shutdown
3. Programmable Maximum VOUT (Regulated)
4. Open/Short LED Protection & Fault Flags
5. Programmable LED Current Derating
6. Synchronizable to an External Clock
7. Analog Dimming up to 20:1
8. Programmable Input UVLO with Hysteresis


The LT3599EUH is available in a 32-lead 5mm x 5mm QFN package and the LT3599EFE is offered in a TSSOP-28E. 1,000-piece pricing starts at $3.25 each and $3.35 each, respectively. Industrial grade versions, the LT3599IUF and LT3599IFE, are tested and guaranteed to operate to the -40°C to 125°C operating junction temperature and are priced at $3.82 each and $3.94 each, respectively, in 1,000-piece quantities. All versions are available from stock. For more information, visit www.linear.com.