Smart Linear LED Driver LM3466 Reference Design

TI's LM3466 is an intelligent linear LED driver for multi-channel LED systems. It can automatically balance the current of each LED channel, easily preset and fine-tune the current between LED strings, and has a current accuracy of ±1% at room temperature and ±1.5% over the temperature range. If a string of LEDs is open, it can maintain the same output power. The input voltage ranges from 6V to 70V. It is mainly used in street lighting and solid-state lighting systems. This article introduces the main features of LM3466, block diagram, lighting system application circuit diagram, LM3466 evaluation board reference design circuit diagram, bill of materials, connection diagram and PCB component layout diagram.

LM3466 Smart Linear LED Driver for Multi-Channel LED Systems The LM3466 integrates a linear LED driver for lighting systems which consist of multiple LED strings powered by a constant current power supply. It equalizes the current provided by the supply in a pre-set ratio for each active LED string, where an active string is a fully turned on LED string, regardless of the number of strings connected to the supply or the forward voltage of each LED string. If any LED string opens during operation, the LM3466 automatically equalizes the supply current through all of the remaining active LED strings. As a result, the overall brightness of the lighting system is maintained even if some LED strings open during operation.

The LM3466 lighting system is simple to design owing to a proprietary control scheme. To minimize the component count, the LM3466 integrates a 70V, 1.5A N-channel power MOSFET with a current limit of 2.06A. To add one more LED string to the system, only a single resistor, a capacitor, and a LM3466 are required. Other supervisory features of the LM3466 include under-voltage lock-out, fault reporting, thermal latch off, and thermal shutdown protection.

The LM3466 consists of only linear circuitry so that the EMI of the application circuit is not deteriorated. The LM3466 lighting system is EMI friendly if the constant current power supply used is complied to EMI standards. The LM3466 is available in the PSOP-8 exposed DAP package.

LM3466 main features:

■ Easy to design and use for lighting systems consisting of multiple LED strings (support modular design)

■ Automatically equalizes the current of every active LED string, even the forward voltage of each string is different

■ Easy to pre-set and fine-tune current ratio among LED strings (e.g. color temperature adjustment or CRI enhancement)

LM3466 Demo Board Reference Design

This application note details the design of an LM3466 evaluation board that drives 5 LED strings, each of which consists of 14 LEDs. The input current IS (of the constant current power supply) is 1.75A such that the LED current is 0.35A per string.

The evaluation board schematic, PCB layout, Bill of Materials, and circuit design procedures are shown. Typical performance and operating waveforms are also provided for reference.

■ ±1% current accuracy at room temperature and ±1.5% over temperature

■ Maintains constant output power if some strings open (inactive) by automatically equalizing the current of remaining active LED strings

■ Works with a constant current power supply (ac/dc or dc/ dc), and no communication to/from the constant current power supply is required

■ Operates with minimum voltage overhead to maximize power efficiency

■ Wide input voltage range from 6V to 70V

■ Fault status output

■ Thermal shutdown

■ Integrated 70V 1.5A MOSFET with 2.06A current limit

■ Maximum 70V per LED string, 20 LEDs

■ Linear circuitry does not deteriorate EMI

■ PSOP-8 exposed DAP package

LM3466 Applications:

■ Street lamps

■ Solid state lighting systems

LM3466 Demo Board Reference Design

This application note details the design of an LM3466 evaluation board that drives 5 LED strings, each of which consists of 14 LEDs. The input current IS (of the constant current power supply) is 1.75A such that the LED current is 0.35A per string.

The evaluation board schematic, PCB layout, Bill of Materials, and circuit design procedures are shown. Typical performance and operating waveforms are also provided for reference.