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LED drivers enable greener lighting solutions

Posted: 26 Aug 2008     Print Version  Bookmark and Share

Keywords:high-brightness  LED drivers  integrated MOSFET  current-sense circuitry 

Maxim Integrated Products introduces the MAX16822A/B and MAX16832A/C family of 2MHz, high-brightness (HB) LED drivers with an integrated MOSFET and high-side current-sense circuitry. These integrated devices reduce the size, complexity, and cost of solid-state lighting (SSL) designs, simplifying the implementation of green lighting technology. They provide the high conversion efficiency and advanced thermal-management capabilities critical to LED system designs. The MAX16822A/B and MAX16832A/C are ideal for MR16, MR111, and other architectural lighting applications, as well as front and rear automotive lighting (RCL, DRL, and fog/low-beam lights).

These high-voltage, switch-mode HB LED drivers are capable of delivering over 18W (MAX16822A/B) or 36W (MAX16832A/C) of output power with up to 95 per cent efficiency, while driving as many as 15 white LEDs in series. The MAX16822A/B can deliver up to 350mA of continuous DC current, while the MAX16832A/C can deliver up to 700mA of continuous DC current to the LED string. These devices offer an analogue dimming feature that allows the LED current to be controlled by an external DC voltage and PWM dimming input for a wide range of brightness levels.

These HB LED drivers require only a few external passive components for the design of a low-cost LED driver circuit. By integrating a 65V switching MOSFET with RDSON values of 0.85Ω (MAX16822A/B) and 0.45Ω (MAX16832A/C), they eliminate the need for an external power transistor. Additionally, high-side current sensing and integrated current-setting circuitry further reduce the number of external components required, while delivering ±3 per cent LED current accuracy.

A hysteretic, step-down (buck) mode enables these devices to drive a long string of HB LEDs from input voltages as high as 65V DC. This control method renders control-loop compensation unnecessary, thus simplifying the design and minimising component count. The MAX16822A/B and MAX16832A/C are designed to hold the LED current ripple to within 10 per cent (A versions) and 30 per cent (B and C versions) without the use of an output capacitor. Moreover, the devices support switching frequencies up to 2MHz, allowing the use of small-sized components.

The MAX16822A/B and MAX16832A/C integrate thermal- shutdown circuitry to protect the driver under excessive thermal conditions. Their 200mV, high-side current-sensing minimises the voltage drop across the external sense resistor, thereby reducing power dissipation. Additionally, they provide analogue thermal-foldback protection that reduces the LED current in conjunction with an external negative temperature coefficient (NTC) thermistor when the temperature of the LED string exceeds a specified limit.

This robust family of HB LED drivers operates from a 6.5V to 65V input voltage and is fully specified over the -40°C to +125°C automotive temperature range. The MAX16822A/B are available in a lead-free, 8-pin SO package, while the MAX16832A/C are offered in an 8-pin SO package with exposed paddle. Prices start at Rs.42.43 ($0.99) for the MAX16822A/B, and Rs.56.14 ($1.31) for the MAX16832A/C (1000-up, FOB USA).





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