National Semiconductor claims that it has produced the industry's first LED driver with dynamic headroom control and multiple outputs for high-power applications that accurately and efficiently drives up to four strings of LEDs. The new member of the PowerWise family, the LM3464, is designed for LED-intensive applications such as industrial, street and automotive lighting. Unlike traditional high-brightness LED drivers that drive current to each string independently, its four channels drive up to 20 LEDs/channel, reducing system complexity and cost, according to the company. The dynamic headroom control feature dynamically adjusts the LED supply voltage through the power supply feedback to the lowest level required to provide optimal system efficiency. The high-voltage current controller with four individual current regulator channels works in conjunction with external N-channel MOSFETs and sense resistors to accurately drive current to each LED string. Input range is up to 80V to drive multiple LEDs per string. A thermal foldback feature protects the LEDs from unsafe temperatures that can significantly degrade the light output or lifetime of the LEDs. A user-programmable feature is that during an over-temperature condition, the thermal foldback reduces the current through the LEDs until the junction temperature returns to a safe operating temperature. This is claimed to ensure the lifetime and light output of the LEDs over time and through temperature variances. The dynamic headroom control feature monitors the forward voltages of the LED strings and dynamically adjusts the supply voltage through the power supply feedback to the lowest level required. By directly controlling the output of the offline regulator, the driver can eliminate the second stage switching regulator commonly required for offline LED power supplies.
