A new LED driver with dynamic headroom control has been developed by National Semiconductor. The company’s LM3492 drives current to two independently dimmable strings of LEDs. The device is part of National’s PowerWise energy-efficient product family, it maximises system efficiency and reduces system complexity and cost in automotive LCD backlight applications.
The headroom control feature adjusts the LED supply voltage through the boost converter feedback to the lowest level required to provide system efficiency. Three embedded MOSFETs reduce system complexity and cost.
The driver integrates a boost converter and a two-channel current regulator to efficiently drive two independently dimmable LED strings with a maximum power of 15W and an output voltage of up to 65V. Integrated fast slew rate current regulators allow high frequency and narrow pulse width dimming signals to achieve a very high contrast ratio of 1000:1. The LED current is programmable from 50 mA to 200 mA by a single resistor.
To maximise efficiency, the dynamic headroom control (DHC) automatically adjusts the LED driving voltage to a minimum level. DHC also facilitates a single bill of materials for different number of LEDs in a string.
