Micrel MIC2287 PWM White LED Drivers
Micrel's MIC2287 PWM White LED Drivers are a 1.2MHz pulse width modulated (PWM), boost-switching regulator that is optimized for constant-current, white LED driver applications. With a maximum output voltage of 34V and a switch current of over 500mA, the MIC2287 easily drives a string of up to eight white LEDs in series, ensuring uniform brightness and eliminating several ballast resistors. The MIC2287 implements a constant frequency, 1.2MHz PWM control scheme. The high frequency PWM operation saves board space by reducing external component sizes. The added benefit of the constant frequency PWM scheme as opposed to variable frequency topologies is much lower noise and input ripple injected back to the battery source. To optimize efficiency, the feedback voltage is set to only 95mV. This reduces the power dissipation in the current set resistor and allows the lowest total output voltage, hence minimal current draw from the battery.