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A very simple LED driver electronic project can be designed using the CAT3649 high efficiency quad mode R fractional charge pump IC that can drive up to six LEDs. The inclusion of a 1.33x fractional charge pump mode increases the device efficiency by up to 10% over traditional 1.5x charge pumps with no added external capacitors.Low noise input ripple is achieved by operating at a constant switching frequency which allows the use of small external ceramic capacitors. The multi−fractional charge pump supports a wide range of input voltages from 2.4 V to 5.5 V.



The LED current can be adjusted in different ways. The full−scale LED current is set to 25 mA once the device is enabled. Analog dimming in 32 linear steps is achieved via a 1−wire pulse−dimming input (ADIM)
Further adjustment of the LED current can be done by applying a pulse width modulation (PWM) signal on the PWM input.The CAT3649 can be shut down by holding the ADIM or PWM input in a logic low condition for greater than 30 ms. This electronic design CAT3649 charge pump LED driver can be used in applications like : LCD Display Backlight , Cellular Phones , Digital Still Cameras and some other handheld devices .

If the input voltage is insufficient or falls to a level where the regulated currents cannot be maintained, the CAT3649 automatically switches into 1.33x mode. In 1.33x mode, the output voltage is approximately equal to 1.33 times the input supply voltage . This sequence repeats in the 1.33x and 1.5x mode until the driver enters the 2x mode.While in 2x mode, the output is approximately equal to 2 times the input supply voltage.If the CAT3649 charge pump LED driver detects a sufficient input voltage to drive all LED currents in 1x mode, it will change automatically back to 1x mode.