This Led driver circuit is designed using the CAT3661 high efficiency low power LED driver, that can be used for low power LCD display backlight, or low power hand-held device backlight. CAT2261 circuit use a charge pump that drives one LED with up to 5 mA of current.
The quad-mode charge pump supports a wide range of input voltages from 2.0 V to 5.5 V.
The CAT3661 circuit has a built in circuitry to provide feedback to a microcontroller of Open/Short LED and Low battery events. Also it has an soft-start current limiting and shortcircuit protection functions optimized for use with coin cell batteries.
As you can see in the circuit diagram , this led driver circuit require few external components and is very easy to design .
The low battery indicator trip point can be calculated by the following formula: VLB =VADJxGADJ where , VLB = Low Battery Voltage Trip Point , VADJ = Low Battery Comparator Trip point (0.6 V) and GADJ = Resistor Divider Gain (4 internally) .
If you want to modify the resistor divider gain , you can apply the following formula :
GADJM =(RADJ+RH)/[(RADJ/GADJ)+RL] where , GADJM = Modified resistor divider gain , RADJ = Total resistance of divider (800 kohms typ.) , RH = High external resistor (ADJH to VIN) , RL = Low external resistor (ADHL to GND) .
The current in the LED channel can be calculate by the following equation :