Low-power LEDs enliven various devices, from mobile phones to gaming machines, as well as decorative lighting. These applications typically use 25 mA LEDs along with some color mixing and dimming features. Our solution uses the P89LPC925 microcontroller and PCA9633 LED driver to control Red, Green, Blue and Amber LEDs. The system is also fully programmable allowing you to create different colors using a diffuser.
Optimized for RGBA color mixing applications, the PCA9633 can set four LEDS to a specific brightness value, and dim or blink all of them with that same value. It is equipped with four individual 8-bit (256-linear steps), fixed frequency PWM controllers. These operate at 97 kHz and feature an adjustable duty cycle from 0 to 99.6% in 256 steps for blinking and dimming control. The PCA9633 also has a group PWM controller that can dim or blink all the LEDs with the same value. For group blinking, it uses a fixed frequency of 190 Hz or an adjustable frequency between 24 Hz and 10.73 seconds in 255 linear steps. Its duty cycle can be adjusted from 0 to 99.6% in 256 linear steps.
The P89LPC925 programs the PWM registers of the PCA9633 via an I2C port. The registers are used to control the individual outputs of the PCA9633, which can be in the on (no PWM control), off, set to the value of its individual PWM controller, or set to both individual and group PWM controller values. You can program the PCA9633 to continuously blend different colors, randomly show different colors without blending transitions, display predefined selected colors, or generate a chase pattern of multiple colors using the PCA9633’s group-call feature and additional PCA9633s, depending on the application and what LED control is required.
To drive higher power LEDs, external FETs can be placed between the PCA9633 and the LEDs. For example, to drive a 350 mA LED with a 40 V rail, the gate of the suggested 60 V FET can be driven by the PCA9633 output which in turn drives the LED.