PCA9533D/02,112

PCA9533D/02,112 2. Features

PCA9533D/02,112 1. General description

The PCA9533 is a 4-bit I2C-bus and SMBus I/O expander optimized for dimming LEDs in256 discrete steps for Red/Green/Blue (RGB) color mixing and back light applications.The PCA9533 contains an internal oscillator with two user programmable blink rates andduty cycles coupled to the output PWM. The LED brightness is controlled by setting theblink rate high enough (> 100 Hz) that the blinking cannot be seen and then using the dutycycle to vary the amount of time the LED is on and thus the average current through theLED.The initial setup sequence programs the two blink rates/duty cycles for each individualPWM. From then on, only one command from the bus master is required to turn individualLEDs ON, OFF, BLINK RATE 1 or BLINK RATE 2. Based on the programmed frequencyand duty cycle, BLINK RATE 1 and BLINK RATE 2 will cause the LEDs to appear at adifferent brightness or blink at periods up to 1.69 second. The open-drain outputs directlydrive the LEDs with maximum output sink current of 25 mA per bit and 100 mA perpackage.To blink LEDs at periods greater than 1.69 second the bus master (MCU, MPU, DSP,chip set, etc.) must send repeated commands to turn the LED on and off as is currentlydone when using normal I/O expanders like the NXP Semiconductors PCF8574 orPCA9554. Any bits not used for controlling the LEDs can be used for General Purposeparallel Input/Output (GPIO) expansion, which provides a simple solution when additionalI/O is needed for ACPI power switches, sensors, push-buttons, alarm monitoring, fans,etc.The Power-On Reset (POR) initializes the registers to their default state, causing the bitsto be set HIGH (LED off).Due to pin limitations, the PCA9533 is not featured with hardware address pins. ThePCA9533/01 and the PCA9533/02 have different fixed I2C-bus addresses allowingoperation of both on the same bus.n 4 LED drivers (on, off, flashing at a programmable rate)n Two selectable, fully programmable blink rates (frequency and duty cycle) between0.591 Hz and 152 Hz (1.69 second and 6.58 milliseconds)n 256 brightness stepsn Input/outputs not used as LED drivers can be used as regular GPIOsn Internal oscillator requires no external componentsn I2C-bus interface logic compatible with SMBus

PCA9533D/02,112 5.2 Pin description