1.

General description

256 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 and

duty cycles coupled to the output PWM. The LED brightness is controlled by setting the

blink rate high enough (> 100 Hz) that the blinking cannot be seen and then using the duty

cycle to vary the amount of time the LED is on and thus the average current through the

LED.

The initial setup sequence programs the two blink rates/duty cycles for each individual

PWM. From then on, only one command from the bus master is required to turn individual

LEDs ON, OFF, BLINK RATE 1 or BLINK RATE 2. Based on the programmed frequency

and duty cycle, BLINK RATE 1 and BLINK RATE 2 will cause the LEDs to appear at a

different brightness or blink at periods up to 1.69 second. The open-drain outputs directly

drive the LEDs with maximum output sink current of 25 mA per bit and 100 mA per

package.

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 currently

done when using normal I/O expanders like the NXP Semiconductors PCF8574 or

PCA9554. Any bits not used for controlling the LEDs can be used for General Purpose

parallel Input/Output (GPIO) expansion, which provides a simple solution when additional

I/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 bits

to be set HIGH (LED off).

Due to pin limitations, the PCA9533 is not featured with hardware address pins. The

operation of both on the same bus.

2.

Features

0.591 Hz and 152 Hz (1.69 second and 6.58 milliseconds)

PCA9533

Rev. 03 — 27 April 2009

Product data sheet