1. General description
The PCA9531 is an 8-bit I
2
C-bus and SMBus I/O expander optimized for dimming LEDs in
256 discrete steps for Red/Green/Blue (RGB) color mixing and back light applications.
The PCA9531 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 active LOW hardware reset pin (RESET) and Power-On Reset (POR) initializes the
registers to their default state causing the bits to be set HIGH (LED off).
Three hardware address pins on the PCA9531 allow eight devices to operate on the same
bus.
2. Features
n Eight LED drivers (on, off, flashing at a programmable rate)
n Two selectable, fully programmable blink rates (frequency and duty cycle) between
0.59 Hz and 152 Hz (1.69 second and 6.58 milliseconds)
n 256 brightness steps
n Input/outputs not used as LED drivers can be used as regular GPIOs
n Internal oscillator requires no external components
n I
2
C-bus interface logic compatible with SMBus
n Internal power-on reset
PCA9531
8-bit I
2
C-bus LED dimmer
Rev. 06 — 19 February 2009 Product data sheet
