General description
The PCA9551 LED blinker blinks LEDs in I2C-bus and SMBus applications where it is necessary to limit bus traffic or free up the I2C-bus master's (MCU, MPU, DSP, chip set, etc.) timer. The uniqueness of this device is the internal oscillator with two programmable blink rates. To blink LEDs using normal I/O expanders like the PCF8574 or PCA9554, the bus master must send repeated commands to turn the LED on and off. This greatly increases the amount of traffic on the I2C-bus and uses up one of the master's timers. The PCA9551 LED blinker instead requires only the initial set-up command to program BLINK RATE 1 and BLINK RATE 2 (i.e., the frequency and duty cycle) for each individual output. From then on, only one command from the bus master is required to turn each individual open-drain output on, off, or to cycle at BLINK RATE 1 or BLINK RATE 2.

FEATUREs
8 LED drivers (on, off, flashing at a programmable rate)
2 selectable, fully programmable blink rates (frequency and duty cycle) between 0.148 Hz and 38 Hz (6.74 seconds and 0.026 seconds)
Input/outputs not used as LED drivers can be used as regular GPIOs
Internal oscillator requires no external components
I2C-bus interface logic compatible with SMBus
Internal power-on reset
Noise filter on SCL/SDA inputs
Active LOW reset input
8 open-drain outputs directly drive LEDs to 25 mA
Edge rate control on outputs
Maximum output sink current is 25 mA per bit and 100 mA per package.