1.

General description

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

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). 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. Maximum output sink current is 25 mA per bit

and 50 mA per package.

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

Input/Output (GPIO) expansion.

The active LOW hardware reset pin (RESET) and Power-On Reset (POR) initializes the

registers to their default state, all zeroes, causing the bits to be set HIGH (LED off).

One hardware address pin on the PCA9550 allows two devices to operate on the same

bus.

2.

Features

0.172 Hz and 44 Hz (5.82 seconds and 0.023 second)

PCA9550

Rev. 05 — 13 October 2008

Product data sheet