1.

General description

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

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.

Maximum output sink current is 25 mA per bit and 100 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).

Three hardware address pins on the PCA9551 allow eight devices to operate on the same

bus.

The newer Fast-mode Plus PCA9634 8-bit LED controller offers an individual PWM

dimming control for each channel for better color mixing capabilities with a global PWM for

dimming or blinking all channels at the same time. There are 126 possible address

combinations and the maximum output sink current is 25 mA per bit and 200 mA per

package.

2.

Features

0.148 Hz and 38 Hz (6.74 seconds and 0.026 seconds)

PCA9551

Rev. 08 — 31 July 2008

Product data sheet