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1. General description
The PCA9553 LED blinker blinks LEDs in I
2
C-bus and SMBus applications where it is
necessary to limit bus traffic or free up the I
2
C-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 I
2
C-bus and uses up one of the master's timers. The
PCA9553 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 100 mA per package.
Any bits not used for controlling the LEDs can be used for General Purpose Parallel
Input/Output (GPIO) expansion.
Power-On Reset (POR) initializes the registers to their default state, all zeroes, causing
the bits to be set HIGH (LED off).
Due to pin limitations, the PCA9553 is not featured with hardware address pins. The
PCA9553/01 and the PCA9553/02 have different fixed I
2
C-bus addresses allowing
operation of both on the same bus.
2. Features
n 4 LED drivers (on, off, flashing at a programmable rate)
n 2 selectable, fully programmable blink rates (frequency and duty cycle) between
0.172 Hz and 44 Hz (5.82 seconds and 0.023 seconds)
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
n Noise filter on SCL/SDA inputs
n 4 open-drain outputs directly drive LEDs to 25 mA
n Controlled edge rates to minimize ground bounce
n No glitch on power-up
n Supports hot insertion
n Low standby current
n Operating power supply voltage range of 2.3 V to 5.5 V
n 0 Hz to 400 kHz clock frequency
PCA9553
4-bit I
2
C-bus LED driver with programmable blink rates
Rev. 06 — 29 December 2008 Product data sheet
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