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Part Number Description I/O Pull-Up Number of Device Address Number of I/Os Standby Current Max Output device current Default POR Output State Hardware Reset input Configuration Registers Cross Reference Max frequency (kHz) I2C Adress Vcc Range(V) Interrupt 5V-to lerant I/O Output type max I/O voltage tolerance Pin/Package
AT9550 2 2 1.9μA 25mA Hi-Z Input PCA9550 400 1100xxx 2.3~5.5 Open-Drain 5.5V SOP8 MSOP8


      The AT9550 LED blinker blinks LEDs in 12C-bus and SMBus applications where it is necessary to limit bus traffic or free up the I2C 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 AT8574 or AT9554, 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 AT9550LED blinker instead requires only the initial set-up command to program BLINK RATE1 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 AT9550 allows two devices to operate on the same bus.


  • LED drivers (on, off, flashing at a programmable rate)

  • selectable, fully programmable blink rates (frequency and duty cycle) between 0.172Hz and 44Hz (5.82 seconds and 0.023 second)

  • Input/output 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

  • 2 open-drain outputs directly drive LEDs to 25 mA

  • Controlled edge rates to minimize ground bounce

  • No glitch on power-up

  • Supports hot insertion

  • Low standby current

  • Operating power supply voltage range of 2.3 V to 5.5 V

  • 0kHz to 400kHz clock frequency

  • ESD protection exceeds 2000V HBM per JESD22-A114, 150 V MM perJESD22-A115 and 1000V CDM per JESD22-C101.

  • Latch-up testing is done to JEDEC Standard JESD78 which exceeds 100 mA

  • Packages offered: SO8, TSSOP8 (MSOP8), HVSON8

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