Home > Products > AT9551
Part Number Description 5V-to lerant I/O Output type max I/O voltage tolerance Number of I/Os Standby Current Max Output device current Default POR Output State Hardware Reset input Configuration Registers I/O Pull-Up Number of Device Address Cross Reference Max frequency (kHz) I2C Adress Vcc Range(V) Interrupt Pin/Package
AT9551 Open-Drain 5.5V 8 1.9μA 25mA Hi-Z Input 8 PCA9551 400 1100xxx 2.3~5.5 TSSOP16 QFN16


        The AT9551 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 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 l2C-bus and uses up one of the master's timers.The AT9551 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 AT9551 allow eight devices to operate on the same bus.

      The newer Fast-mode Plus AT9634 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.


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

  • 2 selectable, fully programmable blink rates (frequency and duty cycle) between0.148Hz 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

  • 12C-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

  • No glitch on power-up

  • Supports hot insertion

  • Low standby current

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

  • 0Hz to 400kHz clock frequency

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

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

  • Packages offered: SO16, TSSOP16, HVQFN16

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