The AT9552 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 I2C-bus and uses up one of the master's timers. The AT9552 LED blinker instead requires only the initial setup command to program BLINK RATE 1 and BLINK RATE 2 (that is, 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 200 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 AT9552 allow eight devices to operate on the same bus.


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

  • 2 selectable, fully programmable blink rates (frequency and duty cycle) between

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

  • Input/outputs 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

  • 16 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 2.3 V to 5.5 V

  • 0 Hz to 400 kHz clock frequency

Block diagram

Typical Application Circuit