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Part Number Description ESD Protect.(±KV) Tx EN Rx EN ICC (Shutdn)(μA) Tx/Rx Duplex VSUPPLY(V) ICC(mA)(mA) Data Rate (kbps) Pin/Package
AT9555 15 No No 2.8 1Tx + 1Rx Half 3.3-5 8 32000 TSSOP24 QFN24


     The AT9555 is a 24-pin CMOS device that provides 16 bits of General Purpose parallel Input/Output (GPIO) expansion for I2C-bus/SMBus applications and was developed to enhance the AnalogTek Semiconductors family of I2C-bus I/O expanders. The improvements include higher drive capability, 5 V I/O tolerance, lower supply current, individual I/O configuration, and smaller packaging. I/O expanders provide a simple solution when additional I/O is needed for ACPI power switches, sensors, push buttons, LEDs, fans, etc.

      The AT9555 consists of two 8-bit Configuration (Input or Output selection); Input, Output and Polarity Inversion (active HIGH or active LOW operation) registers. The system master can enable the I/Os as either inputs or outputs by writing to the I/O configuration bits. The data for each Input or Output is kept in the corresponding Input or Output register. The polarity of the read register can be inverted with the Polarity Inversion register. All registers can be read by the system master. Although pin-to-pin and I2C-bus address compatible with the AT8575, software changes are required due to the enhancements.

     The AT9555 open-drain interrupt output is activated when any input state differs from its corresponding input port register state and is used to indicate to the system master that an input state has changed. The power-on reset sets the registers to their default values and initializes the device state machine.

     Three hardware pins (A0, A1, A2) vary the fixed I2C-bus address and allow up to eight devices to share the same I2C-bus/SMBus. The fixed I2C-bus address of the AT9555 is the same as the AT9554, allowing up to eight of these devices in any combination to share the same I2C-bus/SMBus.


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

  • 5 V tolerant I/Os

  • Polarity Inversion register

  • Active LOW interrupt output

  • Low standby current

  • Noise filter on SCL/SDA inputs

  • No glitch on power-up

  • Internal power-on reset

  • 16 I/O pins which default to 16 inputs

  • 0 Hz to 400 kHz clock frequency

  • ESD protection exceeds 2000V HBM per JESD22-A114, 200V MM per JESD22-A115, and 1000V CDM per JESD22-C101

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

  • Six packages offered: DIP24, SO24, SSOP24, TSSOP24, HVQFN24 and HWQFN24

Typical Application


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