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PCA9555

Public Made by Adom

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NXP 16-bit I2C I/O expander, SO-24. Two 8-bit ports, interrupt output, polarity inversion, 3 address pins. Datasheet-verified.

componentinterfaceio-expanderi2cgpioso-24nxp
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Contents

README

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PCA9555

NXP Semiconductors · I2C 16-bit I/O expander · SO-24

A 16-bit general-purpose I/O expander with an I2C interface, in SO-24, NXP's take on the port-expander and a peer of the MCP23017. It gives a microcontroller sixteen more pins across two 8-bit ports (IO0 and IO1), each pin independently input or output, with a per-pin polarity-inversion register and an open-drain interrupt (INT) that fires on an input change so the host need not poll. Three address pins (A0-A2) put up to eight on one bus for 128 I/O. It runs I2C at up to 400 kHz over a 1.65-5.5 V supply, and unlike the PCF8574 it has real direction control per pin.

Pinout

Pin Name Type Function
1 INT output Active-LOW open-drain interrupt output. Asserts when any input port pin state differs from its input port register value; requires an external pull-up to VDD.
2 A1 input I2C-bus slave address input bit 1. Tie to VDD or VSS to set the programmable portion of the 7-bit slave address (0100 A2 A1 A0).
3 A2 input I2C-bus slave address input bit 2. Tie to VDD or VSS to set the programmable portion of the 7-bit slave address.
4 IO0_0 bidirectional Port 0 bit 0 general-purpose I/O. Configurable per bit as input (default, high-Z with weak 100 kΩ pull-up to VDD) or push-pull output. 5 V-tolerant input.
5 IO0_1 bidirectional Port 0 bit 1 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
6 IO0_2 bidirectional Port 0 bit 2 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
7 IO0_3 bidirectional Port 0 bit 3 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
8 IO0_4 bidirectional Port 0 bit 4 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
9 IO0_5 bidirectional Port 0 bit 5 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
10 IO0_6 bidirectional Port 0 bit 6 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
11 IO0_7 bidirectional Port 0 bit 7 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
12 VSS power_in Supply ground (0 V) reference for the device.
13 IO1_0 bidirectional Port 1 bit 0 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
14 IO1_1 bidirectional Port 1 bit 1 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
15 IO1_2 bidirectional Port 1 bit 2 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
16 IO1_3 bidirectional Port 1 bit 3 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
17 IO1_4 bidirectional Port 1 bit 4 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
18 IO1_5 bidirectional Port 1 bit 5 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
19 IO1_6 bidirectional Port 1 bit 6 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
20 IO1_7 bidirectional Port 1 bit 7 general-purpose I/O. Configurable per bit as input (default) or push-pull output. 5 V-tolerant input.
21 A0 input I2C-bus slave address input bit 0. Tie to VDD or VSS to set the programmable portion of the 7-bit slave address (0100 A2 A1 A0).
22 SCL input I2C-bus serial clock input line. 0 Hz to 400 kHz clock frequency; requires external pull-up to VDD.
23 SDA bidirectional I2C-bus serial data line (open-drain). Requires external pull-up to VDD.
24 VDD power_in Positive supply voltage input. Operating range 2.3 V to 5.5 V; bypass locally with a 100 nF ceramic capacitor to VSS.

Key specifications

Parameter Value
Type I2C 16-bit I/O expander
I/O lines 16 (ports IO0, IO1)
Bus I2C up to 400 kHz
Per-pin direction + polarity inversion
Interrupt open-drain INT on change
Address pins A0-A2 (8 per bus)
Supply voltage 1.65-5.5 V
Package SO-24

Ordering variants

Same part, different packaging or reel option.

  • PCA9555D (SO-24)
  • PCA9555PW (TSSOP-24)

CAD (KiCad official)

  • Symbol: Interface_Expansion:PCA9555D
  • Footprint: Package_SO:SOIC-24W_7.5x15.4mm_P1.27mm
  • 3D model: SOIC-24W (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: NXP Semiconductors datasheet (34 pp, sha256 9f4f9c0ce4c461d7, retrieved 2026-08-17, tier: manufacturer)
  • Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF