NXP Semiconductors PCA8574D,512

Overview

PCA8574D,512 from NXP Semiconductors is an 8-bit quasi-bidirectional I/O expander for the I²C-bus, operating from 2.3 V to 5.5 V with 400 kHz Fast-mode support. It features eight I/O ports (P0–P7), active-low open-drain interrupt output (INT), three hardware address pins (A0–A2) enabling eight device addresses, and 25 mA per-pin sink capability for direct LED drive. It is used in embedded systems requiring remote GPIO expansion with low-power interrupt-driven monitoring - such as industrial control panels and LED signage.

For engineers reviewing the PCA8574D,512 datasheet, PCA8574D,512 pinout, PCA8574D,512 application, or PCA8574D,512 equivalent, this device delivers deterministic I²C-based I/O extension with latch-up immunity (>100 mA), ESD protection (>2000 V HBM), and Power-On Reset initialization - critical for reliable integration into microcontroller-based designs with space- and power-constrained layouts.

Technical Context

The PCA8574D,512 implements a single-register quasi-bidirectional I/O architecture: each port pin functions as input or output without direction register overhead, initialized at power-on as input with 100 µA weak pull-up to VDD. Its interrupt logic asserts INT (active LOW) on any input state change relative to the input port register, eliminating polling.

It uses standard I²C Fast-mode timing (400 kHz), supports slave addresses 0x40–0x47 (PCA8574 family), and integrates internal POR to initialize all I/Os as inputs. The SO16 package enables board-level compatibility with legacy PCF8574T/3 designs while delivering higher sink current (25 mA/pin vs. ~15 mA) and extended voltage range (2.3–5.5 V vs. 2.5–6 V).

Key Specifications

Pinout & Package

PCA8574D,512 is housed in a plastic small outline package (SO16) with 16 leads and 7.5 mm body width (SOT162-1). Pin assignments are validated per NXP's official pin configuration diagram for SO16.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I²C I/O expander applications.

Compared with PCF8574T/3, PCA8574D,512 offers 4× faster I²C speed and wider voltage range; compared with PCA9674APW,118, it retains SO16 compatibility and lower cost but lacks Fm+ timing and advanced filtering - making PCA8574D,512 optimal for cost-sensitive, space-constrained upgrades of legacy PCF8574-based systems.

Availability

PCA8574D,512 is available at Aetrix Electronics and suitable for industrial control, medical device status panels, and LED signage requiring stable component supply across extended temperature ranges (−40 °C to +85 °C) and long production lifecycles.

Supply support for PCA8574D,512 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

NXP Semiconductors is a global semiconductor leader specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with deep expertise in I²C peripheral IP and robust mixed-signal design.

The PCA8574 series was designed specifically for cost-effective, low-power remote I/O expansion in resource-constrained embedded systems - prioritizing simplicity, interrupt efficiency, and broad voltage compatibility over high-speed or feature-rich alternatives.

FAQ

What is the I²C address range supported by PCA8574D,512?

The PCA8574D,512 supports eight fixed 7-bit slave addresses: 0x40 through 0x47. These are determined by the logic states of hardware address pins A2, A1, and A0. Each combination selects a unique address, allowing up to eight PCA8574D,512 devices on the same I²C bus without conflict. This address range is specific to the PCA8574 (not PCA8574A) variant and is confirmed in NXP's official datasheet revision 3.

Does PCA8574D,512 require external pull-up resistors on SDA and SCL lines?

Yes, PCA8574D,512 requires external pull-up resistors on both SDA and SCL lines to ensure proper I²C bus operation. The device has open-drain outputs on these lines and does not integrate internal pull-ups. Typical values range from 2.2 kΩ to 10 kΩ depending on bus capacitance and speed; 4.7 kΩ is commonly used for 400 kHz Fast-mode operation with moderate node count.

Can PCA8574D,512 drive LEDs directly without current-limiting resistors?

No, PCA8574D,512 cannot drive LEDs without external current-limiting resistors. While it provides 25 mA sink capability per pin, the LED forward voltage and desired current must be controlled externally. A resistor between VDD and the LED anode sets the current; omitting it risks exceeding absolute maximum ratings and damaging the PCA8574D,512 output stage.

How does the interrupt (INT) pin behave during power-on reset?

At power-on, the internal POR initializes all I/Os as inputs with 100 µA weak pull-up to VDD. If any port pin (e.g., P0) is externally pulled LOW during this state, the INT pin immediately asserts active LOW. This occurs because the input state differs from the default register value (HIGH), satisfying the interrupt condition. INT remains asserted until the host reads the input register or writes to the port.

Is PCA8574D,512 pin-compatible with PCF8574T/3?

Yes, PCA8574D,512 is a documented drop-in replacement for PCF8574T/3 per NXP's ordering information table. Both share identical SO16 pinout, register structure, and functional behavior. Key improvements include 400 kHz I²C support (vs. 100 kHz), extended 2.3–5.5 V supply range (vs. 2.5–6 V), and higher 25 mA sink capability (vs. ~15 mA), making PCA8574D,512 backward-compatible with no PCB changes required.