NXP Semiconductors PCF8575CTS/1,112

Overview

PCF8575CTS/1,112 from NXP Semiconductors (formerly Philips) is a 16-bit quasi-bidirectional I/O expander IC for the I²C-bus, operating at 4.5–5.5 V with 400 kbit/s FAST-mode support. It features latched outputs capable of directly driving LEDs, an open-drain interrupt output (INT), and hardware addressability via three pins (A0–A2) for up to eight devices on one bus. It serves as a remote parallel port interface in microcontroller-based industrial control panels.

For engineers reviewing the PCF8575CTS/1,112 datasheet, PCF8575CTS/1,112 pinout, PCF8575CTS/1,112 application, or PCF8575CTS/1,112 equivalent, key selection considerations include its 16-bit I/O expansion capability, interrupt-driven input change detection, quasi-bidirectional port behavior without direction control, and SSOP24 package compatibility with space-constrained PCB layouts.

Technical Context

The PCF8575CTS/1,112 implements a two-byte I²C transaction protocol where the first byte always maps to Port 0 (P00–P07) and the second to Port 1 (P10–P17). Its quasi-bidirectional I/Os use internal transient pull-up current (IOHt) for fast rising edges and enter high-impedance state after SCL falling edge - eliminating external direction lines but requiring ports be written HIGH before use as inputs.

It functions exclusively as an I²C slave transmitter/receiver with built-in power-on reset (VPOR = 1.2–1.8 V) that initializes all I/Os to logic 1. The INT pin asserts active-low on any rising or falling edge at input ports, with tiv = 4 µs input valid time and tir = 4 µs reset delay, enabling low-latency event notification without polling the bus.

Key Specifications

Pinout & Package

PCF8575CTS/1,112 is housed in a plastic shrink small outline package (SSOP24, SOT340-1) with 24 leads and 0.65 mm lead pitch. The package measures 8.4 × 5.4 mm with 1.8 mm height and is rated for reflow soldering only - wave soldering is not recommended per manufacturer guidelines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9555PW,118 and TCA6424ARGJR, the PCF8575CTS/1,112 offers simpler initialization, native 5 V operation, and proven reliability in long-lifecycle industrial deployments - making it ideal where design stability, minimal firmware overhead, and backward compatibility outweigh feature richness.

Availability

PCF8575CTS/1,112 is available at Aetrix Electronics and suitable for industrial HMI panels, automated test equipment, and building automation controllers requiring stable component supply across extended production lifecycles.

Supply support for PCF8575CTS/1,112 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 markets, with roots in Philips' pioneering analog and mixed-signal IC development.

The PCF8575CTS/1,112 belongs to NXP's legacy I²C peripheral portfolio designed specifically for robust, low-cost remote I/O expansion in resource-constrained microcontroller systems - emphasizing simplicity, interoperability, and long-term manufacturability.

FAQ

What is the maximum I²C clock frequency supported by the PCF8575CTS/1,112?

The PCF8575CTS/1,112 supports FAST-mode I²C operation up to 400 kHz, as specified in its timing characteristics table. This allows reliable communication with standard microcontrollers without requiring custom bit-banging routines. Exceeding 400 kHz may result in timing violations, especially under capacitive bus loads exceeding 400 pF. The device includes internal input filtering to reject spikes narrower than 50 ns, enhancing noise immunity at this speed. Always verify bus rise/fall times and pull-up strength when operating near the maximum frequency.

How does the quasi-bidirectional I/O behavior of the PCF8575CTS/1,112 differ from standard GPIOs?

The PCF8575CTS/1,112's quasi-bidirectional I/Os combine output drive and input sensing on the same pin without a dedicated direction register. Writing a '1' activates a strong transient pull-up (IOHt) for fast rising edges, then switches to high-impedance - allowing the pin to read external signals. Writing a '0' enables a low-impedance sink. This eliminates direction-control overhead but requires writing '1' before reading. Misuse - e.g., driving a pin LOW externally while written LOW - risks excessive current flow per datasheet Note 3.

Can the PCF8575CTS/1,112 drive LEDs directly, and what are the current limits?

Yes, the PCF8575CTS/1,112 can drive LEDs directly due to its high-current output capability: up to 25 mA per pin at VOL = 1 V, with a total device limit of 100 mA for all sinking outputs simultaneously. Each output includes latching to maintain state without continuous MCU intervention. For typical 20 mA LEDs, no external transistor is needed - simply connect the LED anode to VDD and cathode to a PCF8575CTS/1,112 output pin with a series resistor calculated for the forward voltage drop. Avoid exceeding per-pin or aggregate current limits to prevent thermal stress.

What happens to the I/O pins during power-up, and how is the initial state ensured?

At power-up, the PCF8575CTS/1,112's internal power-on reset circuit activates when VDD rises above VPOR (1.2–1.8 V), forcing all 16 I/O pins into a logic HIGH state with current sourced to VDD. This ensures a known, safe initial condition - preventing floating inputs or unintended actuator activation. The reset also clears the I²C interface logic, requiring the master to reinitialize communication. No external reset pin is provided; behavior is fully autonomous and repeatable across voltage ramps, making it suitable for unattended industrial restarts.

Is the PCF8575CTS/1,112 compatible with 3.3 V microcontrollers, and what level-shifting considerations apply?

The PCF8575CTS/1,112 is specified for 4.5–5.5 V operation and is not 3.3 V tolerant on its VDD or I/O pins. Direct connection to a 3.3 V microcontroller's I²C bus (SDA/SCL) risks damaging the PCF8575CTS/1,112 due to overvoltage on inputs and violates VIH/VIL thresholds. A bidirectional level shifter (e.g., TXB0104 or discrete MOSFET solution) is mandatory to translate 3.3 V logic levels to 5 V for SDA/SCL. Powering the PCF8575CTS/1,112 from 5 V while interfacing to 3.3 V logic requires careful isolation of voltage domains to avoid latch-up or parametric failure.