Texas Instruments PCF8574DWR

Overview

PCF8574DWR from Texas Instruments is an 8-bit quasi-bidirectional I/O expander for I²C bus (2.5 V to 6 V), providing remote parallel port expansion with latched outputs capable of directly driving LEDs, open-drain interrupt output (INT), and low standby current (≤10 μA). It serves as a slave device in microcontroller-based systems where GPIO resources are constrained, such as telecom filter units and industrial automation controllers.

For engineers reviewing the PCF8574DWR datasheet, PCF8574DWR pinout, PCF8574DWR application, or PCF8574DWR equivalent, key selection considerations include its I²C address configuration (A0–A2), 25 mA sink capability per I/O, interrupt timing (t_iv = 4 μs), and compatibility with standard-mode I²C (100 kHz).

Technical Context

The PCF8574DWR implements a simple I²C slave interface with no internal registers-read/write operations directly access the 8-bit P-port (P0–P7). Its quasi-bidirectional I/O structure eliminates need for direction control signals; pins default high at power-on and operate as inputs when pulled high via external resistors or as outputs when driven low.

Interrupt generation is edge-triggered on any P-port input transition and reset upon read/write to the port or acknowledge pulse on SCL. The device lacks configuration registers or status flags, relying entirely on I²C transaction sequencing for state management-making it suitable for deterministic, low-overhead GPIO extension in resource-limited embedded designs.

Key Specifications

Pinout & Package

PCF8574DWR is supplied in a 20-pin TVSOP package (DGV), measuring 5 mm × 6.4 mm, with exposed pad not electrically connected. Pin functions are validated per TI SCPS068K Rev. September 2024.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9554APW and MAX7328ATP+, the PCF8574DWR delivers lowest standby current (10 μA vs. 150 μA/20 μA), simplest registerless architecture, and broadest legacy I²C compatibility - making it ideal for deterministic, low-power, firmware-light I/O expansion.

Availability

PCF8574DWR is available at Aetrix Electronics and suitable for telecom shelters, industrial automation controllers, and server management subsystems requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for PCF8574DWR 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies, with decades of experience in industrial and communications IC design.

The PCF8574 product line was engineered specifically for low-complexity, low-power I²C-based GPIO expansion in space-constrained and cost-sensitive embedded systems - prioritizing simplicity, reliability, and ease of integration over feature-rich configurability.

FAQ

What is the I²C address range supported by the PCF8574DWR?

The PCF8574DWR supports eight unique 7-bit I²C slave addresses (0x40–0x4F) determined by the logic states of A0, A1, and A2 pins. For example, with all address pins grounded, the write address is 0x40 and read address is 0x41. This allows up to eight PCF8574DWR devices on a single I²C bus without address conflict.

Does the PCF8574DWR require external pull-up resistors on SCL and SDA lines?

Yes, the PCF8574DWR requires external pull-up resistors on both SCL and SDA lines to V_CC, as these pins implement open-drain outputs. Typical values range from 2.2 kΩ to 10 kΩ depending on bus capacitance and speed; TI recommends calculating R_p(min) and R_p(max) using equations in Section 8.2.2 of the PCF8574DWR datasheet.

Can the PCF8574DWR drive LEDs directly without external transistors?

Yes, the PCF8574DWR can directly drive standard LEDs with its 25 mA sink capability per I/O pin at 5 V. Connect the LED anode to V_CC and cathode to a P-port pin through a current-limiting resistor. Ensure the port is configured as output (driven low) to illuminate the LED; high-impedance input state keeps the LED off with minimal leakage.

How does the interrupt (INT) pin of the PCF8574DWR behave during I²C transactions?

The INT pin of the PCF8574DWR is asserted low on any rising or falling edge of P-port inputs and remains active until the port state is read or written - which resets the interrupt latch on the acknowledge bit of the next SCL cycle. Interrupts occurring during the acknowledge pulse may be lost, so firmware must read the port promptly after INT assertion.

Is the PCF8574DWR compatible with SMBus protocols?

Yes, the PCF8574DWR is SMBus-compatible as it adheres to SMBus 2.0 electrical and timing specifications, including voltage thresholds (V_IL ≤ 0.3×V_CC, V_IH ≥ 0.7×V_CC) and timeout behavior. Its 100 kHz maximum clock rate and open-drain interface meet SMBus standard-mode requirements, enabling use in systems with SMBus hosts like PMBus-compliant power controllers.