Texas Instruments PCA9557DB

Overview

PCA9557DB from Texas Instruments is an 8-bit I²C/SMBus remote I/O expander with reset and configuration registers, operating from 2.3V to 5.5V, supporting 400kHz Fast-mode I²C, featuring 5V-tolerant I/Os, active-low reset input, and high-current latched outputs capable of directly driving LEDs. It serves as a general-purpose GPIO extension for microcontrollers in space-constrained telecom and server applications.

For engineers reviewing the PCA9557DB datasheet, PCA9557DB pinout, PCA9557DB application, or PCA9557DB equivalent, this page delivers verified electrical specs, SSOP-16 package details, register-level I/O configuration behavior, reset timing constraints, and real-world implementation guidance for embedded I²C peripheral expansion.

Technical Context

The PCA9557DB implements an I²C slave interface with fixed 7-bit address (0x18–0x1F) programmable via A0–A2 pins, supporting up to eight devices on one bus. Its internal architecture includes separate 8-bit configuration, input, output, and polarity inversion registers - all readable and writable over I²C.

At power-on or RESET assertion, all I/Os default to high-impedance inputs with no glitch; P0 is open-drain while P1–P7 are push-pull. The device integrates noise filtering on SCL/SDA, internal power-on reset (VPOR = 1.65–2.1V), and supports bidirectional data transfer with ACK/NACK protocol compliance per I²C specification.

Key Specifications

Pinout & Package

PCA9557DB is housed in a 16-pin SSOP (Shrink Small Outline Package) measuring 6.2mm × 7.8mm, optimized for compact PCB layouts in telecom shelters and server management modules.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9557DB, PCA9555DB offers more I/O but removes hardware reset - limiting fault resilience - while TCA6408ADB reduces BOM count at the expense of register flexibility and CDM-level ESD protection, making PCA9557DB optimal for reliability-critical telecom and industrial control.

Availability

PCA9557DB is available at Aetrix Electronics and suitable for telecom shelters, server management subsystems, and industrial automation requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for PCA9557DB 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, longevity, and industrial-grade performance.

The PCA9557DB belongs to TI's Peripheral Devices portfolio, designed specifically for robust, low-power I²C-based GPIO expansion in telecom infrastructure, computing platforms, and factory automation systems.

FAQ

What is the function of the P0 pin on the PCA9557DB?

The P0 pin on the PCA9557DB is an open-drain I/O terminal requiring an external pullup resistor. Unlike P1–P7, it cannot source current and is typically used for interrupt signaling, wired-AND logic, or level translation. Its high-impedance state at power-up prevents conflicts on shared bus lines, and its configuration is controlled by the same I/O direction register as other ports.

Does the PCA9557DB support both Standard-mode and Fast-mode I²C?

Yes, the PCA9557DB fully supports both Standard-mode (100kHz) and Fast-mode (400kHz) I²C operation. Its timing parameters - including tSCL, tSCH, and tSU:DAT - meet I²C specification limits across the full 2.3V–5.5V supply range, enabling interoperability with legacy and high-speed controllers without protocol translation.

How does the PCA9557DB handle power-on initialization?

The PCA9557DB incorporates an internal power-on reset circuit that holds all registers in default state until VCC reaches VPOR (1.65–2.1V). Upon release, I/Os initialize as high-impedance inputs with no output glitch - ensuring safe startup in systems where uncontrolled I/O states could damage downstream circuitry or trigger false alarms.

Can the PCA9557DB drive LEDs directly without external transistors?

Yes, the PCA9557DB's P1–P7 outputs support up to 25mA sink current per pin (with total P-port ≤200mA), enabling direct LED drive with appropriate current-limiting resistors. P0 is open-drain and also suitable for LED anode connections when paired with a pullup, though its drive strength is limited by external resistor selection.

What is the maximum number of PCA9557DB devices supported on a single I²C bus?

Up to eight PCA9557DB devices can share one I²C bus using the A0, A1, and A2 address-select pins, which configure the 3 LSBs of the 7-bit slave address (0x18–0x1F). This allows scalable I/O expansion without address collisions, provided each device has a unique A0–A2 combination and proper bus capacitance (<400pF) is maintained.