PCA9557PW - 8-Bit I2C I/O Expander | NXP | 16-TSSOP
MPN: PCA9557PW ✓ Active| Qty | Unit Price | Extended |
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| 1 | $0 | $0.00 |
| 10 | $0 | $0.00 |
| 100 | $0 | $0.00 |
| 500 | $0 | $0.00 |
| 1,000 | $0 | $0.00 |
PCA9557PW Overview
An I/O expander is an interface IC that extends the number of general-purpose inputs and outputs available to a host processor. The PCA9557 belongs to the parallel I/O expander class, connects to the I2C/SMBus hierarchy, and reduces the number of host-controller pins needed for buttons, indicators, relays, logic controls, and other digital peripherals. Its operating voltage range supports both 3.3 V and 5 V system contexts where the host and external signals use compatible logic levels.
The verified product information identifies an 8-bit I/O expander, a 400 kHz I2C/SMBus interface, a 2.3 V to 5.5 V VCC range, and a 16-TSSOP package. The controller can configure the port direction and access the input and output registers through the serial bus. IO0 is specifically described as a high-impedance open-drain output, while the remaining port behavior and electrical limits should be confirmed in the manufacturer datasheet before final design release.
Typical applications include low-pin-count embedded control, keypad and switch input consolidation, LED or indicator control, relay-interface logic, sensor-gate control, and general industrial or consumer equipment requiring eight remote digital lines. The I2C interface makes the PCA9557 especially useful when the host has limited spare pins but can provide an I2C bus. Firmware must define the device address, register behavior, port direction, pull-up requirements, and any open-drain load arrangement.
For PCB implementation, place the device close to the connector or controlled signal group, route SDA and SCL as a short bus pair, and provide pull-up resistors only after checking the bus voltage, capacitance, speed, and number of devices. Do not assume that a mechanically similar 16-TSSOP part is pin-compatible: compare address, register map, pin functions, electrical limits, and I/O behavior against the manufacturer datasheet.
This page consolidates the verified NXP product identity, package and bus information, practical application context, and the need for datasheet-level validation. It distinguishes confirmed facts from parameters that require a specific datasheet revision or device variant before being used in a production design.
Drop-in alternatives for PCA9557PW — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with PCA9557PW (same form factor and footprint) — differing in Bus Interface, Package, Product Type, RoHS Status.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PCA9557PW,118
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9557PWR
✅ Drop-In📋 Reference alternative (not in catalog)
PI4IOE5V9557LEX
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9557PW Specifications
| Product Type | 8-bit parallel I/O expander |
| Bus Interface | I2C/SMBus |
| VCC Operating Voltage | 2.3 V to 5.5 V |
| I2C/SMBus Maximum Frequency | 400 kHz |
| Input Port | 8-bit |
| Output Port | 8-bit |
| IO0 Output Type | High-impedance open-drain output |
| Parallel I/O Count | 8 I/O |
| Package | 16-pin TSSOP |
| Mounting Type | Surface mount |
| RoHS Status | unknown |
| REACH Status | unknown |
| AEC-Q100 Qualification | unknown |
PCA9557PW 16-pin tssop Pin Configuration Guide
Pin configuration for PCA9557PW (16-pin tssop package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for PCA9557PW.
Refer to the datasheet for full pin configuration.
Typical Applications
PCA9557PW is suitable for 6 applications: Industrial Control Panel I/O Expansion, LED and Indicator Control, Keypad and Switch Consolidation, Relay and Discrete Control Interface, Embedded Sensor and Alarm Interface, Low-Pin-Count Consumer Device.
Industrial Control Panel I/O Expansion
The PCA9557PW is useful when a compact industrial controller needs more switch, lamp, or interlock inputs and outputs than its host MCU provides directly. The verified 8-bit parallel I/O capability and 2.3 V to 5.5 V operating range make it suitable for low-voltage control panels, while the 400 kHz I2C/SMBus interface keeps the host connection compact. Firmware can use the serial bus to read the input register and update the output register, reducing MCU pin pressure. Before deployment, verify the exact logic thresholds, port direction, address, and reset requirements against the NXP datasheet.
Recommended
LED and Indicator Control
The PCA9557PW can centralize control of eight LED or indicator signals when the host controller has limited direct GPIO resources. The verified 8-bit output port allows software-defined on/off states, patterns, and status reporting over I2C/SMBus. A 16-TSSOP package also helps keep the expander compact on a densely populated control board. The design must account for the output port's verified IO0 open-drain behavior and confirm the current limits for every other output pin before adding buffers or driver transistors.
Recommended
Keypad and Switch Consolidation
The PCA9557PW can serve as an 8-bit remote input port for switches, selectors, limit sensors, or a small keypad matrix interface. Its verified 400 kHz I2C/SMBus rate is suitable for many embedded control loops where human or mechanical inputs do not require microsecond-level response. The 2.3 V to 5.5 V supply range supports common 3.3 V and 5 V systems, but pull-up and input-threshold design must match the actual bus voltage. Use debounce and polarity logic in firmware rather than relying only on raw port reads.
Recommended
Relay and Discrete Control Interface
The PCA9557PW can provide logic-level control for relays, solenoids, latches, and other discrete loads when the external circuitry provides suitable drive current and protection. The verified 8-bit output register makes software sequencing straightforward, while the serial interface reduces the number of host pins needed for control signals. Do not directly drive inductive loads from the expander unless the manufacturer data confirms the applicable current and voltage limits; use transistors, relays, flyback protection, and appropriate pull-ups. The 400 kHz bus is suitable for supervisory control rather than high-speed pulse sequencing.
Recommended
Embedded Sensor and Alarm Interface
The PCA9557PW can add digital alarm, tamper, door, or sensor-enable lines to a microcontroller-based system. The verified 8-bit input and output registers allow one serial-connected device to handle both sensed states and control lines, while the 2.3 V to 5.5 V VCC range supports common embedded rails. Firmware should define whether each line is input or output, debounce mechanical events, and handle bus faults deterministically. Confirm the exact address and reset configuration because those details are not included in the supplied search snippets.
Recommended
Low-Pin-Count Consumer Device
The PCA9557PW is appropriate for consumer and appliance controllers that need several discrete controls without dedicating eight or more MCU pins. Its verified 16-TSSOP package and low-current-consumption description suit compact embedded boards, while the I2C/SMBus interface allows the MCU to manage status LEDs, buttons, and external logic from a shared bus. Production firmware should include device detection, bus timeout handling, and a defined startup state for every output. Validate the exact TSSOP pinout and electrical limits before final routing.
Recommended
Recommended Products Summary
Engineering reference data for PCA9557PW — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCA9557PW,118 | PCA9557PWR | PI4IOE5V9557LEX |
|---|---|---|---|---|
| Package | 16-TSSOP | 16-TSSOP | 16-TSSOP | 16-TSSOP |
| Brand | NXP Semiconductors | NXP Semiconductors | Texas Instruments | Diodes Incorporated |
| Function | 8-bit I/O expander | 8-bit I/O expander | I/O expander | I/O expander |
| I2C/SMBus Interface | Yes | Yes | Yes | Yes |
| RoHS Status | unknown | unknown | unknown | unknown |
| REACH Status | unknown | unknown | unknown | unknown |
Key Differentiators
- Verified 8-bit I/O expansion in a compact 16-TSSOP package (vs PCA9500PW)
- Supports common embedded supply ranges (vs PI4IOE5V9557LEX)
- Supports 400 kHz serial control (vs PCA9557PWR)
- Provides a documented open-drain IO0 (vs Generic 16-TSSOP I/O expanders)
Design Notes
Design the I2C pull-ups for the actual bus voltage and total capacitance rather than copying a single resistor value. The verified PCA9557PW operating range is 2.3 V to 5.5 V, while the serial bus may be pulled to a different logic rail. Check the absolute maximum ratings, input thresholds, output leakage, and IO0 open-drain behavior in the NXP datasheet before selecting pull-ups. Account for current from every bus device and ensure the host rail can sink the required pull-up current.
Route SDA and SCL as a compact, continuous bus pair and keep the expander close to the connector or controlled I/O group when practical. Provide the datasheet-required supply and ground connections, maintain adequate return paths, and place optional bus capacitors at locations recommended by the device and system design. Avoid long stubs from the main I2C bus, because capacitance can reduce margin at the verified 400 kHz operating rate and increase susceptibility to ringing.
Do not assume that all eight port pins have identical output architectures. The verified product description specifically identifies IO0 as a high-impedance open-drain output, so external pull-up and load design may be required for that pin. Also verify the device address, reset configuration, input/output direction defaults, and register map from the manufacturer datasheet. A mechanically similar 16-TSSOP substitute is not drop-in compatible unless these details match.
For longer or faster system buses, validate rise and fall times with the actual cable, connectors, pull-ups, peripheral capacitance, and bus loading. The verified 400 kHz figure describes the supported interface rate, not a guarantee for every PCB or harness. Use scope measurements or an appropriate bus analyzer during design verification, especially when the PCA9557PW is placed near relays, motors, display cables, or other noisy systems. Keep switching-node copper and high-current return paths away from SDA and SCL.
Compliance Information
The supplied verified snippets do not explicitly state RoHS, REACH, AEC-Q100, lead-free, halogen-free, or conflict-minerals status. Confirm these attributes on the manufacturer product page, datasheet, or authorized distributor record.
