PCA9557PWT - 8-Bit I2C I/O Expander | Texas Instruments
N.º da peça: PCA9557PWT ✓ AtivoPCA9557PWT Visão geral
An I/O expander is an interface IC that extends the number of digital input and output lines available to an embedded system. The PCA9557 combines an 8-bit input port register, an 8-bit output port register, reset and configuration registers, and an I2C/SMBus interface. This hierarchy places it within interface ICs, digital logic, and broader semiconductor-based system expansion designs.
The PCA9557 supports both input and output operation through its port registers, while the configuration register controls each pin's direction. It is suitable for reading switches and logic states or driving digital inputs. The device also includes a reset function and low-current operation, helping it fit low-power embedded control, industrial automation, consumer electronics, and communication equipment.
The I2C interface provides a compact connection between the expander and a host microcontroller or processor. Its 400 kHz bus capability supports straightforward communication rates for control and monitoring systems. Because the device is controlled through registers rather than a parallel data bus, it reduces the number of host pins required for additional digital I/O.
Typical uses include configurable input/output modules, LED and relay-control interfaces, keypad and switch sensing, industrial control panels, and auxiliary port expansion for embedded systems. The 2.3 V to 5.5 V operating range also supports both 3.3 V and 5 V system rails.
When designing a board around the PCA9557PWT, connect pull-up resistors to the I2C bus and keep the bus routing compact. Confirm the intended direction and reset state of every port bit in firmware, and verify the host's logic levels before using the device across mixed-voltage sections. The TSSOP-16 footprint also requires careful assembly planning because its lead pitch is narrower than a standard SOIC package.
This page combines manufacturer specifications, practical application guidance, interface design notes, and drop-in replacement information to help engineers evaluate the PCA9557PWT for compact embedded I/O expansion.
Alternativas drop-in para PCA9557PWT — mesmo encapsulamento, compatível pino a pino. Peças de encapsulamento diferente que exigem retrabalho na PCB são excluídas.
Variantes desta série
Modelos da mesma série compatíveis como drop-in com PCA9557PWT (mesmo formato e footprint) — diferindo em IO0 Output Type, Package.
PCA9557PWR
✅ Drop-InConsulte o preço
Ver ficha técnica →PCA9557PW,112
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9557PWTG4
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9557PWT Especificações
| Number of I/O Ports | 8 ports |
| Interface | I2C/SMBus |
| I2C Bus Frequency | 400 kHz |
| Tensão de alimentação de operação | 2.3 V to 5.5 V |
| Port Register Width | 8 bits |
| Input Port Register | 8-bit register |
| Output Port Register | 8-bit register |
| Configuration Register | 8-bit configuration register |
| Reset Function | Yes |
| IO0 Output Type | High-impedance open-drain |
| Encapsulamento | 16-pin TSSOP (PW) |
| Package Type | TSSOP |
| Tipo de montagem | Surface mount |
| Faixa de temperatura de operação | -40 °C to +85 °C |
Guia de Configuração de Pinos do PCA9557PWT tssop
Configuração de pinos para PCA9557PWT (pacote tssop). A numeração dos pinos, funções e diagramas de conexão estão definidos no datasheet do fabricante. Consulte-o para o footprint exato e diretrizes de soldagem.
Nenhum dado detalhado de pinagem disponível para PCA9557PWT.
Consulte a ficha técnica para a configuração completa dos pinos.
Aplicações típicas
PCA9557PWT é adequado para 6 aplicaçãos: Industrial Control Panel I/O Expansion, LED and Relay Control Interface, Switch and Keypad Sensing, Embedded System Port Expansion, Communication Equipment Status Control, Low-Power Sensor and Actuator Hub.
Industrial Control Panel I/O Expansion
The PCA9557PWT expands a compact controller by adding eight configurable digital lines while preserving communication through a 400 kHz I2C/SMBus bus. Its 2.3 V to 5.5 V supply range accommodates common industrial logic rails, and its separate input and output registers let the host read limit switches while commanding discrete outputs. The 16-pin TSSOP package supports dense control boards, although industrial systems must also verify isolation, surge, and environmental requirements for the complete assembly.
Recomendado
LED and Relay Control Interface
Use the PCA9557PWT to translate a serial I2C command stream into eight independently programmable digital outputs for LEDs, relay drivers, or status indicators. The 8-bit output port reduces the GPIO burden on the host, while the configuration register lets unused pins become inputs. Its 400 kHz bus rate is suitable for ordinary control updates, and its 2.3 V to 5.5 V operating range supports both 3.3 V and 5 V controller platforms. External driver circuits remain necessary for loads beyond direct logic-pin capability.
Recomendado
Switch and Keypad Sensing
The PCA9557PWT provides a practical remote sensing interface for matrix-free switch banks, keypads, configuration selectors, and digital status inputs. The host reads the 8-bit input register over I2C and determines which switches have changed, avoiding several dedicated host GPIO pins. Because the interface operates up to 400 kHz, scan rates can suit human-operated panels and low-speed control signals. Firmware should debounce the inputs and account for the device's reset state before presenting switch data to the application.
Recomendado
Embedded System Port Expansion
When a microcontroller has too few available pins for external controls, the PCA9557PWT adds eight serial-accessed ports without requiring a parallel expansion bus. This is useful in compact consumer and embedded products where board area is constrained and the required control traffic is modest. The 16-pin TSSOP footprint is smaller than a conventional SOIC package, while the 2.3 V to 5.5 V range simplifies integration with 3.3 V and 5 V designs. Software must define startup outputs before external circuitry becomes active.
Recomendado
Communication Equipment Status Control
The PCA9557PWT can supervise discrete status and control signals in communication equipment through its I2C/SMBus interface. Eight ports may monitor equipment alarms, module presence, or fault flags and can also drive compatible control signals where the electrical limits permit. The 400 kHz bus supports straightforward status polling, and the register-based architecture simplifies diagnostics. Designers should use appropriate isolation, level translation, and protection when connecting the ports to long cables or external equipment racks.
Recomendado
Low-Power Sensor and Actuator Hub
Build a compact sensor-and-actuator hub around the PCA9557PWT when a battery-powered or space-constrained controller needs extra digital connections. The low-power I/O-expander architecture lets the host keep its serial interface active while controlling local discrete devices and reading state flags. The 2.3 V minimum supply voltage supports low-voltage designs, and the 400 kHz bus is adequate for infrequent sensor and actuator updates. Power-budget calculations must use the electrical characteristics for the actual bus speed, port direction, and external load.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para PCA9557PWT — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | PCA9557PWR | PCA9557PW,112 | PCA9557PWTG4 |
|---|---|---|---|---|
| Package | 16-pin TSSOP (PW) | 16-pin TSSOP (PW) | 16-pin TSSOP (PW) | 16-pin TSSOP (PW) |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments |
| I/O Port Count | 8 | 8 | 8 | 8 |
| Interface | I2C/SMBus | I2C/SMBus | I2C/SMBus | I2C/SMBus |
| Maximum Bus Frequency | 400 kHz | 400 kHz | 400 kHz | 400 kHz |
| Operating Supply Voltage | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V |
| Reset and Configuration Registers | Yes | Yes | Yes | Yes |
| Drop-In Compatibility | Reference device | Identical family, package, terminals, and main performance characteristics | Identical PCA9557 function in the PW package family | Identical PCA9557 function in the PW package family |
Principais diferenciais
- Direct order-code reuse on the same PCB footprint (vs PCA9557PWR)
- Same register-based peripheral architecture (vs PCA9557PW,112)
- Green-package order option with unchanged interface (vs PCA9557PWTG4)
Notas de projeto
Keep the I2C clock and data traces short, route them as a pair, and place pull-up resistors close to the bus nodes according to the system capacitance and voltage level. Avoid routing these traces beside switching regulators, inductors, relay contacts, or high-speed edges. Confirm the address-selection pins and reset polarity against the PCA9557 datasheet before finalizing the schematic, because incorrect strap connections can prevent reliable register access.
Establish every port's direction and initial output state in firmware immediately after reset so external actuators do not receive unintended commands. If a connected load can inject current into an output pin, verify the absolute-maximum and output-drive limits in the manufacturer datasheet. The PCA9557PWT's 2.3 V to 5.5 V operating range supports common logic rails, but the complete system still requires a supply source with adequate noise performance and decoupling.
Do not assume all eight ports behave identically: IO0 is described as a high-impedance open-drain output, while the remaining port behavior must be checked in the datasheet's pin-functions and electrical-characteristics tables. Design pull-up arrangements for open-drain usage and avoid exceeding port voltage limits when connected to external circuitry. Also account for bus recovery after a master or peripheral holds the clock or data line low.
Use a 16-pin TSSOP land pattern with the correct lead pitch and exposed no-pad geometry specified by the manufacturer package drawing. TSSOP-16 is narrower than many SOIC-16 packages, so verify the PCB library against the PW mechanical drawing rather than reusing a generic SOIC footprint. Pay attention to solder-paste volume, courtyard clearance, and assembly access around adjacent components.
Informações de conformidade
The manufacturer information identifies the PCA9557 family and orderable part but does not state the requested compliance attributes. AEC-Q100 is not applicable to this non-automotive interface-expander order code.
