PCA9557DT - 8-Bit I2C I/O Expander | Texas Instruments
MPN: PCA9557DT ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0 | $0.00 |
| 10 | $0 | $0.00 |
| 100 | $0 | $0.00 |
| 500 | $0 | $0.00 |
| 1,000 | $0 | $0.00 |
PCA9557DT Overview
An I/O expander is an interface IC that translates serial commands from an I2C or SMBus controller into parallel digital inputs or outputs. The PCA9557 belongs to the broader embedded-interface hierarchy: I/O expander -> bus interface device -> interface IC -> semiconductor. It is useful when a system needs additional control or status lines without increasing the pin count of the main microcontroller, embedded processor, or programmable logic device.
Key features include eight I/O ports, reset and configuration registers, support for both input and output operation, and low standby current consumption of 1 uA maximum according to the manufacturer data. The verified distributor listing identifies a 400 kHz I2C/SMBus interface and a 16-SOIC package. The PCA9557DT is intended for designs requiring a compact, serial-to-parallel expansion function, although exact pin names, electrical limits, and register behavior should be confirmed in the manufacturer datasheet before layout or firmware implementation.
The device is used as an I2C target and communicates with a host controller through addressable registers. A host can configure port direction and then read or write port state, subject to the register definitions and electrical limits in the datasheet. Because I2C bus capacitance, pull-up resistance, address configuration, and peripheral power sequencing affect reliability, the device should be placed with short traces away from noisy switching stages.
Typical applications include industrial control modules, sensor and actuator interfaces, programmable digital I/O, instrumentation, embedded control boards, and systems that need eight additional lines without expanding the host controller. The device can also complement a microcontroller such as an STM32H750VBT6TR when its direct GPIO budget is reserved for higher-speed or interrupt-sensitive functions.
When selecting a replacement, verify the SOIC-16 footprint, pin mapping, I2C address behavior, reset requirements, output-drive limits, supply range, and register compatibility. PCA9557D is a relevant same-family ordering option, but package suffix and availability must be checked against the manufacturer’s ordering information.
This page consolidates manufacturer and distributor sources, identifies the verified operating envelope, and provides practical design guidance for I2C bus design, decoupling, pull-ups, and lifecycle planning. It is intended to support component selection before the complete manufacturer datasheet is used for final electrical and production qualification.
Drop-in alternatives for PCA9557DT — 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 PCA9557DT (same form factor and footprint) — differing in Interface, Package.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PCA9557D
✅ Drop-In✓ In Stock
$0.71 / Unit
View Datasheet →PCA9557DT Specifications
| Device Type | 8-bit I2C/SMBus low-power I/O expander |
| Number of I/O Ports | 8 |
| Operating Supply Voltage Range | 2.3 V to 5.5 V |
| I2C/SMBus Clock Frequency | 400 kHz |
| Standby Current Consumption | 1 uA maximum |
| Interface | I2C and SMBus |
| Output Type | Open-drain and push-pull |
| Output Source Current | 10 mA |
| Output Sink Current | 25 mA |
| Reset Function | Reset register and reset input functionality |
| Configuration Function | Configuration register |
| Interrupt Output | No interrupt output |
| Programmability | Not verified |
| Operating Temperature | -40 C to +85 C |
| Package | 16-SOIC |
| Package Width | 3.90 mm |
| Mounting Type | Surface mount |
| Lifecycle Status | Obsolete according to Digi-Electronics listing |
PCA9557DT 3.90 mm Pin Configuration Guide
Pin configuration for PCA9557DT (3.90 mm 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 PCA9557DT.
Refer to the datasheet for full pin configuration.
Typical Applications
PCA9557DT is suitable for 6 applications: STM32 Embedded I/O Expansion, Industrial Digital Control Module, Sensor and Actuator Interface, Programmable Logic Control Panel, Battery-Powered Instrumentation, Networked Embedded Control.
STM32 Embedded I/O Expansion
The PCA9557DT fits an STM32-based controller that needs eight additional digital lines while conserving host GPIO resources. Its 8-bit I/O organization, 2.3 V to 5.5 V supply range, and 400 kHz I2C/SMBus interface allow the MCU to configure input or output behavior through the register interface. The STM32H750VBT6TR is a suitable host-class companion when its supply levels, I2C peripheral, and firmware support match the board requirements. Keep the expansion bus away from high-current switching paths and validate the PCA9557DT pin-level limits from the manufacturer datasheet.
Recommended
Industrial Digital Control Module
The PCA9557DT is suitable for industrial control boards that need a compact serial-to-parallel interface for relays, indicators, interlocks, or discrete control inputs. The 8-bit I/O port count and configurable direction support reduce the number of host-controller pins needed for simple digital functions. Its 400 kHz bus capability is appropriate for low- and moderate-speed supervisory control, while the 2.3 V to 5.5 V operating range supports common embedded supply levels. Production designs must verify output current limits, logic thresholds, isolation needs, and any required industrial qualification from the manufacturer documentation.
Recommended
Sensor and Actuator Interface
The PCA9557DT can act as the digital companion to analog sensors and actuator-control circuits in a measurement system. Host firmware can use the configurable ports to read discrete status signals, select measurement paths, or enable low-power actuator stages. The I2C interface keeps the parallel wiring concentrated around one serial bus, while the 8-bit port provides a practical grouping for control signals. Because the verified data does not include every input threshold, output-drive curve, or timing parameter, the final design should use the manufacturer datasheet and validate signal levels under worst-case loading.
Recommended
Programmable Logic Control Panel
The PCA9557DT is useful in programmable logic control panels where a serial bus must drive multiple panel functions. The eight configurable I/O lines can represent switches, status LEDs, enable controls, or discrete machine inputs, allowing the controller to focus on sequencing and safety logic. Its 400 kHz maximum I2C/SMBus clock supports deterministic periodic updates, while the low 1 uA maximum standby specification helps when the panel is intermittently powered. Use appropriate current limiting, flyback protection, and isolation for inductive or externally exposed loads.
Recommended
Battery-Powered Instrumentation
The PCA9557DT is a candidate for low-power instrumentation because the verified data specifies a maximum standby current of 1 uA. An instrument controller can power the expander during normal operation and place it in a low-power state when measurements are not active, subject to the device’s actual reset and standby conditions in the datasheet. The eight I/O lines are useful for mode selection, front-panel status, sensor enables, and isolated control inputs. The 2.3 V minimum supply allows compatibility with lower-voltage embedded systems, but battery current, pull-up leakage, and peripheral leakage must be included in the system power budget.
Recommended
Networked Embedded Control
The PCA9557DT can provide local digital I/O for an embedded controller that also communicates through a network interface. For example, a board may use a W5100 or KSZ8001LI for Ethernet connectivity while using PCA9557DT for local status indicators, resets, mode controls, or discrete sensor lines. This separation reduces host-GPIO pressure and keeps serial communication centralized. The design must account for bus topology, pull-ups, ground continuity, and isolation between network transceivers and sensitive control signals. Use the manufacturer’s electrical limits to confirm whether level shifting or buffering is required.
Recommended
Recommended Products Summary
Engineering reference data for PCA9557DT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCA9557D |
|---|---|---|
| Package | 16-SOIC | 16-SOIC - verified cross-reference package |
| Brand | Texas Instruments | Texas Instruments |
| Device Type | 8-bit I/O expander | 8-bit I/O expander |
| Number of I/O Ports | 8 | 8 |
| Operating Supply Voltage | 2.3 V to 5.5 V | 2.3 V to 5.5 V |
| I2C/SMBus Clock Frequency | 400 kHz | 400 kHz |
Key Differentiators
- Eight configurable parallel I/O lines from one serial interface (vs PCA9557D)
- 2.3 V to 5.5 V operating supply range (vs PCA9557D)
- 400 kHz I2C/SMBus interface (vs PCA9557D)
- No interrupt output (vs PCA9674D)
- Low-power standby specification (vs PCA9557D)
Design Notes
Route the I2C SDA and SCL traces as a short, controlled pair from the host controller to PCA9557DT. Place the required pull-ups at the appropriate electrical location, normally near the bus master or the point identified by the system’s bus-design rules. Keep the route away from switching nodes and high-current return paths. Because the supplied data does not specify a complete pull-up calculation, use the manufacturer timing parameters and measured bus capacitance before selecting resistor values.
Provide local supply decoupling close to the PCA9557DT and confirm that the host controller, pull-ups, and attached peripherals do not exceed the device’s allowable voltage and current conditions. The verified operating range is 2.3 V to 5.5 V, while active current and detailed absolute-maximum limits are not included in the supplied data. Validate power-up, power-down, reset, and bus idle behavior across the complete system state sequence before production release.
Do not assume that a 16-SOIC package alone proves drop-in compatibility. Confirm exact pin names, port-direction behavior, address selection, reset polarity and timing, register map, output-drive limits, and lifecycle status in the manufacturer datasheet. PCA9557D is the only verified alternative candidate in the supplied data, and PCA9674D is not approved as a drop-in replacement because equivalent pin and register behavior was not established.
The verified distributor data reports an obsolete status for PCA9557DT, while other listings show different inventory or quote states. Treat stock claims as time-sensitive and confirm authorized sourcing, date code, suffix, and traceability. For new production designs, select a manufacturer-supported lifecycle option or obtain written change-control approval before committing the obsolete part to a long-life BOM.
Compliance Information
The supplied manufacturer and distributor snippets do not state RoHS, REACH, AEC-Q100, lead-free, halogen-free, or conflict-minerals status. Do not infer compliance from the package or application.