PCA8574D - 8-Bit I2C I/O Expander 400kHz SO16 | NXP
N.º de pieza: PCA8574D ✗ Fin de vida| Cant. | Precio unitario | Total |
|---|---|---|
| 1 | $1.25 | $1,25 |
| 10 | $1.13 | $11,30 |
| 100 | $0.98 | $98,00 |
| 500 | $0.86 | $430,00 |
| 1.000 | $0.74 | $740,00 |
PCA8574D Descripción general
An I/O expander is a peripheral IC that increases the number of general-purpose input/output pins available to a microcontroller over a serial bus. In the power-management and interface hierarchy, the PCA8574D sits between the host MCU and external loads or switches: it belongs to the I2C GPIO expander family, which itself is part of the broader interface IC and remote peripheral category. Expanders save PCB traces, connector pins, and MCU pin budgets in pin-constrained designs.
Key features include quasi-bidirectional I/O ports that can be independently assigned as inputs or outputs without a direction register, a latched interrupt output (INT) that flags any input change, totem-pole output capability via the open-drain INT pin, and direct LED driving with 25 mA sink capability per the datasheet family description. The three hardware address pins allow eight PCA8574 devices, or eight each of PCA8574 and PCA8574A, on the same I2C bus - up to 128 I/Os total.
Architecturally, the PCA8574D uses a simple register-less command structure: the last written byte defines the port state, and a read returns port pin levels. Power-on reset initializes all ports high (quasi-bidirectional input mode), enabling simple push-button and key-matrix reads without software initialization.
Typical applications include keypads and push-button interfaces, LED and backplane status indication, LCD bias and control lines in instrumentation, system monitoring for chassis and rack cards, and spare-I/O expansion in industrial controllers.
Design tip: because quasi-bidirectional outputs source only a weak current (100 uA class), drive LEDs and relays by sinking current, and add pull-ups where input levels must be defined.
Note: NXP lists the PCA8574D as End of Life. This page adds drop-in replacements, pricing tiers, and design notes beyond the manufacturer datasheet.
Alternativas directas para PCA8574D — mismo encapsulado, compatible pin a pin. Se excluyen las piezas de otro encapsulado que requieren retrabajo de la PCB.
Variantes de esta serie
Modelos de la misma serie compatibles directamente con PCA8574D (mismo factor de forma y huella) — difiere en Interrupt Output, Function, Package, RoHS Status, Supply Voltage Range.
Herramienta de comparación rápida — seleccione piezas alternativas para compararlas lado a lado:
PCA8574AD
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
PCF8574T
✅ Sustitución directa✓ En stock
$0.61 / unidad
Ver hoja de datos →PCF8574AT/3,518
✅ Sustitución directa✓ En stock
$0.74 / unidad
Ver hoja de datos →TCA9554DWR
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
PCF8574DW
✅ Sustitución directa📋 Alternativa de referencia (no en el catálogo)
PCA8574D Especificaciones
| Función | Remote 8-bit I/O expander for I2C-bus with interrupt |
| Number of I/O Ports | 8 quasi-bidirectional |
| Interfaz | I2C-bus (SCL, SDA) |
| I2C Bus Speed | 400 kHz |
| Supply Voltage Range | 2.3 V to 5.5 V |
| Hardware Address Pins | 3 (A0, A1, A2) - 8 addresses |
| Interrupt Output | Yes, open-drain INT with latched flag |
| Power-on Reset | Yes, ports initialized high (input mode) |
| Encapsulado | SO16 (SOIC-16, SOT109-1) |
| Tipo de montaje | Surface Mount |
| Ordering Suffixes | PCA8574D,512 (Reel 13 inch), PCA8574D,518 (Reel 7 inch) |
| Max Devices per Bus | 8 (PCA8574) or 16 with PCA8574A (128 I/Os total) |
| LED Driving | Direct drive, current-sink mode per family datasheet |
| Estado del ciclo de vida | End of Life (per NXP product page) |
Configuración de pines de PCA8574D
| Pin 1 | A0 — Hardware address input 0 |
| Pin 2 | A1 — Hardware address input 1 |
| Pin 3 | A2 — Hardware address input 2 |
| Pin 4 | P0 — Quasi-bidirectional I/O port 0 |
| Pin 5 | P1 — Quasi-bidirectional I/O port 1 |
| Pin 6 | P2 — Quasi-bidirectional I/O port 2 |
| Pin 7 | P3 — Quasi-bidirectional I/O port 3 |
| Pin 8 | GND — Ground supply |
| Pin 9 | P4 — Quasi-bidirectional I/O port 4 |
| Pin 10 | P5 — Quasi-bidirectional I/O port 5 |
| Pin 11 | P6 — Quasi-bidirectional I/O port 6 |
| Pin 12 | P7 — Quasi-bidirectional I/O port 7 |
| Pin 13 | INT — Interrupt output (open-drain, active-low) |
| Pin 14 | SCL — I2C serial clock input |
| Pin 15 | SDA — I2C serial data input/output |
| Pin 16 | VDD — Supply voltage, 2.3 V to 5.5 V |
Aplicaciones típicas
PCA8574D es adecuado para 6 aplicacións: Keypad and Push-Button Interfaces, LED Status and Backplane Indication, LCD and Display Control Lines, Industrial Chassis and System Monitoring, Automotive and Embedded Controller Spare I/O, IoT Nodes and Sensor Expansion.
Keypad and Push-Button Interfaces
The PCA8574D is a classic keypad scanner expander: on power-up all eight quasi-bidirectional ports initialize high (input mode), so a 4x4 key matrix can be read with zero software initialization - the host simply reads the port byte and detects pulled-low key closures. The latched open-drain INT output lets the MCU sleep or run other tasks and only service the I2C bus when any key changes state, eliminating continuous polling at 400 kHz bus speeds. Operating from 2.3 V to 5.5 V, the same design serves both 3.3 V and 5 V MCU platforms. Since the ports source only weak current, wire matrix rows as outputs sinking column pull-ups. In EOL transition, the TCA9554DWR keeps the identical SOIC-16 footprint and interrupt behavior.
Recomendado
LED Status and Backplane Indication
Eight quasi-bidirectional ports driving LEDs in current-sink mode give an MCU 8 status indicators (or 64 with eight addressed devices on one bus) for the cost of two I2C lines. The NXP datasheet family description highlights direct LED driving capability; LEDs plus series resistors connect from VDD to the port pins, so the port sinks LED current - far exceeding its weak 100 uA-class source capability. The 400 kHz fast-mode interface allows full 8-bit pattern updates in a single byte write within tens of microseconds, supporting animated or multiplexed indication on industrial backplanes and rack cards. With three address pins, multiple PCA8574D devices coexist for per-card identification. The open-drain INT pin is simply left unused in output-only designs.
Recomendado
LCD and Display Control Lines
Character LCD modules in 4-bit mode need six to seven control/data lines; the PCA8574D supplies them over I2C, which is exactly the topology used in common I2C LCD backpack designs built on this expander family. The host writes register-less single bytes toggling RS, E, and D4-D7, and the 400 kHz interface keeps refresh fast enough for menu-driven UIs. The 2.3 V to 5.5 V supply range matches both 3.3 V logic hosts and 5 V LCD modules when the expander is powered at the LCD rail. Quasi-bidirectional ports are ideal because the LCD is write-mostly; the weak source current is irrelevant for CMOS inputs. Designers migrating from EOL PCA8574D stock can drop in the pin-compatible PCF8574T at the cost of 100 kHz bus speed, which barely affects LCD throughput.
Recomendado
Industrial Chassis and System Monitoring
Rack, chassis, and blade systems must monitor dozens of discrete signals - fan-fail flags, door interlocks, PSU status, hot-swap present pins - that do not justify a dedicated MCU pin each. The PCA8574D aggregates eight such inputs per device; the latched INT output alerts the management MCU only when any input changes, so slow monitor loops over I2C at 400 kHz impose negligible bus load. Three address pins allow eight devices (64 monitored points) or sixteen with PCA8574A siblings (128 points) on one bus. The 2.3 V to 5.5 V operating range matches standard 3.3 V management rails. Note that open-drain INT requires a pull-up and shared-INT designs should read all devices on any assertion. For new EOL-safe designs, the TCA9554DWR offers identical SOIC-16 monitoring capability.
Recomendado
Automotive and Embedded Controller Spare I/O
Body controllers, gateways, and sensor nodes frequently run out of GPIO late in development; an I2C expander is the lowest-risk rescue because it adds eight ports without MCU or PCB respin beyond a small SO16 footprint. The PCA8574D's register-less architecture means zero driver software beyond raw I2C reads and writes, trivially portable across RTOS and bare-metal codebases. The 2.3 V to 5.5 V range covers 3.3 V and 5 V embedded rails, and the power-on reset state (all high) guarantees safe, high-impedance input behavior during boot before firmware configures the ports - important for relays and actuators that must not glitch. Select pulls so quasi-bidirectional pins define safe levels. Note this generic part is not AEC-Q100 listed; verify qualification per program requirements.
Recomendado
IoT Nodes and Sensor Expansion
Battery-powered and space-constrained IoT nodes use the PCA8574D to add configuration pins, sensor enables, mode jumpers, and status LEDs over the same I2C bus that already connects the sensors - one two-wire bus replaces a bundle of GPIO traces. The expander's static register-less design draws negligible firmware overhead, and ports idle high as inputs after power-on reset, suiting switch and tamper-swap monitoring in security sensors. Combined with the INT output routing to an MCU wake pin, nodes can sleep in deep low-power states and wake only on physical input changes, conserving battery. The SO16 package occupies roughly 10 x 4 mm of board area. For new designs, prefer the pin-compatible TCA9554DWR given PCA8574D EOL status, verifying the lower 1.65 V supply floor as an advantage for 1.8 V nodes.
Recomendado
Resumen de productos recomendados
Datos de referencia de ingeniería para PCA8574D — comparación, orientación de diseño e información de cumplimiento.
Guía de selección
Comparación con alternativas
| Parámetro | Este producto | PCA8574AD | PCF8574T | PCF8574AT | TCA9554DWR | PCF8574DW |
|---|---|---|---|---|---|---|
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) - same | SO16 (SOIC-16) - same | SO16 (SOIC-16) - same | SOIC-16 - same | SOIC-16 - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | Texas Instruments | Texas Instruments |
| I2C Bus Speed | 400 kHz | 400 kHz | 100 kHz | 100 kHz | 400 kHz | 100 kHz |
| Supply Voltage Range | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.5 V to 6 V | 2.5 V to 6 V | 1.65 V to 5.5 V | 2.5 V to 6 V |
| I/O Ports | 8 quasi-bidirectional | 8 quasi-bidirectional | 8 quasi-bidirectional | 8 quasi-bidirectional | 8 (configurable direction registers) | 8 quasi-bidirectional |
| Fixed I2C Address Bits | PCA8574 base address | PCA8574A base address (A-version) | PCF8574 base address | PCF8574A base address | TCA9554 base address | PCF8574 base address |
| Interrupt Output | Yes, open-drain active-low INT | Yes | Yes | Yes | Yes | Yes |
Diferenciadores clave
- 400 kHz fast-mode I2C vs 100 kHz predecessors (frente a PCF8574T)
- Register-less quasi-bidirectional architecture (frente a TCA9554DWR)
- Companion A-version doubles bus capacity (frente a PCA8574AD)
Notas de diseño
Place 100 nF ceramic decoupling directly across VDD (pin 16) and GND (pin 8) of the SO16 package. SCL, SDA, and INT are all open-drain and require pull-up resistors to VDD: approximately 4.7 kiloohm for 100 kHz operation or approximately 2.2 kiloohm at the 400 kHz fast-mode rate, adjusted for total bus capacitance. Keep the I2C stub to the expander short on multi-drop buses. Follow the NXP I2C-bus specification guidelines for mixed-speed bus design when combining PCA8574 (400 kHz) and PCF8574 (100 kHz) devices.
The quasi-bidirectional ports source only a weak current (100 uA class) but sink much more, so always design LED, relay, and transistor loads as current-sink (load from VDD to pin). Second, the power-on reset forces all ports high - do not connect active-low-critical loads that would glitch at boot. Third, address pins A0-A2 must be tied, never left floating. Finally, note the fixed I2C address differs between PCA8574 and PCA8574A, and again for PCF8574 and TCA9554 families - verify the address table when substituting EOL parts.
The latched INT output asserts low on any input change and holds until the host reads the ports - on multi-device buses wire-OR all INT lines to one MCU pin with a single pull-up, then read each expander in turn to identify and clear the source. Because inputs have no internal hysteresis specified, add RC filtering or debounce in firmware for mechanical switches on long cables. On 400 kHz buses with several expanders and cable capacitance, verify rise times meet the I2C fast-mode specification with the chosen pull-up value.
Estimated: quiescent supply current for this family is on the order of a few microamperes to tens of microamperes typical (consult the datasheet current table for exact values at your VDD and temperature), making the PCA8574D suitable for battery nodes - but LED sink current dominates the budget: 8 LEDs at 5 mA each equals 40 mA through the part and its VDD rail. Size the decoupling and local trace width for the sum of all sink currents, and check the package power rating if driving multiple high-current LEDs continuously.
Información de cumplimiento
NXP product page lists an Environmental Quality section for PCA8574D but specific RoHS/REACH values were not present in the retrieved data; consult the NXP part page for certificates. The ,512 and ,518 suffixes denote lead-free finish per NXP ordering convention, but this was not explicitly confirmed in the provided data.
