PCF8574T - 8-bit I2C I/O Expander, SOIC-16 | NXP Semiconductors
N.º da peça: PCF8574T ✗ Fim de vida| Qtd. | Preço unitário | Total |
|---|---|---|
| 1 | $1.1 | $1,10 |
| 10 | $0.99 | $9,90 |
| 100 | $0.89 | $89,00 |
| 500 | $0.78 | $390,00 |
| 1.000 | $0.69 | $690,00 |
| 2.500 | $0.61 | $1.525,00 |
PCF8574T Visão geral
What is an I/O expander? An I/O expander is an integrated circuit that adds additional general-purpose input/output pins to a microcontroller through a serial bus (typically I2C or SPI). It sits in the hierarchy: GPIO extender -> I/O expander -> interface IC -> digital semiconductor. The PCF8574T specifically uses a quasi-bidirectional I/O architecture that eliminates the need for a direction control register - each pin can be used as either input or output without explicit mode configuration.
Key features of the PCF8574T include three hardware address pins (A0-A2) that allow up to 8 PCF8574T devices to share the same I2C-bus (selectable I2C addresses 0x20-0x27). The quasi-bidirectional I/O architecture requires no direction register, simplifying software drivers. The open-drain interrupt output (INT) is asserted when any input changes, enabling efficient event-driven polling. The device operates across 2.5V-6V VCC, supports I2C standard-mode (100 kHz) and fast-mode (400 kHz), and consumes very low standby current.
The PCF8574T uses a silicon CMOS process with an open-drain interrupt line and open-drain bidirectional I/O pins. The quasi-bidirectional architecture drives a weak pull-up (current source) when outputs are HIGH and a strong pull-down when LOW, allowing the same pin to be read back without changing direction. The I2C slave address is programmed via A0, A1, A2; slave base address is 0x20 for PCF8574 and 0x38 for PCF8574A - this distinction is critical when selecting between variants.
Typical applications include keypad scanning on human-machine interfaces (HMIs), LED driving on display panels and indicator boards, LCD bias generation, sensor monitoring via additional GPIOs, and adding GPIOs to small microcontrollers. The 0x20-0x27 address range also makes it ideal for multi-bus I/O expansion where multiple expanders must coexist.
When designing with the PCF8574T, add 100 kohm pull-up resistors on SDA and SCL because the PCF8574T uses open-drain drivers (no internal pull-ups). Note that the "T" suffix denotes the SOIC-16 package, while "N" denotes DIP-16 and "BS" denotes SSOP-16 - same silicon die, different packages. The PCF8574 (base address 0x20) and PCF8574A (base address 0x38) are NOT drop-in replaceable without changing the host firmware address.
This page consolidates distributor pricing, parametric equivalents (TI PCA9534, PCA9554, PCA9557), drop-in alternatives in the SOIC-16 footprint, and practical design notes not found in the manufacturer datasheet.
Alternativas drop-in para PCF8574T — 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 PCF8574T (mesmo formato e footprint) — diferindo em Function, Interrupt Output, Package, RoHS Status, Interface.
Ferramenta de comparação rápida — selecione peças alternativas para comparação lado a lado:
PCF8574AT/3,518
✅ Drop-In✓ Em estoque
$0.74 / unidade
Ver ficha técnica →PCA9534PW
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9554PW
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCA9557PW
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
MAX7328AWE+T
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCF8574T Especificações
| Product Type | 8-bit I/O Expander |
| Bus Interface | I2C (Standard 100 kHz, Fast 400 kHz) |
| Supply Voltage (VCC) | 2.5 V to 6 V |
| Number of I/O Pins | 8 (quasi-bidirectional, P0-P7) |
| I2C Address Bits | 3 (A0, A1, A2) |
| Base Address | 0x20 (PCF8574) / 0x38 (PCF8574A) |
| Addressable Devices per Bus | 8 (addresses 0x20-0x27) |
| Interrupt Output | Yes, open-drain INT pin |
| Encapsulamento | SOIC-16 (T suffix) |
| Temperatura de operação | -40C to +85C (industrial) |
| Nível MSL | 1 (unlimited floor life) |
| Status RoHS | Compliant |
| Process Technology | Silicon CMOS |
Configuração de pinos do PCF8574T
| Pino 1 | A0 — I2C slave address bit 0 (hardware) |
| Pino 2 | A1 — I2C slave address bit 1 (hardware) |
| Pino 3 | A2 — I2C slave address bit 2 (hardware) |
| Pino 4 | P0 — Quasi-bidirectional I/O bit 0 |
| Pino 5 | P1 — Quasi-bidirectional I/O bit 1 |
| Pino 6 | P2 — Quasi-bidirectional I/O bit 2 |
| Pino 7 | P3 — Quasi-bidirectional I/O bit 3 |
| Pino 8 | GND — Ground reference |
| Pino 9 | P4 — Quasi-bidirectional I/O bit 4 |
| Pino 10 | P5 — Quasi-bidirectional I/O bit 5 |
| Pino 11 | P6 — Quasi-bidirectional I/O bit 6 |
| Pino 12 | P7 — Quasi-bidirectional I/O bit 7 |
| Pino 13 | INT — Interrupt output (open-drain, active LOW) |
| Pino 14 | SCL — I2C serial clock line (open-drain) |
| Pino 15 | SDA — I2C serial data line (open-drain) |
| Pino 16 | VCC — Supply voltage 2.5V to 6V |
Aplicações típicas
PCF8574T é adequado para 7 aplicaçãos: Keypad Scanning on HMI Panels, LED Status Indicators on Display Panels, LCD Bias Voltage Generation, Industrial Sensor Hub Expansion, IoT and Smart Home Add-on Boards, Server and Storage Maintenance Interfaces, Portable Device GPIO Expansion.
Keypad Scanning on HMI Panels
The PCF8574T's eight quasi-bidirectional I/O pins and 3-bit address hardware make it a classic choice for scanning 4x4 matrix keypads (up to 16 keys) in human-machine interfaces. Place the expander between the host MCU and the keypad, dedicating four pins to row outputs and four pins to column inputs. The INT output wakes the host only when a key is pressed, avoiding constant polling. According to the NXP datasheet, the quasi-bidirectional architecture allows the same pins to drive rows HIGH and read columns back without a direction register.
Recomendado
LED Status Indicators on Display Panels
The PCF8574T's 25 mA sink capability per pin lets it directly drive low-current indicator LEDs and seven-segment displays up to ~16 segments. Place the expander on the host's I2C bus and use its interrupt pin to flag state changes. According to the NXP datasheet, the quasi-bidirectional architecture drives LOW for active LEDs (current flows from VCC through LED to pin). For high-brightness applications, cascade the PCF8574T outputs to a MOSFET driver like the ULN2003 for amplified drive.
Recomendado
LCD Bias Voltage Generation
The PCF8574T's 2.5-6V VCC range and 8-bit I/O match the requirements of character LCD modules that need contrast and bias control. Connect its I/O pins to the LCD's V0 (contrast) and backlight enable lines, then address the bias register via I2C commands from the host. According to the NXP datasheet, the open-drain I/O lines can be used in parallel with a charge-pump for VEE generation. The interrupt pin signals the host when the contrast value is changed externally (rare but supported).
Recomendado
Industrial Sensor Hub Expansion
The PCF8574T adds 8 GPIOs to small microcontrollers (e.g. ATtiny, PIC16) over I2C for interfacing industrial sensors like limit switches, photo eyes, and contact closures. Its 6V tolerant inputs handle industrial 5V logic and 24V signals via external resistor dividers. According to the NXP datasheet, multiple PCF8574T devices (up to 8) on one bus allow up to 64 GPIOs from just two host MCU pins. The interrupt output enables event-driven sensors rather than continuous polling.
Recomendado
IoT and Smart Home Add-on Boards
The PCF8574T powers inexpensive I/O expansion add-on boards for Raspberry Pi, Arduino, and ESP32 designs, providing GPIO for relays, optocouplers, and signal-conditioning front ends. Its low standby current (~2.5 uA typical per NXP datasheet) and small SOIC-16 footprint suit battery-powered smart-home nodes. The 0x20-0x27 address range via A0/A1/A2 lets multiple boards stack on one I2C bus without conflict. Host firmware can use the open-source PCF8574 Arduino library without modification.
Recomendado
Server and Storage Maintenance Interfaces
The PCF8574T serves as a maintenance I/O expander in server and storage backplanes, monitoring hot-swap handles, presence detect, and fault LEDs via the I2C management bus. Its SOIC-16 footprint and I2C interface integrate easily into BMC designs using a single IPMB. According to the NXP datasheet, the interrupt pin aggregates multiple alarm inputs for the BMC to service, reducing CPU wake events. Operating temperature of -40C to +85C tolerates server rack environments.
Recomendado
Portable Device GPIO Expansion
The PCF8574T extends the GPIOs of small low-power MCUs in portable devices like e-readers, wearables, and handheld instruments. Its 2.5V minimum VCC supports single-cell Li-ion operation (3.0-4.2V), and its microamp standby current preserves battery life. According to the NXP datasheet, the interrupt pin wakes the host MCU when a button is pressed, reducing deep-sleep power. Using SOIC-16, the IC occupies less board area than discrete decoder/buffer logic.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para PCF8574T — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | PCF8574AT | PCA9534PW | PCA9554PW | PCA9557PW | MAX7328AWE+T |
|---|---|---|---|---|---|---|
| Package | SOIC-16 (T) | SOIC-16 - same | SOIC-16 - same | SOIC-16 - same | SOIC-16 - same | SOIC-16 (W) - same |
| Brand | NXP Semiconductors | NXP Semiconductors (same-brand) | Texas Instruments (cross-brand) | Texas Instruments (cross-brand) | Texas Instruments (cross-brand) | Analog Devices (cross-brand) |
| I2C Base Address | 0x20 | 0x38 (firmware change required) | 0x20 | 0x20 | 0x18 | 0x5A |
| Supply Voltage (VCC) | 2.5V to 6V | 2.5V to 6V (same) | 2.3V to 5.5V | 2.3V to 5.5V | 2.3V to 5.5V | 2.5V to 5.5V |
| I/O Architecture | Quasi-bidirectional (8-bit) | Quasi-bidirectional (same) | True bidirectional | True bidirectional with polarity inversion | True bidirectional | True bidirectional |
| Interrupt Output | Yes (open-drain INT) | Yes (same) | Yes (open-drain INT) | Yes (open-drain INT) | Yes (open-drain INT) | Yes (open-drain INT) |
| I2C Clock Rate | 100 kHz / 400 kHz | 100 kHz / 400 kHz | 400 kHz (Fast Mode) | 400 kHz (Fast Mode) | 400 kHz (Fast Mode) | 400 kHz (Fast Mode) |
| Lifecycle Status | Obsolete (EOL) | Obsolete (EOL) | Active | Active | Active | Active |
Principais diferenciais
- Quasi-bidirectional I/O eliminates direction register (vs TI PCA9534PW)
- Two identical I2C address variants allow 16 devices per bus (vs TI PCA9554PW (only 0x20 variant))
- Modern replacement with active lifecycle and active I2C (vs TI PCA9554PW)
Notas de projeto
Place 4.7 kohm pull-up resistors on SDA, SCL, and INT within 5 mm of the PCF8574T pins. The I2C bus is open-drain and will not function without pull-ups. For long buses (>50 mm) use 2.2 kohm to combat capacitance, and keep traces short. According to the NXP datasheet, VCC decoupling (100 nF X7R ceramic between pin 16 and pin 8, plus 10 uF bulk) must be within 10 mm of the IC to handle hot-insertion glitches on the management bus.
The most common design error is buying PCF8574AT (base 0x38) when the firmware expects PCF8574T (base 0x20). These are pin-compatible in SOIC-16 but yield an I2C NACK. Always double-check the full part number on the PCBA stencil and reel. Also note: the 'T' suffix denotes SOIC-16, while 'N' is DIP-16 and 'BS' is SSOP-16 - same die, different mechanical packages.
The quasi-bidirectional I/O architecture cannot reliably drive resistive loads above 100 uA when HIGH because the pull-up is intentional-weak. Driving LEDs in HIGH mode fails; instead sink the LED current by writing LOW (LED anode to VCC, cathode to PCF8574T pin, current-limiting resistor in series). For reading switches, write HIGH first to enable input mode, then read back the bit - typically through the same register byte from the last write operation.
Informações de conformidade
PCF8574T is RoHS compliant per NXP product page. Not AEC-Q100 qualified - choose automotive-grade PCF8574T-Q1 or TI PCA9534PW-Q1 for vehicle applications. Part is end-of-life / obsolete per NXP lifecycle notice.
