PCF8574TD - 8-bit I2C I/O Expander, SO-16 | NXP Semiconductors
N.º da peça: PCF8574TD ✓ Ativo| Qtd. | Preço unitário | Total |
|---|---|---|
| 1 | $1.85 | $1,85 |
| 10 | $1.62 | $16,20 |
| 100 | $1.38 | $138,00 |
| 500 | $1.14 | $570,00 |
| 1.000 | $0.96 | $960,00 |
PCF8574TD Visão geral
An I2C I/O expander is a type of interface IC that sits between a microcontroller and peripheral signals, translating serial commands from the I2C bus into parallel GPIO operations. The PCF8574 belongs to the I/O expander sub-category of interface ICs, itself part of the broader power management and inter-chip communication hierarchy. By adding eight extra quasi-bidirectional ports over only two wires, the PCF8574 lets small microcontrollers control keypads, LCDs, LEDs, and relays without sacrificing native pins for other functions.
Key features of the PCF8574TD include a maximum standby current of 10 uA, an open-drain interrupt output (INT) that signals the host when an input changes state, and three hardware address pins (A0-A2) that allow up to eight PCF8574 devices on the same I2C bus (64 I/O lines). The quasi-bidirectional I/O architecture requires no direction-control register: a pin set HIGH is weakly pulled up (~100 uA source), and a pin set LOW is strongly pulled down, simplifying firmware and PCB layout.
The PCF8574 uses a fixed I2C slave address of 0x20-0x27 (set by A2:A0), which distinguishes it from the PCF8574A variant (address range 0x38-0x3F). Both share the same SO-16 footprint, enabling dual-sourcing designs. The silicon CMOS process keeps quiescent current low enough for battery-backed applications.
Typical applications include keypad scanning, LED driving arrays, LCD module backpacks, relay/Opto-coupler interfacing, and general-purpose GPIO expansion on 8051, ARM Cortex-M, ESP32, PIC, AVR, and MSP430 microcontrollers. The interrupt pin eliminates polling overhead in button or switch-matrix designs.
When designing with this device, place a 0.1 uF decoupling capacitor close to VCC and 100 kohm pull-up resistors on SDA, SCL, and INT. Verify your firmware does not read the input port during the I2C ACK bit, as a transient high-current condition can occur on the quasi-bidi pins.
This page synthesizes distributor pricing, drop-in alternatives (same-brand NXP variants and cross-brand TI equivalents), and practical design notes that complement, rather than duplicate, the manufacturer datasheet.
Alternativas drop-in para PCF8574TD — 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 PCF8574TD (mesmo formato e footprint) — diferindo em Package.
Ferramenta de comparação rápida — selecione peças alternativas para comparação lado a lado:
PCF8574T
✅ Drop-In✓ Em estoque
$0.61 / unidade
Ver ficha técnica →PCF8574TS
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCF8574DWR
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCF8574DWRG4
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
PCF8574TD Especificações
| Função | Remote 8-bit I/O expander for I2C-bus |
| Number of I/O | 8 (quasi-bidirectional) |
| Interface | I2C-bus (2-wire, up to 400 kHz) |
| Supply Voltage (VCC) | 2.5 V to 6 V |
| Standby Current | 10 uA maximum |
| I2C Address Range (PCF8574) | 0x20 to 0x27 (3 HW address bits) |
| Interrupt Output (INT) | Yes, open-drain, active-low |
| Maximum Bus Frequency | 400 kHz |
| Output Drive Capability | 25 mA sink per pin (quasi-bidirectional) |
| Temperatura de operação | -40C to +85C (industrial) |
| Encapsulamento | SO-16 (Small Outline, 16-pin) |
| Tipo de montagem | Surface Mount |
| Process Technology | Silicon CMOS |
| Status RoHS | Compliant |
Configuração de pinos do PCF8574TD
| Pino 1 | A0 — Hardware address bit 0 (input) |
| Pino 2 | A1 — Hardware address bit 1 (input) |
| Pino 3 | A2 — Hardware address bit 2 (input) |
| Pino 4 | INT — Interrupt output (open-drain, active LOW) |
| Pino 5 | P0 — Quasi-bidirectional I/O port bit 0 |
| Pino 6 | P1 — Quasi-bidirectional I/O port bit 1 |
| Pino 7 | P2 — Quasi-bidirectional I/O port bit 2 |
| Pino 8 | P3 — Quasi-bidirectional I/O port bit 3 |
| Pino 9 | VSS — Ground (0 V) |
| Pino 10 | P4 — Quasi-bidirectional I/O port bit 4 |
| Pino 11 | P5 — Quasi-bidirectional I/O port bit 5 |
| Pino 12 | P6 — Quasi-bidirectional I/O port bit 6 |
| Pino 13 | P7 — Quasi-bidirectional I/O port bit 7 |
| Pino 14 | SCL — I2C serial clock line (input) |
| Pino 15 | SDA — I2C serial data line (open-drain I/O) |
| Pino 16 | VCC — Supply voltage (2.5 V to 6 V) |
Aplicações típicas
PCF8574TD é adequado para 6 aplicaçãos: I2C Keypad Scanning Interface, LCD Module I2C Backpack, LED Array Driver / Relay Control, General-Purpose GPIO Expansion for MCUs, Sensor Hub Aggregator, Industrial Control Panel I/O.
I2C Keypad Scanning Interface
The PCF8574TD is widely used to scan 4x4 or 3x4 matrix keypads via I2C, offloading the row/column scanning from the host MCU. Its quasi-bidirectional I/O pins can drive keypad columns (weak pull-up) and read rows, while the INT pin generates an interrupt whenever a key is pressed, eliminating polling. With 8 I/O pins and 3 hardware address bits, multiple keypads can share one I2C bus for industrial control panels, security keypads, and access control systems. The 2.5-6 V VCC range suits both 3.3 V and 5 V MCU designs.
Recomendado
LCD Module I2C Backpack
Common HD44780-compatible character LCDs (16x2, 20x4) consume 6-11 GPIO pins, which most small MCUs cannot spare. The PCF8574TD serves as an I2C-to-parallel backpack, presenting the LCD's RS, RW, E, and data lines through its quasi-bidirectional I/O. With only 2 MCU pins (SDA/SCL), designers can drive an LCD plus leave room for sensors. The PCF8574's weak pull-up drive matches the LCD's input requirements perfectly, eliminating the need for additional buffers in 3.3 V or 5 V designs.
Recomendado
LED Array Driver / Relay Control
The PCF8574TD's 25 mA sink capability per pin (quasi-bidirectional mode pulls LOW strongly) makes it suitable for driving LED arrays, optocouplers, and small relays directly when used as open-drain outputs. A single PCF8574TD can control 8 status LEDs, 8 optoisolated inputs, or 8 low-power relays with snubber diodes. In industrial automation panels, multiple PCF8574TDs (up to 8 per I2C bus) provide 64 channels of isolated control from a single MCU I2C port.
Recomendado
General-Purpose GPIO Expansion for MCUs
When a host MCU runs out of GPIO pins - common in ESP8266, ATtiny, or small STM32 designs - the PCF8574TD provides 8 additional quasi-bidirectional I/O pins over I2C. Each pin can be set HIGH (weak pull-up, suitable for inputs) or LOW (strong drive, suitable for outputs) with a single byte write. The 400 kHz I2C maximum clock keeps latency low for time-critical applications. The industrial -40C to +85C temperature grade supports outdoor, automotive, and factory-floor deployments.
Recomendado
Sensor Hub Aggregator
The PCF8574TD can aggregate multiple discrete sensor signals (limit switches, door contacts, PIR motion outputs, float switches) into a single I2C transaction for the host MCU. Its INT pin generates an interrupt on any input change, allowing the host to sleep in low-power mode and wake only when an event occurs - critical for battery-powered IoT sensors. The 10 uA standby current keeps quiescent draw minimal when the I2C bus is idle.
Recomendado
Industrial Control Panel I/O
Factory automation panels and PLC I/O modules use the PCF8574TD to interface 24 V industrial signals (with external resistor dividers or optocouplers) back to a 3.3 V or 5 V controller. Its -40C to +85C industrial temperature grade, robust CMOS design, and proven long-term NXP production support make it a mainstay in industrial designs. Up to 8 PCF8574TDs on a single bus provide 64 isolated I/O channels in DIN-rail mountable controllers.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para PCF8574TD — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | PCF8574T | PCF8574DWR | PCF8574DWRG4 |
|---|---|---|---|---|
| Brand | NXP Semiconductors | NXP Semiconductors | Texas Instruments | Texas Instruments |
| Package | SO-16 | SO-16 (same) | SOIC-16 (DW) - same footprint | SOIC-16 (DW) - same footprint |
| I/O Count | 8 | 8 | 8 | 8 |
| I2C Address Range | 0x20 to 0x27 | 0x20 to 0x27 | 0x20 to 0x27 | 0x20 to 0x27 |
| Supply Voltage | 2.5 V to 6 V | 2.5 V to 6 V | 2.5 V to 6 V | 2.5 V to 6 V |
| Max I2C Clock | 400 kHz | 400 kHz | 400 kHz | 400 kHz |
| Standby Current | 10 uA max | 10 uA max | 10 uA max | 10 uA max |
| Interrupt Pin (INT) | Yes (open-drain) | Yes (open-drain) | Yes (open-drain) | Yes (open-drain) |
Principais diferenciais
- Quasi-bidirectional I/O eliminates direction register (vs TI TCA9554PWR)
- Open-drain INT pin eliminates polling (vs MCP23008)
- Dual-sourced from NXP and TI in SO-16 footprint (vs Single-vendor PCF8574T)
Notas de projeto
Place a 0.1 uF decoupling capacitor as close as physically possible to the VCC pin (pin 16) and ground (pin 9). Add 4.7 kohm to 10 kohm pull-up resistors on SDA (pin 15), SCL (pin 14), and INT (pin 4). The pull-ups are mandatory because all three are open-drain outputs. Keep trace lengths under 50 mm to avoid signal-integrity issues at 400 kHz I2C.
Avoid reading the input port during the I2C ACK bit - the PCF8574's quasi-bidirectional architecture causes a transient high-current spike on pins configured as inputs during the acknowledge pulse. Insert a 1 ms delay after a read transaction, or read twice and discard. This is the single most common firmware bug when migrating from push-pull GPIO expanders like the MCP23008.
When cascading multiple PCF8574 devices on a long I2C bus (>30 cm total), add a 100 ohm series resistor near each SDA/SCL pin and place pull-up resistors at both ends of the bus. For 400 kHz operation, total bus capacitance should stay below 200 pF. If the design exceeds this, switch to the PCA9674 or PCA9675 which support higher bus capacitance.
Informações de conformidade
RoHS compliant per NXP product page. Industrial -40C to +85C temperature grade. AEC-Q100 not applicable - this is a consumer/industrial interface IC, not automotive-qualified. For automotive applications, consider NXP's PCA9674 or other AEC-Q100-qualified expanders.
