PCF8574PW - 8-bit I2C I/O Expander 20-TSSOP | Texas Instruments (Tape & Reel)
MPN： PCF8574PW ✓ 啟用中PCF8574PW 概覽
An I/O expander is a type of interface IC that sits between a host controller (typically a microcontroller with limited GPIO) and external peripherals, translating a serial bus into multiple parallel digital lines. The PCF8574 belongs to the I2C I/O expander family -> interface IC -> integrated circuit -> semiconductor. By cascading multiple devices, designers can scale I/O count without redesigning the host board, making I/O expanders essential in space-constrained and pin-limited embedded designs.
Key features include 8 quasi-bidirectional I/O pins, 100 kHz I2C clock rate, three hardware address pins (A0-A2) allowing up to 8 devices on the same bus (16 combined with PCF8574A), an active-low interrupt output that wakes the host on input changes, and low standby current of 2.5 uA typical. The PCF8574 uses the I2C address base 0x20 (PCF8574A uses 0x38), supporting up to 16 devices on a single bus for 128 I/Os.
The quasi-bidirectional I/O architecture eliminates the need for a direction control register by using a clever pull-up/pull-down scheme, simplifying firmware. Each I/O can source 25 mA (LED drive capability) and sink up to 25 mA, sufficient to drive LEDs, keypads, or relay coils directly without buffering.
Typical applications include keypad scanning for human-machine interfaces, LED driving for status indicators and display backlights, GPIO expansion for Raspberry Pi or ESP32-based projects, and industrial control panels. The wide 2.5 V to 6 V VCC range allows interfacing with both 3.3 V and 5 V logic without level shifters.
When designing with this device, note that quasi-bidirectional I/Os are weak when transitioning to high - add an external pull-up resistor (typically 10 kohm) if driving heavy capacitive loads. The INT pin must be acknowledged by the host to clear the interrupt condition.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone.
直接替換替代品，適用於 PCF8574PW — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
此系列的變體
與下列產品可直接替換的同系列型號： PCF8574PW （相同外形與佔位） — 差異在於 Package, Interface, Supply Voltage Range, Interrupt Output, Device Type.
PCF8574APWR
✅ 直接替換📋 參考替代品（不在目錄中）
PCF8574PWRG4
✅ 直接替換📋 參考替代品（不在目錄中）
PCF8574IPWR
✅ 直接替換📋 參考替代品（不在目錄中）
PCA9534PW
✅ 直接替換聯絡詢價
查看資料表 →PCA9670PW
✅ 直接替換📋 參考替代品（不在目錄中）
PCF8574PW 規格
| 功能 | I/O Expander |
| Number of I/O | 8 |
| 介面 | I2C (SMBus compatible) |
| Clock Frequency (Max) | 100 kHz |
| I2C Address Base | 0x20 (PCF8574A: 0x38) |
| Supply Voltage (VCC) | 2.5 V to 6 V |
| Supply Current (Standby) | 2.5 uA typical |
| Interrupt Output | Yes (active-low INT) |
| Hardware Address Pins | 3 (A0, A1, A2) |
| Max Devices on Bus | 8 (16 combined with PCF8574A) |
| Output Drive (Source/Sink) | 25 mA / 25 mA per I/O |
| I/O Type | Quasi-bidirectional (no direction register) |
| 封裝 | 20-pin TSSOP (PW) |
| 工作溫度 | -40 C to +85 C |
| 安裝類型 | Surface Mount |
| RoHS 狀態 | Compliant |
| MSL 等級 | 1 (unlimited floor life) |
PCF8574PW 腳位配置
| 腳位 1 | INT — Interrupt output (active low) |
| 腳位 2 | A0 — Hardware address bit 0 |
| 腳位 3 | A1 — Hardware address bit 1 |
| 腳位 4 | A2 — Hardware address bit 2 |
| 腳位 5 | P0 — Quasi-bidirectional I/O 0 |
| 腳位 6 | P1 — Quasi-bidirectional I/O 1 |
| 腳位 7 | P2 — Quasi-bidirectional I/O 2 |
| 腳位 8 | P3 — Quasi-bidirectional I/O 3 |
| 腳位 9 | VCC — Supply voltage (2.5 V to 6 V) |
| 腳位 10 | GND — Ground |
| 腳位 11 | P4 — Quasi-bidirectional I/O 4 |
| 腳位 12 | P5 — Quasi-bidirectional I/O 5 |
| 腳位 13 | P6 — Quasi-bidirectional I/O 6 |
| 腳位 14 | P7 — Quasi-bidirectional I/O 7 |
| 腳位 15 | SCL — I2C serial clock |
| 腳位 16 | SDA — I2C serial data |
| 腳位 17 | NC — Not connected (per datasheet) |
| 腳位 18 | NC — Not connected (per datasheet) |
| 腳位 19 | NC — Not connected (per datasheet) |
| 腳位 20 | NC — Not connected (per datasheet) |
典型應用
PCF8574PW 適用於 6 應用s: Raspberry Pi / ESP32 GPIO Expansion, Keypad Matrix Scanning, LED Status Indicators and Display Backlights, Industrial Control Panel I/O, I2C Sensor Hub / Multi-Sensor Aggregation, Arduino / Maker Project I/O Expansion.
Raspberry Pi / ESP32 GPIO Expansion
The PCF8574PW adds 8 general-purpose I/O pins to a Raspberry Pi or ESP32 host via the I2C bus, requiring only 2 wires (SCL/SDA) plus VCC/GND. With 25 mA source/sink per pin, it can directly drive LEDs, relays, or read button matrices without buffer transistors. The I2C base address 0x20 (or 0x38 with the A variant) avoids conflicts with common Pi peripherals. Quasi-bidirectional I/Os simplify firmware - no direction register to set before reads. Active-low INT output lets the host sleep and wake on input changes for battery-powered IoT nodes.
推薦
Keypad Matrix Scanning
The PCF8574PW is widely used for 4x4 or 3x4 matrix keypad scanning in human-machine interface (HMI) panels. The 8 quasi-bidirectional I/Os can be split into 4 row outputs and 4 column inputs, decoding up to 16 keys via scan-and-read cycles. The active-low INT pin signals the host MCU only when a key is pressed, eliminating polling overhead. With 2.5-6 V VCC range, it interfaces directly with both 3.3 V and 5 V MCUs. The 25 mA sink capability allows LED backlit key illumination without driver transistors.
推薦
LED Status Indicators and Display Backlights
Each PCF8574PW I/O can sink up to 25 mA, sufficient to directly drive indicator LEDs without driver transistors. With 8 I/Os, one expander controls 8 LEDs from 2 MCU pins. PWM dimming via software bit-banging allows brightness control. The PCF8574A variant (0x38 address) enables two expanders on one I2C bus for 16 LED control from 2 pins. Quasi-bidirectional architecture means no pull-up resistors are needed for low-side drive, simplifying PCB layout. Used in industrial control panels, appliance status displays, and arcade machine button lighting.
推薦
Industrial Control Panel I/O
The PCF8574PW's 2.5-6 V supply and -40 C to +85 C industrial temperature range suit factory automation control panels, PLC digital I/O modules, and sensor interface boards. The I2C bus allows up to 8 expanders per bus segment (16 with PCF8574A), supporting 64-128 isolated I/O points per I2C line. The active-low interrupt signals fault conditions to the host PLC immediately, critical for safety circuits. With 25 mA sink capability, it directly drives optocouplers and 24 V relay coils via external transistors for industrial-grade isolation.
推薦
I2C Sensor Hub / Multi-Sensor Aggregation
In IoT sensor hubs, the PCF8574PW acts as a low-cost I2C mux-like aggregator, allowing multiple sensors with address conflicts to share one bus through its I/Os as chip-select lines. The 2.5-6 V VCC range supports most digital sensors (BME280, MPU6050, etc.). The INT output wakes the host MCU when an external interrupt sensor (PIR, gas alarm) triggers. With 100 kHz I2C clock, polling latency stays below 10 ms for typical sensor reads. Suitable for smart home gateways, environmental monitors, and wearable health bands.
推薦
Arduino / Maker Project I/O Expansion
The PCF8574PW is a staple in Arduino and ESP8266/ESP32 maker communities, providing 8 extra digital I/Os from 2 analog pins (I2C). It directly drives 8 LEDs, reads 8 buttons, or controls 2 hobby servos (limited by current) without shields. The wide 2.5-6 V range works on both 5 V Arduino Uno and 3.3 V ESP32 boards. Libraries like Wire.h and PCF8574.h simplify I2C communication. Each I/O's 25 mA sink drives common-cathode LED arrays directly. The PCF8574APWR variant (0x38) is popular for multi-expander projects needing more than 8 I/Os.
推薦
推薦產品摘要
工程參考資料，適用於 PCF8574PW — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | PCF8574PW | PCF8574APWR | PCF8574PWG4 | PCA9534PW | PCA9670PW |
|---|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | NXP Semiconductors | NXP Semiconductors |
| Package | 20-TSSOP (PW) | 20-TSSOP (PW) - same | 20-TSSOP (PW) - same | 20-TSSOP (PW) - same | 20-TSSOP (PW) - same | 20-TSSOP (PW) - same |
| Number of I/O | 8 | 8 | 8 | 8 | 8 | 16 (double the I/O) |
| 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 | 2.3 V to 5.5 V | 1.0 V to 5.5 V (wider) |
| I2C Clock Max | 100 kHz | 100 kHz | 100 kHz | 100 kHz | 400 kHz (4x faster) | 1 MHz (10x faster) |
| I2C Base Address | 0x20 | 0x20 | 0x38 (different) | 0x20 | 0x20 | 0x20 |
| I/O Type | Quasi-bidirectional | Quasi-bidirectional | Quasi-bidirectional | Quasi-bidirectional | True bidirectional (direction register) | Quasi-bidirectional |
| Interrupt Output | Yes (active-low INT) | Yes | Yes | Yes | Yes (active-low INT) | Yes (active-low INT) |
主要差異化特點
- Quasi-bidirectional I/O eliminates direction register (對比MCP23017)
- Single-bit I2C addressing (A0-A2) for 8 devices per bus (對比PCA9670PW)
- Wide 2.5 V to 6 V supply supports 5 V and 3.3 V systems (對比PCA9534PW)
- 25 mA per-pin LED drive without external transistors (對比PCA9670PW)
設計說明
Quasi-bidirectional I/Os on the PCF8574PW are weakly pulled high internally and require an external pull-up resistor (typically 10 kohm) when used as inputs - the internal pull-up is only ~100 uA. For capacitive loads (long wires, large LED matrices), add a stronger external pull-up to ensure clean logic-high transitions. When driving LEDs as outputs, ground the cathode to the I/O pin and tie the anode to VCC via the LED's current-limiting resistor.
Place the PCF8574PW's 100 nF decoupling capacitor as close to VCC (pin 9) and GND (pin 10) as possible, using a wide ground trace. For I2C bus integrity in noisy industrial environments, add 4.7 kohm pull-ups on SCL (pin 15) and SDA (pin 16) - lower values (2.2 kohm) work better for bus lengths over 10 cm. Keep the I2C traces short and away from switching power or motor drive traces to minimize EMI coupling.
The INT (interrupt) pin on the PCF8574PW is active-low and must be cleared by reading or writing the I/O ports - it does NOT auto-clear. A common mistake is to read the input state without performing an explicit I2C read transaction, leaving the interrupt stuck asserted. According to the TI datasheet, any I2C access (read or write) clears the interrupt condition. For multi-device buses, ensure only the interrupting device's address is acknowledged, otherwise the interrupt will not clear properly.
The PCF8574PW's I2C lines (SCL/SDA) should never be driven above VCC or below GND - this can latch up the IC. Add series resistors or Schottky diodes to VCC/GND on the I2C lines if the bus might be hot-swapped or connected to a higher-voltage controller. According to TI datasheet absolute maximum ratings, DC voltage on any pin must remain within -0.5 V to VCC+0.5 V. The 2.5 uA typical standby current enables battery-powered designs where the expander can be left always-on.
合規資訊
RoHS compliant per TI product page. Not AEC-Q100 qualified - this is a commercial/industrial grade part. Reach SVHC compliant per EU regulation. MSL Level 1 per JEDEC J-STD-020. Lead-free (Pb-free) reflow-compatible per TI packaging specifications.
