PCA8574D,512 - 8-Bit I2C I/O Expander 400kHz SOIC-16 | NXP
MPN: PCA8574D,512 ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.98 | $0.98 |
| 10 | $0.88 | $8.80 |
| 100 | $0.76 | $76.00 |
| 500 | $0.65 | $325.00 |
| 1,000 | $0.55 | $550.00 |
PCA8574D,512 Overview
An I2C I/O expander is a type of interface IC that lets a microcontroller control additional digital inputs and outputs through the two-wire serial bus (SCL and SDA), reducing the number of GPIO pins the MCU itself must provide. Within the interface IC hierarchy, the PCA8574 sits alongside I2C multiplexers, port expanders and level translators, and is a direct successor in function to the industry-standard PCF8574.
Key features include eight quasi-bidirectional ports that can be independently assigned as inputs or outputs, a 400 kHz I2C-bus interface, low standby current of approximately 10 uA, an latched outputs architecture with power-on reset, and an open-drain INT output that notifies the host of any input change. The quasi-bidirectional I/O structure allows a pin to be used as input or output without direction-control registers, simplifying firmware.
The three hardware address pins allow up to eight PCA8574 devices (or eight PCA8574A devices with the alternate fixed slave address) on one bus, supporting up to 16 expanders and 128 I/Os, for example 128 LEDs, from a single two-wire bus. Latched outputs directly drive LEDs with high current sink capability.
Typical applications include keypads and switch matrices, LED and indicator driving in white goods and industrial control panels, SPDT relay expansion, sensor monitoring in battery-powered products, and remote I/O expansion in automotive body electronics.
For design, remember the quasi-bidirectional ports sink strongly but source only weakly (approximately 100 uA at VDD = 5V), so use external pull-ups on input lines and drive LEDs in sink mode.
This page synthesizes distributor pricing, verified drop-in alternatives, practical design notes, and EOL lifecycle guidance not found in the manufacturer datasheet alone.
Drop-in alternatives for PCA8574D,512 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
PCA8574AD,512
✅ Drop-In📋 Reference alternative (not in catalog)
PCA8574AD,118
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
PCF8574D,512
✅ Drop-In📋 Reference alternative (not in catalog)
PCF8574DWR
✅ Drop-In📋 Reference alternative (not in catalog)
PCF8574DW
✅ Drop-In📋 Reference alternative (not in catalog)
PCA8574D,512 Specifications
| Product Type | Remote 8-bit I/O expander for I2C-bus with interrupt |
| Number of I/O Lines | 8 quasi-bidirectional (8 input / 8 output capable) |
| Interface | I2C-bus (2-wire, SCL and SDA) |
| I2C Bus Speed | 400 kHz (Fast-mode) |
| Supply Voltage Range | 2.3 V to 5.5 V |
| Hardware Address Pins | 3 (A0, A1, A2) - up to 8 devices per fixed address |
| Interrupt Output | Yes - open-drain, active-low INT |
| Output Type | Quasi-bidirectional, latched, with power-on reset |
| Package | 16-SO (SOIC-16, SOT109-1) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant (ordering code suffix ,512) |
| Compatible Predecessor | PCF8574 (pin-compatible family member) |
| Typical Applications | Keypads, LED driving, relay expansion, remote I/O |
| Max Devices per Bus | 8 (PCA8574) + 8 (PCA8574A) = 16 expanders / 128 I/Os |
| Lifecycle Status | End of Life per NXP product page |
PCA8574D,512 Pin Configuration
| 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 | VSS — 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) |
Typical Applications
PCA8574D,512 is suitable for 6 applications: Keypad and Switch Matrix Interfaces, LED Indicator and Backlight Driving, Relay and Actuator Expansion in Industrial Control, Battery-Powered Sensor Monitoring, Automotive Body Electronics, LCD and Display Module Control.
Keypad and Switch Matrix Interfaces
The PCA8574D,512 is a natural fit for keypad scanning because its eight quasi-bidirectional ports can be dynamically assigned as scan rows or read columns through the 400 kHz I2C bus - no direction registers needed, since writing a 1 to a port releases the pin for reading. The open-drain INT output flags any key-press transition instantly, letting the host MCU sleep between presses instead of polling, which reduces power and CPU load in battery-powered terminals. With three address pins, several expanders extend a matrix to 32 or more keys on a single two-wire bus. The trade-off is that each scan step requires an I2C transaction, so very fast multi-key rollover designs should budget bus time accordingly at 400 kHz.
Recommended
LED Indicator and Backlight Driving
According to the NXP datasheet, the PCA8574/74A ports can sink enough current to drive LEDs directly, and one bus can support up to 16 expanders - 128 LEDs - for indicator panels in white goods, industrial machinery and appliances. Connect each LED from VDD through a current-limiting resistor into the port pin so the port sinks current; the quasi-bidirectional output sources only weakly (hundreds of uA), so sink mode is mandatory. Latched outputs with power-on reset guarantee that indicators start in a known off state after brownouts. The 400 kHz Fast-mode interface refreshes a full 128-LED panel quickly, though the expander has no PWM, so brightness control must be handled externally or by duty-cycled writes.
Recommended
Relay and Actuator Expansion in Industrial Control
Industrial control panels frequently outgrow the GPIO count of the host controller; the PCA8574D,512 adds eight latched outputs per device over just SCL and SDA, so a 2.3V to 5.5V two-wire bus can command relay drivers, contactors and solenoid interfaces across a panel. Latched outputs hold state without host supervision, and the power-on reset defines safe output levels at startup - important for safety interlocks. The three hardware address pins allow eight devices per fixed address and eight more with PCA8574A, so up to 128 actuation points ride one bus. For higher-current loads, pair the expander with ULN-type transistor arrays, since the quasi-bidirectional pins are logic-level outputs, not relay coil drivers.
Recommended
Battery-Powered Sensor Monitoring
In battery-operated products, the PCA8574D,512 monitors door switches, battery-insertion detectors, cover-open sensors and pushbuttons while drawing minimal power from its 2.3V to 5.5V supply. The key advantage is interrupt-driven operation: the open-drain active-low INT output asserts on any input change and is cleared by a single read, so the host MCU can remain in deep sleep and wake only when a sensor changes state, dramatically extending battery life compared with periodic GPIO polling. The I2C bus itself needs only two traces, reducing harness cost in portable devices. Note that input lines should have defined pull-ups, as quasi-bidirectional inputs float weakly high when written as 1.
Recommended
Automotive Body Electronics
Automotive body controllers - seat memory, mirror adjustment, lamp modules - use the PCA8574D family to multiply the limited GPIO of a body MCU across dozens of switches, indicators and relay outputs. The 400 kHz I2C interface keeps diagnostic reads fast on a shared in-vehicle bus segment, and the wide 2.3V to 5.5V supply tolerates the noisy, sagging conditions of a 12V automotive rail after local regulation. Site MPN host controllers such as the SPC5642AF2MLU1 ( PowerPC for body/gateway) provide hardened I2C peripherals suited to driving the expander. For new automotive designs, verify the specific temperature grade and AEC qualification level of the exact ordering code before release.
Recommended
LCD and Display Module Control
Segment-LCD interface boards, small TFT module backplanes and front-panel display assemblies use the PCA8574D,512 to route backlight enables, reset lines, mode jumpers and brightness switch inputs over the I2C bus, freeing the host graphics controller from spending scarce GPIO on housekeeping. The latched, power-on-reset outputs keep the display in a safe state through supply glitches, and the INT pin catches user front-panel button presses without polling. At 400 kHz, configuration writes complete in well under a millisecond, so display mode changes feel instantaneous. Designs needing hardware PWM dimming should add a dedicated backlight driver IC, as the expander outputs are static latches rather than PWM channels.
Recommended
Recommended Products Summary
Engineering reference data for PCA8574D,512 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCA8574AD,512 | PCF8574D,512 | PCF8574DW |
|---|---|---|---|---|
| Package | SOIC-16 (16-SO) | SOIC-16 - same | SOIC-16 - same | SOIC-16 - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | Texas Instruments |
| I/O Lines | 8 quasi-bidirectional | 8 quasi-bidirectional | 8 quasi-bidirectional | 8 quasi-bidirectional |
| I2C Bus Speed | 400 kHz | 400 kHz | 100 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 |
| Interrupt Output | Yes (open-drain, active-low) | Yes (open-drain, active-low) | Yes (open-drain, active-low) | Yes (open-drain, active-low) |
| Fixed I2C Slave Address | PCA8574 base address (0100 binary family) | PCA8574A alternate address (0111 binary family) | PCF8574 base address (0100 binary family) | PCF8574 base address (0100 binary family) |
Key Differentiators
- 4x faster I2C interface (vs PCF8574DW)
- Wider low-voltage supply floor (vs PCF8574D,512)
- Same footprint with alternate slave address (vs PCA8574AD,512)
- Trade-off: EOL lifecycle (vs PCF8574DW)
Design Notes
Place 100 nF decoupling ceramic capacitor directly across VDD (pin 16) and VSS (pin 8), as close to the package as possible. SCL and SDA are open-drain bus lines and require pull-up resistors to VDD - typical values 2.2 kOhm to 4.7 kOhm for 400 kHz Fast-mode operation at 5V; larger values (10 kOhm) reduce bus speed capability below 400 kHz. Keep I2C traces short (under 30 cm) and route away from switching loads such as relay coils to avoid false clock glitches. Per the NXP PCA8574/74A datasheet, bus capacitance limits also apply at Fast-mode.
The quasi-bidirectional ports source only a weak current (order of 100 uA at VDD = 5V per the quasi-bidirectional output characteristic) but sink strongly. A common mistake is source-driving an LED or relay directly from a port high - the load will barely energize. Always drive loads in sink mode (load tied from VDD to the port pin). Also remember that inputs must be written as 1 to release the quasi-bidirectional pin before reading; reading a pin previously written as 0 will always return 0. This behavior trips up engineers migrating from direction-register style expanders.
Because the part is EOL, design-in risk matters: confirm remaining channel stock (about 46,250 pieces reported February 2026) and qualify PCA8574AD,512 or PCF8574DWR as alternate sources on the same footprint before releasing a new PCB revision. Estimated: at VDD = 5V with all 8 ports sinking a 10 mA LED load, package dissipation is roughly 8 x (5 V - V_OL) x 10 mA, well under the SOIC-16 limit - thermal design is rarely a concern for this logic-level expander; bus pull-up current dominates static consumption.
Compliance Information
Ordering code suffix ,512 denotes RoHS-compliant, lead-free SOIC-16 packaging per NXP ordering scheme. The NXP product page lists EOL with environmental quality and discontinuance sections; detailed REACH and conflict-minerals statements are not included in the provided data.
