PCA9538PW/Q900,118 - 8-bit I2C GPIO Expander 400kHz | NXP
MPN: PCA9538PW/Q900,118 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.35 | $1.35 |
| 10 | $1.21 | $12.10 |
| 100 | $1.05 | $105.00 |
| 500 | $0.92 | $460.00 |
| 1,000 | $0.81 | $810.00 |
PCA9538PW/Q900,118 Overview
An I/O expander is an interface IC that adds general-purpose input/output pins to a microcontroller or chipset over a serial bus such as I2C or SMBus. In the system hierarchy, it sits between the serial bus master (MCU, CPU, or chipset) and the discrete peripherals it controls, letting designers add push-buttons, sensors, LEDs, and power switches without consuming scarce MCU GPIO pins.
Key features include 8 quasi-bidirectional GPIOs with configurable input/output direction via an 8-bit Configuration register, an active-low open-drain INT output that alerts the host to input changes, and an active-low RESET input that restores the power-up default state without a bus cycle. Four hardware address pins (supporting the PCA9538's address scheme) allow multiple expanders on one bus, and registers cover Input Port, Output Port, Polarity Inversion, and Configuration functions.
Technically, the PCA9538 is a CMOS device using a simple register-file architecture addressed over the 7-bit I2C protocol. The open-drain interrupt output requires an external pull-up resistor, and the RESET input permits recovery from bus lock-up conditions - valuable in automotive and industrial environments where electrical noise can corrupt serial communication.
Typical applications include ACPI power-switch control in servers and notebooks, push-button and key switches, sensor status monitoring, LED and relay control, and fan/thermal monitoring in automotive body electronics and industrial control panels.
Design consideration: keep the total bus capacitance below 400 pF to sustain 400 kHz Fast-mode operation, and always fit pull-up resistors on SDA, SCL, and INT; a typical value of 4.7 kilohm at 3.3 V balances speed and power.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for PCA9538PW/Q900,118 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
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PCA9538PW,118
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PCA9538PW
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View Datasheet →TCA9538PW
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PCA9538PW/Q900,118 Specifications
| Function | 8-bit I2C-bus/SMBus I/O expander with interrupt and reset |
| Number of GPIOs | 8 |
| Interface | I2C, SMBus |
| Maximum Bus Frequency | 400 kHz (Fast-mode) |
| Supply Voltage Range | 2.3 V to 5.5 V |
| Interrupt Output | Yes (open-drain, active low) |
| Reset Input | Yes (active low) |
| Registers | Input Port, Output Port, Polarity Inversion, Configuration |
| Technology | CMOS |
| Operating Temperature | -40C to +85C |
| Package | TSSOP-16 (PW) |
| Mounting Type | Surface Mount |
| Grade | Automotive (Q900) |
| Packaging | Tape & Reel |
| RoHS Status | Compliant |
PCA9538PW/Q900,118 Pin Configuration
| Pin 1 | A0 — Address input 0 |
| Pin 2 | A1 — Address input 1 |
| Pin 3 | A2 — Address input 2 |
| Pin 4 | IO0 — Quasi-bidirectional I/O 0 |
| Pin 5 | IO1 — Quasi-bidirectional I/O 1 |
| Pin 6 | IO2 — Quasi-bidirectional I/O 2 |
| Pin 7 | IO3 — Quasi-bidirectional I/O 3 |
| Pin 8 | VSS — Ground |
| Pin 9 | IO4 — Quasi-bidirectional I/O 4 |
| Pin 10 | IO5 — Quasi-bidirectional I/O 5 |
| Pin 11 | IO6 — Quasi-bidirectional I/O 6 |
| Pin 12 | IO7 — Quasi-bidirectional I/O 7 |
| Pin 13 | INT — Interrupt output (open-drain, active low) |
| Pin 14 | RESET — Active-low reset input |
| Pin 15 | SCL — Serial clock line |
| Pin 16 | VDD — Supply voltage, 2.3 V to 5.5 V |
Typical Applications
PCA9538PW/Q900,118 is suitable for 6 applications: ACPI Power Switch Control, Push-Button and Key Switch Monitoring, Automotive Body Electronics, LED and Indicator Control, Sensor and Fault Status Monitoring, Fan and Thermal Zone Control.
ACPI Power Switch Control
In servers, notebooks, and set-top boxes, the PCA9538PW/Q900,118 lets a baseboard controller switch ACPI power states, drives, and peripherals without dedicating MCU GPIOs. The 8 quasi-bidirectional pins drive power-switch enables over the 400 kHz I2C bus, while the open-drain INT output alerts the host the moment a switch or status line changes, enabling event-driven power management instead of polling. The active-low RESET input allows full register recovery after a bus fault without host intervention - a key reliability feature in always-on systems. Place the device near the switches it controls and fit 4.7 kilohm pull-ups on SDA, SCL, and INT; with its 2.3 V to 5.5 V supply it interfaces directly to 3.3 V chipset logic with no level translation.
Recommended
Push-Button and Key Switch Monitoring
Human-machine interfaces often need more button inputs than a microcontroller provides. The PCA9538PW/Q900,118 expands the host with 8 input-configurable GPIOs; the configuration register sets each pin as input, and the INT output (open-drain, active low) signals the host immediately on any state change, so firmware can service key presses without continuous bus polling. The polarity inversion register lets active-low switch wiring be presented as active-high data in software, simplifying firmware logic. Because each input change re-asserts INT only after the Input Port register is read, debouncing can be handled in host software with a simple timer. Supply the expander from the 3.3 V rail; its CMOS inputs tolerate direct switch-to-ground connection with the internal-pull configuration described in the NXP datasheet typical application circuits.
Recommended
Automotive Body Electronics
The /Q900,118 automotive quality flow makes this part suitable for body-control modules controlling door switches, seat sensors, illumination status lines, and accessory enables. Operating from -40C to +85C, it tolerates cabin and engine-bay-adjacent environments, and the RESET pin gives a deterministic recovery path if electrical transients corrupt the I2C bus state - a documented requirement in noisy 12 V automotive harnesses. The 2.3 V to 5.5 V supply supports 3.3 V and 5 V module architectures alike. Designers should route SDA/SCL away from inductive load wiring and consider bus buffers when the expander sits far from the body controller. According to NXP, the PCA9538 family was developed to enhance its I2C I/O expander line specifically for such distributed control applications.
Recommended
LED and Indicator Control
Status LEDs, backlight enables, and alarm indicators can be driven from the PCA9538PW/Q900,118's output-configurable pins, each settable independently through the Output Port register over the 400 kHz I2C bus. CMOS push-pull outputs sink and source sufficient current for LED drive through an appropriate series resistor per the datasheet output characteristics, and all 8 bits update in a single two-byte bus write, giving simultaneously updated indicator states. The configuration register allows bits to be repurposed dynamically - for example, switching a status pin to input for a fault-feedback line - without any hardware change. In instrument panels and rack equipment, this consolidates indicator control into one small TSSOP-16 footprint, reducing MCU pin count and PCB routing complexity while keeping firmware simple through the flat register map.
Recommended
Sensor and Fault Status Monitoring
Distributed systems frequently need to aggregate presence detectors, thermal-flag outputs, door-interlock switches, and power-good signals into one monitor point. The PCA9538PW/Q900,118 reads all 8 status lines in a single Input Port register read over I2C at up to 400 kHz, while the INT output eliminates the need for periodic polling: it asserts on any input transition and remains asserted until the host reads the register, so no event is missed even with a slow host loop. The polarity inversion register normalizes mixed active-high/active-low sensor outputs into a consistent software convention. With 2.3 V to 5.5 V operation, the device matches 3.3 V logic sensors directly. This architecture suits telecom shelves, industrial cabinets, and test racks where wiring many discrete lines to the main controller would be impractical.
Recommended
Fan and Thermal Zone Control
Server and industrial cooling subsystems use the PCA9538PW/Q900,118 to drive fan-enable lines and fan-fault/tach-input multiplexer selects while reading thermal-alert flags from remote sensors. The 8 GPIOs split between outputs (fan enables, speed-select straps) and inputs (tach or fault flags) exactly as the configuration register dictates, and INT lets a fan failure interrupt the host instantly rather than waiting for the next polling cycle - critical where thermal time constants are short. The RESET pin provides a defined recovery state (all inputs) after a bus upset so fans fall back to a safe default. Placed on the same I2C segment as temperature sensors, it consolidates the whole thermal-management interface into two bus wires, simplifying backplane cabling and hot-swap serviceability in rack-level designs.
Recommended
Recommended Products Summary
Engineering reference data for PCA9538PW/Q900,118 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCA9538PW,118 | PCA9538PW | TCA9538PW | PCA9538D,118 |
|---|---|---|---|---|---|
| Package | TSSOP-16 (PW) | TSSOP-16 (PW) - same | TSSOP-16 (PW) - same | TSSOP-16 (PW) - same | SOIC-16 (different footprint) |
| Brand | NXP Semiconductors | NXP Semiconductors | Texas Instruments | Texas Instruments | NXP Semiconductors |
| Supply Voltage Range | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 2.3 V to 5.5 V | 1.65 V to 5.5 V | 2.3 V to 5.5 V |
| I2C Bus Speed | 100 kHz / 400 kHz | 100 kHz / 400 kHz | 100 kHz / 400 kHz | 100 kHz / 400 kHz | 100 kHz / 400 kHz |
| Interrupt Output | Yes (open-drain, active low) | Yes | Yes | Yes | Yes |
| Reset Input | Yes (active low) | Yes | Yes | Yes | Yes |
| Operating Temperature | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +85C | -40C to +85C |
Key Differentiators
- Automotive /Q900 quality flow with full documentation support (vs PCA9538PW,118)
- Integrated RESET pin for lock-up recovery (vs TCA9538PW)
- Footprint reuse across grades and brands (vs PCA9538PW)
Design Notes
Fit external pull-up resistors on SDA, SCL, and INT. A 4.7 kilohm to 10 kilohm pull-up to VDD is typical at 3.3 V; use the lower end for 400 kHz Fast-mode operation or heavily loaded buses. RESET should also have a pull-up (10 kilohm) or be driven actively by the host so the expander cannot float into reset during power sequencing. Place 100 nF ceramic decoupling directly at the VDD/VSS pins.
After power-up, all I/Os default to inputs - outputs used for critical enables (fan or power switches) will stay high-impedance until the host writes the Configuration register. Design any safety-critical load with an external pull-down or pull-up to a defined safe state. Remember that INT is de-asserted only by reading the Input Port register; a host that never reads will see INT stuck low. Use RESET as a recovery path if the I2C state machine ever locks up.
Keep total I2C bus capacitance within the Fast-mode limit (400 pF) to sustain 400 kHz; long backplane runs may need bus buffers or an I2C multiplexer such as the PCA9548A to segment the bus. Route SDA/SCL away from inductive automotive load wiring and motor drives. In noisy environments, slowing the bus to 100 kHz significantly improves noise margin at negligible system cost for an expander device.
Compliance Information
The ,118 suffix denotes NXP RoHS/lead-free reflow-compatible finish. The /Q900 suffix denotes NXP automotive quality flow. Formal REACH, AEC-Q100, halogen-free, and conflict-minerals statements should be obtained from NXP compliance documentation.
