PCA9539PW/Q900 - 16-bit I2C GPIO Expander | NXP
MPN: PCA9539PW/Q900 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.62 | $1.62 |
| 10 | $1.46 | $14.60 |
| 100 | $1.21 | $121.00 |
| 500 | $1.02 | $510.00 |
| 1,000 | $0.86 | $860.00 |
PCA9539PW/Q900 Overview
An I/O expander is an interface IC that adds general-purpose input/output pins to a microcontroller or system controller through a serial bus such as I2C or SMBus. In the system hierarchy it sits between the host processor and discrete signals: I/O expander to GPIO controller to interface IC. Expanders are used when pin count on the host MCU is exhausted or when remote, board-edge I/O must be controlled over a two-wire bus, reducing wiring harness complexity.
Key features include 16 GPIO with configuration registers that set each pin individually as input or output, a polarity inversion register that inverts the read value of any pin, an active-LOW interrupt output that flags any input change, and a RESET input that restores the default register state without a power cycle. The 5 V tolerant I/Os allow direct interface with both 3.3 V and 5 V logic domains.
Architecturally, the PCA9539 is a CMOS slave device with six registers (input, output, polarity inversion, and configuration pairs) addressed through four hardware address pins A0 and A1 plus fixed bits, allowing multiple devices on one bus. Compared with the earlier PCA9555, the PCA9539 removes the internal I/O pull-up resistors, greatly reducing standby current when I/Os are held low, and replaces address pin A2 with the RESET input.
Typical applications include automotive body electronics and door modules (the /Q900 variant is targeted at automotive platforms), industrial automation backplanes, keypad scanning, LED and relay control, fan monitoring, and sensor status readout in servers and telecom equipment.
A key design consideration is that, without internal pull-ups, unused or floating inputs should be driven or externally biased to avoid undefined logic levels. The 400 kHz bus speed suits configuration and status polling rather than high-rate data streaming.
This page synthesizes distributor pricing, drop-in alternatives, automotive-grade variant comparison, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for PCA9539PW/Q900 — 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:
PCA9539PW,118
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9539RPW/Q900J
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9539PWRG4
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9539RPW,118
✅ Drop-In📋 Reference alternative (not in catalog)
PCA9539PW/Q900 Specifications
| Function | 16-bit I2C-bus/SMBus I/O expander with interrupt and reset |
| Number of I/O | 16 |
| Interface | I2C, SMBus |
| Maximum Bus Frequency | 400 kHz |
| Supply Voltage Range (PCA9539PW/Q900) | 3.0 V to 5.5 V |
| Supply Voltage Range (standard PCA9539PW) | 2.3 V to 5.5 V |
| I/O Voltage Tolerance | 5 V tolerant I/Os |
| Interrupt Output | Active LOW |
| Reset Input | Active LOW RESET (replaces A2 of PCA9555) |
| Polarity Inversion Register | Yes, per-pin |
| Internal I/O Pull-ups | None (low-power improvement over PCA9555) |
| Technology | CMOS |
| Package | TSSOP24 (SOT361-1) |
| Mounting Type | Surface Mount |
| Automotive Qualification | Q900 variant for automotive applications |
PCA9539PW/Q900 Pin Configuration
| Pin 1 | A0 — Hardware address input 0 |
| Pin 2 | A1 — Hardware address input 1 |
| Pin 3 | RESET — Active LOW reset input (restores default register state) |
| Pin 4 | P00 — Port 0 I/O, bit 0 |
| Pin 5 | P01 — Port 0 I/O, bit 1 |
| Pin 6 | P02 — Port 0 I/O, bit 2 |
| Pin 7 | P03 — Port 0 I/O, bit 3 |
| Pin 8 | P04 — Port 0 I/O, bit 4 |
| Pin 9 | P05 — Port 0 I/O, bit 5 |
| Pin 10 | P06 — Port 0 I/O, bit 6 |
| Pin 11 | P07 — Port 0 I/O, bit 7 |
| Pin 12 | VSS — Ground |
| Pin 13 | P10 — Port 1 I/O, bit 0 |
| Pin 14 | P11 — Port 1 I/O, bit 1 |
| Pin 15 | P12 — Port 1 I/O, bit 2 |
| Pin 16 | P13 — Port 1 I/O, bit 3 |
| Pin 17 | P14 — Port 1 I/O, bit 4 |
| Pin 18 | P15 — Port 1 I/O, bit 5 |
| Pin 19 | P16 — Port 1 I/O, bit 6 |
| Pin 20 | P17 — Port 1 I/O, bit 7 |
| Pin 21 | INT — Active LOW interrupt output (open-drain) |
| Pin 22 | SCL — I2C-bus serial clock input |
| Pin 23 | SDA — I2C-bus serial data I/O |
| Pin 24 | VDD — Supply voltage (3.0 V to 5.5 V for /Q900) |
Typical Applications
PCA9539PW/Q900 is suitable for 6 applications: Automotive Body and Door Modules, Industrial Automation Backplanes, Keypad and Switch Scanning, LED and Relay Control, Server and Telecom Board Monitoring, Sensor and Module Status Readout.
Automotive Body and Door Modules
The /Q900 suffix designates NXP's automotive qualification flow, making the PCA9539PW/Q900 a natural fit for body control modules, door modules, and seat controllers where dozens of switches, latches, and status lines must be monitored from a single low-cost MCU. The 3.0 V to 5.5 V supply range covers automotive logic rails, and 5 V tolerant I/Os interface directly with 12 V-domain signals through simple conditioning. The active-LOW INT output lets the module MCU sleep and wake only on switch events, while RESET provides fault recovery without power cycling. Removal of internal pull-ups cuts standby current when inputs are held low, important for always-on modules with quiescent-current budgets.
Recommended
Industrial Automation Backplanes
In PLC I/O racks and industrial backplanes, the PCA9539PW/Q900 adds 16 status or control lines per device over a two-wire I2C bus, cutting harness complexity versus discrete wiring. With A0 and A1 hardware address pins, multiple expanders share one bus, and the 400 kHz interface comfortably supports configuration and polling traffic. The polarity inversion register simplifies firmware when card-present or fault signals are active-low, and the configuration registers let each pin independently switch between input and output without hardware changes. The 5 V tolerant I/Os bridge legacy 5 V sensor logic to 3.3 V controllers. Typical usage places a 10 k pull-up on SDA/SCL and routes INT to the backplane controller interrupt line.
Recommended
Keypad and Switch Scanning
The PCA9539PW/Q900 scans matrix or discrete keypads efficiently: inputs are configured through the configuration registers, and any key press asserts the active-LOW INT output so the host MCU need not poll the bus continuously. The input-port read latches the state, and the polarity inversion register normalizes active-low switch closures without external inverters. Because the device has no internal pull-ups, designers add external pull-up or pull-down resistors sized for the required noise immunity - a trade-off that also lets keypad current thresholds be tuned per design. In automotive applications such as steering-wheel or climate-control keypads, the Q900 flow and RESET pin for watchdog-driven recovery support functional-safety-oriented designs.
Recommended
LED and Relay Control
Configured as outputs, the 16 GPIO pins drive LEDs, status indicators, and small relays through appropriate buffer transistors. The configuration and output registers allow the host to change pin directions and states independently, enabling shared use of a port bank for both drive and sense functions. The RESET input provides a safe state (all pins as high-impedance inputs) during faults, preventing uncontrolled relay or LED actuation after a bus upset - an important consideration in automotive lighting modules covered by the Q900 flow. Note that drive capability is logic-level only, so external transistors or driver ICs are required for loads beyond a few milliamps; verify sink/source limits in the datasheet before connecting loads directly.
Recommended
Server and Telecom Board Monitoring
In server, storage, and telecom platforms, the PCA9539PW/Q900 monitors fan-fail signals, power-good lines, presence detectors, and hot-swap handles, reporting status to a baseboard controller over I2C. Multiple expanders are addressed via A0/A1, so a single I2C segment covers dozens of monitor points. The INT output aggregates all input changes into one controller interrupt, reducing polling overhead in always-on infrastructure, while RESET allows a management controller to restore known state after firmware recovery. Low standby current (no internal pull-ups) suits dense boards where leakage budgets are tight. Designers should bias unused inputs and follow SMBus timing when sharing the bus with battery-backed management traffic.
Recommended
Sensor and Module Status Readout
Portable and IoT devices use the PCA9539PW/Q900 to read microswitches, cover-open detectors, battery-pack status lines, and peripheral presence pins where MCU pins are scarce. The 3.0 V supply minimum matches 3.3 V battery-powered logic, and CMOS construction keeps quiescent draw low; the interrupted-read pattern (INT to host, then one register read) minimizes bus activity and average system current. The polarity inversion register adapts mixed-polarity sensor outputs without extra logic gates. For space-constrained designs, the TSSOP24 body fits within a few square millimeters of board area. Add external pull-ups on inputs held floating, since the absence of internal pull-ups means un-driven pins would otherwise sit at undefined levels.
Recommended
Recommended Products Summary
Engineering reference data for PCA9539PW/Q900 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | PCA9539PW,118 | PCA9539RPW/Q900J | PCA9539PWRG4 | PCA9539RPW,118 |
|---|---|---|---|---|---|
| Package | TSSOP24 (SOT361-1) | TSSOP24 (SOT361-1) - same | TSSOP24 (SOT361-1) - same | TSSOP-24 - same | TSSOP24 (SOT361-1) - same |
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | Texas Instruments | NXP Semiconductors |
| I/O Count | 16 | 16 | 16 | 16 | 16 |
| Max Bus Frequency | 400 kHz | 400 kHz | 400 kHz | 400 kHz | 400 kHz |
| Automotive Grade | Yes (Q900) | No (standard) | Yes (Q900) | No (standard) | No (standard) |
| Internal I/O Pull-ups | None (low power) | None (low power) | None (low power, R version) | None (low power) | None (low power, R version) |
| RESET Pin | Yes (active LOW, pin 3) | Yes (active LOW, pin 3) | Yes (active LOW, pin 3) | Yes (active LOW, pin 3) | Yes (active LOW, pin 3) |
Key Differentiators
- Automotive Q900 qualification flow (vs PCA9539PW,118)
- Lower power than PCA9555 family (vs PCA9535CPW (PCA9555-class))
- RESET input for fault recovery (vs PCA9535CPW)
Design Notes
The PCA9539 removes the internal I/O pull-ups present on the PCA9555 specifically to reduce power when I/Os are held low. This means any input pin left un-driven floats to an undefined state and can draw excess current or cause spurious INT assertions. Always bias unused or switch-open inputs with external pull-up/pull-down resistors (typically 10 k to 100 k). If migrating a design from PCA9555, confirm external pull-ups were relying on the internal ones.
Estimated: for the /Q900 variant the supply must stay at or above 3.0 V; a design intending 2.5 V operation will work on standard PCA9539PW,118 but is out of specification on this automotive part. Put a 100 nF ceramic decoupling capacitor directly across VDD (pin 24) and VSS (pin 12), plus a bulk 4.7 uF on the I2C segment supply rail to absorb bus switching transients from SDA/SCL pull-up current.
Keep SDA and SCL traces short with pull-up resistors (typically 4.7 k to 10 k at 400 kHz) placed near the bus master. Route INT (pin 21) as an open-drain line with its own pull-up to VDD and keep it away from the SCL trace to avoid coupling interrupt artifacts. Tie RESET (pin 3) either to a supervisor output or a 10 k pull-up with an RC delay - never leave RESET floating, or a power-up glitch may leave registers in an unknown state.
Compliance Information
The /Q900 suffix designates NXP's automotive qualification flow for automotive applications; detailed RoHS/REACH compliance data was not present in the provided web data and must be confirmed on the NXP product page.
