NXP USA Inc. PCA9535HF,118

Summary of PCA9535HF,118 I/O Expander

The NXP PCA9535HF,118 stands out as a versatile 16-bit I/O expander designed for robust integration with I²C and SMBus systems. Housed in the compact 24-terminal HWQFN package (4 x 4 x 0.75 mm), this device targets applications where board space and high-density parallel input/output functionality are essential. By providing additional general-purpose I/O capability, the PCA9535HF,118 facilitates system scalability in applications such as sensor interfacing, ACPI power management, and control of indicators like LEDs or relays, without increasing microcontroller pin counts.

Design and Setup of PCA9535HF,118

The PCA9535HF,118 is architected with two independent 8-bit ports, totaling 16 bits for flexible GPIO expansion. Each port includes dedicated configuration (input/output selection), input, output, and polarity inversion registers, enabling granular control for each pin. Device communication occurs via standard I²C or SMBus protocol at clock frequencies up to 400 kHz, with support for both read and write operations.

Addressing logic is handled via three hardware inputs (A0, A1, A2), allowing engineers to set the device’s slave address and permitting up to eight PCA9535HF,118 devices to coexist on the same bus. Upon power-up, an internal reset circuit initializes all I/Os as inputs, ensuring predictable startup operation for the connected system.

Electrical Specifications of PCA9535HF,118

From an electrical standpoint, the PCA9535HF,118 operates across a broad supply voltage range of 2.3 V to 5.5 V. The device features 5 V tolerant I/Os and supports maximum output source/sink currents of 10 mA and 25 mA, respectively. Power management is enhanced by low supply and standby currents—an essential factor for battery-powered systems or designs with stringent energy budgets.

To maintain reliability across industrial and commercial settings, the PCA9535HF,118 guarantees an operational temperature range of -40°C to +85°C. The device includes robust ESD protection (exceeding 2000 V HBM, 200 V MM, and 1000 V CDM) and has undergone latch-up testing per JEDEC JESD78 standards beyond 100 mA, satisfying requirements for demanding environments.

Main Engineering Benefits of PCA9535HF,118

Engineers will benefit from several notable features of the PCA9535HF,118:

Interrupt output: The open-drain interrupt pin actively signals the system controller when an input pin's state changes compared to its input port register, enabling efficient event-driven polling and power optimization.

Polarity inversion: Each input's logic polarity can be individually inverted via register control, providing flexible system interfacing without external inverters.

Noise filtering: Integrated SCL/SDA line noise suppression maintains stable data communication, especially in electrically noisy environments.

Power-on glitch protection: The device ensures no unwanted I/O toggling during power cycling, preventing spurious signals to downstream components.

Compliance: The PCA9535HF,118 is RoHS3 compliant and unaffected by REACH directives, supporting environmentally conscious product development.

Pin Layout and Packaging Information for PCA9535HF,118

Pin functions are clearly demarcated, with VDD (supply), SCL (serial clock), SDA (serial data), ground (Vss), and address inputs (A0, A1, A2) designated alongside the sixteen I/O lines divided into Port 0 and Port 1. In the HWQFN24 package, the exposed pad and die supply ground must both connect to the main supply ground, not only for logic operation but also to maximize thermal dissipation in high-density layouts. Proper PCB thermal pad design and the inclusion of thermal vias are crucial for achieving optimal performance and reliability in systems deploying the PCA9535HF,118.

Register Functions and Software Compatibility of PCA9535HF,118

At the software level, control is achieved through command byte selection and register manipulation. The following functional registers define device behavior:

Input port registers: Read-only, presenting the current state of each I/O pin, independent of its configured direction.

Output port registers: Write-only, controlling output state for pins set as outputs.

Polarity inversion registers: Allow software-driven inversion of input logic for specific bit locations.

Configuration registers: Determine the mode (input/output) for each pin.

These registers enable precise pin management and make the PCA9535HF,118 suitable for use in custom logic implementations, programmable event detection, and responsive automation systems. Integration with microcontroller code is straightforward via standard I²C protocol procedures. However, note that software migration from older models, such as the PCF8575, may require minor code changes due to enhanced register definitions and improved performance features.

Use Cases for PCA9535HF,118 in Electronic Devices

The PCA9535HF,118 is frequently employed in designs where expansion of digital I/O is imperative without redesigning the main system controller. Typical engineering applications include:

ACPI power management circuits needing additional control lines

Sensor arrays requiring numerous detection channels interfaced via minimal microcontroller pins

User interface implementations such as keypad matrices, push buttons, or LED status panels

Fan or relay controls in both consumer and industrial devices

Event monitoring via the interrupt function for security, automation, or health monitoring systems

In all scenarios, the flexibility provided by individual pin configuration, together with robust communication and noise immunity features, supports both prototyping and deployment at scale.

Alternative or Substitute Models for PCA9535HF,118

When considering design alternatives or second sourcing, engineers may evaluate several related NXP series models that share substantial compatibility with the PCA9535HF,118:

PCA9535: Available in SO24, TSSOP24, and HVQFN24 packages, with similar electrical and logical characteristics but featuring totem pole outputs.

PCA9535C: Open-drain outputs on all I/O pins, differentiated from PCA9535, suitable for applications demanding external pull-ups or specific output circuitry.

PCA9555: Closely related yet includes internal I/O pull-up resistors, affecting power profile when I/Os are held low.

Notably, although pin-to-pin and I²C address compatibility exist with the earlier PCF8575, careful attention to software adjustment is required due to register enhancements. System designers should reference application note AN469 for specific guidance when migrating designs.

Conclusion

The NXP PCA9535HF,118 16-bit I/O expander in HWQFN24 brings scalable GPIO expansion to I²C and SMBus-based systems, pairing compact form factor with extensive configuration and performance capabilities. By combining wide electrical tolerance, advanced features like interrupts and polarity inversion, and proven robustness, the PCA9535HF,118 is a go-to solution for engineers striving to balance board density, flexibility, and reliability in modern electronic designs. Selection professionals and procurement decision-makers should consider its role and alternatives in building efficient, future-ready product architectures.