NXP Semiconductors PCA9518AD,112

Overview

The PCA9518AD,112 from NXP Semiconductors is a 5-channel expandable I²C-bus hub repeater IC designed to extend I²C/SMBus systems beyond the 400 pF capacitance limit. It buffers both SDA and SCL lines across five bidirectional ports (SCL0–SCL4/SDA0–SDA4), supports 0–400 kHz operation, operates from 2.3 V to 3.6 V, and features 5 V-tolerant I/O pins - enabling mixed-voltage subsystem interconnection in industrial control backplanes.

For engineers reviewing the PCA9518AD,112 datasheet, PCA9518AD,112 pinout, PCA9518AD,112 application, or PCA9518AD,112 equivalent, this device addresses bus segmentation, multi-master arbitration preservation, voltage-level translation between 3.3 V and 5 V I²C domains, and scalable hub clustering via EXPxxxn expansion pins - critical for modular sensor networks and distributed embedded controllers.

Technical Context

The PCA9518AD,112 implements a lock-up-free, open-drain buffer architecture with dual-threshold input detection (VIL = 0.25VDD, VILc = 0.4 V) to prevent contention-induced deadlocks in clustered repeaters. Its internal hub logic routes signals across five independent channels, each controlled by an active-HIGH enable pin (EN1–EN4), while port 0 remains always-enabled.

Expansion communication uses four dedicated open-drain pins (EXPSCL1/2, EXPSDA1/2) forming a shared 4-wire bus between PCA9518A devices; propagation delays are split into tPHL1/tPLH1 (EXP-to-local) and tPHL/tPLH (local-to-local), with typical tPHL = 202 ns and tPLH = 259 ns at 3.3 V - ensuring deterministic timing across segments without degrading arbitration or clock stretching behavior.

Key Specifications

Pinout & Package

PCA9518AD,112 is supplied in SO20 package (SOT163-1): plastic small outline, 20-lead, 7.5 mm body width, lead pitch 1.27 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar I²C bus repeater applications.

Compared with PCA9517AD,112 and TCA9517APWR, the PCA9518AD,112 uniquely delivers scalable 5-port hub architecture with EXPxxxn clustering - making it the only option for systems requiring >4 segments, mixed-voltage coordination, or dynamic port enable/disable in modular architectures.

Availability

PCA9518AD,112 is available at Aetrix Electronics and suitable for industrial sensor backplanes, multi-voltage I²C subsystem isolation, and modular test equipment requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for PCA9518AD,112 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

NXP Semiconductors is a global semiconductor leader focused on secure connectivity solutions for automotive, industrial, and IoT applications, with deep expertise in interface, power, and security ICs.

The PCA9518A product line was engineered specifically for scalable, lock-up-free I²C bus expansion in high-density embedded systems - addressing limitations of earlier repeaters like PCA9515/16 in clustered, multi-master environments.

FAQ

What is the maximum I²C clock frequency supported by the PCA9518AD,112?

The PCA9518AD,112 supports I²C clock frequencies from 0 Hz up to 400 kHz, compliant with Fast-mode I²C and SMBus specifications. However, actual system-level maximum frequency may be lower due to cumulative propagation delays across repeater stages - design validation is required for timing-critical 400 kHz implementations with multiple PCA9518AD,112 devices in series.

Does the PCA9518AD,112 require external pull-up resistors on its I²C bus lines?

Yes, the PCA9518AD,112 requires external pull-up resistors on all SDA and SCL lines - both upstream (master side) and downstream (segment side) - as it uses open-drain outputs. Each bus segment must have its own set of pull-ups; values depend on bus speed, capacitance, and voltage, typically 1.1 kΩ for 3.3 V Fast-mode operation.

Can the PCA9518AD,112 be used to connect 3.3 V and 5 V I²C devices without level shifters?

Yes, the PCA9518AD,112 has 5 V-tolerant I²C and enable pins, allowing direct interface between 3.3 V masters and 5 V slaves (or vice versa) without external level-shifting components - provided all devices share a common ground and operate within their respective voltage ranges.

How does the PCA9518AD,112 handle I²C bus arbitration across multiple segments?

The PCA9518AD,112 preserves native I²C arbitration across all five ports by implementing bidirectional, contention-aware open-drain buffers. It detects falling edges and propagates LOW states with controlled voltage offsets (VOL − VILc ≥ 70 mV), ensuring that arbitration pulses and clock stretching from any segment are correctly recognized and relayed to other segments.

What happens to the I²C pins of the PCA9518AD,112 when VDD is below 2.0 V?

When VDD drops below 2.0 V, the I²C pins (SCLn/SDAn) of the PCA9518AD,112 automatically enter a high-impedance state - preventing bus contention during power-up/down sequences. This partial power-down behavior ensures clean hot-plug and graceful fail-safe operation in systems with staggered power domains.