Texas Instruments PCA9518DBQR

Overview

PCA9518DBQR from Texas Instruments is an expandable five-channel bidirectional I²C bus repeater IC designed to overcome 400-pF bus capacitance limits in multi-segment I²C/SMBus systems. It operates from 3 V to 3.6 V, supports 400-kHz fast-mode operation, features 5-V tolerant SDA/SCL/EN pins for mixed-voltage translation, and enables electrically isolated channel control via four active-high enable inputs (EN1–EN4). It is used in industrial control backplanes where multiple I²C slave clusters require independent timing domains.

For engineers reviewing the PCA9518DBQR datasheet, PCA9518DBQR pinout, PCA9518DBQR application, or PCA9518DBQR equivalent, this page delivers verified technical context, exact pin functions per SSOP-20 package, real-world I²C hub segmentation use cases, and two validated alternative parts with documented functional and application-level differences.

Technical Context

The PCA9518DBQR implements five independent open-drain bidirectional buffers-each with dedicated SDA/SCL pairs (SCL0/SDA0 through SCL4/SDA4)-and uses dual expansion signaling (EXPSCL1/EXPSCL2, EXPSDA1/EXPSDA2) to form a 4-wire inter-hub bus enabling arbitrary-width clustering without added repeater delay. Its lockup-free design enforces asymmetric low-level thresholds (VOL = 0.52 V typical; VILc = VOL − 70 mV) between input and output sides to prevent contention-induced deadlocks.

Each channel is individually enabled by EN1–EN4 (active-high, internal pullups), allowing dynamic isolation of segments-for example, running one segment at 100 kHz while others operate at 400 kHz. The device does not support clock stretching across repeater boundaries and must not be cascaded with other repeaters like PCA9515 due to static offset and signal integrity constraints.

Key Specifications

Pinout & Package

PCA9518DBQR is housed in a 20-pin SSOP (DBQ) package measuring 7.20 mm × 5.30 mm, with 0.65-mm lead pitch and gull-wing leads suitable for automated surface-mount assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9517DGVR and TCA9517PWR, the PCA9518DBQR uniquely delivers five independently enabled channels plus EXP-based clustering-making it the only option for scalable, multi-segment, mixed-voltage I²C systems requiring <1-repeater-delay latency across arbitrary channel counts.

Availability

PCA9518DBQR is available at Aetrix Electronics and suitable for industrial automation backplanes, modular test equipment, multi-voltage sensor hubs, and PLC I/O expansion requiring stable component supply across extended production lifecycles.

Supply support for PCA9518DBQR 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies with over 50 years of innovation in industrial and automotive-grade components.

The PCA9518DBQR belongs to TI's I²C interface portfolio, engineered specifically to solve bus capacitance limitations in large-scale industrial control systems-enabling reliable, scalable, and voltage-flexible I²C expansion without performance compromise.

FAQ

What is the primary function of the PCA9518DBQR in an I²C system?

The PCA9518DBQR functions as an expandable five-channel bidirectional I²C bus repeater that segments a single I²C bus into up to five isolated 400-pF-limited domains. It enables scalable multi-peripheral systems by buffering SDA/SCL signals across channels and supporting inter-device clustering via EXPSCL/EXPSDA expansion pins-ensuring full-system bandwidth remains at 400 kHz without cumulative repeater delay. This architecture is implemented in the PCA9518DBQR to address physical layer limitations in industrial backplanes and modular instrumentation.

Does the PCA9518DBQR support clock stretching across its repeater channels?

No, the PCA9518DBQR does not support clock stretching across its repeater channels. Due to static voltage offsets between input and output sides and potential overshoot above 500 mV during stretching events, TI explicitly documents this as an errata condition. Using rise-time accelerators on the B-side bus may cause logic misinterpretation and I²C communication failure. The PCA9518DBQR is intended for systems where clock stretching is handled locally within each segment-not propagated end-to-end. This limitation is inherent to the PCA9518DBQR's buffer design and is confirmed in Section 8.2.3 of its datasheet.

How are the enable pins (EN1–EN4) used in the PCA9518DBQR?

The EN1–EN4 pins on the PCA9518DBQR are active-high, internally pulled-up control inputs that individually isolate their associated SCLn/SDAn channel pair from the global I²C bus. When ENn is low, the corresponding SCLn and SDAn pins enter high-impedance state-blocking both input sensing and output driving. This allows dynamic segmentation: for example, disabling slower 100-kHz peripherals while maintaining 400-kHz operation on other channels. TI specifies that EN state changes must occur only when both global and local buses are idle to prevent arbitration errors-a requirement strictly enforced in the PCA9518DBQR's functional mode table.

What is the significance of the 70-mV VILc specification for the PCA9518DBQR?

The 70-mV VILc (low-level input voltage contention) specification defines the minimum voltage difference required between the PCA9518DBQR's output low voltage (VOL = 0.52 V typical) and the low-level threshold of downstream devices on the same segment. Specifically, any device asserting a low on SCLn or SDAn must drive below (VOL − 70 mV) = ~0.45 V to ensure reliable recognition and propagation by the PCA9518DBQR. This asymmetric threshold prevents lockup during arbitration by guaranteeing that a released low on one side does not falsely hold the other side low-a core design feature validated in the PCA9518DBQR's lockup-free operation claim.

Can multiple PCA9518DBQR devices be cascaded in series (daisy-chained)?

No, multiple PCA9518DBQR devices must not be cascaded in series-i.e., connecting the output of one PCA9518DBQR directly to the input of another via SCLn/SDAn pins. TI explicitly prohibits this configuration because the PCA9518DBQR's buffered low output (~0.52 V) falls outside the valid low-input range of a second repeater, causing signal recognition failure. Instead, expansion must occur exclusively via the dedicated EXPSCL/EXPSDA pins, which implement synchronized multi-device clustering with single-repeater latency. This architectural constraint is fundamental to the PCA9518DBQR's design and is documented in Section 4 of the datasheet.