Texas Instruments PCA9518PW

Overview

PCA9518PW from Texas Instruments is a five-channel bidirectional I²C bus repeater IC designed to extend I²C/SMBus capacity beyond 400 pF per segment. It operates from 3 V to 3.6 V, supports 400-kHz fast-mode I²C, features 5-V tolerant SDA/SCL/EN pins, and enables mixed-voltage (3.3 V ↔ 5 V) interoperation in multi-segment systems such as server management buses and modular sensor subsystems.

For engineers reviewing the PCA9518PW datasheet, PCA9518PW pinout, PCA9518PW application, or PCA9518PW equivalent, this page delivers verified electrical parameters, validated channel enable behavior, confirmed expansion-bus timing, exact TSSOP-20 package mapping, and two field-deployed alternative parts with documented functional trade-offs.

Technical Context

The PCA9518PW implements five independent open-drain bidirectional buffers, each with active-high enable (EN1–EN4), no direction pin, and lockup-free arbitration logic using differential low-level thresholds (VOL = 0.52 V typical, VILc = VOL – 70 mV). Its expansion interface uses four dedicated pins (EXPSCL1/2, EXPSDA1/2) to form a 4-wire daisy-chainable hub network supporting up to five segments per device.

It does not support clock stretching across repeater boundaries and requires external pullup resistors on all SDA/SCL/EXP lines. The internal power-on-reset (VPOR) ensures deterministic startup, and powered-off I²C pins enter high-impedance state - critical for hot-swap-capable backplane designs.

Key Specifications

Pinout & Package

TSSOP-20 (PW) package: 7.20 mm × 5.30 mm body, 0.65 mm pitch, exposed pad not present, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9518PW, PCA9517APW offers simpler topology support but no expandability, while TCA9517APWR reduces external components yet sacrifices 5-V tolerance - making PCA9518PW the sole choice for scalable, mixed-voltage I²C extension.

Availability

PCA9518PW is available at Aetrix Electronics and suitable for server BMC architectures, modular PLC I/O systems, automotive body controllers, and multi-supply embedded platforms requiring stable component supply and long-term lifecycle continuity.

Supply support for PCA9518PW 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets since 1930.

The PCA9518PW belongs to TI's I²C infrastructure portfolio, engineered specifically to solve bus capacitance limitations and mixed-voltage interoperability in high-density, multi-node embedded systems.

FAQ

What is the maximum number of PCA9518PW devices that can be daisy-chained via EXP pins?

The PCA9518PW supports unlimited daisy-chaining via EXPSCL1/2 and EXPSDA1/2 pins - each additional device adds five more I²C segments without increasing propagation delay beyond one repeater stage. Real-world limits depend on total EXP bus capacitance and signal integrity; TI recommends ≤10 devices per EXP bus for reliable 400-kHz operation. The PCA9518PW itself contributes no added delay to inter-hub communication.

Does PCA9518PW support clock stretching across its repeater channels?

No, the PCA9518PW explicitly does not support clock stretching across repeater boundaries. As stated in the datasheet errata, static offset and potential overshoot during clock-stretch events can cause logic misinterpretation. Systems requiring clock stretching must implement it only on the master side (SCL0/SDA0) or use non-repeater I²C segments. This limitation applies to all PCA9518PW channel pairs - SCL1/SDA1 through SCL4/SDA4 cannot stretch clocks originated on SCL0/SDA0.

Can PCA9518PW operate with VCC = 5 V?

No, the PCA9518PW is rated for VCC = 3 V to 3.6 V only. While its SDA, SCL, and EN pins tolerate up to 7 V (per Absolute Maximum Ratings), the internal logic and buffer drivers require strictly 3.3-V nominal supply. Applying 5 V to VCC will exceed absolute maximum ratings and cause permanent damage. For 5-V supply systems, use level-shifting regulators or select a 5-V-compatible repeater like the TCA9517A.

How does PCA9518PW prevent bus lockup during arbitration?

The PCA9518PW prevents lockup using dual-threshold input detection: standard low-level input voltage (VIL) is 0.3 × VCC, but contention-level detection (VILc) is set 70 mV below the output low voltage (VOL ≈ 0.52 V). This ensures that when a downstream device releases a low, the PCA9518PW recognizes the rising edge before the upstream driver fully releases - breaking feedback loops that cause deadlocks. This mechanism is intrinsic to the PCA9518PW silicon design and requires no external configuration.

Is PCA9518PW pin-compatible with PCA9517APW?

No, PCA9518PW and PCA9517APW are not pin-compatible. Although both use TSSOP-20 (PW) packages, their pinouts differ significantly: PCA9518PW has 20 dedicated pins including four EXP lines and five EN inputs, while PCA9517APW uses a subset of those pins for only two channels and omits EXP functionality entirely. PCB layout reuse is not possible - routing, footprint, and decoupling must be redesigned for either part.