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Texas Instruments PCA9518DBT
- Part No.:
- PCA9518DBT
- Manufacturer:
- Texas Instruments
- Category:
- Specialized
- Package:
- 20-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
PCA9518DBT.pdf
- Description:
- IC INTERFACE SPECIALIZED 20SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:963
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Product details
Overview
PCA9518DBT from Texas Instruments is an expandable five-channel bidirectional I²C/SMBus buffer IC designed to overcome 400-pF bus capacitance limits by segmenting and buffering SDA/SCL lines. It operates from 3 V to 3.6 V, supports 400-kHz fast-mode I²C, features 5-V tolerant I²C and enable pins, and enables mixed-voltage (3.3 V/5 V) system interoperation in server backplanes and modular embedded systems.
For engineers reviewing the PCA9518DBT datasheet, PCA9518DBT pinout, PCA9518DBT application, or PCA9518DBT equivalent, this page delivers verified pin functions, real-world timing behavior (tPHLs ≤ 389 ns), voltage-level translation capability, lockup-free arbitration handling, and validated alternative options for multi-segment I²C expansion architectures.
Technical Context
The PCA9518DBT implements five independent open-drain bidirectional buffers with active-high individual enables (EN1–EN4), each isolating its associated SDA/SCL pair when deasserted. Its expansion architecture uses four dedicated EXP pins (EXPSCL1/2, EXPSDA1/2) to form a 4-wire inter-hub bus enabling cluster-based scaling without added repeater delay.
It employs differential low-level detection (VILc = VOL – 70 mV) across internal buffers to prevent lockup during contention, and incorporates internal power-on-reset (VPOR) for reliable startup. The device does not support clock stretching across segments and must not be cascaded with other repeaters like PCA9515 or standalone PCA9518 clusters.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 3 V to 3.6 V - defines strict single-supply operation; 5-V tolerance on I²C/EN pins enables level translation without external circuitry. |
| Max Bus Speed | 400 kHz - supports Fast-mode I²C; actual system frequency may be lower due to repeater propagation delays (tPHLs up to 389 ns). |
| I/O Voltage Tolerance | 5 V - allows direct connection to 5-V slaves/masters while powered from 3.3 V, eliminating level-shifters in mixed-voltage topologies. |
| Low-Level Recognition | VILc = VOL – 70 mV - ensures robust arbitration detection across buffered segments; requires slave VOL ≤ 0.43 V when PCA9518DBT VOL = 0.52 V. |
| Quiescent Current | 1.75–6 mA - scales with enabled channels and bus state; 9–11 mA during contention reflects active arbitration handling. |
| Propagation Delay | tPHLs ≤ 389 ns - worst-case SDA/SCL high-to-low delay; critical for timing budgeting in multi-hop I²C trees. |
| ESD Rating | HBM ±2000 V - meets industrial-grade ESD robustness per JESD22-A114A, supporting handling in non-cleanroom assembly. |
Pinout & Package
PCA9518DBT is housed in a 20-pin SSOP (DB) package measuring 7.20 mm × 5.30 mm, with 0.65-mm lead pitch and RoHS-compliant NiPdAu (NIPDAU) finish. It carries MSL Level-1 rating (unlimited floor life at ≤30 °C/60% RH).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| EXPSCL1 / EXPSCL2 | Expansion clock input/output | Open-drain signals forming 4-wire inter-hub bus; require external pullups to VCC; detect SCL transitions for cluster synchronization. |
| EXPSDA1 / EXPSDA2 | Expansion data input/output | Open-drain signals carrying buffered SDA state between PCA9518DBT units; enable lossless multi-device clustering without added latency. |
| SCL0–SCL4 / SDA0–SDA4 | Segmented I²C clock/data buses | Five independent bidirectional I²C ports; SCL0/SDA0 serve as primary hub interface; others connect to downstream segments. |
| EN1–EN4 | Active-high enable controls | Individually gate SCLn/SDAn pairs; internal pullups allow default-enable; must transition only during bus idle to avoid corruption. |
| VCC / GND | Power supply terminals | Single 3.3-V supply; GND reference for all I/O; no separate analog/digital ground required. |
Key Features
| Feature | Design Value |
|---|---|
| Expandable five-channel architecture | Enables arbitrary-width I²C hubs via EXP pins-no fixed topology limit; supports >5 segments using multiple PCA9518DBT units. |
| 5-V tolerant I²C and enable inputs | Permits direct interfacing between 3.3-V masters and 5-V slaves without level shifters, reducing BOM count and signal integrity risk. |
| Lockup-free arbitration handling | Differential low-level thresholds (VILc = VOL – 70 mV) prevent metastability during multi-master contention across buffered segments. |
| Powered-off high-impedance I²C pins | SDA/SCL pins enter Hi-Z state when VCC = 0 V, preventing backdrive and enabling hot-swap capability in modular systems. |
| Individual active-high repeater enables | EN1–EN4 allow dynamic segmentation-e.g., isolate 100-kHz peripherals while keeping 400-kHz subsystems active on same hub. |
Applications
| Server Backplane Management | Industrial PLC I/O Expansion |
|---|---|
Use Scenario: A rack-mounted server uses multiple hot-swappable FRUs (fans, PSUs, DIMMs), each with its own I²C sensor/MCU, connected to a central BMC via segmented buses. IC Role / Device Role / Timing Role: PCA9518DBT acts as a voltage-translating, capacitance-isolating hub-segmenting FRU buses to stay within 400-pF limit while enabling 3.3-V BMC to communicate with 5-V PSU monitors. Use Value: Eliminates need for discrete level shifters and reduces bus loading; EN-controlled isolation allows firmware to disable faulty FRU segments without disrupting others. | Use Scenario: A programmable logic controller connects to distributed I/O modules (analog input, digital output, RTD) over long cables, exceeding I²C capacitance limits. IC Role / Device Role / Timing Role: PCA9518DBT serves as a buffered repeater node-partitioning cable runs into sub-400-pF segments while preserving arbitration and clock timing integrity. Use Value: Enables deterministic 400-kHz communication over 2+ meter cable lengths; powered-off Hi-Z pins prevent backfeed during module replacement. |
| Automotive Domain Controller Interconnect | Medical Imaging Subsystem Integration |
Use Scenario: An ADAS domain controller integrates camera, radar, and ultrasonic sensors-each with vendor-specific I²C configuration interfaces operating at different voltages and speeds. IC Role / Device Role / Timing Role: PCA9518DBT functions as a mixed-voltage I²C router-enabling 3.3-V controller access to 5-V radar EEPROMs and 2.8-V camera registers via isolated EN-gated channels. Use Value: Avoids voltage-domain conflicts and timing skew; individual EN control permits staggered initialization of sensor subsystems during boot. | Use Scenario: A CT scanner's detector array contains dozens of ASICs requiring calibration data reads via I²C, but trace capacitance exceeds 400 pF across the PCB stack-up. IC Role / Device Role / Timing Role: PCA9518DBT operates as a local repeater-buffering SDA/SCL between FPGA host and detector ASIC clusters to maintain signal integrity and meet 400-kHz timing margins. Use Value: Guarantees reliable calibration data transfer without signal degradation; latchup immunity (>100 mA) protects against transient faults in high-noise imaging environments. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar I²C bus expansion applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| PCA9517ADPW | Two-channel buffer; no expansion pins; 2.3-V to 3.6-V VCC; lacks EN control per channel. | Suitable only for simple point-to-point extension-not scalable clusters or mixed-voltage translation. | Select when only two isolated segments are needed and 5-V tolerance is unnecessary. |
| TCA9517APWR | Two-channel with auto-direction sensing; 1.65-V to 5.5-V dual-supply; includes automatic direction control logic. | Supports asymmetric voltage translation (e.g., 1.8-V ↔ 3.3-V) but cannot scale beyond two segments or support EXP-based clustering. | Choose for low-voltage microcontroller interfaces where automatic direction detection simplifies design, but avoid for >2-segment or 5-V slave integration. |
Compared with PCA9518DBT, PCA9517ADPW offers simpler integration for basic repeater needs but lacks scalability and voltage translation; TCA9517APWR adds flexible dual-supply operation yet omits the expandable hub architecture essential for large-scale I²C tree deployment.
Availability
PCA9518DBT is available at Aetrix Electronics and suitable for server backplane management, industrial PLC I/O expansion, and automotive domain controller interconnect requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.
Supply support for PCA9518DBT 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 delivering analog and embedded processing solutions, with leadership in interface, power management, and signal chain technologies.
The PCA9518DBT belongs to TI's I²C infrastructure portfolio, engineered specifically for high-reliability, multi-segment I²C expansion in systems where bus capacitance, voltage translation, and dynamic segmentation are critical constraints.
FAQ
Does PCA9518DBT support clock stretching across buffered segments?
No, PCA9518DBT does not support clock stretching across repeater segments. The device's static offset and internal timing architecture prevent reliable propagation of stretched clock cycles, and TI explicitly documents this limitation in the Clock Stretching Errata section. Using rise-time accelerators with PCA9518DBT may cause I²C communication failure due to overshoot above 500 mV. For applications requiring clock stretching, alternative architectures without intermediate repeaters must be used.
What is the minimum valid low voltage that PCA9518DBT recognizes on SDA/SCL inputs during arbitration?
The PCA9518DBT recognizes a low input during arbitration only if it falls below VILc = VOL – 70 mV. With typical VOL = 0.52 V, this means the input must reach ≤0.45 V to be detected and propagated. This threshold is stricter than the standard VIL (≤0.3 × VCC = 0.99 V max) and ensures reliable cross-segment arbitration without lockup. External devices driving SDA/SCL must meet this condition to guarantee correct signal forwarding by PCA9518DBT.
Can PCA9518DBT be used in series with another PCA9518DBT or a PCA9515 repeater?
No, PCA9518DBT must not be placed in series with another PCA9518DBT cluster or any other repeater such as the PCA9515. TI's documentation explicitly prohibits this configuration because the EXP pin signaling protocol and differential low-level thresholds are incompatible with cascaded repeater topologies. Doing so results in unrecognized low states and communication failure. Clustering must occur only via the dedicated EXPSCL1/2 and EXPSDA1/2 pins in parallel hub arrangements.
How does the EN pin behavior affect bus isolation when PCA9518DBT is powered down?
When PCA9518DBT is unpowered (VCC = 0 V), all SDA/SCL pins enter a high-impedance state regardless of EN pin voltage-preventing backdrive from live buses. However, EN pins themselves are not Hi-Z when unpowered; they retain their last logic state but have no functional effect. True electrical isolation of a segment requires both VCC removal *and* EN deassertion before power-down, or use of external switches. The Hi-Z I²C pins enable safe hot-swap in modular systems where PCA9518DBT remains powered.
What pullup resistor values are recommended for PCA9518DBT's SDA/SCL and EXP pins?
TI specifies 1.1-kΩ pullups for I²C buses (SCLn/SDAn) and 500-Ω pullups for EXP pins (EXPSCL1/2, EXPSDA1/2). These values ensure proper rise times under 400-pF load conditions and match the test circuit defined in the datasheet (Figure 1). Using higher values (e.g., 10 kΩ) on EXP pins risks violating timing requirements for inter-hub signaling, while undersized I²C pullups increase power consumption and may exceed the 6-mA sink capability of PCA9518DBT's outputs.
PCA9518DBT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-SSOP (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Applications:
- Buffer
- Interface:
- I2C
- Voltage - Supply:
- 3V ~ 3.6V
- Supplier Device Package:
- 20-SSOP
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
PCA9518DBT FAQ
1.How can I place an order for PCA9518DBT through Aetrix?
Please submit a Request for Quotation (RFQ) for PCA9518DBT on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for PCA9518DBT reliable?
The price and inventory of PCA9518DBT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for PCA9518DBT is usually 5 days.
3.What payment methods are accepted for PCA9518DBT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for PCA9518DBT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for PCA9518DBT?
PCA9518DBT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your PCA9518DBT order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for PCA9518DBT?
For technical support, including PCA9518DBT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your PCA9518DBT requirements.
6.How does Aetrix verify that PCA9518DBT is sourced from the original manufacturer or authorized distributors?
All PCA9518DBT products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that PCA9518DBT meets industry standards.
7.What is the process for return or replacement of PCA9518DBT?
All PCA9518DBT units undergo pre-shipment inspection (PSI). If there is an issue with PCA9518DBT, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The PCA9518DBT part is unused and in its original packaging.
Return procedure for PCA9518DBT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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