Texas Instruments PCA9544APWT

Overview

PCA9544APWT from Texas Instruments is a low-voltage, 4-channel bidirectional I²C/SMBus multiplexer with integrated interrupt logic and voltage-level translation capability. It enables one master to selectively route SCL/SDA signals to one of four downstream slave buses, supports 1.8-V to 5-V bus translation, operates from 2.3 V to 5.5 V, features active-low interrupt inputs (INT0–INT3) and a shared active-low interrupt output (INT), and is used in server backplanes and telecom switching equipment to resolve I²C slave address conflicts.

For engineers reviewing the PCA9544APWT datasheet, PCA9544APWT pinout, PCA9544APWT application, or PCA9544APWT equivalent, this device serves as a channel-selectable I²C bus isolator with built-in interrupt aggregation, voltage translation across mixed-voltage slave domains, and power-on reset recovery-critical for high-density embedded systems requiring reliable multi-slave I²C arbitration and fault resilience.

Technical Context

The PCA9544APWT implements a single-control-register architecture where three LSBs select exactly one of four downstream SCn/SDn channels, while four MSBs reflect real-time interrupt status from each slave bus. Its pass-gate switches use VCC-referenced conduction to enable bidirectional level shifting without external translators.

Interrupt logic performs wired-AND aggregation: INT asserts low when any INTn input is low, and deasserts only after all INTn inputs return high. Power-on reset initializes the control register to zero (all channels deselected) and resets the I²C state machine, ensuring deterministic startup even after bus lockup on downstream segments.

Key Specifications

Pinout & Package

TSSOP-20 (PW) package: 6.50 mm × 4.40 mm body, 0.65-mm lead pitch, exposed thermal pad optional. Compatible with standard surface-mount reflow profiles and automated optical inspection.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TCA9544APWR, PCA9544APWT offers tighter plating control for high-reliability aerospace/industrial use; compared with PCA9548APW, it delivers optimal channel density and pin efficiency for 4-bus systems without over-provisioning.

Availability

PCA9544APWT is available at Aetrix Electronics and suitable for server backplane management, telecom switching equipment, and factory automation I/O modules requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for PCA9544APWT 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, precision, and energy efficiency across industrial, automotive, and communications markets.

The PCA9544A belongs to TI's I²C infrastructure portfolio, designed specifically to solve bus contention, voltage mismatch, and interrupt scalability challenges in dense multi-peripheral embedded systems.

FAQ

What is the primary function of the PCA9544APWT in an I²C system?

The PCA9544APWT functions as a 4-channel bidirectional I²C multiplexer that allows a single master to communicate with up to four isolated downstream I²C buses. It resolves slave address conflicts by enabling only one channel at a time, supports voltage-level translation between 1.8-V, 2.5-V, 3.3-V, and 5-V domains, and aggregates interrupts from each channel into a single active-low output. This makes PCA9544APWT essential for scalable, mixed-voltage I²C architectures in servers and telecom gear.

Does the PCA9544APWT require external pull-up resistors, and why?

Yes, the PCA9544APWT requires external pull-up resistors on all SDA/SCL lines-including upstream (SCL, SDA) and all four downstream pairs (SC0/SD0 through SC3/SD3)-because it contains no internal pull-ups. These resistors set the logic-high voltage level for each bus segment and enable proper I²C open-drain signaling. Their values determine rise time and noise immunity; typical values range from 1 kΩ to 10 kΩ depending on bus capacitance and speed. This design ensures PCA9544APWT supports mixed-voltage translation by allowing independent V_DPU references per channel.

How does the interrupt logic work on the PCA9544APWT?

The PCA9544APWT provides four active-low interrupt inputs (INT0–INT3), one per downstream channel, and one active-low interrupt output (INT). The INT pin acts as a wired-AND of all INTn inputs: it asserts low whenever any INTn is low and deasserts only after all INTn return high. This behavior is implemented in hardware and requires no register access. The interrupt status is also reflected in bits 7–4 of the read-only control register, enabling software polling. This dual-path mechanism makes PCA9544APWT ideal for real-time fault detection in mission-critical systems.

Can the PCA9544APWT operate with a 1.8-V supply voltage?

No, the PCA9544APWT cannot operate with a 1.8-V supply voltage. Its recommended operating supply range is 2.3 V to 5.5 V, and its absolute minimum VCC is 2.3 V per the datasheet's Recommended Operating Conditions table. While PCA9544APWT supports communication with 1.8-V slaves via voltage translation (using external pull-ups to 1.8 V on downstream lines), the device itself must be powered within its specified VCC range. Attempting to run PCA9544APWT below 2.3 V risks undefined behavior, failed power-on reset, or incomplete register initialization.

Is the PCA9544APWT pin-compatible with the PCA9548A series?

No, the PCA9544APWT is not pin-compatible with the PCA9548A series. Although both are I²C multiplexers from Texas Instruments with similar functional blocks, PCA9544APWT uses a 20-pin TSSOP (PW) package, while PCA9548A variants use 24-pin TSSOP packages. Pin counts, pin assignments (e.g., additional address and interrupt lines), and footprint dimensions differ. Substituting PCA9544APWT for PCA9548A-or vice versa-requires PCB redesign. Always verify mechanical compatibility and register mapping before interchange; PCA9544APWT remains the correct choice for validated 4-channel implementations.