Texas Instruments PCA9545APWT

Overview

PCA9545APWT from Texas Instruments is a low-voltage, quad-channel I²C/SMBus switch with interrupt aggregation and active-low reset. It functions as a bidirectional translating multiplexer that routes one upstream SCL/SDA pair to up to four downstream SCn/SDn channels, supports voltage-level translation between 1.8-V, 2.5-V, 3.3-V, and 5-V buses, features four active-low interrupt inputs (INT3–INT0) and one active-low interrupt output (INT), and operates across 2.3 V to 5.5 V supply range - used in server motherboard I²C bus isolation and multi-sensor subsystems where slave address conflicts occur.

For engineers reviewing the PCA9545APWT datasheet, PCA9545APWT pinout, PCA9545APWT application, or PCA9545APWT equivalent, key selection considerations include its 4-channel programmable channel selection via I²C control register, 5.5-V tolerant I/O, 400-kHz Fast-Mode support, low R_ON (≤11 Ω at 3.3 V), and integrated power-on reset with VPOR = 1.6–2.1 V - all critical for robust I²C bus arbitration in industrial embedded systems.

Technical Context

The PCA9545APWT implements a state-machine-controlled I²C switch architecture with independent channel enable/disable logic driven by a single 8-bit control register (bits B0–B3 for channel selection; bits B4–B7 for interrupt status). Its pass-gate switches use VCC-referenced threshold control to enable bidirectional level translation without external translators.

Interrupt handling is asynchronous: each INTn input feeds an internal latch whose status appears in the read-only upper nibble of the control register; the open-drain INT output performs a wired-AND of all four INTn signals. The active-low RESET pin forces full state machine reset and channel deselection, overriding I²C commands and recovering from stuck-bus conditions.

Key Specifications

Pinout & Package

TSSOP-20 package (6.50 mm × 4.40 mm), thermally enhanced with exposed pad; pin-compatible with DGV, DW, PW, and RGY variants per TI SCPS147D datasheet.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TCA9544APWR, PCA9545APWT adds essential interrupt visibility and fault recovery; versus PCA9548APW, it delivers tighter timing, smaller footprint, and lower system cost for fixed 4-channel needs - making it optimal for space-constrained server and telecom management interfaces.

Availability

PCA9545APWT is available at Aetrix Electronics and suitable for server baseboard management, telecom router subsystems, and factory automation PLCs requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for PCA9545APWT 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 PCA9545APWT belongs to TI's I²C switch and multiplexer product line, designed specifically for robust bus isolation, voltage translation, and interrupt consolidation in high-density computing and communications infrastructure.

FAQ

What is the I²C slave address configuration for PCA9545APWT?

The PCA9545APWT uses a 7-bit hardware-configurable slave address: 1110A1A0, where A1 and A0 are hardwired to VCC or GND. This yields four possible addresses (0xE0, 0xE2, 0xE4, 0xE6) - enabling up to four PCA9545APWT devices on the same I²C bus without address collision. No internal pull-ups exist on A0/A1; external termination is mandatory for deterministic addressing.

How does the PCA9545APWT handle voltage-level translation between different I²C buses?

The PCA9545APWT achieves voltage-level translation using VCC-referenced pass-gate switches: the maximum voltage passed equals VCC, so 1.8-V, 2.5-V, or 3.3-V slave buses can interoperate with a 5-V master by setting VCC = 5 V and using separate pull-up resistors on each SDn/SCn pair tied to their respective rail voltages. All I/O pins are 5.5-V tolerant, ensuring safe operation across mixed-supply domains without external level shifters.

What happens to the PCA9545APWT channels during power-up or RESET assertion?

Upon power-up, the PCA9545APWT enters a known state when VCC crosses VPOR (1.6–2.1 V): all four channels are automatically deselected, the control register resets to 0x00, and INT is released high. Similarly, asserting RESET low for ≥6 ns forces immediate deselection of all channels and resets the I²C state machine - both mechanisms prevent bus contention and ensure deterministic initialization before host firmware begins configuration.

Can the PCA9545APWT select multiple channels simultaneously, and what are the design implications?

Yes, the PCA9545APWT supports simultaneous selection of any combination of its four channels via bits B0–B3 in the control register (e.g., 0x0F enables all channels). However, doing so electrically connects all selected SCn/SDn pairs to the upstream SCL/SDA lines - increasing total bus capacitance and potentially violating I²C timing (max 400 pF). Designers must verify combined load meets t_BUF, t_RISE, and t_FALL specs; TI recommends limiting concurrent channels in high-speed or long-trace deployments.

How does the interrupt logic of PCA9545APWT work, and how is interrupt source identified?

The PCA9545APWT provides four active-low interrupt inputs (INT0–INT3), one per channel, and one active-low open-drain interrupt output (INT) that is the logical AND of all four inputs. When any INTn is pulled low, INT goes low and the corresponding bit (B4–B7) in the control register is set. The host reads this register over I²C to identify which channel generated the interrupt - enabling targeted reconfiguration and clearing without polling or additional GPIOs. The latch persists until the host reads the register.