NXP Semiconductors PCA9545APW,112

Overview

PCA9545APW,112 from NXP Semiconductors is a 4-channel bidirectional I²C-bus switch with integrated interrupt logic and active-low reset. It enables selective routing of SCL/SDA signals to one or more of four downstream I²C buses, supports voltage translation between 1.8 V, 2.5 V, 3.3 V, and 5 V domains, and operates across 2.3 V to 5.5 V supply. It is used in multi-sensor server management systems where bus isolation and interrupt aggregation are required.

For engineers reviewing the PCA9545APW,112 datasheet, PCA9545APW,112 pinout, PCA9545APW,112 application, or PCA9545APW,112 equivalent, key selection criteria include channel-selectable I²C fanout, 400 kHz Fast-mode support, 5 V-tolerant I/O, low Ron (≤11 Ω at 3.6 V), and interrupt-input aggregation via open-drain INT output.

Technical Context

The PCA9545APW,112 implements a register-controlled 1-of-4 (or multi-channel) switching matrix using low-Ron pass-gate transistors. Its control register (read/write) uses 4 LSBs for channel enable/disable and upper 4 bits for read-only interrupt status reporting (INT0–INT3).

Interrupt handling is asynchronous: each INTn input drives its corresponding bit in the control register regardless of channel selection state, and the single INT output performs a wired-AND of all four inputs. The active-low RESET pin forces internal state machine reset and deselects all channels, independent of I²C activity.

Key Specifications

Pinout & Package

TSSOP20 package (SOT360-1): plastic thin shrink small outline, 20 leads, body width 4.4 mm, thermal resistance R_th(j-a) = 146 °C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9545APW,112, the TCA9545A offers vendor redundancy but lower ESD robustness, while the PCA9544A omits interrupt handling entirely-making PCA9545APW,112 the only option when both bus switching and hardware interrupt consolidation are required in a single TSSOP20 device.

Availability

PCA9545APW,112 is available at Aetrix Electronics and suitable for server management, industrial sensor hubs, automotive body control modules, and automated test equipment requiring stable component supply and long-term design-in support.

Supply support for PCA9545APW,112 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

NXP Semiconductors is a global semiconductor company specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with leadership in interface, power management, and embedded processing technologies.

The PCA9545A belongs to NXP's I²C-bus switch and multiplexer product line, designed specifically to solve bus contention, voltage domain bridging, and interrupt scalability challenges in complex embedded systems with multiple I²C peripherals.

FAQ

What is the maximum I²C clock frequency supported by the PCA9545APW,112?

The PCA9545APW,112 supports Fast-mode I²C operation up to 400 kHz. This is confirmed in Section 12 of the official datasheet (Table 10), where fSCL(max) = 400 kHz under Fast-mode conditions. The device maintains signal integrity within this range due to low Ron and controlled propagation delay (tPD ≤ 0.3 ns).

Does the PCA9545APW,112 require external pull-up resistors on its I²C lines?

Yes, the PCA9545APW,112 requires external pull-up resistors on all SCL, SDA, and SCx/SDx lines. As stated in Section 1, "External pull-up resistors pull the bus up to the desired voltage level for each channel." No internal pull-ups are present, and proper bus termination is essential for reliable communication.

How does voltage translation work on the PCA9545APW,112?

Voltage translation in the PCA9545APW,112 is achieved via VDD-referenced pass-gate transistors. As described in Section 6.5, Vo(sw) - the maximum passed voltage - is determined by VDD (e.g., Vo(sw) ≤ 1.9 V when VDD = 3.3 V). This allows 5 V upstream devices to safely communicate with 1.8 V or 3.3 V downstream peripherals when paired with appropriate pull-ups.

Can multiple channels of the PCA9545APW,112 be enabled simultaneously?

Yes, the PCA9545APW,112 supports simultaneous activation of any combination of its four channels. Section 6.2.1 explicitly states: "Several channels can be enabled at the same time," and Table 4 shows valid configurations such as B3=0, B2=1, B1=1, B0=0 (enabling channels 1 and 2). Care must be taken not to exceed total bus capacitance limits.

What happens to the PCA9545APW,112 during power-on or reset?

On power-on, the PCA9545APW,112 asserts an internal Power-On Reset (POR) until VDD reaches VPOR (1.6–2.1 V), initializing all registers to zero and deselecting all channels. Asserting the RESET pin low also clears the control register and deselects all channels, as specified in Sections 6.3 and 6.4 - ensuring predictable startup and fault recovery behavior.