Texas Instruments PCA9545ADW

Overview

PCA9545ADW from Texas Instruments is a low-voltage, quad-channel I²C/SMBus switch with interrupt logic and active-low reset. It functions as a bidirectional translating multiplexer that routes one upstream SCL/SDA pair to any combination of four downstream SCn/SDn channels, supports voltage-level translation across 1.8 V, 2.5 V, 3.3 V, and 5 V buses, and features four independent active-low interrupt inputs (INT3–INT0) with a single open-drain ANDed output (INT). It is used in server backplanes to isolate I²C slave address conflicts among identical temperature sensors.

For engineers reviewing the PCA9545ADW datasheet, PCA9545ADW pinout, PCA9545ADW application, or PCA9545ADW equivalent, this device enables scalable I²C bus expansion in space-constrained embedded systems requiring channel-selectable isolation, fault recovery via hardware reset, and mixed-voltage slave interoperability without level-shifter components.

Technical Context

The PCA9545ADW implements a register-controlled 1-of-4 bidirectional analog switch matrix with integrated interrupt arbitration logic. Its control register (8-bit, read/write) uses bits B0–B3 for channel enable/disable selection and bits B4–B7 to reflect real-time interrupt status from each downstream channel.

It employs pass-gate architecture with VCC-referenced R_ON (max 20 Ω at 3.3 V), supports Standard-Mode (100 kHz) and Fast-Mode (400 kHz) I²C timing, and includes an internal power-on reset circuit triggered at VCC < 1.6 V (typ) and a dedicated active-low RESET pin with 6 ns minimum pulse width requirement.

Key Specifications

Pinout & Package

TSSOP-20 package (6.50 mm × 4.40 mm), lead-free, RoHS-compliant, with exposed thermal pad (not electrically connected).

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9545ADW, TCA9545APWR offers broader voltage support and higher ruggedness but at slightly higher unit cost, while PCA9544ADW reduces channel count and BOM cost but eliminates expansion headroom-making PCA9545ADW optimal for balanced scalability, compatibility, and industrial reliability.

Availability

PCA9545ADW is available at Aetrix Electronics and suitable for server backplane management, telecom router chassis monitoring, and industrial PLC I/O expansion requiring stable component supply across multi-year production cycles.

Supply support for PCA9545ADW 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 specializing in analog, embedded processing, and connectivity technologies, with over 50 years of innovation in industrial and communications infrastructure ICs.

The PCA9545ADW belongs to TI's I²C switch and multiplexer product line, designed specifically to resolve slave address conflicts and enable modular, fault-tolerant I²C system architectures in high-density computing and networking equipment.

FAQ

What is the I²C slave address range supported by the PCA9545ADW?

The PCA9545ADW supports four fixed I²C slave addresses: 0x70, 0x71, 0x72, and 0x73. These are determined by the logic levels applied to the A0 and A1 pins-both grounded yields 0x70, A0 high/A1 low yields 0x71, A0 low/A1 high yields 0x72, and both high yields 0x73. This addressing scheme allows up to four PCA9545ADW devices to coexist on the same I²C bus without conflict.

Does the PCA9545ADW require external pull-up resistors on all I²C lines?

Yes, the PCA9545ADW requires external pull-up resistors on all I²C lines: SDA and SCL (upstream), plus each SDn and SCn pair (downstream channels 0–3). Pull-up voltages must match the respective bus domain-VDPUM for upstream and VDPU0–VDPU3 for each downstream channel-to enable proper voltage-level translation. No internal pull-ups are provided.

How does the PCA9545ADW handle a stuck SDA line on one downstream channel?

The PCA9545ADW recovers from a stuck SDA condition using its active-low RESET pin: asserting RESET low for ≥6 ns resets the internal I²C state machine and forces all channels to deselect. This isolates the faulty channel without affecting upstream communication. The device also features a power-on reset that triggers automatically when VCC rises above 1.6 V (typ), ensuring safe initialization.

Can multiple channels of the PCA9545ADW be enabled simultaneously?

Yes, the PCA9545ADW allows any combination of its four channels (0–3) to be enabled simultaneously via bits B0–B3 in the 8-bit control register. For example, writing 0x0F enables all channels, while 0x05 enables Channels 0 and 2. However, simultaneous activation must respect total bus capacitance limits (≤400 pF) to maintain I²C timing compliance at 400 kHz.

What is the maximum capacitive load the PCA9545ADW can drive on a downstream channel?

The PCA9545ADW is characterized for downstream bus loads up to 400 pF per SCn/SDn pair, as specified in the I²C timing requirements (Cb ≤ 400 pF). Exceeding this limit may violate t_BUF, t_HD;STA, and fall-time specifications-particularly in Fast-Mode (400 kHz) operation. Layout best practices recommend minimizing trace length and avoiding stubs to stay within this constraint for reliable PCA9545ADW operation.