Texas Instruments PCA9545APW

Overview

PCA9545APW from Texas Instruments is a low-voltage, quad-channel I²C and 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 to 5-V buses, features four independent active-low interrupt inputs (INT3–INT0), and provides an ANDed active-low interrupt output (INT). It is used in server motherboard I²C bus expansion where multiple temperature sensors share identical slave addresses.

For engineers reviewing the PCA9545APW datasheet, PCA9545APW pinout, PCA9545APW application, or PCA9545APW equivalent, key selection considerations include its 4-channel programmable switching capability via I²C control register, 2.3 V to 5.5 V operating supply range, 400-kHz Fast-Mode I²C compatibility, integrated interrupt aggregation, and active-low hardware reset for bus recovery - all critical for fault-tolerant embedded system bus management.

Technical Context

The PCA9545APW implements a register-controlled, bidirectional pass-gate switch architecture with independent channel enable/disable via bits B0–B3 of its 8-bit I²C-accessible control register. Its interrupt logic performs real-time OR-ing of INT0–INT3 inputs and drives the open-drain INT output as their logical AND, enabling master-side interrupt source identification without polling.

Each channel's SCn/SDn pair uses voltage-translating pass gates referenced to VCC, allowing interoperability between 1.8-V, 2.5-V, 3.3-V, and 5-V I²C domains using external pull-up resistors. The device resets its control register and deselects all channels on power-on or when RESET is asserted low for ≥6 ns, ensuring deterministic startup and bus-fault recovery.

Key Specifications

Pinout & Package

TSSOP-20 package (6.50 mm × 4.40 mm), lead-free, RoHS-compliant, surface-mount.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TCA9544APWR and PCA9548APW, the PCA9545APW delivers optimal balance of channel count (4), interrupt coverage (full 4-input aggregation), and package size (TSSOP-20), making it the preferred choice for mid-density I²C bus expansion in space-constrained server and telecom platforms.

Availability

PCA9545APW is available at Aetrix Electronics and suitable for server management, telecom switching equipment, factory automation, and industrial PC peripheral expansion requiring stable component supply and long-term lifecycle assurance.

Supply support for PCA9545APW 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 designing analog ICs, embedded processors, and connectivity solutions for industrial, automotive, and communications markets.

The PCA9545APW belongs to TI's I²C switch and multiplexer product line, engineered specifically to resolve I²C slave address conflicts and enable voltage-domain isolation in dense, multi-peripheral embedded systems.

FAQ

What is the I²C slave address range for PCA9545APW?

The PCA9545APW supports four fixed I²C slave addresses: 0x70, 0x71, 0x72, and 0x73. These are determined by the logic states 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. The PCA9545APW datasheet confirms this mapping in Figure 10 and Section 9.6.1, and all addresses are valid across the full 2.3 V to 5.5 V operating range.

Does PCA9545APW require external pull-up resistors on all I²C lines?

Yes, the PCA9545APW requires external pull-up resistors on all I²C lines: upstream SDA/SCL, and each downstream SDn/SCn pair. Pull-up voltage must match the target domain (e.g., 3.3 V for a 3.3-V slave bus, 5 V for a 5-V bus), as the device itself does not provide internal pull-ups. The PCA9545APW's pass-gate architecture relies on these external resistors to establish proper logic levels and ensure reliable signal integrity across voltage-translating channels.

How does the PCA9545APW handle simultaneous interrupts from multiple channels?

The PCA9545APW aggregates all active interrupts (INT0–INT3) onto a single open-drain INT output using wired-AND logic - meaning INT goes low if *any* channel asserts its interrupt. To identify the source, the host reads the PCA9545APW's control register: bits B4–B7 reflect the instantaneous state of INT0–INT3. The host then selects the asserted channel(s) and polls downstream devices directly. This mechanism is documented in Section 9.6.4 and Table 2 of the PCA9545APW datasheet.

Can PCA9545APW operate with a 1.8-V master and 5-V slaves?

Yes, the PCA9545APW supports 1.8-V ↔ 5-V voltage translation. When VCC = 1.8 V, the pass gates limit high-level output to ~1.8 V, protecting 1.8-V masters from 5-V slave signals. Conversely, with VCC = 5 V, the device passes up to 5 V, enabling 5-V slaves to drive the upstream bus. External pull-up resistors on each side set the logic threshold - e.g., 1.8-V pull-ups on SDA/SCL, 5-V pull-ups on SD3/SC3 - as confirmed in Section 3 (Description) and Figure 1 of the PCA9545APW datasheet.

What happens to channel selection during a PCA9545APW power-on reset?

During power-on reset (POR), the PCA9545APW initializes its internal control register to 0x00, which deselects all four channels (B0–B3 = 0) and clears all interrupt status bits (B4–B7 = 0). This behavior is guaranteed by the internal POR circuit, which holds the device in reset until VCC exceeds VPOR (min. 1.6 V, typ. 2.1 V). The PCA9545APW datasheet specifies this in Sections 7.4 (VPOR parameter), 9.1 (Overview), and 9.4.2 (Power-On Reset), ensuring deterministic, glitch-free startup with no channel contention.