Texas Instruments PCA9545AGQNR

Overview

PCA9545AGQNR from Texas Instruments is a low-voltage 4-channel I²C and SMBus switch with interrupt logic and reset functionality. It functions as a bidirectional translating multiplexer that routes one upstream SCL/SDA pair to any combination of four downstream SCn/SDn channels. Key confirmed parameters include 2.3 V to 5.5 V operating supply, 0–400 kHz clock support, 5.5 V tolerant inputs, active-low RESET and INT outputs, and 4-channel interrupt aggregation (INT3–INT0 → INT). It is used in server backplanes to resolve I²C slave address conflicts among identical temperature sensors.

For engineers reviewing the PCA9545AGQNR datasheet, PCA9545AGQNR pinout, PCA9545AGQNR application, or PCA9545AGQNR equivalent, this page delivers verified technical context on channel selection via I²C control register, voltage-level translation between 1.8-V/2.5-V/3.3-V and 5-V buses, interrupt handling logic, reset recovery behavior, and TSSOP-20 package constraints - all critical for embedded system bus architecture and fault-tolerant I²C design.

Technical Context

The PCA9545AGQNR implements a programmable 1-of-4 bidirectional translating switch controlled by an 8-bit I²C-accessible control register, where bits B0–B3 select active channels and bits B4–B7 reflect real-time interrupt status per channel. Its pass-gate architecture uses VCC as voltage-limiting reference, enabling level translation without external level shifters.

Interrupt logic performs wired-AND aggregation: any asserted INTn (active-low) pulls the open-drain INT output low, while the corresponding bit in the control register latches the event. The active-low RESET input forces full state-machine reset and channel deselection, independent of I²C communication - essential for recovering stuck-bus conditions on downstream channels.

Key Specifications

Pinout & Package

GQN package: 20-pin TSSOP (6.50 mm × 4.40 mm), lead pitch 0.65 mm, exposed pad not electrically connected. Pin numbering follows TI standard top-view orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with PCA9545AGQNR, PCA9544APW omits interrupt logic entirely - reducing component count but requiring software polling - while TCA9544APWR retains interrupt functionality yet mandates register-level firmware changes due to non-identical control register layout and interrupt status access method.

Availability

PCA9545AGQNR is available at Aetrix Electronics and suitable for server backplane management, rack-mount telecom switching, and factory automation PLC I/O modules requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for PCA9545AGQNR 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 headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

The PCA9545A product line was designed specifically for I²C/SMBus bus expansion and conflict resolution in dense multi-slave systems, emphasizing robust reset recovery, voltage translation, and interrupt-aware channel management.

FAQ

What is the function of the RESET pin on the PCA9545AGQNR?

The RESET pin on the PCA9545AGQNR is an active-low asynchronous input that forces a full internal state-machine reset and deselects all four channels immediately. When asserted for ≥6 ns, it clears the control register to its default (all channels disabled), releases stuck SDA lines on downstream buses, and restores I²C communication integrity - critical for recovering from bus lockup without power cycling. This behavior is identical across all PCA9545AGQNR units and is documented in TI's SCPS147D datasheet section 7.7.

How does the PCA9545AGQNR handle I²C voltage-level translation between different bus domains?

PCA9545AGQNR enables voltage-level translation by using its VCC pin as the maximum pass-through voltage reference for all internal pass gates. External pull-up resistors on each SCn/SDn channel are connected to their respective domain voltages (e.g., 1.8 V for sensors, 5 V for EEPROMs), while the upstream SDA/SCL lines pull up to the master-side VDPUM. The device's 5.5 V tolerant I/O pins and low RON switches (≤45 Ω) ensure signal integrity across combinations like 1.8-V ↔ 5-V without external level shifters - a capability confirmed in datasheet sections 3 and 9.1.

Can multiple PCA9545AGQNR devices share the same I²C bus?

Yes, up to four PCA9545AGQNR devices can coexist on the same I²C bus using hardware-configurable slave addresses. Pins A0 and A1 determine the base address: A1A0 = 00 selects 0x70, 01 selects 0x71, 10 selects 0x72, and 11 selects 0x73. Each device responds only to its assigned address, enabling hierarchical bus expansion - for example, one PCA9545AGQNR managing four sensor clusters, each with its own downstream PCA9545AGQNR. This addressing scheme is defined in datasheet Figure 10 and section 9.6.1.

What is the purpose of the INT output and how does it relate to INT0–INT3 inputs on the PCA9545AGQNR?

The INT output on the PCA9545AGQNR is an open-drain active-low signal that functions as a wired-AND of the four INT0–INT3 inputs. When any downstream I²C slave asserts its INTn line (low), the PCA9545AGQNR pulls INT low and latches the event in bits B4–B7 of its control register. This allows the master to detect interrupt activity without polling and then read the register to identify the exact source channel - a feature validated in datasheet sections 2, 9.4, and Table 2. No channel selection is required for interrupt detection.

Does the PCA9545AGQNR support Fast-Mode I²C (400 kHz) operation?

Yes, the PCA9545AGQNR fully supports Fast-Mode I²C operation up to 400 kHz, as specified in datasheet section 7.5 and confirmed in the "Features" list. Its propagation delay (tpd) is ≤1 ns at CL = 50 pF (section 7.6), and its electrical characteristics - including VOL, VOH, and timing margins - are characterized across the full 0–400 kHz range under recommended operating conditions (VCC = 2.3 V to 5.5 V, TA = –40°C to 85°C). This makes PCA9545AGQNR suitable for time-critical applications such as PMBus-compliant power system management.