Texas Instruments PCA9545APWR

Overview

PCA9545APWR 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 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. It is used in server motherboard I²C bus expansion where multiple temperature sensors share identical slave addresses.

For engineers reviewing the PCA9545APWR datasheet, PCA9545APWR pinout, PCA9545APWR application, or PCA9545APWR equivalent, key selection considerations include its 4-channel programmable switching capability via I²C control register, interrupt aggregation logic for fault detection across isolated I²C segments, active-low reset recovery from stuck-bus conditions, and compatibility with Standard-Mode (100 kHz) and Fast-Mode (400 kHz) I²C timing.

Technical Context

The PCA9545APWR implements a fully synchronous I²C-controlled switch matrix with independent channel enable/disable via a single 8-bit control register - bits B0–B3 select channels 0–3, while bits B4–B7 reflect real-time interrupt status from INT0–INT3. Its pass-gate architecture enables bidirectional signal translation without direction control pins, and VCC-referenced level shifting allows mixed-voltage I²C domain interconnection.

Interrupt handling is asynchronous and edge-insensitive: each INTn input drives an internal latch that sets the corresponding bit in the control register; the AND-combined INT output asserts low when any INTn is active. The RESET pin forces hardware reset of the I²C state machine and clears all channel selections, independent of clock or data activity.

Key Specifications

Pinout & Package

TSSOP-20 package (6.50 mm × 4.40 mm), lead pitch 0.65 mm, 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, PCA9545APWR adds essential interrupt visibility for fault isolation; compared with PCA9548APWR, it offers lower standby current and reduced channel count-ideal for compact, cost-sensitive 4-domain designs where interrupt awareness is mandatory.

Availability

PCA9545APWR is available at Aetrix Electronics and suitable for server management, telecom switching equipment, factory automation, and embedded sensor hub applications requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for PCA9545APWR 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 PCA9545APWR belongs to TI's I²C infrastructure portfolio, designed specifically to resolve slave address conflicts and enable scalable, fault-resilient multi-peripheral I²C architectures in space-constrained embedded systems.

FAQ

What is the I²C slave address range supported by the PCA9545APWR?

The PCA9545APWR 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 allows up to four PCA9545APWR devices to coexist on the same I²C bus without address collision.

How does the PCA9545APWR handle voltage-level translation between different I²C domains?

The PCA9545APWR uses VCC-referenced pass-gate switches to enable voltage translation: each SCn/SDn channel can operate at a different logic level (1.8 V, 2.5 V, 3.3 V, or 5 V) by using local pull-up resistors tied to their respective domain voltages. The VCC pin defines the maximum voltage passed through the switch, so external pull-ups on downstream channels set their operating voltage independently of the upstream master's VCC.

Can the PCA9545APWR recover from a stuck I²C bus condition without power cycling?

Yes - the PCA9545APWR includes an active-low RESET pin that asynchronously resets the internal I²C state machine and deselects all channels when asserted. This allows full recovery from downstream bus lockup (e.g., a slave holding SDA low) without removing power. The RESET pulse must be held low for ≥6 ns, after which the device resumes normal operation with all channels disabled.

What happens to the PCA9545APWR's channel selection state after a power-on reset?

Upon power-on reset, the PCA9545APWR initializes its internal control register to 0x00, deselecting all four channels (B0–B3 = 0). This "no channel selected" state prevents unintended bus connections during power ramp-up and ensures deterministic startup behavior. The device remains in this state until the host processor writes a new channel-enable value to the control register via I²C.

Is the PCA9545APWR compatible with Fast-Mode Plus (1 MHz) I²C operation?

No - the PCA9545APWR is specified for Standard-Mode (100 kHz) and Fast-Mode (400 kHz) I²C operation only. Its electrical characteristics, including propagation delay (≤1 ns) and rise/fall time limits, are validated up to 400 kHz. Fast-Mode Plus timing requirements exceed the device's guaranteed performance envelope, so use in 1 MHz systems is not supported and may result in communication errors or missed ACKs.