Analog Devices Inc. LTC4305CDHD#TRPBF

Overview

LTC4305CDHD#TRPBF from Analog Devices (formerly Linear Technology) is a 2-channel, bidirectional I²C/SMBus bus multiplexer with capacitive isolation, level-shifting buffers, and programmable stuck-bus timeout. It supports 2.7V–5.5V supply, operates from 0°C to 70°C, delivers ≤100mV buffer offset, and enables independent 2.2V–5.5V pull-up on each downstream channel - used in multi-SFP module backplanes and hot-pluggable I²C subsystems.

For engineers reviewing the LTC4305CDHD#TRPBF datasheet, LTC4305CDHD#TRPBF pinout, LTC4305CDHD#TRPBF application, or LTC4305CDHD#TRPBF equivalent, key selection criteria include its 16-pin DFN (4mm × 5mm) package, I²C-compliant 400kHz timing, rise time accelerator current (4–5.5mA), programmable 7.5/15/30ms timeout modes, and nested addressing via ADR0–ADR2 pins enabling 27 unique addresses.

Technical Context

The LTC4305CDHD#TRPBF implements dual upstream-downstream bidirectional buffers using FET-based switching with regulated offset voltage (≤160mV at 5.5V), ensuring clock stretching, arbitration, and ACK protocol integrity across connected buses. Its stuck-low detection uses dual 0.52V threshold comparators with hysteresis (80mV) and three selectable timeout windows (6.25–30ms).

Rise time acceleration activates only when downstream channels are connected and bus slew rate exceeds 0.4V/µs; it sources up to 5.5mA per pin while limiting edge speed via internal regulation. The device supports SMBus Alert Response Address (ARA) protocol and provides dedicated ALERT1/ALERT2 fault inputs with open-drain ALERT output compliant to SMBus alert signaling.

Key Specifications

Pinout & Package

Package: 16-lead (4mm × 5mm) plastic DFN with exposed pad (Pin 17), θ_JA = 43°C/W when pad is connected to PCB ground.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TCA9548AIPWR and PCA9546ADW, the LTC4305CDHD#TRPBF uniquely integrates rise time acceleration, programmable stuck-bus recovery, dual ALERT inputs, and true supply-independent level translation - making it the only option among the three qualified for hot-pluggable, mixed-voltage, fault-critical I²C backplanes.

Availability

LTC4305CDHD#TRPBF is available at Aetrix Electronics and suitable for multi-SFP backplanes, hot-pluggable sensor hubs, and industrial I/O expansion systems requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for LTC4305CDHD#TRPBF 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

Analog Devices, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.

The LTC4305CDHD#TRPBF belongs to the Linear Technology LTC® bus protection and signal integrity product line, designed specifically for robust, fault-tolerant I²C/SMBus infrastructure in telecom, datacenter, and industrial systems.

FAQ

What is the maximum bus capacitance the LTC4305CDHD#TRPBF can drive while maintaining 400kHz I²C timing?

The LTC4305CDHD#TRPBF supports up to 800pF total bus capacitance on downstream channels when using its rise time accelerator (IBOOST = 4–5.5mA) and appropriate pull-up resistors. At VCC = 3.3V and RBUS = 10kΩ, typical rise time remains <300ns even with 600pF load - well within I²C Fast-mode specification. Performance degrades above 800pF due to internal buffer limitations.

Does the LTC4305CDHD#TRPBF require external pull-up resistors on all SDA/SCL lines?

Yes, the LTC4305CDHD#TRPBF requires external pull-up resistors on SDAIN, SCLIN, SDA1, SCL1, SDA2, and SCL2. The device does not integrate pull-ups; each line must be pulled to its respective domain voltage (e.g., 3.3V for upstream, 2.5V for SFP module Bus 1). ALERT and READY also require 10kΩ pull-ups to valid supply rails.

How does the LTC4305CDHD#TRPBF handle conflicting pull-up voltages when multiple downstream buses are active simultaneously?

The LTC4305CDHD#TRPBF does not prevent DC current flow between downstream buses with mismatched pull-up voltages. If Bus 1 (5V pull-up) and Bus 2 (2.5V pull-up) are both active, current flows from VBUS1 through internal FETs into VBUS2, potentially lowering SDA1 voltage and corrupting logic highs. The datasheet explicitly warns against activating both buses simultaneously in such configurations.

Can the LTC4305CDHD#TRPBF be used without connecting the exposed thermal pad?

Yes, the exposed pad (Pin 17) may be left unconnected, but thermal performance degrades significantly: θ_JA increases from 43°C/W to 140°C/W. At full load (ICC ≈ 8mA) and 70°C ambient, junction temperature could exceed 125°C limit. For reliable operation above 40°C ambient or continuous use, Analog Devices recommends soldering the pad to a PCB ground plane.

What happens to the READY pin when both downstream channels are connected?

When either or both downstream channels (Bus 1 and/or Bus 2) are connected to the upstream bus, the READY pin turns OFF (high-impedance state), allowing its external 10kΩ pull-up resistor to drive it to logic high. READY goes low only when *no* downstream channel is connected - serving as a hardware-ready flag for system initialization and hot-plug detection.