1.3 Selecting the Appropriate Device

Selecting the appropriate LAN9645x configuration depends on the required feature set and level of system management. The LAN9645x family can be viewed as a four-tier solution, ranging from fully managed to fully unmanaged operation.

Below is a shortened Decision Guide based on the LAN9645x - Choosing the Correct Switch for your Application Knowledge Base Article referenced in Documentation.

Decision Guide

Use the following hierarchy to select the appropriate device and configuration:

Figure 1-2. Decision Guide Hierarchy

Tier 1 – Full Feature Managed (Highest Capability)

LAN9645xF + External Host (Linux DSA)

Use this configuration if your application requires:

  • TSN / AVB features (TAS, CQF, frame preemption, shaping)
  • High-availability redundancy (HSR, PRP)
  • Advanced traffic control and deterministic networking

Requirements:

  • External Linux-capable host processor
  • SPI (control plane via Linux DSA)
  • Network Processor Interface (data interface)

Tier 2 – Standard Managed

LAN9645xS + External Host (Linux DSA)

Use this configuration if you need:

  • Dynamic configuration and monitoring
  • PTP (events, clocks, synchronization)
  • FRER
  • MRP / RSTP and other managed features
  • QoS control, MAC table updates, diagnostics

Requirements:

  • External Linux-capable host processor
  • SPI (control plane via Linux DSA)
  • Network Processor Interface (data interface)

Tier 3 – Unmanaged with EEPROM / SPI Flash (Static Configuration)

LAN9645xS + External EEPROM / SPI Flash

Use this configuration if your design requires:

  • Fixed VLANs, QoS, and traffic shaping
  • Static port configuration and PHY initialization
  • Features such as SyncE, and filtering, preconfigured at boot

Requirements:

  • EEPROM module (I2C table) or SPI Flash module (SPI table)
  • Configuration is generated using the LAN9645x EEPROM GUI Configurator Tool
  • Loaded automatically at startup (no host required)

Tier 4 – Unmanaged (Strap-Only, Lowest Complexity)

LAN9645xS (No EEPROM / SPI Flash, Strap Configuration)

Use this configuration for:

  • Basic Layer 2 switching
  • Simple port connectivity and bring-up
  • Minimal configuration, lowest cost and complexity

Limitations:

  • No dynamic or advanced feature control
  • Only basic functionality enabled via hardware straps

Summary

  • Use LAN9645xF (Tier 1) for TSN, AVB, or high-availability networking
  • Use LAN9645xS + host (Tier 2) for managed switching without TSN or high-availability redundancy
  • Use LAN9645xS + EEPROM / SPI Flash (Tier 3) for static, preconfigured systems
  • Use LAN9645xS strap-only (Tier 4) for simple unmanaged designs
Note: Microchip-supported managed operation is based on Linux® DSA over SPI. Other management interfaces are not part of the standard supported software model.