USB Hubs
1. What are the Functions and Features of USB Hubs?
USB Hubs are electronic components used to expand the host USB interface, which can expand a single USB interface into multiple independently working downstream ports. Core functions include:
Interface Expansion: Connect multiple devices (such as USB flash drives, mice, keyboards, etc.) through a star topology to solve the problem of insufficient host interfaces.
Power Management: Support bus-powered or self-powered modes, distribute power to downstream devices (voltage range is usually 4.4V-5.25V), and have built-in overcurrent/short-circuit protection mechanisms.
Data Transmission: Support USB protocols of different speeds (such as USB 2.0/3.0), and achieve rate matching between high-speed and low-speed devices through transaction translators.
2. How does USB Hubs Work?
Data Transmission Process: When a device is inserted into the Hub, the Hub detects the level change and reports it to the host. The host allocates power and transmission rate through initialization commands and then starts data transmission.
Topology: Adopting hierarchical star topology, Hub acts as a relay node, responsible for signal enhancement, power distribution, and data forwarding (bidirectional transmission: host ↔ device).
Internal Modules:
Hub Repeater: Bidirectional data forwarding (uplink ↔ downlink).
Hub Controller: Communicates with the host and implements Hub control.
Transaction Translator: Converts high-speed/full-speed/low-speed transmission transactions.
3. Hardware Design and Protocol Support of USB Hubs
Chip Solution: For example, high-performance chips such as CH334/CH335 support MTT (multi-transaction translator) mode, and each port has an independent bandwidth of 12Mbps (USB 2.0).
Power Circuit: Cooperate with the current limiting switch chip to realize current detection (GANG mode or independent mode), and integrate ESD protection (anti-electrostatic discharge).
Protocol Compatibility:
USB 2.0 Hub: Theoretical bandwidth 480Mbps, compatible with USB 1.1 devices.
USB 3.0/3.1 Hub: bandwidth increased to 5Gbps/10Gbps, backward compatible with old protocols.
4. Application Scenarios and Precautions for USB Hubs
Scenarios: home/office equipment expansion, industrial computer interface expansion, embedded systems, etc.
Bandwidth Allocation: downstream ports share upstream bandwidth, and the actual rate is affected by Hub loss (such as USB 3.0 Hub total bandwidth ≤5Gbps).
Selection Suggestions: Comprehensive selection based on the number of devices, power supply requirements (self-powered devices are preferred over high-power devices), and transmission rate (MTT chips are preferred).