Design Guide for the Microchip USB2514B/M2 4-Port USB 2.0 Hub Controller
The Microchip USB2514B/M2 is a highly integrated, low-power, and cost-effective 4-port USB 2.0 hub controller. It is designed to provide a seamless and robust expansion solution for Universal Serial Bus (USB) ports in a wide range of applications, from desktop computers and notebooks to embedded systems and docking stations. This design guide outlines the critical considerations for successfully implementing this hub IC.
Key Features and Benefits
The core of the hub's functionality lies in its advanced feature set. It supports both low-speed (1.5 Mbps), full-speed (12 Mbps), and high-speed (480 Mbps) USB data rates on its downstream ports, ensuring backward compatibility with a vast array of peripheral devices. A significant advantage is its MultiTRAK™ technology, which incorporates multiple transaction translators. This architecture significantly improves overall data throughput by allowing simultaneous transactions to different downstream devices, eliminating bottlenecks common in single-TT hubs.
Furthermore, the hub supports port disable and configuration options. Individual downstream ports can be enabled or disabled via strapping options or through the serial I²C interface, providing design flexibility. The inclusion of on-board 5V-to-3.3V and 1.2V regulators simplifies the power architecture by reducing the number of external components required, thereby saving board space and total system cost.
Critical Design Considerations
1. Power Scheme and Decoupling:
The hub can be configured in two primary power modes: self-powered or bus-powered. The chosen mode must be correctly set using the `SP_SEL` strap pin. Proper decoupling is absolutely essential for stable operation. A combination of bulk, ceramic, and tantalum capacitors should be placed as close as possible to the VDD and regulator pins as specified in the datasheet to ensure a clean power supply and minimize noise.
2. Clock Source:
The USB2514B/M2 requires a precise 24 MHz clock source. This can be provided by a crystal resonator connected across the XI and XO pins, along with appropriate load capacitors, or by an external oscillator driving the XI pin. The stability of this clock is critical for reliable USB data transfer; thus, PCB layout for the crystal should be kept compact and away from noisy signal lines.
3. USB Signal Integrity (SI):
Maintaining signal integrity on the differential D+ and D- pairs is paramount for high-speed USB operation. Design rules must be followed meticulously:
Impedance Control: The differential pairs must be routed with a controlled differential impedance of 90Ω.
Length Matching: The traces within a differential pair must be length-matched to minimize skew.
Minimize Vias: Avoid using vias on these high-speed lines. If unavoidable, ensure the via structure is symmetric for both signals in the pair.
Keep Lengths Short: Route USB signals first and as directly as possible.
4. Configuration Strapping and I²C:
The hub's default configuration (e.g., vendor ID, product ID, port numbering) is set at power-up through pull-up or pull-down resistors on specific strap pins. For dynamic customization, the SMBus/I²C interface can be used. This allows an external host controller to read from and write to the hub's internal registers, enabling features like custom product string descriptors or individual port power control.
5. ESD Protection:
While the hub includes some integrated ESD protection on its USB pins, for environments with higher ESD risk (e.g., user-accessible ports), adding external ESD protection diodes on each downstream data line is a highly recommended practice to enhance system robustness and meet stringent IEC standards.
PCB Layout Recommendations
A solid ground plane is the foundation of a good layout. Route high-speed USB signals over an unbroken ground plane to provide a clear return path. Keep digital and analog power domains separate and use ferrite beads or 0Ω resistors for isolation where recommended. The decoupling capacitors for the core and PHY must be placed immediately adjacent to their respective pins.
Conclusion
The USB2514B/M2 offers a powerful and flexible solution for USB expansion. A successful design hinges on careful attention to power delivery, clock accuracy, signal integrity for high-speed data lines, and correct device configuration. By adhering to these guidelines, designers can fully leverage the hub's capabilities to create reliable and high-performance products.
ICGOODFIND: The USB2514B/M2 stands out for its integration, performance-per-watt, and design flexibility, making it an excellent choice for simplifying USB hub implementation in modern electronic designs.
Keywords: USB 2.0 Hub, Signal Integrity, MultiTRAK™, I²C Configuration, Power Modes
