I want to use the USB hub internally in my laptop but the available ones are very bulky and do not satisfy all the required conditions. Usually a USB hub is made to be recognized by the PC when inserted in the port. Similarly the USB hub extra port comes with a port detection option. Whenever we plug USB it will be detected by the system automatically.
But I want to use a USB hub inside of my laptop to add extra Wi-Fi and Bluetooth in it without compromising the USB ports. I want to not detect the USB again and again because once it is placed in the laptop, I will never disconnect it. And this is the type of settings which is done on the hardware level.
I got my hands on a USB series IC from microchip USB2422 which supports two downstream ports and the functions are programmable. Which is the best option for this project. To make the minimal system using this IC the only way to proceed is with Custom PCB from PCBWAY.
The Microchip USB2422 hub is a low-power, single transaction translator, hub controller IC with two downstream ports for embedded USB solutions. The hub controller can attach to an upstream port as a Hi-Speed and Full-Speed hub or as a Full-Speed only hub. The hub supports Low-Speed, Full-Speed, and Hi-Speed (when configured as a Hi-Speed hub) downstream devices on the enabled downstream ports. All required resistors on the USB ports are integrated into the hub. This includes all series termination resistors on D+ and D- pins and all required pull-down and pull-up resistors on D+ and D- pins. The over-current sense inputs for the downstream facing ports have internal pull-up resistors.
- Supports a single external 3.3 V supply source
- On-chip driver for 24 MHz crystal resonator
- ESD protection up to 6 kV on all USB pins
- Supports self-powered operation
- Downstream ports as non-removable ports
- USB Battery Charging options
- Overcurrent detection
SPX3819 3.3V Linear voltage regulator
24MHz Crystal Resonator
18pf loading capacitors
1uf, 100nf, 1nf power line filtering capacitor
47K resistor for pull up/down settings
Custom PCB from PCBWAY
I modified the circuit using the instruction from the datasheet according to a one time USB detection feature (strap options and configuration settings) which may be changed by changing the settings of pull-up and pull-down resistors.
In the datasheet the value of capacitors required for the filtration of power supply, phase lock loop and internal signal is mentioned which is connected accordingly. The IC is powered by the SPX3819 3.3v regulator because it is not compatible with the 5v logic of the USB. External Crystal resonators with 18pf loading capacitors are required on the XTAL pins of the IC. Other configuration settings are Pulled up/ down with a 47k resistor as both the downstream port behave as non detachable and disable the USB charging mode. Reset is pulled up with a small 10k resistor and can be replaced with a tactile switch to reset the Hub in attached conditions.
PCB design Consideration:
While designing the PCB keep all the filtering capacitors near to the IC which help to remove the EMI. Because the hub works on high speed 2.0 so it is very crucial to route the power lines and data lines separately. USB data lines are differential input and outputs, so it is recommended to route both the D+ and D- lines parallel to each other. In high speed data transfer clock skew also plays an important role so it is suggested to keep the length of both the data lines the same. Any vias and other circuit elements crossing over these data lines are not endorsed.
Connections and PCB work:
Power to 2 downstream ports is provided directly by the 5v logic from the laptop not from the voltage regulator. Now any external connector USB 2.0 can be connected directly to the port and speeds can be tested under different conditions. Outer connections are quite straightforward; one upstream...Read more »