We are developing a new PCB which uses the TUSB8020B 2 port USB 3.0 hub IC to interface to an external USB 3.0 peripheral as well as onboard MCU through a USB to UART connection. The PCB was designed following the example circuits in the datasheet, reference design, and evaluation board. However, when we tested the board, it does not enumerate on the upstream PC when connected. As a result the downstream devices also don't connect. In fact, no USB error of any kind is presented, the PC acts as though nothing is connected.
We performed the following tests to see where a possible problem may lie:
- Used USBTreeView to check for any connection
- Tested multiple PCs and multiple USB ports
- Verified the voltage rails were at the correct values
- Power up reset time (GRSTz > 2V after Vcc=3.3V steady state) was measured to be around 10ms which >3ms recommended
- Crystal oscillator XO correctly outputs a ~24MHz clock signal
- Pin 9 USB_VBUS reads ~0.5V
- Since the TUSB8020 first attempts to load the configuration from EEPROM in I2C mode if pins 2 (SCL/SMBCLK), 3 (SDA/SMBDAT) are pulled high, the pullup resistors R1 and R2 were removed to disable configuration reading
- Downstream port wasn’t receiving power so the enable pin 3 of the power switch was pulled high
- Power management was disabled by removing R19
- Pin 22 was probed and the transition from the in circuit pull-up (HIGH) state to the not SuperSpeed connection flag (LOW) state was observed
- Traces to MSP430 on SCL and SDA were cut
- FTDI chip removed
- SMBUSZ I2C mode resistor R23 was removed (still internally pulled up) to match example in datasheet and reference design
Based on the tests performed, it seems as though the chip is running, and despite our modifications to attempt to alleviate any possible issues, it still refuses to connect to the upstream. In the process of debugging we also looked through responses on the help forum and could not find anything that helped us with our particular issue. We are not sure where to proceed in debugging of the TUSB8020B connectivity issues, so any assistance in getting this design to work would be greatly appreciated. I have attached the schematic of our design for reference.
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