allsey87
Member level 4
Hi All,
I'm designing a compound USB device (based on SMSC's **broken link removed**) with an upstream interface connecting back to a PC. On the downstream ports I have UART to Serial convert (FT232RL) and an OTG (permanently configured as a peripheral) connection back to my main processor. Since these two devices are permanently connected via routing on the same PCB, I believe I should set these ports in the hub as non-removable and set the configuration header for the hub to indicate that we are functioning as a compound device (although this might be automatically done in the **broken link removed** silicon)
My question is regarding the electrical interface between the hub and permanently connected peripherals, I have found scattered information about this around the internet stating things like the (untwisted) traces of the DP/DM paths should not exceed 10cm etc. I have also had a look at the "Inter-Chip USB Supplement to the USB 2.0 Specification" which I think is quite relevant to my design. Although I find the section about voltage classes a bit confusing, I thought the voltages used on the DP/DM lines was standard for all devices/hubs etc.
In short my questions are:
1. Do I need to take voltage classes into consideration when designing a compound peripheral?
2. What sort of (if any) capacitors, ferrite beads and pull-up/pull-down resistors do I need on the DP/DM lines?
Any insights, comments and suggestions welcome!
I'm designing a compound USB device (based on SMSC's **broken link removed**) with an upstream interface connecting back to a PC. On the downstream ports I have UART to Serial convert (FT232RL) and an OTG (permanently configured as a peripheral) connection back to my main processor. Since these two devices are permanently connected via routing on the same PCB, I believe I should set these ports in the hub as non-removable and set the configuration header for the hub to indicate that we are functioning as a compound device (although this might be automatically done in the **broken link removed** silicon)
My question is regarding the electrical interface between the hub and permanently connected peripherals, I have found scattered information about this around the internet stating things like the (untwisted) traces of the DP/DM paths should not exceed 10cm etc. I have also had a look at the "Inter-Chip USB Supplement to the USB 2.0 Specification" which I think is quite relevant to my design. Although I find the section about voltage classes a bit confusing, I thought the voltages used on the DP/DM lines was standard for all devices/hubs etc.
In short my questions are:
1. Do I need to take voltage classes into consideration when designing a compound peripheral?
2. What sort of (if any) capacitors, ferrite beads and pull-up/pull-down resistors do I need on the DP/DM lines?
Any insights, comments and suggestions welcome!