I have a customer that is using the TPS65950 in the following manner:
We currently use the USB port on TPS65950 to interface to USB-serial or USB-Ethernet device using the USB power from TPS65950 directly. Since the current drawn by a USB-Ethernet circuitry we are considering can be greater than 100 mA, we want to change the design to be self-powered, instead of USB bus-powered.
In our design, TPS65950 drives USB connector directly. There is no secondary circuitry, such as overcurrent protection between TPS65950 and USB connector. We are not using OTG either. Just strictly USB 2.0 host only configuration. We are running Linux in this embedded application.
They have the following questions regarding the application:
1. In the self-powered design, we won’t be using USB 5V power from TPS656590. Do we leave USB 5V float? Or do we need to create an artificial load on the USB 5V, so that TPS65950 can at least sense there is a device attached to the USB port?
2. Does self-powered have any impact to USB enumeration process? In other words, if we draw about 10-15 mA statically and constantly from USB 5V line, does it somehow affect the enumeration process? Do you foresee any problem if we draw 10-15 mA?
3. Unlike bus-powered where TPS65950 can remove or control USB 5V, the self-powered device is always on. If TPS65950 ever removes USB 5V (and I am not sure if it would), the attached device won’t know it. Is it a problem?
Please let me know if you have any questions for the customer.
Thanks for your help with this!
Richard Elmquist
