AM5K2E04: USB Host without 5V VBUS and DRVVBUS

Hi Gunter,

Please refer the recommended USB host connection for keystone II devices from below wiki.

http://processors.wiki.ti.com/index.php/Keystone_Multicore_Device_Family_Schematic_Checklist#USB

Thank you.

Thanks, Raja.

The wiki page you referenced covers the cases where there is a USB connector, and VUSB is either being sourced (K2E in USB host mode), or provided externally (K2E in USB device mode).

In this case the K2E is the USB host to an on-board microcontroller as a USB device. There is no need for +5V and VUSB in this situation. Are we required to generate a +5V supply just to feed it back into the VBUS input of the K2E?

Gunter,

When you operate the AM5K2E04 USB1 port in host mode, it is required to connect the USB1VBUS to 5V to detect the VBUS level. The USB1DRVVBUS signal may be used to control the 5V source connected to USB1VBUS.

Regards,
Senthil

Hi Senthil,

are you saying that even if the 5V is not used for anything else, the 5V needs to be enabled (with USB1DRVVBUS) and connected back into the USB1VBUS, in order to detect the correct VBUS level? Is this the only way to make the USB Host mode work? Are there no internal registers that can bypass this check?

Thanks,

--Gunter

Gunter

The internal VBUS comparator is used to generate the PCS signal, pipeP_power_present to the USB3 controller. If the PHY’s VBUS pin is not  connected, this PCS signal will not be valid. An external VBUS comparator must then be needed to generate the required USB 3.0 controller power-present signal.

How does the microcontroller as a device enable its pullup on DP without VBUS? 

Thanks

David

Hi David,

I will let Gregg comment on the Micro and its DP PU enable without VBUS.

If the external VBUS comparator output were chosen, is there an external input pin on the K2E, that this should be connected to? How is the VBUS comparator result fed back into the K2E?

Thanks,
--Gunter

David,

Thanks for the update.

The microcontroller we are using as the USB device has an option to disable the VBUS sensing option, in which case the VBUS is always considered internally to be at a valid level. Apparently the K2E does not have an equivalent configuration option and we will have to source the +5V VBUS externally.

Regarding your question about the D+ pull-up from the microcontroller to signal USB full-speed mode to the K2E. The pull-up resistor for USB is to a 3.3V supply, not the +5V VBUS supply anyway, so the microcontoller simply switches the D+ pull-up to its internal +3.3V supply voltage.

Thanks,
Gregg.

Hi David,

I wanted to re-iterate that for this customer's usecase, the USB port is only operated with the USB2.0 PHY and not with the USB3.0 PHY. Given this, can you confirm that the 5V VBUS needs to be sourced externally and provided to the K2E USB Host port, and there is no other way of getting around this.

Thanks,
--Gunter

Gunter

USB2 has a same function pin called VBUSVALID. But we still need to have a 5V source connected to the VBUS pin.

Thanks
David